The Oxford Handbook of Philosophy of Perception 9780199600472, 0199600473

Table of contents :
Cover
The Oxford Handbook of  Philosophy of Perception
Copyright
Contents
List of Contributors
Introduction
Part I Historical Background
1. Perception in Ancient Greek Philosophy
2. Perception in Medieval Philosophy
3. Skepticism and Perception
4. Perception in Early Modern Philosophy
5. Perception in Philosophy and Psychology in the 19th and Early 20th Centuries
6. Sense-Data
7. Phenomenological Approaches
Part II Contemporary Philosophical Approaches
8. Perceptual Representation/Perceptual Content
9. Perception and the First Person
10. Nonconceptual Content
11. Disjunctivism
12. Action-Based Accounts of Perception
13. Perceptual Reports
Part III The Senses
14. Vision
15. Audition
16. Touch
17. The Chemical Senses
18. The Bodily Senses
19. Unconscious Perception
part IV What We Perceive
20. Object Perception
21. Primary and Secondary Qualities
22. Colour Perception
23. Perception and Space
24. Perception and Time
25. Speech Perception
26. Musical Perception
27. Own-Body Perception
28. Perception of Pain
29. Perceiving Nothings
Part V Integrating Sensory Information
30. The Individuation of the Senses
31. Perceptual Attention
32. Multisensory Perception
33. Perceptual Constancy
34. How Do Synaesthetes Experience the World?
35. Substituting the Senses
part VI Frameworks for Perception
36. Similarity Spaces
37. Bayesian Perceptual Psychology
38. Signal Detection Theory
39. Information Theory
40. Modularity of Perception
part VII Broader Philosophical Issues
41. The Epistemology of Perception
42. Perceptual Learning
43. Perception and Demonstratives
44. Nonhuman Animal Senses
45. Perception and Art
Author Index
Subject Index

Citation preview

The Oxford Handbook of 

PHILOSOPHY OF PERCEPTION

The Oxford Handbook of 

PHILOSOPHY OF PERCEPTION Edited by

MOH A N M AT T H E N

1

3 Great Clarendon Street, Oxford, ox2  6dp, United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark  of Oxford University Press in the UK and in certain other countries © The several contributors 2015 The moral rights of the authors have been asserted First Edition published  2015 Impression:  1 All rights reserved. No part of this publication may be reproduced, stored  in a retrieval system, or transmitted, in any form or by any means, without  the prior permission in writing of Oxford University Press, or as expressly permitted by law, by licence or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope  of  the above should be sent to the Rights Department, Oxford University Press,  at  the address  above You must not circulate this work in any other  form and you must impose this same condition on any acquirer Published in the United States of America by Oxford University  Press 198 Madison Avenue, New  York, NY 10016, United States of America British Library Cataloguing in Publication  Data Data available Library of Congress Control Number: 2015931387 ISBN 978–0–19–960047–2 Printed and bound  by CPI Group (UK) Ltd, Croydon, cr0  4yy Links to third party websites are provided by Oxford in good faith  and for information only. Oxford disclaims any responsibility for the materials contained in any third party website referenced in this  work.

Contents

List of Contributors 

Introduction  Mohan Matthen

ix 1

PA RT I   H I S TOR IC A L BAC KGROU N D 1. Perception in Ancient Greek Philosophy  Victor Caston

29

2. Perception in Medieval Philosophy  Dominik Perler

51

3. Skepticism and Perception  Baron Reed

66

4. Perception in Early Modern Philosophy  Alison Simmons

81

5. Perception in Philosophy and Psychology in the 19th and Early 20th Centuries  100 Gary Hatfield 6. Sense-Data  Paul Snowdon

118

7. Phenomenological Approaches  Charles Siewert

136

PA RT I I   C ON T E M P OR A RY PH I L O S OPH IC A L  A PPROAC H E S 8. Perceptual Representation/Perceptual Content  Bence Nanay

153

9. Perception and the First Person  Christopher Peacocke

168

vi   Contents 10. Nonconceptual Content  Wayne Wright

181

11. Disjunctivism  Heather Logue

198

12. Action-Based Accounts of Perception  Pierre Jacob

217

13. Perceptual Reports  Berit Brogaard

237

PA RT I I I   T H E  SE N SE S 14. Vision  David R. Hilbert

257

15. Audition  Matthew Nudds

274

16. Touch  Frédérique de Vignemont and Olivier Massin

294

17. The Chemical Senses  Barry C. Smith

314

18. The Bodily Senses  J. Brendan Ritchie and Peter Carruthers

353

19. Unconscious Perception  Jesse J. Prinz

371

PA RT I V   W H AT W E PE RC E I V E 20. Object Perception  Roberto Casati

393

21. Primary and Secondary Qualities  Peter Ross

405

22. Colour Perception  Kathleen Akins and Martin Hahn

422

Contents   vii 23. Perception and Space  Jérôme Dokic

441

24. Perception and Time  Robin Le Poidevin

459

25. Speech Perception  Casey O’Callaghan

475

26. Musical Perception  Charles Nussbaum

495

27. Own-Body Perception  Alisa Mandrigin and Evan Thompson

515

28. Perception of Pain  Valerie Gray Hardcastle

530

29. Perceiving Nothings  Roy Sorensen

542

PA RT V   I N T E GR AT I NG SE N S ORY I N F OR M AT ION 30. The Individuation of the Senses  Mohan Matthen

567

31. Perceptual Attention  John Campbell

587

32. Multisensory Perception  Tim Bayne and Charles Spence

603

33. Perceptual Constancy  Jonathan Cohen

621

34. How Do Synaesthetes Experience the World?  Malika Auvray and Ophelia Deroy

640

35. Substituting the Senses  Julian Kiverstein, Mirko Farina, and Andy Clark

659

viii   Contents

PA RT V I   F R A M E WOR K S F OR PE RC E P T ION 36. Similarity Spaces  Diana Raffman

679

37. Bayesian Perceptual Psychology  Michael Rescorla

694

38. Signal Detection Theory  E. Samuel Winer and Michael Snodgrass

717

39. Information Theory  John Kulvicki

734

40. Modularity of Perception  Ophelia Deroy

755

PA RT V I I   BROA DE R PH I L O S OPH IC A L  I S SU E S 41. The Epistemology of Perception  Susanna Siegel and Nicholas Silins

781

42. Perceptual Learning  Robert L. Goldstone and Lisa A. Byrge

812

43. Perception and Demonstratives  Imogen Dickie

833

44. Nonhuman Animal Senses  Brian L. Keeley

853

45. Perception and Art  Dominic  McIver Lopes

871

Author Index  Subject Index

885 907

List of Contributors

Kathleen Akins  Simon Fraser University Malika Auvray CNRS-CR1 Tim Bayne  University of Manchester Berit Brogaard  University of Miami Lisa A. Byrge  Indiana University John Campbell  University of California, Berkeley Peter Carruthers  University of Maryland Roberto Casati  École Normale Supérieure, Paris Victor Caston  University of Michigan Andy Clark  The University of Edinburgh Jonathan Cohen  University of California, San Diego Ophelia Deroy  University of London Imogen Dickie  University of Toronto Jérôme Dokic  École des Hautes Études en Sciences Sociales and Institut Jean-Nicod Mirko Farina  Macquarie University Robert L. Goldstone  Indiana University Martin Hahn  Simon Fraser University Valerie Gray Hardcastle  University of Cincinnati Gary Hatfield  University of Pennsylvania David R. Hilbert  University of Illinois at Chicago Pierre Jacob  École Normale Supérieure, Paris Brian L. Keeley  Pitzer College Julian Kiverstein  University of Amsterdam John Kulvicki  Dartmouth College Robin Le Poidevin  University of Leeds

x   List of Contributors Heather Logue  University of Leeds Dominic McIver Lopes  University of British Columbia Alisa Mandrigin  University of Warwick Olivier Massin  Université de Genève Mohan Matthen  University of Toronto Bence Nanay  University of Antwerp and University of Cambridge Matthew Nudds  University of Warwick Charles Nussbaum  University of Texas at Arlington Casey O’Callaghan  Washington University in St Louis Christopher Peacocke  Columbia University Dominik Perler  Humboldt-Universität zu Berlin Jesse J. Prinz  The Graduate Center, CUNY Diana Raffman  University of Toronto Baron Reed  Northwestern University Michael Rescorla  University of California, Santa Barbara J. Brendan Ritchie  University of Maryland Peter Ross  California State University, Pomona Susanna Siegel  Harvard University Charles Siewert  Rice University Nicholas Silins  Cornell University; Yale-NUS College, Singapore Alison Simmons  Harvard University Barry C. Smith  University of London Michael Snodgrass  University of Michigan Paul Snowdon  University College London Roy Sorensen  Washington University in St Louis Charles Spence  University of Oxford Evan Thompson  University of British Columbia Frédérique de Vignemont CNRS E. Samuel Winer  Mississippi State University Wayne Wright  California State University, Long Beach

I n troduction Mohan Matthen

Perception is the ultimate source of knowledge about contingent facts.1 We know about our surroundings because we are able to experience them through perception; we know about scientific phenomena because they are observed. Epistemology is therefore very much concerned with the evidential value of perception. Analytic epistemology is concerned with the rational grounding that perception lends belief; empiricist philosophy of science erects the entire edifice of scientific knowledge on the back of perceptual observation. The rationality of perceptual grounding is contested, of course. On one side, it is contested by those, like Hume, who think we never have reason to believe in contingencies. According to him, we arrive at contingent beliefs about matters beyond mere sense-impressions by the association of ideas, and not by reason. On the other side, it is impugned by rationalists like Plato and Descartes, who think that perception is incoherent—both complain, for example, that it fails to intimate shape in a way that suffices to ground geometry, the authoritative science of shape—and far too evanescent to offer genuine and secure knowledge. Still even the opposition focuses on a critique or reinterpretation of observation and its epistemic value. Given the centrality of perception to epistemology, one would expect that the philosophical study of perception would be a focal philosophical topic. It has not been: neither traditional epistemology nor traditional philosophy of science has been particularly concerned to engage in a determined and scientifically informed investigation of the nature of perception itself. Both articulate puzzles and theories that come out of deep and original thinking about the problem of knowledge yoked to relatively superficial and dogmatic thinking about perception. In the last part of the twentieth century, this situation began to change. Philosophers began to use sensory psychology as a source of new insights about the nature of perception. Thanks to growing interest in perception—how it operates, what it reveals—and the development of new analytic tools, the philosophy of perception is, once again, a vital area of philosophical inquiry. Taken together, the chapters of this Handbook are an introduction to new philosophical thinking about perception. This Introduction presents an overview of some global 1 I  am grateful to Ophelia Deroy and Barry Smith for critically reading through the whole Introduction. Lynne Godfroy was (as always) very helpful in matters of exposition. Other more specific debts are recorded in other notes below.

2   Mohan Matthen issues, with the aim of contextualizing perception within broader philosophical concerns. It does not attempt to summarize or discuss individual chapters. Without exception, these are intellectually sophisticated introductions to sub-areas and as such they stand alone, requiring no additional exposition here. Accordingly, individual chapters are discussed only when they are directly relevant to the more synoptic topics taken up in the Introduction, though each is at least mentioned to show their place in the whole. Thus, the Introduction does not attempt to touch, even very lightly, on all of the many original and often surprising insights that readers will find in each and every individual chapter. It also suppresses bibliographical references; these are found in the relevant chapters.

I Until very recently, and to an extent even now, the epistemologist’s paradigm of perception remains much unchanged since the seventeenth century. According to this view, what we directly perceive—the message given to us by perception unsupplemented by inference from other sources—is a conscious presentation that closely parallels the excitation of sensory receptors. Call this the Receptoral Image Model (RIM). RIM takes slightly different forms in psychology and philosophy, as I shall now explain. RIM traces back at least as far as Johannes Kepler’s theory of the eye. As David Hilbert (Chapter 14) explains, the great astronomer came to realize that the lens of the eye refractively focuses all the light rays arriving from any given external location onto a single retinal place; thus, it creates an image on the retina. According to Kepler, this image is what we directly see. This discovery of the retinal image was greatly impressive to those who followed, though it took more than 200 years for the realization to dawn that optics is not enough. It was not until the early nineteenth century that the eminent German physiologist, Johannes Müller, came to realize that the optical image is not directly the starting point of vision. (It is, rather, the last item in the external causal chain that links object to perception.) For the optical image that is focused on the retina to affect conscious sensation, it must first be converted into a pattern of nerve energy. The retina is packed with neurons that are activated proportionately to the amount of light that falls on each; the activity of these neurons determines visual consciousness, Müller proposed. This is an important advance on Kepler, though it made little, if any, impact on philosophical theory. Philosophers still show little awareness that the conversion into nerve energy destroys much of the wavelength-specific information that is available in the optical image—information that could be extracted by a spectrometer. (See section VI of this Introduction.) Müller’s realization is the basis for generalizing Kepler’s theory beyond vision. Corresponding patterns of receptor activation could be assumed, and do indeed exist, for the other senses—the senses all have specialized receptors that are differentially activated by environmental energy incident on them. RIM assumes that receptor activations correspond closely to what we perceive in each modality—the activation of auditory neurons corresponds to what we hear; the activation of haptic neurons corresponds to what we feel, and so on. The receptoral images in these other senses do not have exactly the same

Introduction   3 properties as the retinal image—the auditory image in particular is poor in spatial information. Nonetheless, the sensory neurons provide us with what we now call sensory information. RIM identifies this information with what philosophers call the perceptual given, in other words, with what we perceive directly and non-inferentially. Psychology and philosophy worked with somewhat different versions of RIM. • Psychologists assumed that conscious awareness in each sense modality corresponds to the receptoral image, and they tended to assume, though less explicitly, that perception beyond the receptoral image is indirect, or inferred by learned association. For example, since the visual receptoral image is two-dimensional, they assumed that direct visual awareness must also be of a two-dimensional array. Perceptual awareness of depth and of three-dimensional objects is inferred. Nineteenth-century psychology realized that we possess two such retinal images, and they tried to work out how the discrepancies between these images could provide a basis for the inference of depth. • Philosophers made a convergent assumption. In early modern philosophy, and for a long time after, it was commonly assumed that the perceptual given—what we directly see, or hear, etc.—is that which is certain or indubitable given our state of sensory awareness. In the case of vision, two coloured regions might be seen side by side, but it is uncertain, given visual evidence, how far away each is. Consequently, philosophers too assumed that depth was not directly given in vision. Berkeley made this inference explicitly, but it is implicit in Descartes and others. The important difference between philosophers and psychologists is that the former are concerned with rational justification and the latter with physiology and conscious awareness. However, they arrive at comparable conclusions. Both conclude that visual awareness of three-dimensionality is indirect, the result of learned association or (according to some philosophers) rational inference. Psychologists and philosophers use Kepler’s theory differently, because philosophy is supposed to be a priori, which means that it cannot use a scientific theory as a foundation for knowledge. For this reason, philosophers cannot explicitly appeal to Kepler’s optics. Nevertheless, philosophers as diverse as Descartes and Berkeley commonly used the retinal image as a heuristic: it serves for them (though not explicitly) as a model of what we see and as the basis for generalizing to the other senses. RIM encourages many misconceptions regarding perception; collectively these misconceptions constitute a traditional view of perception that is slowly eroding away. RIM implies, for example, that: • Perceptual experience is necessarily unimodal (because the receptors and nerve energies are). (See Tim Bayne and Charles Spence, Chapter 32, for a re-evaluation.) • Objects can be made to look a different colour simply by shining coloured light on them (because this changes the colour of light that reaches the visual receptors). (Jonathan Cohen discusses the limitations of this notion in Chapter 33, as well as distortions of shape and size in the optical image; Kathleen Akins and Martin Hahn discuss the case of colour in Chapter 22.) Similar assumptions can be made in other modalities, though it was unusual for them to be explicitly worked out. For example, it could be assumed that since the activation of auditory receptors is changed by new sounds, direct auditory

4   Mohan Matthen awareness of continuing sounds would be modified by new sounds. Again, it could be assumed (with somewhat greater empirical justification) that gustatory awareness of the taste of honey would be modified by taking lemon into one’s mouth. • Like the retinal array, the visual image is a two-dimensional ‘colour mosaic’—that is, it consists of a two-dimensional matrix of minimally sized coloured dots—that does not contain depth information. (How do ‘coloured dots’ match up with the representation of colour in the system? See Akins and Hahn, Chapter 22, for discussion.) Analogously, audition offers us a confused melange of sound that does not directly inform us of spatially separated sources of sound. (Roberto Casati, Chapter 20, Jérôme Dokic, Chapter 23, and Matthew Nudds, Chapter 15, have relevant discussions.) • Flavour is sensed through the tongue alone, for the only receptors that are specialized for flavour perception reside in the tongue. (Barry Smith, Chapter 17, reconceptualizes flavour as a multisensory quality, and recounts, in particular, how wrong it is to think that it is restricted to taste receptors in the tongue—olfactory receptors are involved too, but in an unusual way.) • Because sensory receptors can in principle be excited without any external stimulus, perception must be subjectively indistinguishable from hallucination. Since hallucination is not about external events, perception cannot be either. Thus, RIM encourages the idea that ordinary perceptual experience is of sensory events internal to consciousness, not of the world beyond. (See Baron Reed, Chapter 3, and Paul Snowdon, Chapter 6, for critical discussion.) Additionally, philosophers have often assumed that since the receptoral image is constantly in flux, perception is momentary; temporally extended experience is a fusion of successive receptoral images, and involves memory, which is epistemically on a different footing. Consequently, they assume that: • Experience of change and movement are due to fused temporal sequences of momentary experiences of positions or qualities. (See Robin Le Poidevin, Chapter 24, about temporally extended perception.) • By the same token, insofar as speech and music are perceived, it is by fusing experience of a stream of momentary tones. (See Casey O’Callaghan, Chapter 25, on speech perception, and Charles Nussbaum, Chapter 26, on music perception.) These assumptions are, for the most part, gross oversimplifications; some (such as those concerning the colour mosaic, flavour, and speech) are completely false.

II What explains the dominance and long persistence of momentary RIM in philosophical theorizing? In large part, the answer is historical. RIM, in particular the claims (a) that certain aspects of perception, such as depth, are fallibly inferred, and (b) that hallucination is subjectively indistinguishable from ordinary perceptual experience (Snowdon, Chapter 6), leads quite naturally to the problem of scepticism (Reed, Chapter 3). Scepticism is one of the

Introduction   5 central problems of epistemology, with proponents vying with opponents who quest for theories of justification and of knowledge that can withstand the sceptical threat. Philosophers concentrated over the years on the ins and outs of the sceptical threat to knowledge, leaving unexamined the route by which they arrived at this dangerous place. Scepticism is a real philosophical problem, but it does not necessarily rest on RIM. In fact, as explained earlier, the explicit basis for this and other epistemological theories is a consideration of the role of inference in situations of uncertainty; preconceptions regarding sensory receptors play a merely heuristic role. Nevertheless, theoretical progress in epistemological conceptions of perception was retarded by RIM, because this framework provided a familiar context for motivating scepticism in relation to perception. The philosophy of perception has long been dominated by the so-called ‘problem of perception,’ the problem of how perception, which is often misleading about the external world, can nonetheless be a foundation for knowledge about the external world. Much less effort has gone into figuring out the nature of perception. To wit: is it really true that direct awareness is as RIM would have it? Traditionally, epistemologists took their main problem with regard to perception to be the uncertainty of beliefs that are based on perception. One might think, however, that epistemologists should be at least as vitally concerned to understand how we arrive at ordinary perceptual beliefs—how we get to a belief is, after all, at least partially independent of why it might be mistaken. Take this very simple question. Do we recognize a musical beat by internally timing successive pulses, or do we feel the beat more holistically? This is a positive question about how we arrive at a belief; it is relevant to whether the perception of musical rhythm depends entirely on a sense of temporal duration, and whether, if it does, this would show that it rests on memory. This question is independent of the sceptical question of whether what we hear is real or merely an illusion, and of the question whether we can ever be absolutely certain that a piece of music has a particular time signature. It is a question about the perceptual basis for the belief that a piece of music is a waltz. Is this belief directly delivered to us by perception, or does it rely on a more complex calculation? Considered in this context, the problem regarding the traditional RIM paradigm of perception is not that it encourages scepticism—there is nothing wrong with this—but rather that it offers an incomplete and often misleading account of quotidian perceptual belief and knowledge. It is true that colour mosaics sometimes simulate ordinary visual perception. This is precisely how object perception and motion perception is simulated on TV. Nevertheless, RIM is uninformative about the normal process of forming rational beliefs about objects and their movements in three-dimensional space. And here it is relevant that the psychological heuristic of momentary receptoral activation is based on false assumptions. For instance, it turns out to be false that the visual experience of movement is created by a post-perceptual summation of momentary experiences of objects in successive positions. The fact is rather that a specialized part of the visual brain detects distal motion (differentiating it from shifts of the retinal displays that are due to the subject’s own motion) without the intervention of the subject’s rational acuity in inference. It is also not true that we perceive objects by summing up retinal colour pixels; the brain has specialized pattern-detecting mechanisms for this (Roberto Casati, Chapter 20). As it turns out, our perception of movement and of objects does not depend on perceiving all of the temporal or spatial parts of these entities.

6   Mohan Matthen The philosophical theory about the uncertainty of inference from perception to belief could have been, should have been, and was maintained even after the psychological theory of sensory receptoral images had been long abandoned. This divergence, however, makes it all the more urgent to give a theory of the formation of ordinary perceptual beliefs. The best psychological theories of sensory awareness urge that consciousness presents us with something more substantial than receptoral arrays. At the same time, it is acknowledged that this sensory given is uncertain. (In fact, one important way of probing the perceptual given is to study the illusions that occur in normal perceptual situations.) This gives epistemologists strong motivation to offer better theories of how we ordinarily justify perceptual beliefs. (Susanna Siegel and Nicholas Silins, Chapter 41, discuss reason giving for fallible perceptual belief; Michael Rescorla, Chapter 37, E. Samuel Winer and Michael Snodgrass, Chapter 38, and John Kulvicki, Chapter 39, explain frameworks relevant for posing the problem of the perceptual given.) In a similar vein, the model of speech perception implicit in the music-analogy mentioned earlier gives us a false idea of how we come to know what people around us are saying (O’Callaghan, Chapter 25). Phoneme perception is not a summation of temporally punctate auditory experience; phonemes are temporally extended (though very brief) sound patterns—phonemes are minimal meaning-bearing units of spoken language; no part of a phoneme is heard as a speech sound, yet they are so heard as a whole. By itself, this is proof that perceptual experience is not merely a summation of temporally punctate sensations. As far as music is concerned, rhythm and phrasing is temporally extended (and of relatively long duration, compared to phonemes) but these too are perceived as wholes, not as units that the perceiver has to put together by her own agency (Nussbaum, Chapter 26). As well, vision is involved in speech perception; perception of speakers’ facial gestures modifies what we seem to hear. Speech and musical perception thus contradict the notion that intermodal and cross-temporal integration are always extra-perceptual mental operations. Auditory perception, in general, is experience of temporally extended objects—sounds—that often appear to change (Matthew Nudds, Chapter 15), or at least to have a non-uniform temporal profile. For instance, we might experience a single voiced melody as ululating; or a siren as rising in pitch. (These questions about speech and music perception are illuminated by the considerations about time discussed in Le Poidevin, Chapter 24.) Something like this is true of flavour too: when we savour food or wine, there is an early attack followed by extended finish. Think of spearmint gum: it might start sweet, then become cool, and finish with a slightly bitter ‘aftertaste’. This has to do in part with the dissipation of sugar, and it could be argued that spearmint offers us a progression of flavour experiences, rather than perception of one temporally extended flavour. However that might be, such progressions are predictable; they are, moreover, repeatable, and therefore important in the identification and evaluation of food and wine. In short, they are ecologically salient. (Barry Smith, Chapter 17, discusses.) Expert tasters become able to use such temporal profiles to refine expert discriminations by perceptual learning. (Robert Goldstone and Lisa Byrge, Chapter 42, provide a general introduction to perceptual learning.) The scientific study of perception was, until early in the twentieth century, rooted in many of the same philosophical assumptions that led to the wrong assumptions recounted in section I (and many others). For example, visual perception was thought, in the nineteenth century, to consist first in the transference of retinal images to the primary

Introduction   7 visual cortex, and then the extraction of information from this so-called ‘cortical retina’ by exploiting associations between retinal stimulations and distal features. This is a model that applies to the brain in a not very much modified version of Berkeley’s theory of vision. This model has two fatal weaknesses. First, it misconstrues the nature of the retinal image: the relevant entity is not the image thrown by the lens, but the firing of sensory neurons caused by this pattern of light. Secondly, the model does not transfer smoothly to other modalities. For example, the auditory cortex is a frequency-intensity mapping, not a spatial image. That is, the activation-level of different regions of this cortex corresponds to energy levels associated with a particular frequency, not with energy levels coming from a particular spatial direction.

III The laboratory study of perception began in the middle of the nineteenth century. (See Gary Hatfield, Chapter 5.) At first, it was dominated by the RIM paradigm: Müller held that the retinal image was transmitted to consciousness by the physical action of nerves. One of the great controversies of the late nineteenth century was the battle between Ewald Hering and Hermann von Helmholtz about the extraction of depth information from the disparity of the two retinal images. Helmholtz thought that the perception of three-dimensional space was learned by the association of ideas; Hering was more of a nativist. Science does not stand still. Gradually new discoveries began to widen the research focus. • In the Russo-Japanese War and the First World War, surgery had progressed to the point where soldiers who had been shot in the head could survive; often they survived with severe but localized brain lesions along the path of the bullet that penetrated their skulls. Starting in the early part of the twentieth century, many specialized perceptual deficits were discovered in patients with such lesions, some produced by injury, others by other adverse events, such as strokes or prolonged hypoxia. It was found, for example, that some people with normal visual acuity with respect to colours and lines were nonetheless unable to recognize forms that are composed of the lines they could see normally: familiar objects, such as shapes, faces, places, motion, speech, and alphanumeric symbols. These deficits are specialized—for example, the inability to recognize faces does not predict the inability to recognize shapes, and vice versa. • The perceptual deficits just mentioned are known as ‘agnosias’—they are recognitional failures with regard to a restricted domain of ‘higher-level’ (or composed) objects and features sitting on top of normal acuity with regard to their ‘lower-level’ components. The agnosias directly contradict the Receptoral Image Theory. They indicate perceptual deficits in the absence of receptoral defects. The existence of agnosia shows that awareness of objects is not entirely dependent on awareness of the parts out of which these objects are constructed. Agnosia cannot be a failure of inference as such, at least not if inference is construed as a general purpose capacity, since each agnosia is domain specific—a patient who fails to recognize faces may have no difficulty discerning motion and vice versa. Each agnosia is associated with a brain lesion

8   Mohan Matthen











in a specific area; each highlights a part of the brain that is specialized to extract from receptoral images content about a particular kind of higher-level perceptual object. • The agnosias indicate what is known as modular function in perception—separated processes for the extraction of distinct perceptual features (Ophelia Deroy, Chapter  40). As time passed, it became clear that there are separate processes for the extraction of even the lowest-level features, for example colour and form in vision. • Psychological evidence for awareness of higher-level perceptual objects was accumulated by the Gestalt psychologists, who articulated principles of object awareness (Hatfield, Chapter 5 and Casati, Chapter 20). They demonstrated that certain types of displays result in seeming awareness of objects, while others, though very similar, either do not or result in awareness of very differently shaped or configured objects. It can be inferred that object awareness is not learned by relations of association among receptoral arrays. • Along similar lines, Albert Michotte demonstrated that certain very simple types of temporal sequence have the look of causal connectedness—for example, one in which a simple shape (such as a square) approaches another simple shape, stops when the two touch, at which point the second shape starts moving. Perceivers typically find it hard to resist the appearance of causation (and even of animacy) in such displays. This shows that Hume was wrong to say we have no impression of ‘power’, and that the appearance of causality is nothing but a projection onto displays of the mind’s propensity to infer one event from another. There is a primitive impression of causal connection. • Single neuronal-cell electrical recordings and fMRI imaging demonstrated that certain brain areas are active when certain types of higher-level object are presented to perceivers: for example, colour (the fusiform gyrus), motion (visual area 5), faces (the fusiform face area), places (the hippocampal formation), speech (Wernicke’s area). This bolsters the conclusions drawn from agnosias above, inasmuch as it shows that specialized neuroanatomical structures are dedicated to extracting content about higher-level objects of specific kinds. (Deroy, Chapter 40 discusses the significance of the anatomical localization of this kind of function; see also Hilbert, Chapter 14). • Starting in the last two decades of the twentieth century, greater attention has been paid to multisensory integration (Bayne and Spence, Chapter 32; Smith, Chapter 17, O’Callaghan, Chapter 25). For example, when two simple shapes move along straight intersecting lines, they are seen as passing each other, describing an X. However, when a sound such as a pop or beep is played at the moment of intersection, the two shapes are seen as bouncing off one another (rather than as continuing along their own prior trajectories undisturbed). (This is as a multisensory version of Michotte’s experiments on the perception of causation.) Again, when a subject’s hand is hidden from view and stroked with a brush, while a clearly visible rubber toy hand is synchronously stroked with a brush, the feeling of stroking is spatially shifted to the visible rubber hand. This is, again, an integration of sensory stimulations in two modalities resulting in a single unified percept. Additionally, subjects report feeling that the rubber hand is their own, so there is also an involvement of interoception. (See Frédérique de Vignemont and Olivier Massin, Chapter 16; Alisa Mandrigin and Evan Thompson, Chapter 27; and Brendan Ritchie and Peter Carruthers, Chapter 18 for discussion of the rubber hand illusion.)

Introduction   9 These findings indicate that perception is not simply a matter of receiving external influences, but is rather a process which filters and analyses incoming data in a search for indications of significant external occurrences and states of affairs. Moreover, they indicate that consciousness can be perceptual; it is awareness of external objects and processes, not merely a reproduction of the state of our receptors within our bodies. Thus, RIM is increasingly giving way to the idea that perception presents us with a rich scene: objects of many sorts with properties that do not directly affect the sensory receptors. We literally and directly see objects, faces, places, and shapes; we hear melodies, voices, and phonemes, once again directly and not by painstakingly piecing them together by the use of learned experiential associations. We sense the location of events by both touch and sight working together; the modalities are not correlated by learned associations. Neuroscience and psychology are not the only sources of models for perception. Functional models treat perceptual systems as performing a ‘task’ without being specific about the physical means by which the task is performed. One particularly fruitful idea in this arena has been to treat of sensory receptor response as data, and the task as data processing with the aim of providing the organism with the means to respond productively to a changing environment. Note that data here are abstractly conceived. New analytic tools have also come to the forefront in the last few years to substantiate this conception. The models that are employed to understand perception have a significant constraint. Sensory data processing is ‘analogue’, in the sense that the system (a) has states that causally respond to sensory inputs, and (b) vary in a roughly continuous way with firing rates of neurons etc. Consequently, digital models that are widely used to model thought processes are of limited utility in the perceptual domain. The following have become entrenched in philosophical thinking: • Bayesian reasoning from probabilities, which neural sensory processing is found widely to implement. (Michael Rescorla writes about this in Chapter 37.) • Signal detection theory, which provides a framework for understanding how conscious perception is influenced by the context of inquiry, and perhaps by voluntary attention (E. Samuel Winer and Michael Snodgrass, Chapter 38). • Information theory, which gives an account of what kind of use can be made of environmental signals to adjust to the events from which they emanate (John Kulvicki, Chapter 39). Other analytic tools either are emerging or have receded from prominence—predictive coding is a candidate for future prominence, while connectionism seems to have faded; the current status of dynamic systems theory is clouded. The philosophy of perception tends to be conservatively selective in its attention to such structures, being more in tune with cognitive neuroscience, broadly speaking, than with the abstract mathematics of data processing. No doubt, this has a lot to do with the history of the subject; there are established problem areas in the field that arise from thinking about psychological function and neurological implementation. Abstract modelling has been slower to yield fruitful approaches to established philosophical problem areas—this could be the fault of philosophers, of course—the above-mentioned tools being exceptions. This could well change in the next few decades.

10   Mohan Matthen

IV In Europe, the very idea of perception emerged relatively late. Victor Caston contends in his chapter on Ancient Theories (Chapter 1) that the early Greek thinkers did not clearly distinguish perception from cognition, possessing only the verb ‘perceive’ to carve out the category—in Greek as in English, this verb does not necessarily connote sense perception. It was perhaps Plato who first attempted an analysis, saying that perception is passive, related specifically to certain bodily organs, and outside of rationality and thus shared with animals. This initiates a very long tradition of distinguishing between sense perception and discursive rationality: even today, it is not entirely clear what part of our awareness should be attributed to the senses, and what to learning and rational inference. It is this distinction, precisely, that is at issue when we speak of literally and directly seeing faces, hearing melodies, and (following Michotte) of apprehending causality perceptually. The developments related above tend to shift such entities from the realm of rational inference or learned association to that of perception. How does perception inform us of our surroundings? Two issues dominated the ancient debate and continue to have considerable importance today.2 The first concerns the causal influence of the object. For though it has always been agreed that objects make themselves known by causally influencing the sense organs and (further downstream) the mind, the exact nature of this influence has been hotly debated. A bright light makes me blink; a sudden loud sound startles me. This is perception. On the other hand, the Sun makes my skin get darker; it also makes heliotropic flowers change their orientation. It seems that these organic responses are not perception. Why not? Like the bright light, the Sun causally evokes an organic response. Aristotle charged his predecessors with being insufficiently mindful of the distinction between perception and changes of the latter sort. Aristotle himself considered perception to be the transference of form to the sense organ without matter: for example, when we see a coloured object, the colour is transferred to the sense organ, but without the physical substrate in which it resides. The sense organ has, according to this view, a neutral state that is disturbed by the reception of sensory form; when the organ is no longer in contact with the object, it returns to its neutral state. It ceases to reflect the form of the object with which it is causally connected, and returns to a state of receptivity to a fresh object of perception. Perception is a state of a specific kind, which must be maintained by the ongoing causal influence of the object. Aristotle’s form-without-matter theory appears to be modelled on the so-called telic senses, vision and audition, which record the presence and characteristics of distant objects and events. When we see or hear them, Aristotle wants to say something within us takes on the colour and sound of distant objects. It is unclear how this is meant to apply to the contact senses of touch, smell, and taste. Aristotle posits a medium for these, and presumably he thought that form is transmitted through the medium; in effect, this seems

2 

Brad Inwood contributed a great deal, including stretches of text, to my discussion of ancient theories. His help was indispensable because there is no separate chapter on the Epicureans and Stoics in this Handbook, and the Introduction serves partially to fill the gap.

Introduction   11 to subsume the contact senses to a telic model—just as colour is transmitted through ‘the transparent’ to the eye, so the fuzziness of a peach is transferred to the tactile sense organ by flesh. What could it mean to say that we receive the form of fuzziness when we feel a peach? Is there supposed to be something in us that becomes fuzzy, though without taking in the matter of the peach? This is implausible—even more so than to hold that the eye takes on the colour of the peach without its matter. (As noted earlier, the doctrine about colour is mistaken because, while it is true that the peach throws an orange image on the retina, the only thing relevant to perception is the neural activation caused by the image of the peach. Neural activation has no colour.) However this may be, why is the Sun’s influence on my skin not perception in Aristotle’s system? Perhaps, because my skin does not take on the Sun’s form in this causal transaction, but takes on a different form, a dark colour. This in turn means that the skin, by contrast with the sense organs, lacks the right sort of responsiveness. Perhaps more importantly, skin does not have a neutral state or ‘perceptual mean’, to which it immediately returns when it is not under the influence of the Sun. We perceive colour when the visual organ is pulled off its naturally colourless state by receiving an object’s form of colour. When the coloured object goes out of sight, its effect disappears; the visual organ immediately returns to the mean, and is then ready to take on the colour of whatever else comes into view. This is not true of my skin’s darkness when the Sun sets. Plausibly, though, my skin might perceive the Sun’s warmth. When it is warmed by the Sun, it does take on the Sun’s form, warmth; at night when the Sun has gone down, my skin ceases to register its warmth. Epicureans and Stoics, causal theorists along broadly similar lines, also built their theories of perception on the basis of their distinctive physical theories—atomic films shed by objects entering the sense organs for the Epicureans, qualitative changes in the organs of perception transmitted through a continuous physical medium for the Stoics. These philosophers do not use the distinctively Aristotelian apparatus of form and matter, but they echo Aristotle, nevertheless, by adopting a causal model based on the telic senses. A second issue in the ancient debate concerns the mental significance of perception from the point of view of the perceiver. According to Plato, perception competes with reason; according to Aristotle, it complements it. The senses ‘tell’ us that certain states of affairs obtain; reason and memory can equally well ‘tell’ us that perception is mistaken, or that it is correct. In short, perception delivers a message that can be evaluated as true or false. Both Plato and Aristotle are thereby committed to the view that just as reason delivers propositions for our consideration, so also does perception—what they disagree about is the reliability and coherence of the propositions delivered. Supposing that perception carries propositional content, what is the nature of the content? Both Plato and Aristotle restricted the features of which we are perceptually aware to those that the senses are especially attuned to. Colour, shape, and pitch are properties to which the senses are peculiarly attuned; being and unity are not. Colour, then, is a (or rather the) ‘proper sensible’ for vision. Both Plato and Aristotle insist, however, that the sensible qualities must come together in a central cognitive faculty. I apprehend the pale woman singing, her hand on my shoulder: this is a synthesis of what vision, audition, and touch tell me, a synthesis that cannot be performed by the individual senses since, for instance, colour is not special to touch and pressure not special to vision. It must,

12   Mohan Matthen therefore, be performed by some facility for sensory confluence. I recognize, moreover, that the woman’s pallor is different from the pitch of the notes she emits. This is an act of rational differentiation. Epicurus disagreed with Plato and Aristotle about the first point; he did not think that perception could be false. Provided that we properly focus our thoughts, he held, perception always leads us to the truth; ‘falsehood and error are always located in the opinion we add.’ It is likely that he blamed the faculty of judgement for false propositional content: if we form judgements in an appropriately receptive way, we will not err, but if we add something to ‘impression', then we risk error. (It would have been odd for Epicurus to think that falsity, but not truth, was ‘located in the opinion we add’. Most likely, this is what he thought—error is due to wrongful insistence. It was also open to him to take the position that perception is neither true nor false. Propositional content comes with judgement, or opinion.) Like Plato and Aristotle, the Stoics held that, in humans, perceptual states (which they called phantasiai, or ‘impressions’) convey articulable propositional content that leads to perceptual belief when accepted or rejected. They held, in addition, that these impressions ‘reveal themselves and their cause’, but here their position is nuanced. They hold that perception is generally reliable, but acknowledge that some impressions bring misinformation about the world. Sceptics conclude that this impugns the entire class of impressions. The Stoics disagree. For them, an important subset of perceptual impressions is marked by a self-validating clarity and reliability. When I look at something attentively in good light, for example, I can be certain that I see it as it actually is. Such ‘apprehensive impressions’ (katalēptikai phantasiai) are the foundation and touchstone by reference to which they believe that we can achieve certainty about the physical world. On the other hand, a square tower viewed from the distance looks round—this impression carries on its face its failure to be apprehensive, because the tower looks far away and shimmery. By taking this position, it should be noted, the Stoics align themselves with the idea that rational belief requires certainty. They both underestimate how illusions can take place even in the best conditions, and are also myopic with regard to the efficacy of probable reasoning, which was recognized by the Academic sceptic, Arcesilaus. On the other hand, they were prescient, as it turns out, in suggesting that the perceptual given includes self-regarding reliability estimates—vision doesn’t just tell you that a shape is concave; in many instances, it also includes an estimate of the reliability of this attribution, depending on the goodness of the illumination, the sharpness of resolution, and so on. RIM might suggest that estimates of reliability are necessarily post-perceptual, but there is reason to doubt this. (Rescorla, Chapter 37, discusses Bayesian models of perceptual processing, in which such estimates play a role.) The thinkers we have considered so far evaluate perception as true or as false. (I suggested that Epicurus had a bit of wiggle room here.) One could deny this; one could hold that perception, or rather sensation, is simply an effect created in consciousness by the outside world. We draw inferences about the external world from these effects, it could be held, but the accuracy or error of these inferences is not to be attributed to perception itself. This attitude becomes more prominent in the early modern period, when (as Alison Simmons notes in Chapter 4) Descartes distinguished between physical motions in the sense organs, the sensations occasioned by these, and judgements that we make on the back of these sensations. Only the last of these has propositional content. Descartes’s

Introduction   13 position on the issue of propositional content is thus importantly different from both Epicureanism and Stoicism, though his focus on clarity and distinctness is something he shares with both Hellenistic schools. These questions continue into medieval philosophy as Dominik Perler recounts in Chapter 2. He focuses on three key problems, each of which continues and draws on ancient philosophical discussion: What is the object of perception? What is the nature of the cognitive faculties that we need in order to apprehend these objects? And how trustworthy are the perceptual faculties with respect to what they reveal?

V Aristotle and Epicurus are in the same camp about the reliability of the senses. As we noted in section IV, Epicurus is the more optimistic—he does not think that there is false perception—but Aristotle too thinks that perception leads to rational knowledge (see especially Posterior Analytics II, 19). The Stoics too held that perception could be the foundation for knowledge, since for them, the ‘apprehensive impression’ is, once successfully identified, a reliable foundation for all further cognition. Plato was much more pessimistic on this matter. According to him, the senses deliver constantly shifting and contradictory information. They deliver a vague and confused message, which cannot be a foundation for knowledge even where they serve as a rough and ready guide to ordinary talk and action. The ancient sceptics (Reed, Chapter 3) took Plato’s pessimism to an extreme. Reacting against Stoics, Epicureans, and Aristotle alike, they sought to show that the senses are not to be trusted. Up until now, they say—that is, up until the moment of speaking—they have never been convinced of anything, neither by the senses nor by rational argument. Perhaps some day they will encounter an apprehensive impression that is so clear and distinct that it is self-validating, as the Stoics claim—but so far they haven’t experienced anything like this. Perhaps they will, sometime in the future, encounter a convincing argument that knowledge can be founded on the senses, but so far all that they have experienced is doubt. The sceptical ideology prevents them from making positive pronouncements about the reliability of the senses—they know nothing, not even that knowledge is impossible. They parade a comprehensive armoury of arguments against all possible claims to knowledge, but they do not affirm the completeness of their armoury against all possible challenge. There is, of course, a certain irony in this show of modesty. Though scepticism never completely slipped out of view as a philosophical tradition, it grew less important in the medieval period, with its emphasis on religious faith. Even then, the influential Persian Muslim philosopher, al Ghazali, had considerable affinity with scepticism, and sceptical aperçus are occasionally to be found in such Christian thinkers as Augustine. But outright scepticism was not an option for these thinkers in their culture. The ancient sceptics held that it was fine to play along with religious practice as a matter of ‘custom’, but not as a matter of belief. ‘Bend your head to worship: to do otherwise, would be to defy society, thereby showing epistemic arrogance. But do not believe in God.’ Such prevarication would have gone down as smoothly in medieval centres of Islam and Christianity as it does in contemporary South Carolina or Qom. Much later, scepticism re-emerged forcefully, first in fifteenth-century Italy, then when Henri Estienne translated

14   Mohan Matthen Sextus into Latin in 1562, and shortly thereafter in France with the essays of Montaigne. Descartes’s methodological scepticism, which owes much to Sextus, had a profoundly disruptive and revolutionary influence in the early modern period. Alison Simmons says in Chapter 4 that it led to a re-examination of ‘almost all aspects of perception’. Simmons points out, interestingly enough, that received views of perception came under attack, at this juncture, from science. The Scientific Revolution of the sixteenth and seventeenth centuries posited a world that was in its essence very different from the world that perception reveals. Atoms do not, for example, have colour or smell, not even unperceived colour and smell. If, as was increasingly popular to suppose, atoms are the ultimate stuff of physical reality, how can the larger objects composed of atoms have colour or smell? And what does this say about the veracity of our senses? This disjuncture between science and perception was addressed by a distinction between primary and secondary qualities discussed by Simmons and by Peter Ross (in Chapter 21). The idea traces back to Democritus: ‘by convention sweet and by convention bitter, by convention hot, by convention cold, by convention color; but in reality atoms and void’. The term ‘by convention’ is meant here to contrast with ‘by nature’. The idea is that things are not sweet, hot, or coloured in themselves, or by nature. Rather, they are so relative to the perceptual response of the observer. As Ross shows, Democritus’ idea and its successor, Locke’s distinction between primary and secondary qualities, has many different incarnations. Ontologically, some such distinction is needed to bridge the divide between the physical world as posited by science, and the ‘manifest image’ by which we initially know it. Perhaps the most enduring legacy of scepticism is the notion of a ‘veil of ideas’. Why should we refrain from accepting the evidence of our senses? One major reason is that this evidence is held to be equivocal, much more so than it appears to the naive observer. Objects of different sizes or colours can create the same sense perception if they are at different distances or in different conditions of illumination; the same thing can sound loud close up and faint further away; touch is modulated by pressure exerted; and so on (but see Cohen, Chapter 33, on Perceptual Constancy). According to the sceptic, this implies that any given perceptual state betokens many different real world situations, and thus fails to validate inference to any one of these. What is the similarity that defines sameness of perceptual state? The standard view in both medieval and early modern philosophy was that sameness was determined by the ideas entertained by the perceiver. These ideas constitute an intermediary or ‘veil’ through which we observe the world; perception offers us certainty with regard to the ideas, but not with regard to the world that lies beyond. The power of this doctrine is attested to by discussions in Perler (Chapter 2), Simmons (Chapter 4), Paul Snowdon (Chapter 6), Bence Nanay (Chapter 8), and Heather Logue (Chapter 11). Susanna Siegel and Nicholas Silins (Chapter 41) discuss how perception is reason-giving with respect to belief, and the implications for scepticism.

VI It has now become almost commonplace to note that the philosophy of perception suffered, until recently, from an excessive concentration on vision, which was taken as the proxy for all of the other senses. The result is, as David Hilbert puts it, that ‘vision itself,

Introduction   15 with its own peculiarities and distinctive features has a tendency to fade from view and what we are left with is a generic sense’ (Chapter 14). As Aristotle urged, it is necessary to bring the senses under a unified rubric. Otherwise, we will be unable to differentiate them from other information-gathering facilities such as the immune system. (Matthen, Chapter 30, and Ritchie and Carruthers, Chapter 18, take different approaches to this problem.) However, this unified rubric is insufficiently informative about the ‘peculiarities and distinctive features’ of individual sense modalities. Aristotle was aware of this. He gave a comprehensive characterization of sense perception (form without matter, neutral state of sense organs), but he also discusses the medium, special objects, and limitations of the individual senses separately. In actual fact, the senses are very diverse in character.3 It helps to remember that they are biological systems that evolved to give organisms an advantage by providing them with the means by which to respond effectively to the challenges of living and reproducing in surroundings that are constantly in flux. Thought of in this way, the senses are not simply information sinks—organs that happen to receive ambient information at their sensory receptors, leaving their possessors to determine how to use this information. Nor are they engineered to seek information optimal for the organism’s pre-existing needs. Rather, they are evolved systems, with all of the random fit to the environment that such systems display. The evolution of sensory systems usually begins modestly with an ecologically sensitive receptor that allows an organism to modify its behaviour to suit circumstances. The evolution of vision, for example, begins with molecules known as opsins, possibly derived from molecules involved in photosynthesis. These molecules afforded primitive organisms access to information carried by light; at first, the information available from this source is minimal—perhaps just enough to regulate circadian rhythms. In the case of audition, evolution starts from a fluid filled chamber that picks up vibrations from bones and other rigid structures; again, an organism would benefit from this, miniscule though the quantity of available information would have been. In both cases, evolution needs to add nerves that can communicate the state of these receptors to behaviour controllers. In time, it adds facilities to refine information collection. Given that each such step is a small advantage that a particular population of organisms manages to gain in its local environment, it is path dependent and unpredictable in advance how these systems evolve. The complex utilization of information carried by light and sound that we find in more recently evolved animals, such as mammals, is the outcome of a historically contingent evolutionary pathway from a starting point that could have presaged different outcomes if chance had played differently. Vision and audition illustrate the path dependency and contingency of these developments. Vision receives information from light, audition from sound. The wavelength of light closely matches the size of the molecules that make up the everyday objects light bounces off. Consequently, light interacts with the molecules of things that it encounters and is modified when it is reflected; reflected light is informative about enduring characteristics of the objects. Moreover, because of its short wavelength, light can be, and is,

3  I am grateful to Jonathan Cohen, Yasmina Jraissati, and Diana Raffman for critical discussion of this section.

16   Mohan Matthen focused by a lens; the resulting image recapitulates the spatial distribution of environmental sources of light (including self-luminous objects and reflecting objects). Combining these, vision extracts from light a ‘map’ or image of luminous and reflecting objects together with informational content concerning certain characteristics of these objects. Sound is very different. First, auditory information does not depend on ambient energy. Visual images come (in the main) from light reflected off objects. The source of this light, for example daylight, is constant and enveloping; it is a background condition of the information that arrives at the eye. Sound, on the other hand, has too long a wavelength to be focussed by a lens. Thus, the energy that carries auditory information comes from myriad local events, and is highly variable. (Right now, I am looking at a calm blue sky that illuminates everything outside my window and, more diffusely, everything inside. Sonically, however, I  hear only the banging of a garbage truck, which will shortly be replaced by silence.) Secondly, reflection scarcely (if at all) modifies sound, so reflected sound carries information about its ultimate source, not about the objects off which it is reflected. Finally, biology (and also, for that matter, human engineering) has not succeeded in constructing a lens that would produce a spatial image of the objects from which sound is reflected. (Ultrasound machines produce such images, but they have to produce sound, or ultrasound, and capture the returning echo. Ambient sound, which is unpredictable in direction and amplitude, will not do. Bats, of course, do the same, as do some blind people who produce a stream of sonic clicks, which affords them very rough echo-location.) Put all of this together, and the result is that sound carries information about events that produce it, but hardly any about objects off which it is reflected. Turning now to the receptors, the frequency composition of light cannot be exactly analysed by any biological system, while frequency composition of sound is much more easily analysed, using mechanical resonators. The basilar membrane in the inner ear consists of fibres, each of which has a different resonance frequency. To exaggerate just a little, it incorporates a dedicated receptor for each and every acoustic frequency. The analogue for light—specialized receptors for every frequency in the visible spectrum—is not biologically feasible. The visual system computes colour from the responses of just a few types of cells (three in the case of most humans), each of which responds to a broad visiblefrequency range. Colour vision does little more than register total energy in these broad ranges. (More precisely, it registers normalized differences between energy levels in these ranges. For more about colour vision, particularly about the extraction of information from cone cells, and the derivative character of colour perception in many situations, see Kathleen Akins and Martin Hahn, Chapter 22.) Audition extracts information about material objects by analysing the frequency composition of the sounds they produce. It identifies voices by timbre in speech; it identifies musical instruments and materials by the sounds they emit when struck, plucked, or bowed. This is event based: we recognize humans by the timbre of their voices, but only when they speak. The quality of this act of speech—somebody reciting ‘Mary had a little lamb’—reveals something about the voice—that it is a rich baritone from Lancashire—and enables us to recognize the voice when it sings something entirely different. Vision is different; the shape and colour of the face is directly revealed when light falls on it—these characteristics are not computed via the character of events. Light yields up only crude information about frequency composition—colour is subjectively one of the more salient characteristics of vision, but frequency (colour) information

Introduction   17 is actually surprisingly sparse by comparison to sound, and surprisingly little used by the visual system by comparison with brightness contrasts. Primates and birds—animals that have ‘good’ colour vision—share many perceptual discriminatory capacities with animals that do not possess equally good colour vision, and typically do not use colour information in exercising these capacities. In particular, visual perception of depth, three-dimensional shape, movement, and spatial layout are all available in black and white, as one can tell by looking at a black-and-white movie. To summarize: audition is concerned primarily with sound-producing events (Nudds, Chapter 15), the temporal order of these events, and properties of material objects that can be computed from the acoustic frequency composition of the sounds they produce. Light, on the other hand, yields to the visual system information primarily about the spatial configuration and distribution of objects, and their brightness relative to other things seen at the same time. (See Jérôme Dokic, Chapter 23, for a rich account of the structure of the visual representation of space.) Because vision is dependent on constant ambient illumination, and not so much on events involving objects, it engages more directly with the place and character of objects. The spatial character of both vision and touch give these senses dominant roles in our identification of particular objects. They are associated with demonstratives and pointing—‘that object,’ we say, pointing with our fingers or our eyes, and this attracts the gaze of our auditors. (How do vision and touch enable us to think about individual objects? Imogen Dickie poses the question in Chapter 43.) Vision and audition go in different directions in their engagement with the environment because they have different information-gathering resources available to them. Within their respective parameters, they target specialized objects, depending on the interests of species. Both birds and humans are specialized for identifying others of their species both visually and auditorily—humans are adept at recognizing human faces and voices, and at understanding human speech; birds tend to be specialized for producing and recognizing identifying song. These are ‘higher-level’ capacities. Let’s suppose, for the sake of argument, that humans and birds are equally good at discriminating lines and colours. It would not follow that they are equally good at recognizing birds and humans. Birds recognize bird song, not human speech; humans have it the other way around. This kind of specialization holds true for other sense modalities. Consider de Vignemont and Massin, Chapter 16, who argue that the proper object of touch is pressure. (They exclude temperature perception as a separate modality, as do Ritchie and Carruthers, Chapter 18.) Superficially, this conforms to the Aristotelian framework of proper sensibles. Their point is that the tactile perceptions of ‘texture, vibration, weight, contact, hardness, solidity’, etc. ‘depend on the perception of pressure and tension.’ ‘There is no sui generis sense of texture distinct from the sense of pressure,’ they write, ‘for we feel the texture of a surface by feeling a spatio-temporal pattern of pressure when stroking it.’ However, de Vignemont and Massin do not think that we go from experience of pressure to awareness of texture by inference. They are fully aware that the sense of touch delivers such haptic properties as texture and weight to sensory experience. This marks a departure from the traditional articulation of the special object view as proposed by philosophers as diverse as Aristotle and Hume—these traditional philosophers imply that we have sensory consciousness only of the proper sensibles such as pressure, and inferred knowledge of other properties such as texture. What scientists began to understand with the discovery of the agnosias (section II above) was that the ability to

18   Mohan Matthen recognize certain complex objects of the senses and awareness of these objects is simply provided to us by the perceptual brain. It does not require learning or inference in the classic sense of those terms. The specialized objects of perception are explored in Part IV of this Handbook. Flavour perception is quite a different entity from these senses. (See Smith, Chapter  17, for full discussion.) Whereas vision and audition are shaped by receptors and the kind of energy they receive, flavour is unified by its object: food and drink. The tongue has receptors for basic tastes—sweet, sour, bitter, salty, etc. These basic tastes differentiate many foods; the bitter warns of unhealthy toxins, and sweetness attracts us toward energy-rich foods. Flavour comprises a great deal more than these basic tastes. Take two sherbets, one of cherry, one of raspberry. The basic tastes differentiate them, but not by much. And why should they? Both are healthy, at least as far as our savannah-dwelling ancestors go. Both are sweet, and that is pretty much all the information the tongue gives us. As far as flavour goes, however, the two confections are very different. They are very easy to tell apart. The puzzle is this: if the tongue and its basic tastes do not differentiate, what does? The additional qualities come mainly from olfactory receptors in the nasal cavity. These receptors provide smell when we breathe and sniff. When we take substances into the mouth, their vapours rise to the nasal cavity and flow over the olfactory receptors. The flow is in the direction opposite to that when we breathe through the nose. Olfaction from the mouth is known as ‘retronasal’ olfaction. ‘Smells’ detected retronasally are experienced not as smells; rather, they contribute to the flavour properties of food. They are responsible for the experience of food over and above the basic tastes—but note that they meld in with taste and provide a unitary experience. The ‘taste’ of a cherry . . . no, that is just the sweetness and bit of sourness. The flavour of cherry, that’s the whole thing. Though olfaction contributes to the flavour of cherry, we cannot phenomenologically separate out the contribution of the olfactory receptors. We don’t experience a smell plus a taste; we experience a unified percept. Flavour perception is different from vision and audition in that it does not have information-humble beginnings. It has recruited an evolutionarily well-developed nasal system very late in evolutionary history—humans are almost unique in their use of retronasal olfaction—to work conjointly with another well-developed glottal system. Olfaction is well developed in animals; so is the taste system. Flavour perception in humans is the result of a coalition between the two. Flavour recruits olfactory receptors to enhance a preexisting system that already has a sophisticated nutrition-regulation function. The result is a system that discriminates food and drink far more finely than we need to discern what is healthy to eat and what is not. It seems as if all possible senses get involved when we put food in our mouths—taste, olfaction, touch (which plays a role in binding taste and olfactory qualities), the trigeminal pain system (Smith, Chapter 17)—and arrive together at a much finer discriminatory ability than even the higher primates can deploy. What is the biological point? Why do we not just make do with the system that the higher primates use? It may well be that, like language, flavour plays a role in the highly creative sociocultural system in which only humans participate. Perhaps, humans are more adaptable because of their flavour sense, and this could have contributed to their spread across the planet. Or perhaps flavour does not simply have utility for nutrition, but has as well a social and communicative role.

Introduction   19 The bodily senses (Ritchie and Carruthers, Chapter 18) provide another example of heterogeneous sensory processes that are nonetheless highly integrated. Models based on the external senses do not work smoothly with these. For, first, some internal sense events seem to lack a characteristic phenomenology. Consider the vestibular sense, which determines how we are oriented relative to gravitational forces. Ritchie and Carruthers (Chapter 18) suggest (though they do not come to a firm conclusion about this) that this sense may not present us with a direct message (e.g. that we are upright). It may, instead, feed this information to vision, in the form of visual field orientation, and proprioception, in the form of information about the positioning of our bodily parts. In other words, we may sense gravitational orientation only in terms of the orientation of objects, external and bodily. This puts the status of the vestibular sense into question. Is it a sense modality if it does not have a separate phenomenology? A second source of conceptual cloudiness is that it is difficult to decide whether the internal senses represent objective states of affairs, that is, events or states of the body, as opposed to presenting us merely with sensations. (Bence Nanay, Chapter 8, offers an overview of questions about perceptual representation.) Is an itch, for example, a perception (or misperception) of a certain type of objective event in the body, or is it merely a feeling? Recall the view (Simmons, Chapter 4, and section IV above) that perception is neither true nor false, but only a conscious event, or sensation, that we use to make judgements about the world outside us. This view, applied to bodily feelings, is thought by many to be unavoidable given the facts about bodily awareness. The question is closely related to another: if pains and other bodily feelings are perceptions of occurrences in the body, then it should be possible for this kind of occurrence to go unperceived, just as it is possible for a sound to occur unheard. Is it possible for me to have a pain in my finger of which I am completely unconscious? Many think that this makes no sense—pain is essentially conscious. What does this do to the idea that pain is perception? Valerie Hardcastle discusses these questions in Chapter 28. Jesse Prinz (Chapter 19) has a wide-ranging discussion of further questions about unconscious perception. For example, it is well demonstrated that subjects fail outwardly to respond to or inwardly to notice certain large events in their visual fields. Should we say that they nonetheless see these events? The answer is far from obvious. One important feature of internal perception is that it carries a certain feeling of ownership—the internal states of our bodies are felt as our own, and moreover our bodies are felt as the subjects of internal states. This intimate connection between ourselves and the things that happen in our bodies can be disrupted, but it has been argued, notably by Wittgenstein, that it is ultimately immune to error. Mandrigin and Thompson review the issue in Chapter 27, and Christopher Peacocke, Chapter 9, takes us through philosophically vital related issues of the first person perspective on objects of perception.

VII Despite the differences among individual senses discussed in section VI, commonalities of function and functioning should also be noted. It is characteristic of all of the senses that they present at least some of their content as a continuously varying quantity. As Diana Raffman writes, Chapter 36: ‘one object will

20   Mohan Matthen look bluer or larger, or darker or brighter, than another, and one tone will be louder than another, or sound more stable or more tonally centred in a given musical key.’ Plato was the first explicitly to notice this, in the Philebus. He argued that it was an indication of the incoherence of the senses (and also of pleasure) that their content is presented comparatively, in terms of ‘more and less’. It is a virtue of reason, he argues, that it imposes absolute limits on this indefinite substrate of the more and the less. Syllables and numbers mark well-defined absolute measures on pitch and tone and on indefinite quantity, he claims; they are contributed by the rational mind. Putting aside the normatively loaded claim about reason, Plato was prescient. In speech, pitch, tone, and timbre are comparative, while phonemes are not. In the realm of phonemes, there is ‘categorical perception’, by which a phoneme like /ba/ can be recognized as the same across different speakers, despite differences among them as to how they voice these phonemes—how loud, how high-pitched, whether in a bass or baritone, and so on. There is a somewhat analogous situation in colour perception too, where the named ‘basic’ colours (blue, red, green, etc.) look sharply different from one another, despite a continuously graded difference underlying these boundaries. It is because of this perceptual jump across colour boundaries that the rainbow appears banded, though it is actually a continuous wavelength gradient—there is a phenomenological jump between wavelengthadjacent shades of blue and green, but no such jump within blue or within green. Harmony might also be an instance of this: a gradient of gradually less discordant chords abruptly jumps to harmony. Diana Raffman (Chapter 36) deals with these issues; she also introduces us to the representation of similarity relations as abstract ‘spaces’ in which closeness represents similarity. Another characteristic of all of the senses is that they display ‘constancies’ (Cohen, Chapter 33). Constancy is most apparent and has been most studied in vision. The retinal image is a product not only of characteristics of external objects, but also of the circumstances of viewing. A white cloth will, for example, throw a red image onto the retina when it is bathed in red light. Yet, visual system function is to extract from this image a message about the characteristics of the colour of the object independently of the illumination in which it stands; the white object should look white, and within limits, it usually does. (Akins and Hahn, Chapter 22, have a nuanced discussion, relevant here, of how we come to see things as being of a colour.) The same sort of thing is true of the other senses. In audition, a voice can be heard as possessing constant qualities despite interfering noise from other sources; the sound of the car is kept separate from that of your passenger’s voice. In touch, a granite countertop is felt to be hard even when it is stroked with a soft polishing cloth, which presents its yielding structure to the hand. Constancy is generally thought of as revealing the orientation of the senses toward detecting properties of a stable external environment. As Cohen (Chapter 33) writes: ‘it seems clear that constancy is an absolutely fundamental aspect of perception, [which] will figure centrally in our ultimate understanding of mind–world interaction.’ Attention is a feature of perceptual systems, the facility by means of which we are able consciously to extract information from a perceptual state. There are many forms of attention. In the 1980s, Anne Treisman and co-workers showed that one form enabled ‘binding’. In the traditional RIM paradigm, form is extracted from colour and brightness, and this view is intuitively plausible because it seems, phenomenologically, that the boundaries of form and shape are in fact colour and brightness boundaries. However, it was becoming

Introduction   21 increasingly clear by the 1980s that form and colour were separately detected by separate parts of the brain. Treisman’s discovery was that, having been separately detected, colour and form are ‘bound’ together when the subject attends to them. This shows that the fundamental phenomenology of vision—that of the coincidence of colour and form boundaries—is in fact a product of attention, not just of simple perception. Attention and perception work together to produce characteristic visual appearances. John Campbell, Chapter 31, is on the trail of analogous synergies between perception (mainly vision) and attention. He explores how it makes knowledge possible and how it modifies perceptual experience. Though, as we saw in section VI, the senses are very different from one another in how they process information and how they present the world around us, there are clear communicative channels between them. Earlier we noticed that the perception of speech and of flavour are multi-modal; some say that touch is multi-modal as well. In Chapter 32, Bayne and Spence discuss forms of multi-modal perception. (Their view is nuanced, as they argue that we might never be conscious of more than one modality at any given time. Barry Smith also discusses multi-modal perception in Chapter 17.) One consequence of multi-modal interactions is that the modalities can sometimes get mixed up. One such confusion is synaesthesia. In a significant number of people, perception in one modality gets expressed in another. For example, some experience a particular colour whenever a particular musical note is played. There is also within-modality synaesthesia: some associate individual alphanumeric characters with individual colour, always experiencing, for instance, red when they read ‘6’. Malika Auvray and Ophelia Deroy discuss the varieties of the phenomenon and its proper philosophical description in Chapter 34. Another cross-modal ‘confusion’, often constructively employed, is the ability to use one modality in place of another—for instance, to retrieve visual information from specially arranged tactile stimulation. The phenomenon was discovered by Paul Bach-y-Rita in the 1970s. He converted the brightness levels in a scene into a vibratory field projected onto subjects’ backs. (Small vibrators were set to respond proportionally to the brightness of their field positions.) The result was astonishing. The subjects began to discern characteristically visual phenomena such as perspective and occlusion in the scenes before them, and were able to do so using just the tactile image projected onto their backs. This is the phenomenon called ‘sensory substitution’. Can we say that Bach-y-Rita’s patients saw the scenes in front of them? Julian Kiverstein, Mirko Farina, and Andy Clark explore the ramifications of this and other questions in Chapter 35. One particularly interesting feature about perception is that we are not all equally good at it. Some wine consumers cannot tell the difference between white and red wine; expert tasters can make fine distinctions regarding the origin and the age of wine. (There has been a good deal of scepticism evinced on this topic lately; some of it should be quashed by watching the documentary film Somm, which follows the trials of four candidates vying for the designation of master sommelier. However that might be, my point is quite simple—there are some who cannot make even the simplest distinction in this domain; there are others who can make quite a few more.) There are those who can recognize in a glance the provenance of an old painting; there are others who can barely tell whether it is Indonesian or French. Robert Goldstone and Lisa Byrge, Chapter 42, argue that at least some of these differences in discernment arise from ‘perceptual learning’. Perceptual discrimination is sharpened by repeated practice and exposure. Or, as Goldstone and Byrge write, ‘Perception can be learned. Experience shapes the way people see and hear.’

22   Mohan Matthen To end this section, a word about pictures. What is it about visual perception that allows us to see three-dimensional scenes in two-dimensional arrays of pigment? What is it about auditory perception that makes a musical sequence of tones bear emotional content? Why do we find value in these seemingly ephemeral exercises of our perceptual capacity? Dominic Lopes explores these questions in Chapter 45.

VIII The two preceding sections took up questions about sensory processes. For instance, we asked about visual processing and whether it is property based or event based; we asked about the vestibular sense and whether it has a distinctive phenomenology. Philosophers of perception also ask, more broadly, about the nature of perception as a general faculty. We have touched on some aspects of this question earlier, especially in connection with the history of the subject in sections IV and V above. Further questions remain. What is the nature of the connection between perceiver and the world they perceive? How does perception relate to belief and the rational justification of belief? Let us put idealism to one side—the position that there is nothing outside minds—and also scepticism—the position that we have no reason to believe anything about the external world. On neither of these views does the question arise of how perception rationally grounds belief about the external world: for the idealist, we do not perceive an external world; for the sceptic, beliefs about the external world are not justified by perception. The question then is this. Suppose we take it for granted that we have, or can have, rational beliefs about the external world. How would perception justify such a belief? The standard view in the seventeenth century up until the beginning of the twentieth, and among empiricists, for much longer, was that perception was directly of a realm of ideas, or sense data, that come between us and the external world, and only indirectly of the latter. As we saw in our earlier discussion of scepticism (section V), indirect realism is motivated by the argument from illusion—the idea that perception can fail. If two perceptual states are the same—say a mirage and a veridical perception of a distant body of water—then they must have the same object. Since the mirage fails, then, and by definition lacks an external object, the veridical perception must lack an external object too. Both lack an external object. They must both be directed to their common apparent object, which is internal. They are both directed toward a sense-datum; the difference is that the veridical perception happens to be validated by the actual presence of water on the horizon. As Paul Snowdon relates in his chapter, Chapter 6, this seems to posit an unanalysed psychological act-object relation and a realm of immaterial objects, sense-data. Sense-data are decidedly queer: when I see something blue, sense-datum theorists say, my visual state is directed at something in the mind. Things in the mind don’t have extension or colour. They are not literally blue, or literally any other colour. This rather mystical approach to the objects of perception did not sit well with the increasingly dominant mid-century ethos of naturalism and materialism. A. J. Ayer tried to wriggle out of the quandary by saying that the sense-datum theory was just a way of talking, an ‘alternative language’, as he put it, not a substantive ontological proposal. Coming from a strong partisan of the theory, this seemed like a desperate stratagem, for it is unclear how exactly the supposed

Introduction   23 sameness of two perceptual states is accommodated by a simple terminological shift away from ordinary object talk. Sense-datum theory passed out of fashion after Ayer; by 1980, despite some revisionary attempts to revive it by two Australians, Frank Jackson and Brian O’Shaughnessy, it was essentially gone from the scene. Some credit J. L. Austin and Ludwig Wittgenstein for the defeat of sense-datum theory. It is equally plausible to lay the blame at the feet of its last great proponent. Another view of the perceptual relation originates from the works of Franz Brentano and Edmund Husserl, treated together with the philosophy of Maurice Merleau-Ponty by Charles Siewert in his chapter on Phenomenological Approaches, Chapter 7. At some level, Brentano’s approach is similar to that of sense-datum theory. He proposes that, in a way, the ‘referent’ of perceptual states exists in the mind, and this is just the sense-datum view. However, Brentano introduced an important analogy between perception and linguistic affirmation. When I judge that there is a body of water on the horizon, I affirm something. There is something that I affirm, regardless of whether it is true or false. Something of the sort holds also for perception. The mirage of water on the horizon and the veridical perception of an actual wadi both ‘affirm’ the presence of water—that is what they have in common. The mirage is false; that is how it differs from the veridical perception. Husserl brought a sophisticated theory of meaning to Brentano’s basic insight and was thus able to evade the idea that the sameness of perceptual states must consist in the sameness of their ‘referent’. According to him, perceptual states have a noêma as sentences have a meaning, or Fregean sense. (Nanay, Chapter 8, shows how this approach is elaborated in contemporary analytic philosophy of perception, which deals with perceptual representation in terms taken from analytic philosophy of language.) This enabled him to show how two different perceptual states could have the same noêma, but, when external circumstances change, have different external referents. According to this way of thinking, the situation is analogous to the following: ‘Versailles is where the King of France lives,’ had the same meaning in the eighteenth century as it does now, but it was true then (the circumstances made it so) but false now. This provided Husserl with a new approach to defusing failures of perception. Perceptual states can also have different meanings but the same external referent. This is something that both Brentano and sense-datum theorists are unable to accommodate, but crucial to showing how perceptual states can have external referents. Husserl rids himself of intermediate entities in between the mind and the external world. He is a direct realist who has no need for an intermediate realm of immaterial entities. As Siewert tells us, there is an anti-scientistic strain in phenomenology, though this is later much tempered by Merleau-Ponty. Brentano and Husserl both insist that the meaning of perceptual states is directly available to perceivers. This attitude is the underpinning of Husserl’s later notion of a Lebenswelt or ‘life-world’: a socially constructed but deeply entrenched way of understanding the world given in perception. Scientific concepts, such as those that were employed by the psychologists of the time, were out of place in the psychological description of perceptual states. We do not, for example, perceive ordinary things as possessing reflectance or as emitting compression waves; rather, we perceive them as coloured and as noisy. This aspect of phenomenology has received less attention in analytic circles than it deserves. Two new approaches to the relationship between perception and world have entered the field in the last few decades:  ‘naive realism’, or disjunctivism, which Heather Logue writes about in Chapter 11, and ‘enactive’ accounts, which are dealt with in Pierre Jacob’s

24   Mohan Matthen chapter, Chapter 12. Disjunctivism is a return to a reference-only account of the sort that Husserl tried to escape with his notion of noêma. A perceptual state is, on this view, partially constituted by its object (or referent). As a consequence, a perceptual relation that I bear to one thing is as such different from the same perceptual relation borne to another, or to nothing. It follows that a hallucination, which has no object, is as such different from a veridical perception, which has an object. Perceivers may not be able to discern this difference, but it exists nonetheless. (Hallucinations and veridical perceptions may be indiscernible, but still they share no specific commonality; thus, they can be united only by a disjunction—hence the name, ‘disjunctivism’.) Logue details four different contexts in which this position has been advanced. John Campbell, in his chapter on attention, Chapter 31, argues that this phenomenon can be properly understood only on a disjunctive approach. Pierre Jacob introduces ‘action based accounts’ in Chapter 12—accounts which have also been called ‘sensorimotor’ and ‘enactivist’. Unlike disjunctivism, the primary motivation for these approaches is empirical; the idea is that enactivism best makes sense of certain experimentally determined facts about perception. This line of thought goes back to the work of J. J. Gibson, who claimed that we perceive ‘affordances’, or the possibilities for action that objects ‘afford’ us. For example, birds perceive branches of trees as possible places to perch; we perceive chairs and stools in an analogous way. An even earlier antecedent is Jakob von Uexküll’s influential notion that animals perceive the world in terms only of how it affects their actions, which is faintly echoed in Husserl’s notion of the life-world. Enactivism is sometimes applied to specific sorts of perception, rather than across the board. Jacob illustrates this with the perception of the actions of others. According to one important paradigm, we observe action by covertly simulating it. For instance, Giacomo Rizzolati and co-workers at the University of Parma have developed a paradigm in which perceiving somebody else reaching for an object is inwardly re-enacting oneself reaching for an object. They found, for example, that when a monkey looked at somebody reaching for an object or grasping it, the corresponding motor neuron, that is, the one by which the monkey would control the same action, is activated. By extension, we might perceive speech by inwardly mimicking it, attribute thoughts to others by rehearsing how we would ourselves think in their situation, and so on. Perceiving action is intimately tied up with performing it.

IX How we talk about perception—how we use verbs like ‘see’, for example—offers us some clues about how we use it. Berit Brogaard writes about perceptual reports in Chapter 13. She observes that the verb ‘seem’, which we often use non-perceptually, is an etymological cousin of ‘see’, and that the other perceptual verbs similarly have non-perceptual uses. These perceptual verbs are often used ‘epistemically’, that is, they are used to report beliefs, usually (but not always) beliefs that are perceptually supported—for example, ‘It looks as if the lecturer is late.’ (This, interestingly enough, reports an absence—Roy Sorensen, Chapter 29, discusses ways of approaching ‘Perceiving Nothings’.) As we noted earlier, perception was probably not recognized as a distinct faculty in early Greek philosophy; it was not clearly marked off in linguistic terms then, and it still is not

Introduction   25 in modern languages. As well, we use learned associations to describe beliefs, as Roderick Chisholm’s ‘comparative use’ shows: ‘The cliff looked like a dried-out body,’ to repeat a slightly macabre example of Brogaard’s. It seems plausible, then, to say that perception and belief are not clearly distinguished in ordinary talk. The philosophical question of how perception relates to and rationally supports belief is of relatively recent origin, and should be regarded not as intuitively founded, but the product of science and philosophical analysis. Ordinary speech does not make a clear distinction. If there is a rational connection between perception and belief, what does this tell us about perception? Some say that since belief is conceptually articulated, perception must be so as well. If my perceptual state is to rationalize the belief that this ball is white and smooth, and if white and smooth are concepts applied to the ball, then the perceptual state must contain these concepts too. How else would it rationalize the belief? John McDowell affirms this connection in a particularly strong form, holding (after Kant) that perception itself would not be possible if concepts were not drawn upon in the ‘receptivity’ that leads to perceptual experience. There are doubts. Some point out that animals would not be capable of perception on this account since they do not possess concepts. It could be argued in response that the explicit possession of concepts may not be needed for the reception of conceptually articulated content—there may be ways of registering the application of perceptual concepts to the ball that do not demand this. It is well to note that McDowell’s version of conceptual content would not be mitigated by this stipulation, since he requires that the concepts be drawn on in receptivity itself. The nest of issues surrounding perception and concepts are fully discussed by Wayne Wright, Chapter 10; animal perception is treated of by Brian Keeley in Chapter 44, who discusses the comparability of animal perception to that in humans. Let this suffice as a review of some broad issues about perception and to demonstrate the richness of the study and its utility for philosophical inquiry. The authors of this Handbook have produced original and searching, but at the same time introductory, surveys of issues at the forefront. I hope that you, the reader, benefit from their efforts.

Acknowledgements I am very grateful to the Canada Research Chairs programme, the Social Sciences and Humanities Research Council of Canada, and the University of Toronto for sustained support of my research. My post-graduate fellows, Dustin Stokes and Stephen Biggs, and my graduate students, Matthew Fulkerson and Kevin Connolly, have been an inspiration and a source of instruction. (Kevin served as post-doctoral fellow as well.) Peter Momtchiloff of Oxford University Press suggested this project and offered encouragement at times when things seemed especially difficult; Barry Smith, Ophelia Deroy, and the Centre for the Study of the Senses in London drew me in, pushed the project forward, and introduced me to the world beyond. Lana Kühle brought the project to completion with her invaluable editorial assistance and taught me a lot about phenomenological approaches while she was at it. Steven Coyne took on the preparation of the index with calm competence, and I am hugely appreciative.

Pa rt  I

H ISTOR IC A L BAC KGROU N D

Chapter 1

Perception i n A ncien t Gr eek Phil osoph y Victor Caston

Many of the central questions in the Western philosophical tradition about perception— regarding the metaphysics of perception, the nature of perceptual content, and the role of perception as a basis for empirical knowledge—were first raised in ancient Greece and Rome, where they were the subject of detailed discussion and debate. This chapter will concentrate on the first two concerns, the metaphysics of perception and its content, from the beginnings of Greek philosophy through Plato and Aristotle, when the main lines of inquiry are initially formed. The subsequent development of these issues in later antiquity—most notably, the treatment of propositional content in the Stoics; the Epicureans’ distinction between perceptual belief and what is given in perception; the sceptics’ worries about illusions and phenomenal indiscernibility; and the role of concepts in perception in later Platonism—is too large a subject to cover here.1 For each set of philosophers, I will touch briefly on four issues: how perception is related to the body and soul; the nature of perception itself, including accounts of individual senses; what can be perceived; and perceptual awareness.2

1  The emergence of perception as a philosophical topic There can be no doubt that the Greeks, from Homer on, frequently speak of seeing, hearing, smelling, tasting, and touching. But did early Greek philosophers regard these as

1  For a fuller treatment of these issues from the beginnings of Greek philosophy to later Neoplatonism, with translations and more extensive references to primary sources and scholarship, see my Perception in Ancient Philosophy (in progress). 2  In what follows, all translations are my own. I use standard abbreviations for the titles of ancient works, along with citations for Presocratic fragments and testimonia from H. Diels and W. Kranz, Die Fragmente der Vorsokratiker, 6th edn (= DK).

30   Victor Caston activities that naturally belong together and are distinct in kind from the other activities of living things? It might seem odd to question this, given the obviousness of organs like the eyes, ears, nose, tongue, and hands, not to mention the familiar manipulation of our bodies to get a better look at something or to come within earshot, as well as the inevitable impairments and injuries that frustrate such access. In light of these facts, it is easy to take talk about the senses for granted, as necessarily presupposing the concept of perception. But this presumption has been challenged in two opposing ways. Some have argued that perception was not originally viewed as a distinctive type of cognition. The early Greeks understood all cognitive functions on the model of the senses, taking thought and emotion to be closely identified with specific bodily organs similar to the eyes and ears, though internal to the body. Higher cognitive functions were only distinguished from perception gradually over time.3 At the other extreme, it has been argued that it is perception that is the latecomer here. Remarkably late, in fact. On this view, the original notion of perception is due to Plato (427–347 bce), developed for philosophical purposes in a specific passage of the Theaetetus (184–186). It is something confined to the organs, passive in nature, and non-cognitive, in contrast with the cognitive, rational activity of the soul by itself.4 So there is a question as to when a concept of perception first emerges, whether it is present from the beginning of reflection on the topic, or only a later development. Both views agree, however, that perception is not distinguished from other forms of cognition by earlier thinkers. This observation is not new. Aristotle (384–322 bce) and Theophrastus (371–287 bce), his colleague and former student, claim that their predecessors believed that perception and thought were ‘the same’ and a kind of bodily alteration.5 This is an overstatement in several regards, as Theophrastus seems to have recognized himself.6 But there is an element of truth as well in it that needs to be acknowledged. The verb aisthanesthai, which is standardly used by later philosophers for perceiving as a specific type of cognitive activity, occurs early on predominantly in a broad epistemic sense for noticing, realizing, or grasping some fact, much like broader uses of the English ‘perceive’. In such uses, what is noticed or recognized need not be an object of direct observation, but may be something arrived at by testimony or inference.7 The noun aisthêsis, in contrast, is used more narrowly for sense perception. But it only begins to appear somewhat later in the fifth century bce, much as the two views we considered above would predict. Still, it would be a mistake, methodologically speaking, to rely so heavily on a single term or family of cognate terms. There is no good reason to think that the use of a concept is ever tied so closely to a single word: terminology often develops later, well after conceptual distinctions have emerged and begun to firm up. Restricting our scope to specific terms would unnecessarily blinker our investigation. To appreciate this, we need only think of one of the more central themes in early Greek philosophy, the opposition between experience and reason, where the former is usually expressed simply by reference to the eyes and the ears. This opposition is unintelligible 3 

See esp. Snell, 1960: ch. 1 (‘Homer’s View of Man’). For a healthy corrective, see the excellent articles of Lesher (1994) and Hussey (1990). 4  Frede (1987). 5 Arist. DA 3.3, 427a21–7; Metaph. 4.5, 1009b12–15; Theophr. De sens. 4, 23. 6  For an excellent critical examination of these claims, see Laks, 1999: 255–62 and Lesher, 1994: 11–12; see also Caston, 1996: 25–7, 33–8. 7  For wide-ranging and detailed examination of the use of this family of terms before Plato, in both Ionic and Attic, philosophical and non-philosophical authors, see Schirren (1998).

Perception in Ancient Greek Philosophy    31 unless there is some significant contrast between two broad types of cognition, where the eyes, ears, and other sense organs represent a more or less unified group, whether or not they are denominated by a single noun like aisthêsis. On their own, we are repeatedly warned, our eyes and ears lead us into confusion and error; if they are to be of any use, we must bring our powers of understanding to bear. Heraclitus (6th–5th century bce) complains that the eyes and ears are ‘bad witnesses’ for those who do not understand the language of the senses, literally, those who have ‘barbarian’ souls (DK 22 B107). Epicharmus (early 5th century bce) goes further. He claims that it is the understanding (nous) which sees and hears, in contrast with ‘the others’—the ears and eyes themselves—which are paradoxically said to be ‘deaf and blind’ (DK 23 B12). Parmenides (early 5th century bce) suggests that we may have to disregard our sensory experience in an even more radical way. The goddess in his poem admonishes us not to follow our ‘aimless eye and echoing ear’, but to judge her argument solely by reason (logos),8 a trope echoed later by Empedocles (c.495–435 bce).9 Later in the fifth century, the Hippocratic treatise On Art claims that the causes of disease elude the ‘sight of the eyes’ and can only be grasped by the ‘sight of the mind’ (têi tês gnômês opsei, 11.1–2). The point of the contrast is not simply rhetorical or protreptic. The same opposition can be seen in Melissus’ argument (mid-5th century bce) that our experience of sensory qualities conflicts with the principles of logic, which can only be resolved by accepting monism (DK 30 B8). The contrast is likewise central in the epistemology of Democritus (mid-late 5th century bce). In his Canons, he distinguishes two forms of cognition (gnômê), one ‘legitimate,’ the other ‘illegitimate’ (skotiê, literally, ‘born in the shadows’), to which ‘all of these belong: sight, hearing, smell, taste, contact’ (DK 68 B11).10 The list of all five canonical senses, including touch, is striking and he even uses the verb aisthanesthai later in the fragment, making it clear that is ‘perceiving by contact’, rather than just coming into contact. Unlike Melissus, though, Democritus does not see the relationship between these two types of knowledge as a simple either/or choice. In another fragment he imagines the senses in a court of law, accusing reason of taking its evidence from them and using it to refute them; in so doing, the senses warn, reason will only undermine itself (DK 68 B125). The sophist Critias (460–403 bce) also uses the verb in a restricted sense, when he contrasts what is known by the mind (gignôskei) with ‘what is perceived by the rest of the body’ (aisthanetai, DK 88 B39). The noun aisthêsis likewise occurs before Plato in the relevant sense. It may be used as early as Alcmaeon of Croton (early 5th century) in a fragment that contrasts understanding with sense perception: he claims that while only humans possess understanding, all animals have perception (DK 24 B1a). Even if one questioned whether this is a verbatim quotation though, the general distinction is not in doubt. And the noun certainly occurs in the Pythagorean Philoloaus of Croton (c.470–380s bce), to mark a similar distinction between animals, humans, and plants, where the heart is the organ that governs animals and perception (DK 44 B13). A broad distinction between perception and reason, then, which had 8 

DK 28 B7.4–5. Something similar is reported for Xenophanes (DK 21 A32). In DK 31 B17.21, he urges us to look on the cosmological role of Love, not with ‘confused eyes’, but with our understanding instead. 10  For discussion, see Kahn, 1985:  19–21, although I  see Democritus as more continuous with the tradition than Kahn does. 9 

32   Victor Caston begun to emerge early in the 5th century bce, is firmly in place by the end of that century, well before Plato wrote. This is not to say that there are not competing conceptions of perception or of its range. When Plato offers a theory of perception in support of Protagorean relativism—which he hyperbolically claims is shared by nearly all of his predecessors (see section 3)—he not only characterizes the activities of canonical sense modalities like seeing, hearing, smelling, and feeling heat or cold as ‘perceptions’ (aisthêseis), but also pleasures and pains, desires, fears, and ‘countless others without a name’ (Tht. 156b2–7), a list that suggests a broader category of feeling or experience.11 But the existence of competing views over the extension of the concept, or even over its exact nature, is compatible with there already being to hand some broad notion of perception, as distinct from thought or reasoning.

2  The presocratics As far as we can tell from our sources, the Presocratics’ discussions of the senses were devoted largely to the physics and physiology of perception.12 Much of our evidence concerns how information about distant objects is transmitted by physical means across the intervening medium and into the orifices of various organs,13 along with a certain amount of detail on the structure and material constitution of these organs. One of the more elaborate and interesting accounts occurs in Empedocles, who describes humans as having narrow ‘receptors’—literally, ‘palms’ or devices for grasping (palamai)—spread throughout the body, though he complains that they are limited in what they are exposed to and wear down over time (DK 31 B2.1–3). He urges us to make use of every type of receptor and not to favour sight over hearing or hearing over taste or any others through which there is a ‘conduit for understanding’ (poros noêsai), so that we may understand ‘how each thing is manifest’ (DK 31 B3.9–13). The idea that perception involves conduits or channels (poroi) in the body is common among the Presocratics and goes back at least to Alcmaeon, who claimed that the peripheral sense organs were connected by conduits to a central organ, which he located in the brain (DK 24 A5; cf. A11). In Empedocles, the channels lie instead at the interface between subject and object. Their openings take in the ‘emanations’ (aporrhoiai) or streams of matter that flow from external objects through the intervening medium and enter not only obvious orifices such as ears or nostrils, but also tiny, imperceptible passageways that make up the crystalline lens of the eye and the porous membrane of the tongue.14

11 

Solmsen (1968) generalizes this point, in fact, arguing that the Greek aisthêsis and Latin sensus are ambiguous between perception and feeling throughout ancient philosophy. 12  Beare (1906), though questionable and outdated on many points, is still useful as a compendium for a preliminary survey of the evidence. Much of it derives from critical summaries in Aristotle and above all from Theophrastus’ De sensibus, an invaluable resource for early theories of perception. There is an English translation and commentary of the latter by the psychologist G. M. Stratton (1917), though it too is very dated and needs to be redone in light of recent advances. For an examination of the methodology of Theophrastus’ treatise, see Baltussen (2000). 13  On the ‘topology of sensation’, see Laks, 1999: 263–7. 14  The longest (and most famous) description of the poroi is not attributed to Empedocles directly, but to Gorgias as the student of Empedocles (DK 31 A92). But it is confirmed for Empedocles as the mechanism

Perception in Ancient Greek Philosophy    33 The conduits for each sense differ in gauge, so that only matter of a ‘commensurate’ size (summetros) can ‘fit’ into them snugly (enharmottein). This, Empedocles claims, explains why each sense has its own proper objects and cannot perceive those of another. A sense will not perceive qualities whose material is either too large to enter or so small that it passes through without making contact (DK 31 A86 §7; A90; cf. A87). Fitting into a conduit is merely a necessary condition, however. For perception to take place, the emanation must further encounter material of a similar kind within the subject, on the principle that ‘Like is known by Like’ (DK 31 A86 §15).15 This principle has both a causal dimension and an intentional one, concerning the content of perception: what we perceive on a given occasion must be like material inside our organs because (1) a perceptible object can only affect something like itself and thereby (2) bring about perception of itself. Both Aristotle and Theophrastus contrast this principle with Anaxagoras’ view that only unlike or contrary materials can affect each other and so stimulate perception (which they also connect to his view that all perception involves a kind of irritation or pain).16 In Empedocles, the likeness principle has a further significance, though. It is not possible without the analysis or separation of compounds into their constituent elements that he associates with the cosmological force of Strife. At the same time, perception also brings disparate things together, by fitting of matter into orifices and joining subject to object, and to this extent performs the work of Love (not unlike ‘knowing’ in the biblical sense). In his poem, Empedocles offers detailed and colourful descriptions of the mechanisms involved for the individual senses, most famously comparing the eye to a lantern, whose light passes through screens made of horn into the surrounding darkness. It has often been thought, starting with Aristotle, that this was part of extromission theory of vision, prefiguring the theory in Plato’s Timaeus (see section 3). But it is more likely a part of Empedocles’ account of night vision, which he appears to have discussed in some detail. Nocturnal animals must compensate for the surrounding darkness with larger amounts of fire inside the eye, which we can observe when we see their eyes flash in the night; diurnal animals, in contrast, require more water in order to compensate for the increased brightness during the day.17 He compared the ear to a bell, in which the sounds from our environment echo (De sens. 9 = DK 31 A86), though it is unclear exactly how an internal sound is supposed to help. As Theophrastus rightly objects, how would we in turn hear it? The same thing needs to be explained all over again, he complains, and a homuncular regress looms.18 for perception in general at DK 31 A86 (§§7, 9) and A87. On emanations (aporrhoiai) specifically, see DK 31 B89; also A86, §7. 15 

For the principle that ‘like is known by like’: DK 31 B109 (also Arist. DA 3.3, 427a27–9); DK 31 A86 §§1, 2, 10, 15, 17. Cf. DK 31 B90. 16  On contraries: Theophr. De sens. 27 (cf. 31–3); cf. Arist. DA 2.5, 416b35–417a2. On pain: Theophr. De sens. 17, 29. For a thorough examination of Anaxagoras’ general views on perception, especially his views that all perception involves pain or irritation and that there are least perceptible differences beyond which we cannot discriminate (DK 59 B21), see Warren, 2007: 19–36. 17  Lantern fragment: DK 31 B84; cf. A86 §7. Day and night vision: DK 31 A86 §§8, 18; cf. A91. For a defence of the interpretation here, see Caston (1986) and, along somewhat different lines, Sedley (1992). Katerina Ierodiakonou (2005) has demonstrated convincingly that Empedocles’ account of colour vision acknowledges only two primary colours, white and black (or more exactly, light and dark), the rest being the result of their mixture in various proportions (DK 31 A86 §59; cf. also DK 68 A135 §79). 18  De sens. 21 (= DK 31 A86 §21), reading to gar auto with the mss. Empedocles has little to say about the remaining senses. According to Theophrastus, he only links smelling to breathing and says nothing about

34   Victor Caston In virtually every ancient theory of perception, despite differences in physical theory and many details, one can find the basic framework of a causal theory of perception, the idea that the sensible characteristics of an object are in some way transmitted to the animal and affect its sense organs so as to produce a perception of those very characteristics and the object to which it belongs. Some of the variations, however, are significant and influential in their own right. The sophist Gorgias (early 5th century to early 4th bce), for example, is represented in Plato’s Meno as having been a student of Empedocles’ and accepted his theory of vision (76c4–e1 = DK 31 A92). Nevertheless, in his own work, the Encomium of Helen, Gorgias speaks of the soul being ‘impressed’ or ‘moulded’ (tupoutai) through sight with profound emotional and motivational effects (§15 = DK 82 B11), because of the way sight ‘inscribes on the mind likenesses of the things seen’ (eikonas tôn horômenôn pragmatôn hê opsis enegrapsen en tôi phronêmati, §17 = DK 82 B11), analogies which recur in Plato, Aristotle, and the Stoics. Democritus similarly speaks of an ‘impression’ (entupô­ sis) in explaining how sight comes about, comparing it to the moulds or imprints made in wax (hôsper kai autos legei paraballôn . . . hoion ei ekmaxeias eis kêron, DK 68 A135 §51, cf. 52).19 The image (emphasis) is not produced directly in the eye, however, but is impressed (tupousthai) into the air in front of it, which gets compressed between the eye and the emanation from the object (§50; cf. 74, 80). At first glance, this seems like a quite different theory than the one commonly ascribed to Democritus, which appeals to so-called ‘simulacra’ (eidôla) or ‘replicas’ (deikela), as he also called them (DK 68 B123): thin surface layers which are continually shed by objects and more or less preserve their shape as they move through space. But the two mechanisms are plainly compatible, and it is arguable that both are necessary. Distant objects cannot directly make an impression on the air in front of the eye, given their location. But their surface layers can, once they have become detached, so long as the arrangement of atoms retains a similar contour to the original object. On the other hand, it is plausible to think that only something fine and light like air could enter the eye, rather than the vast assortment of atoms emitted by objects. Democritus appears to have discussed the structure of the eye in extraordinary detail and paid special attention to the material conditions that would allow it to receive the impression. Among other things, the surface of the eye must be moist and have a thin exterior coating, free of thick grease or flesh, with fine, straight, empty passages to adapt to the impression’s shape (DK 68 A135 §50, cf. 52). Through these mechanisms, Democritus hoped to explain how the contours of an object could be transferred to the eye’s interior, along with information about perspective and possibly distance as well.20 Democritus devotes a great deal of attention to perceptible qualities such as colours and flavours, as well as certain tactile qualities like weight and hardness.21 He consistently appeals to the microstructure of objects to explain these qualities and geometric properties in particular. Most often these are characteristics of molecular structures: their overall size and shape, as well as the position and arrangement of specific types of atoms and void touch and taste beyond the general claim that all perception is due to emanations fitting into conduits (DK 31 A86 §§9, 20). 19 

Accepting Burchard’s correction of sklêron; cf. apomattetai kathaper kêros in §52. On the role of perspective, see Rudolph (2011); on the perception of distance, see Avotins (1980); on the structure of the eye, see Rudolph (2012). 21  DK 68 A135 §§61–82. The list of Democritus’ works includes titles for separate essays on colours and flavours (DK 68 B5g & h; A33). 20 

Perception in Ancient Greek Philosophy    35 within them (DK 68 A135 §§60, 67). In fact, it is unclear whether his explanations ever turn on the geometric features of individual atoms. Molecular structures are indisputably at issue in his explanations of the weight and hardness, which are functions not merely of the size and density of macroscopic objects, and so the amount of void included, but also whether the atoms are arranged in regular patterns. Iron is lighter than lead because it contains more void, but harder because of the irregular distribution of atoms, with certain areas more densely packed than others (DK 68 A135 §§61–2). But the ‘shapes’ (skhêmata) of molecular structures are also plainly at issue in his explanation of colours, which appeals to conduits and passages, or to lattices involving alternating pairings of atoms, or to large or small conglomerations of atoms (§§73–6, cf. 82).22 Democritus distinguished four primary colours:  white, black, red, and yellow-green (§§73–5). He seems to have allowed for something like metamerism, at least in the case of white: not only are the inner surfaces of shells white, because of their hard, smooth surfaces and straight conduits, but also substances that are soft and crumble easily, which are composed of lattices of spherical atoms in alternating offset pairs (§73, cf. 79). Black, in contrast, is due to rough, uneven surfaces, with crooked and tangled conduits (§§74, 80); red to the fine-textured atoms that cause heat, though only in larger agglomerations; and yellow-green to various specific arrangements of atoms and void (§75). The remaining colours result from mixtures of other colours, each mixed colour corresponding to a distinct proportion (§78). Democritus thinks there are an infinite number of them, but gives specific combinations for at least eight types of greens, blues, and browns (§§76–8). Flavours are also explained by reference to microscopic shapes (§68), though Theophrastus’ report never makes clear whether these are shapes of molecules or individual atoms. A spicy or piquant flavour, for example, is due to tiny, jagged, angular shapes, while sweet flavours are due to somewhat larger, round ones: the former tear at our organs and create spaces, thereby heating them, while the latter permeate our body slowly and gently, moistening it and causing other atoms to flow. His explanations for sour, sharp, salty, and acrid flavours all turn on the extent to which the microstructures in food heat or cool the organs, dry or moisten them, solidify or loosen them, pass through them, or plug them up.23 It is because of such explanations, no doubt, that Aristotle claimed that Democritus effectively reduced perceptible qualities to geometric properties. According to Aristotle, he refers all perceptible qualities back to what Aristotle calls ‘common perceptibles’ such as shape and size (eis tauta anagousin, eis ta skhêmata anagei, Sens. 4, 442b4–12) and so ‘makes them all tangible’ (hapta poiousin, 442a29–b1). But Theophrastus complains that these explanations contradict other things Democritus says, which effectively make perceptible qualities into ‘modifications of the senses’ (pathê poiôn tês aisthêseôs); he even goes so far as to say that on Democritus’ account there is no nature to any of the perceptible qualities (oudenos phusin), despite the detailed accounts of the microstructures involved that Theophrastus reports (DK 68 A135 §§60–1, 63, 71; cf. also A49). For Democritus also seems to have maintained that perceptible objects do not appear the same to every perceiver, and that would have to be explained, Theophrastus argues, by appealing to the 22 

See Fritz, 1953: 95–9, who was the first to emphasize this. For the explanation of different flavours, see DK 68 A135 §§65–7; A129. For a general statement of the underlying explanatory strategy in terms of physical effects, see DK 68 A130. 23 

36   Victor Caston different constitutions perceivers have or the different conditions they are presently in, rather than the nature of the objects themselves—as the Epicurean Colotes would later charge, they will ‘not be qualified one way rather than another’ (ou mallon toion ê toion).24 This might even be taken to suggest a subjectivist reading of Democritus’ notorious saying ‘by convention bitter, by convention sweet; but in reality, nothing but atoms and the void’ (DK 68 B9). On this reading, perceptible qualities just belong to our experience of objects and not to the objects themselves; if we believe they do, we will be in error quite globally.25 It is clear from Theophrastus’ reasoning, however, that Democritus is anything but a subjectivist about perceptible qualities, much less an eliminativist. His explanation of conflicting perceptual appearances is objective and causal: how things appear perceptually is a result of the way objects affect different perceivers, in their current condition (DK 68 B9 §136). This is also evident from the detailed explanations Theophrastus cites, which take the geometrical properties of objects to be the central explanatory factor of the qualitative character of our experiences, along with Democritus’ general view that not only perceptions, but the content of beliefs and other mental states are a function of our bodily condition, to be understood ultimately in terms of its microstructure.26 Finally, he also seems to have claimed that whatever appears to us perceptually is true.27 So he cannot have thought that we were generally in error about perceptible qualities. How can these different reports be reconciled? Here is one suggestion. First, distinguish perceptible qualities and perceptible objects, both of which can equally be expressed by the Greek aisthêta, and accept the detailed explanations we find in Theophrastus at face value. Then on Democritus’ view, whenever we have an experience of a certain quality, we have been affected by a specific type of microstructure that impinges on our organs.28 If he further identifies the perceptible quality with this microstructure, then every perception will be true of something in our environment, namely, the object which possesses the microstructure affecting us. On the other hand, even if it does belong to the object, it may not be the only microstructure the object possesses. Wine contains microstructures that taste sweet as well as those that taste sour; a pigeon’s neck possesses structures that look green as well as those that look purple. Which ones happen to affect us on a particular occasion will be a function of the conditions in our environment, how we are situated in it, and the nature and state of our organs. The jagged character of spicy particles of food cannot do anything other than tear animals’ tongues. But it may be prevented from achieving this effect, or at least lessened, because of the yogurt that presently coats my tongue. Similarly, if I eat a dessert between glasses of wine, I will no longer be affected predominantly by the sweet structures in the wine that moisten my tongue, but only the tannic ones. But it will not be any more (ou mallon) true to say that 24 

DK 68 A135 §§63–4, 69 and the context of DK 68 B156 (= Plut. Adv. Colot. 4, 1108f–1109a). our ancient sources, a subjectivist reading is most strongly suggested by Galen’s gloss on the quotation at Elem. Hipp. 1.2 (= DK 68 A49). 26  Perception: DK 68 A135 §64. Belief and other mental states: DK 68 B7; A135 §58; cf. A101. 27  DK 68 A112; A101; A135 §69. Some reports suggest that Democritus held the contrary view that no perception was true and so was caught in contradiction; but the view they cite as evidence for this only claims that no one class of perceptions has any greater claim to truth than any other, which is plainly compatible with them all being equally true. 28  In speaking of a ‘microstructure’ in a Democritean context, I mean a molecular compound, which is a part of something larger. What matters is structure and parthood, not absolute size. 25  Of

Perception in Ancient Greek Philosophy    37 the wine is sweet rather than sour (DK 68 A134; A112). It has both kinds of structure and so my perceptions are both equally true of it, since they accurately correspond to the flavour structures in it that are then affecting me. Whether it is true to say that the wine is sweet (or sour), therefore, is precisely a matter of ‘convention’ (nomos): it is a matter of which characterizations of wine are accepted predominantly by perceivers in the relevant community. But the truth of the matter, as Democritus says, is ‘in the depths’ (DK 68 B117). It depends on which microstructures an object possesses and which ones are actually affecting a perceiver on a given occasion, detailed facts from which we are ‘removed’ (DK 68 B6). Hence, we quite frequently do not grasp how each object truly is or is not (DK 68 B10). The perceptual variability Democritus invokes thus concerns how objects can appear differently to different perceivers or on different occasions. The specific microstructures, in contrast, will always ‘appear the same to everyone and so be a test of their truth’, a remark Theophrastus is otherwise at a complete loss to explain (DK 68 A135 §69). Where all causal conditions are the same, including the situation and state of the observer, how things qualitatively seem to a perceiver will be the same, ‘as he himself seems to attest’ (hoper kai autos an dox­ eien epimarturein), because the underlying nature of these qualities is the same (§70). The appearance of qualities is thus invariant. The only variation is in how objects appear, about the qualities they seem to have, which is a function of just which microstructures in an object are actually affecting a subject in a given set of circumstances.

3 Plato Perception looms large in the writings of Plato, not least because of the contrast he draws time and again between the ever-changing realm of perceptible objects and the stable realm of intelligible Forms.29 But his remarks about perception in its own right are also of interest independently of this and cast a long shadow over the subsequent tradition. Because most of his works are in dialogue form, it is difficult to determine whether the views expressed in them can be attributed to Plato himself, or even whether the views expressed in one work can be conjoined with those in another. But thankfully these questions do not need to be answered here. It is sufficient that Plato found such views worth exploring, critically and at length, whether or not he subscribed to them himself or even found them tempting. A feature that recurs in many of Plato’s works is a very strong form of dualism of soul and body, for which he offers some of the most striking statements that can be found in the Western tradition. Not only does he regularly distinguish between the two, but he also stresses the independence and autonomy of the soul in relation to the body. On several occasions he argues not only for the soul’s continued existence after death, but its also having existed prior to this life, separate from a body and knowing things by itself on its own. But if we ask where perception is to be located within this scheme, interestingly Plato’s works differ widely as to whether it is primarily the work of the body, the soul, or both body and soul; and, if it belongs to both, as to how their respective roles are to be distinguished.

29 E.g., Phd. 78b4–79e7; Rep. V, 475e6–480a13; VI, 509d1–511e3; Tim. 27d5–31b3, 51b6–52d1.

38   Victor Caston In the Phaedo, for example, the senses are treated as powers of the body. When Socrates urges us to leave sense experience behind and to use reason purely by itself, he characterizes this as a separation of the soul from the body. When, moreover, he disparages the senses unremittingly as not offering any clear or accurate information and as leading the soul into error and confusion, he assumes that perceptions have content.30 Thus, perceptual activity both belongs to the body and has content on this view. Several later dialogues, in contrast, regard the soul as the locus of perceptual awareness. Even if the body and the soul are both affected in perception (Phlb. 33d4–6, 34a3–5), we are not conscious of this stimulation unless this affection is transmitted through the body to the soul (epi tên psukhên, mekhri tês psukhês) or mind (epi ton phronimon).31 In a pivotal passage of the Theaetetus, Socrates argues that we do not perceive with (hois) our senses, but through (di’ hôn) them (184c1–e7). Instead, we perceive with our souls (184d4–5, 185d3–4). The senses on this view are merely ‘instruments’ or ‘tools’ (organa) through which we access the world.32 He then goes on to argue, even more strongly, that perceptions cannot themselves constitute knowledge because they cannot ‘attain truth’ (186d2–e10). The interpretation of this last claim is controversial. But some take it to mean that perceptions do not have content (for discussion, see below in this section). Republic VII falls somewhere between these extremes. Like the Phaedo, it contrasts the senses with the soul (523a10–525a2). The senses also plainly transmit information: they are said to ‘report’ to the soul (parangellei têi psukhêi, 524a3; têi psukhêi hai hermêneiai, b1). But sometimes they do this in seemingly contradictory ways. When touch, for example, ‘says’ (legei) that my finger is both hard and soft, or sight says it is both large and small, the soul puzzles over what the relevant sense ‘means’ (sêmainei) by ‘hard’ (524a6–10) and calls upon thought and reasoning to sort it out (524b3–d5; cf. X, 602c4–603a9). But other features can be fully discerned by the senses (ta hupo tês aisthêseôs krinomena), which ‘reveal’ (dêloi) their nature, as for example when I see that my finger is a finger (523a10–b4, cf. c3, d5). In both cases, the activity of the senses has content and in the second they can even attain truth (cf. Phdr. 249b6–c1). In various dialogues, there is also discussion of the nature of perception as such and how it comes about. In the Theaetetus, Plato examines at length a causal theory of perception, which holds that our perceptions are about the very objects that bring them about.33 Discussion of it is complicated by the highly dialectical context in which it occurs. Socrates offers it in support of Protagorean relativism—the view that things actually are just as they appear for each person, at least as far as perception is concerned (152a1–c6)— to which the first half of the dialogue is devoted. But he also makes clear that this causal theory is not something the historical Protagoras was ever known to advocate. Socrates mischievously presents it as an esoteric ‘secret doctrine’ that Protagoras revealed only to his inner circle (152c8–10; 155d9–e1) and a ‘mystery’ which only the initiated know about (156a2–4, cf. 155e3), and in developing it draws heavily on Heraclitean notions of flux. 30 

65a9–b7; 65e6–66a8; 66d7–67b2; 79a1–c8; 83a1–b4; cf. 83d4–e3. Tim. 43c4–7, 45d1–3, 64b3–c7; Phlb. 33d2–34a5; cf. Tht. 186b11–c2. In these dialogues Plato seems to be saying that the perceiver is aware not merely of external objects, but of how they affect our body as well. On the bifurcated character of perception that results, see Ganson, 2005: esp. 1–2, 3–4. 32  Tht.184d4, 185c7–8; cf. 184d7–e7, 185d1–2, e7. 33  There are interesting parallels with Aristotle’s own theory, although they differ on several points. See section 4. 31 

Perception in Ancient Greek Philosophy    39 There is no decisive evidence that Plato accepted this causal theory himself either, though this is often assumed.34 It is explicitly offered as an amalgam of views shared by virtually all of his predecessors, from Homer on down, with Parmenides being the sole exception (152e1–153a4; cf. 155e–156a). The core idea is that perception arises when a perceptible object and a perceiver’s sense organ encounter each other and causally interact (153d8–154a3, 160c4–5). The object has the power to act, the organ the power to be acted upon (156a6–7, 182a6–9), and when they have ‘intercourse’, they produce a pair of ‘twins’ as offspring, an act of perceiving (aisthêsis) and a perceptible quality (aisthêton, 156a7–b1)—in fact, Plato coins the word ‘quality’ (poiotês) to characterize the latter more generally when he later summarizes this view (182a9–b1). The twins in turn qualify the ‘parents’: when the eye, for example, encounters a stone or a piece of wood and they together generate the twins whiteness and sight, the eye ‘becomes, not sight, but a seeing eye’ and the stone or wood ‘becomes not whiteness, but white’ (156d3–e9, 182a7–9). This sort of view, Plato argues, entails that objects only have perceptible qualities while a perceiver perceives them on a given occasion (156d5, 160b1–8). They are ‘private’ (idion) in the sense that they exist only in these individual encounters, in relation to the perceiver to whom it appears (154a2–3; cf. 166c4–7). No one else, he claims, can perceive the very same quality, just as that particular act of perceiving can only be directed at it (159e7–160a3, 160c4–5). But if perception is always directed at the object it is presently interacting with, as it is qualified through the interaction, then perception necessarily corresponds to its object and is unerringly true (160c7–9). In Plato’s view, the causal theory of perception underlying his predecessors’ views thus leads to and supports Protagoras’ relativism (160d1–3), as least with regard to perceptible qualities.35 Plato also explores a causal theory of perception in the Timaeus, where one likewise perceives objects as having certain qualities as a result of those very qualities acting on the relevant sense, but adds extensive details about the physical mechanisms of perception and the nature of the perceptible qualities themselves. He distinguishes between those affections which are common to the body as a whole—essentially those relating to touch, along with pleasure and pain—and those which are exclusive to particular organs, such as the tongue, the nose, the ears, and the eyes (65b4–c1; cf. 64a2–5). Like Democritus, all of his accounts are based on the magnitudes and geometric structure of physical objects, together with the causal powers they have as a consequence, except that Plato appeals to the geometrical properties of elemental particles rather than molecular structures. He seems to take perceptible qualities, moreover, to be the effect (pathêma) of these geometric properties on our body, rather than the properties themselves. Among tactile qualities, for example, the searing quality of heat is due to the sharpness of the fire atoms responsible for it and the way they cut and penetrate our body (61d5–62a5); things feel soft when their particles yield and give way, because they have a smaller width, and hard when they are more 34  Day (1997) offers an extended and detailed critique of this assumption, though the position is anticipated in basic outline by Fine (1988). The following, though, can perhaps be admitted. Because the ‘secret doctrine’ of the Theaetetus is embedded in a discussion of Heracliteanism, the exact nature of the theory is something of a moving target (appropriately enough). The extreme form it ultimately takes in the Theaetetus (181d9–182a1), therefore, and which makes it vulnerable to refutation, may not imperil the more moderate version that is first introduced — a view, in fact, that Plato never expressly rejects. 35 Socrates twice concedes that the theory might be more defensible if restricted to perceptible properties, especially those with which one is presently interacting (171d9–e3, 179c2–7).

40   Victor Caston rectangular and resistant (62b7–8); other tactile qualities are handled in a similar way.36 In bringing about perception, most qualities either consolidate or disperse the elements composing bodies (65a3–5); and because the same mechanism is involved, the quality spaces of the different sense modalities share certain correspondences, despite producing different phenomenal experiences (67d6–e4). In the case of flavours, these changes are due mostly to roughness and smoothness, and whether these characteristics melt or cut the tongue, produce tiny blisters, or moisten and assuage it (65c1–66c7).37 The sense of smell constitutes an interesting exception. Since none of the elemental shapes is inherently suited to the nostrils, on his view odour does not belong to any of the elements on their own, but only compound bodies undergoing a change of state, to liquid or gas (66d1–67a6).38 Sound is air striking the brain and blood, via the ears, which is transmitted to the soul, and the change caused by this is hearing. It is high-pitched when the blow occurs quickly, and low when it occurs slowly (67a7–b6).39 Plato devotes the most space to vision. There is a special kind of fire inside the eye that flows out through the pupil in a ‘visual stream’ (to tês opseôs rheuma) to meet an emanation from the object, which together form a single continuous, material link to the object and transmit changes originating from the object back to the subject’s soul, where seeing occurs (45b–d; cf. 58c5–7). Depending on the size of the particles emanating from an object, different colours are seen. Those which are bigger than the ones in the visual stream consolidate the stream and are dark; those which are smaller fragment or disperse it and are light; those which are equal in size cannot be seen (67d2–e6). When fire particles penetrate into the eyes’ channels and meet the fire inside, a dazzling effect occurs (67e6–68b1). Various hues are explained as mixtures of the brilliance that produces this together with white and then subsequently with other colours, although Plato insists that it is impossible for mortals to give a precise account of these matters (68d2–7; cf. b6–8).40 Plato’s views on perceptual content are harder to elicit. But many recent commentators have taken one of the central arguments in the Theaetetus to have profound consequences for his conception of it, at least at one stage. As has been mentioned, Socrates argues that we do not perceive qualities like white and black or high and low with our sense organs (184b7–c8). Instead, we perceive through the senses: the effects perceptible objects have on them are transmitted through the body to a single ‘form, soul, or whatever it ought to be called’.41 If they did not converge on some single thing, the senses would be like the different soldiers inside the Trojan Horse (184d1–2), rather than parts of a unified subject of experience. It would be impossible to differentiate or compare the different things we do perceive, since none of the senses is able to perceive the objects of another (184e8–185c8). Any features these things exhibit in common, moreover—such as being, number, sameness or difference, 36  See the analyses for cold (62a5–b6), hard (62b6–c3), rough (63e10), and smooth (63e10–64a1). Plato also discusses heavy and light, understood in terms of the heft of an object, at length: 62c3–e4. 37  Plato offers detailed explanations for why foods taste acrid (65d3), sour (65d4), bitter (65d4–e1), salty (65e1–4), spicy (65e4–66a2), acidic (66a2–b7), and sweet (66b7–c7). 38  There are only two types of odour, according to Plato, neither of which has a name, but one is pleasant, the other painful (67a1–6). 39  Plato also distinguishes between smooth and rough sounds (67b7) and loud and soft ones (67c1). 40 Plato offers explanations for red (68b3–5), golden (68b5–6), purple (68b8–c1), indigo (68c1–2), amber (68c3), gray (68c3–4), yellow (68c4), blue (68c5–6), azure (68c6–7), and green (68c7). For a general discussion of the theory of perception in the Timaeus, see Brisson (1997), including the appendix (167–76), which provides a running commentary on the passage on colours. 41  Tht. 184d3–5, 185a5, c7–8; cf. 185d8.

Perception in Ancient Greek Philosophy    41 similarity or dissimilarity, and being admirable or shameful, good and bad—are things which the soul is aware of on its own, not through any bodily organ (185c4–d3, 186a2–b1).42 One of these common features in particular is pivotal to Socrates’ argument. Being, he reiterates, is not something grasped through perception, but only by the soul on its own (186a2–c5; cf. 185d8–e2). But since one cannot attain truth without ‘attaining being’ (186c7–d1), it follows that perception cannot attain truth (d4–5, e4–5); and given that one cannot attain knowledge without truth, Socrates argues, knowledge cannot be found in perception itself, but only in our reasoning about perception (186d2–3, e4–7). What is it to ‘attain’ or ‘grasp’ being, though? If we follow the interpretations most prevalent today,43 what is at issue is the predicative or copulative use of the verb ‘to be’, that is, whether we can perceive that a given object is a certain sort of thing or perceive it as being some sort of thing— in short, whether perception has propositional content or indeed any content at all. If things do not seem to be a certain way in perception, then perceptions cannot even be true and so a fortiori cannot constitute knowledge. Only the soul’s judgements about perception will have content. The resulting view radically degrades perception. It is hard to see how it can involve awareness or even ‘registering’, as some of these interpretations claim, much less the transmission of information or ‘reports’, such as we find in the Republic. If touch does not enable us to feel something as hard or soft (cf. 186b2–4), for example, and so does not have the power to discriminate between different tactile qualities, it is not clear what the activity of the senses involves beyond a mere bodily affection. This might be a reason why Socrates goes on to speak about the soul becoming aware of the affections in the body which are transmitted to it (186c1–2). Another possibility, though, is that Socrates is not denying that perception in general has content, but only that it has content involving the ‘common’ features he focuses on, of which being is just one. His concern with being, moreover, is not a concern with predication and truth generally, but rather with what things really are—that is, with what their essence or nature is—along with other ‘common’ concerns, such as whether they are the same or different as other things, similar or dissimilar, good or bad, and so forth. In short, he is concerned with knowledge of deeper, underlying truths about things that go beyond mere appearance.44 This would not only fit dialectically with the rest of the dialogue, as part of a general stance against Protagoras and his sympathizers, but would connect this discussion with one of the main themes that runs throughout earlier Greek philosophy, namely, the search for the real 42  Several

of these topics—namely, the unity of consciousness, the ability to discriminate qualities from different modalities, and the ability to perceive features common to the different modalities—are developed in somewhat different ways by Aristotle: see section 4; see also Turnbull (1978). 43  Most current readings are influenced in one way or another by a trio of papers, originally written in the early 1970s: Burnyeat (1976), Frede (1987), and Cooper (1970). Burnyeat and Frede both take the hard line traced out here, while Cooper explores more moderate, hybrid positions. 44  This reading is especially natural if we read the gloss on ‘being’ (ousia) at 186b6, kai hoti eston, as ‘that is, what they are’ rather than ‘that is, the fact that they are’, as it is standardly rendered. (McDowell (1973) is an exception: for his defence of the former reading, see 111, cf. 191.) One need not think that some ‘rational intuition’ of Platonic Forms is intended here, as is sometimes claimed. All that is required is that the being (ousia) of things should be understood, as so often, in terms of what something really is, its nature or essence. Nothing further need be intimated here about the metaphysics involved, such as that they are Platonic Forms with certain distinctive characteristics. As for how we know them, Plato is quite explicit in this passage that it is not through some kind of rational ‘vision’, but rather by reasoning: making comparisons, drawing inferences, and testing (see also Rep. X, 602c4–603a9).

42   Victor Caston nature of things beneath the play of conflicting appearances. On this alternative reading, the senses do transmit information about the world and do have content. But they cannot grasp the deeper truth about things on their own, because they cannot compare and sift through our experiences, to reach an underlying explanation. To accomplish this, we must work over the information that comes through the senses with the reasoning powers of the soul. If something like this is right, then this passage is not so far off views we have already come across in the Republic or even the Phaedo. There is reason, moreover, to think that in the later dialogues perception does have content of some kind. In the Philebus, Plato discusses how we can be puzzled over what appears to us, for example, about whether something near a rock under a tree is a human or not (38c12–d10). This sort of reflective questioning and weighing up of alternatives is how Plato elsewhere characterizes thinking more generally, as a ‘silent dialogue’ the soul has with itself, uttering its thoughts in a kind of silent speech—a language of thought, if you will—which finally issues in a belief, if the soul succeeds in arriving at a conclusion.45 In the Philebus, he playfully compares the soul to a book and suggests that there is a scribe inside of us writing down what appears to us to be the case. But he elucidates this metaphor by saying that it is our perceptions, memories, and experiences which ‘inscribe’ these words in our souls (hoion graphein hêmôn en tais psukhais logous, 38e12–39a7). Perception is not a passive, inarticulate affection, about which we form interpretations separately in thought. On the contrary, perception articulates a view about how things are, which we may or may not accept, based on how it agrees or disagrees with our other perceptions, memories, and experiences. The resulting discourse in the soul is not pure and abstract either. He suggests that there is also a painter in our soul who illustrates it, providing images from sight or other senses which can in some sense be seen within ourselves (39b3–c1). In the Sophist, belief similarly does not arise just from the soul’s silent thought on its own, but from perception as well, in which case it is called ‘representation’ (phantasia, 264a4–6). But he emphasizes that all of these states are ‘akin to language’ (tôi logôi sungenôn) and so capable of falsehood (264b1–4). There is no strict division of labour here with regard to content, where perception is viewed as entirely non-cognitive and interpreted separately by thought—all of these states have articulable content. The contrast that interests Plato is rather between how things immediately appear to us and how they appear on reflection, through the cooperation of all of our faculties, especially rational ones. Plato has a few, mostly critical things to say about perceiving that we perceive, made in passing, since it serves mainly as a foil to self-knowledge, which is his primary concern. In Alcibiades I, Socrates suggests that our eyes could follow the Delphic inscription to ‘Know Thyself’ by looking in a mirror at ourselves, in particular our pupils, where seeing is said to occur (132d5–133b5). But we cannot achieve self-knowledge in this way, since the self, considered on its own, cannot be identified with the body or with the composite of body and soul, but only with the soul alone (129b1–131a3). In the Charmides, Plato considers reflexive mental attitudes more generally to see whether it is even coherent to speak about selfknowledge. Using sight and hearing as his prime examples, he says that we could not see that we see or hear that we hear, unless seeing or hearing were themselves visible and audible and so possessed colour or sound respectively (168d3–169a7; cf. 167c8–d10). None of this, however, precludes the possibility that we might perceive that we see or hear, without 45 

Tht. 189e4–190a6; Soph. 263e12–264b1.

Perception in Ancient Greek Philosophy    43 literally seeing or hearing these activities, a suggestion Aristotle would make in due course when taking up very similar objections.46

4 Aristotle In the opening chapter of his treatise On the Soul, Aristotle considers whether any psychological state—in which he explicitly includes ‘perceiving generally’ (holôs aisthanesthai)— occurs exclusively (idion) in the soul. He argues that none does. Rather, they are all ‘shared’ (koinon) with the body, which in each case does or undergoes something at the same time (1.1, 403a3–7, a16–19).47 An adequate definition of perception must therefore refer not only to the kinds of formal characteristics the analytic philosopher (ho dialektikos) focuses on, but also the underlying material structures and changes the natural philosopher (ho phusikos) studies (403a29–b9). Thus, while Aristotle distinguishes between what it is to be a sense—that is, the power to perceive—and what it is to be a sense organ, he nonetheless regards a sense and the corresponding sense organ as ‘one and the same’ (2.12, 424a24– 8). Like the soul and the body, they are one in the way that matter and form in general are one (2.1, 412b6–9; cf. 412b17–413a3). As with other psychological states, Aristotle distinguishes between the power (dunamis) to perceive and its exercise or activity (energeia). Having this power, whether it is being exercised or not, is what distinguishes animals from plants and is the basis for other related powers that they share, such as the capacity for feelings of pleasure and pain, desire, representation, and dreams.48 Perceiving is the exercise of this power: it is not a modification or alteration away from this power, in the way that acquiring or losing the ability would be, but rather the realization of its own nature (2.5, 417b2–16).49 Perceiving is a change brought about by the object of perception itself: the object has the active power to affect the sense organ and by acting on it brings it into activity. As with other agent–patient interactions, the activity of the perceptible object and the activity of the sense are not two parallel events, but a single event, taking place in the organ acted upon. They are ‘one and 46  DA 3.2, 425b17–25; Somn. 2, 455a15–22; see section 4. For discussion of the Charmides passage and Aristotle’s response to it, see Caston, 2002: 768–73, esp. 772–3 and 79. 47  The only possible exception Aristotle considers is understanding (noein), and even here he insists that if understanding requires representation (phantasia)—something he later acknowledges, at least for humans—it will be inseparable from the body and its activities (1.1, 403a7–16). For understanding’s dependence on representation, see DA 3.7, 431a16–17; 3.8, 432a8–10; Mem. 1, 449b31. This will not be true of God, who is nothing but understanding (Metaph. 12.7 & 9), or true of the second understanding mentioned in DA 3.5. But it is arguable that the latter just is God: for a defence of this reading, see Caston (1999). 48  What distinguishes animals from plants: e.g., DA 2.2, 413b1–4; Sens. 1, 436b10–12; GA 1.23, 731a30– b4, though see Lloyd, 1996: ch. 3 on possible exceptions to this rule, like the jellyfish, which Aristotle regards as an animal but without perception (PA 4.5, 681a19–20). On the relation to pleasure, desire, and representation to perception: DA 2.2, 413b22–3; 2.3, 414b4–5; 3.11, 434a2–3. 49 Some have thought that this distinction precludes any other modification or alteration being involved in perception, in particular underlying material changes (e.g., Burnyeat, 1995: 19, 21–2). But Aristotle believes that perceptible objects as such produce a material change in the organ when they produce perception, as bright colours do on the moisture in the eye (GA 5.1, 779b26–780a7; cf. DA 1.1, 403a16–19), even though perceiving is not to be identified with the material changes underlying it: each is a distinct type of change. For more detailed discussion, see Caston, 2005: esp. 265–9 and 288–90.

44   Victor Caston the same’, even though their ‘being’ is different (to einai heteron), since what it is to perceive differs from what it is to be perceived (3.2, 425b26–426a19; cf. Phys. 3.3). What can be perceived—colours, sounds, flavours, odours, heat, and moisture, for example—continue to exist apart from perception, because they exist even when they are not exercising their power to affect perceivers. They are objective features of the world, independent of being perceived. Aristotle criticizes his predecessors for failing to realize this, when they assumed that the objects of perception cannot exist unperceived (426a20–6).50 Because perceiving depends on the objects of perception to bring it about and the latter are external to the perceiver, it follows that perception is not something that is ‘up to us’, but depends upon what is furnished by our environment.51 What can perceive and what can be perceived are thus relative (pros ti) to one another (Categ. 7, 6b3, b35–6), where the latter causally acts on the former and is therefore prior in nature.52 Each sense is a power to perceive a certain type of object and its essence is defined by reference to it. The object is thus the sort of thing that, as such, is intrinsically (kath’ hauto) capable of causing that sense exclusively (idion) to perceive it (DA 2.6, 418a24–5). The power of sight, for example, is defined in terms of what can be seen. This turns out to be colour—not by definition, Aristotle is quick to add, but because colour possesses within itself what is responsible for being seen (2.7, 418a29–b2). To be visible and to be a colour are thus not the same (Phys. 3.1, 201b2–4; Metaph. 11.9, 1065b32–3), even if colours are in fact the sorts of things that can be seen.53 Aristotle offers extensive accounts of the different senses,54 the perceptible qualities they are directed at,55 and the various organs that subserve them.56 As with any other agent–patient interaction for Aristotle, the object of perception causes the sense to become like itself. The active quality or form of the agent—in this case, the 50  One naturally thinks of Protagoras here, although there is no explicit mention of him in the text. But Aristotle’s criticism is certainly relevant to the theory of perception Plato offers in support of Protagoras in the Theaetetus, as part of his ‘secret doctrine’ (see section 3): an object is only white while it is being perceived as white by someone. Also note that on this theory, the causal interaction of subject and object always generates ‘twins’—whiteness and seeing, for example—in contrast with Aristotle’s view, where the resulting activity of the power to perceive and the activity of the perceptible object are ‘one and the same’ (though differing ‘in being’). For close comparison of these two texts, see Turnbull (1978). 51  DA 2.5, 417b19–25; cf. Sens. 2, 438b22–3; 6, 445b7–8; Insomn. 2, 459a24–5. 52  Metaph. 4.5, 1010b30–1011a2; cf. Categ. 7, 7b35–8a12; 8, 9a28–b9, esp. b5–7. On relatives which are causally prior (or prior ‘in nature’), see Categ. 12, 14b11–13. 53  Colour is not the only thing that is visible either. Phosphorescent objects—for which, Aristotle notes, there is no Greek word—are visible in the dark, although this is not their proper colour. The proper colour of objects is only manifest in the light (418a27–8, 419a1–7). 54  The senses: sight (DA 2.7, Sens. 2; cf. GA 5.1); hearing (DA 2.8; cf. GA 5.2); smell (DA 2.9); taste (DA 2.10); and touch (DA 2.11). There are interesting discussions in the last chapter about whether touch is a single sense, given the different range of qualities it is sensitive to (422b17–33); and whether flesh is the organ of touch or rather a medium, as the other senses have, the organ being deeper within (422b34–423b26). 55  Perceptible qualities: colour (Sens. 3); flavours (Sens. 4); odours (Sens. 5); sounds (DA 2.8; cf. Sens. 4). For discussion of tactile qualities, see DA 2.11, 423b27–424a15; see also GC 2.2 and PA 2.2, 648b11–649b8, esp. 648b14–17 (cf. b30–3). On light, darkness, and phosphorescence, see DA 2.7. For analogies between the quality spaces of odours and flavours, see also Sens. 5, 443b3–16 and DA 2.9, 421a26–b3. 56  For sense organs in general, see PA 2.1, 647a3–33; see also assorted comments on individual sense organs in HA 4.8. For discussions of specific sense organs: eyes (PA 2.13; GA 5.1; cf. Sens. 2); ears (PA 2.11–12; GA 5.2); nostrils (PA 2.16); tongue (PA 2.17); and flesh (PA 2.8, 653b19–33; cf. DA 2.11, 422b34–423b26). For a comprehensive examination of Aristotle’s discussions of the sense organs and possible implications for his theory of perception, see Johansen (1998).

Perception in Ancient Greek Philosophy    45 perceptible quality itself—is transmitted to the patient, which ‘receives’ it or takes it on. Thus, having been unlike the object initially, the sense organ becomes similar to the object (DA 2.5, 417a17–20, 418a3–6; 2.11, 424a1–2). But not every patient perceives the agent acting on it. Plants, for example, are made warm by the sun, but they do not feel warmth, even though according to Aristotle they have a soul and warmth is a perceptible quality (2.12, 424a32–b1). Plants are unable to perceive because they lack a ‘mean’ or balance (mestotês) along a range of sensible qualities that would make them sensitive to the various qualities along that range. Consequently, they are modified by a sensible quality like warmth ‘along with the matter’ and transformed as a result (424b1–3). Each sense, in contrast, is capable of receiving the perceptible form of the object ‘without the matter’, something Aristotle compares to the way sealing wax receives the insignia from a signet ring, without the ring’s iron or gold (424a17–24). Just how to understand this contrast is quite controversial. Some, like Aquinas, take it to mark off a special kind of reception, where the form is received ‘immaterially’—or, as he also says, spiritually or intentionally—which consists in nothing more than perception’s coming to be directed at the object. Against this, others think that the perceptible quality is literally instantiated in the sense organ (cf. 3.2, 425b22–4), but without the matter of the object in which the form was originally instantiated. It seems unlikely that literal instantiation is at issue, though, since that would no longer offer a contrast with plants, as Aristotle intends, given that plants also become warm without receiving matter from the source of the heat. On two occasions, moreover, Aristotle actually ridicules the view that cognition requires a literal replica of the object within ourselves (1.5, 410a7–11; 3.8, 431b28–9). On the other hand, it seems unlikely that receiving form ‘without the matter’ could merely consist in its being directed at an object, without any further underlying material change, given the comparison to a signet ring’s producing a seal in wax. A third alternative lies between these extremes, however. Perception might be directed at an object in virtue of material changes in the sense organ without the object’s perceptible form being literally embodied. To receive the form ‘without the matter’ would instead be to embody only certain essential features of the form in a different type of material, without producing a replica. For example, according to Aristotle each colour is defined by a ratio of black to white (Sens. 3, 440b14–26). On the present suggestion, the eye would receive a colour ‘without the matter’ by embodying the same numerical ratio in a different pair of opposites—hot and cold, say, or runny and viscous—in the vitreous jelly, which Aristotle believes is the sensitive part of the eye, without the jelly needing to change colour at all. In effect, the senses would act as transducers: they would preserve certain essential features of the perceptible form in a new medium and in so doing transmit information about the character of the objects in the world acting on our senses.57 What is perceptible according to Aristotle, at least in the basic or fundamental case, are (1) the qualities that are intrinsically (kath’ hauto) perceptible to a single sense exclusively (idia), or ‘exclusive’ perceptibles, for short: colours, for example, are intrinsically perceptible exclusively to sight, tones to hearing, odours to smell, flavours to taste, and temperature and moisture to touch (DA 2.6, 418a11–15, a24–5). Since on Aristotle’s theory a perception is about what brings it about, the resulting perceptions of these qualities cannot be mistaken, 57  For a full defence of this position, see my ‘Receiving Form without the Matter:  Aristotle on the Transmission of Information’ (unpublished).

46   Victor Caston although he adds we can be mistaken about the coloured object, with regard to what it is, for example, or where.58 As these remarks suggest, Aristotle does not think that exclusive perceptibles are the only thing we can perceive, even if they are what is fundamentally perceptible (kuriôs aisthêta, 418a24). There are also features of objects that are (2) intrinsically perceptible to more than one sense, the so-called shared or ‘common’ (koina) perceptibles, such as change and rest, number and unity, shape, extension, and duration.59 Finally, there are (3) ‘extrinsic’ (kata sumbebêkos) perceptibles, features that are extrinsic to features that are intrinsically perceptible to a given sense.60 This last category includes features that are intrinsically perceptible to a different sense, but it extends much more widely, to include perceiving the son of Diares and even a universal like colour.61 It seems that many of the features relevant for human action and animal behaviour would fall in this last category, such as when a dog and a lion smell or hear their prey (EN 3.10, 1118a16–23). With the last two kinds of perceptible, error is not only possible, but frequent.62 Aristotle makes clear, moreover, that in such cases the perceptions themselves are false, as distinct from representations generated from them (DA 3.3, 428b25–30), not to mention the judgements subsequently formed on their basis. Given Aristotle’s physics and the range of things he thinks can be perceived, the aetiology of perception in these three cases must be very different. This is especially clear with the last kind, where Aristotle explicitly says that our senses are not affected by the extrinsic characteristics in question as such (DA 2.6, 418a23–4). But Aristotle still regards them all as genuine forms of perception, even if he regards one, the perception of exclusive qualities, as the fundamental case (2.6, 418a24–5).63 Whenever we mis-see or mis-hear, Aristotle says, we nonetheless see or hear something real; it is just not what we take it to be (Insomn. 1, 458b31–3).64 This suggests that in all perception, what we perceive are the individuals acting on us, but we always perceive them as being certain sorts of things, a point on which we can be mistaken. Thus, we not only perceive an individual, like Callias; our perception is of a certain sort of thing, ‘of a human, Callias’ (An. Post. 2.19, 100a16–b1; cf. 1.31, 87b28–30). That is why perception is a discriminative power (kritikê, 99b35): it allows us to distinguish between different types of things in our environment and thereby contributes 58 

DA 2.6, 418a12, a15–16; 3.3, 427b12, 428b21–2; 3.6, 430b29–30; Sens. 4, 442b8–10; Metaph. 4.5, 1010b2–3. But compare DA 3.3 428b18–19, where Aristotle seems to qualify this claim:  the perception of such perceptibles is ‘true, or possesses the least possible amount of falsehood’. For a possible explanation of this apparent exception, see Caston, 1998: 272 n. 56. 59  DA 2.6, 418a17–20 (cf. a10–11); 3.1, 425a14–20; Sens. 1, 437a8–9; 4, 442b4–10; Mem. 450a9–12. Apart from number, this list of common objects is quite different, we should note, from the ones Plato speaks of at Tht. 185c–186b; see section 3. 60  DA 2.6, 418a20–4; 3.1, 425a21–27, a30–b3; cf. An. Pr. 1.27, 43a33–5. 61  For objects intrinsically perceptible to another sense: DA 3.1, 425a30–1; cf. a21–4. Other examples: DA 2.6, 418a21 (Diares’ son); 3.1, 425a24–7 (Cleon’s son); Metaph. 13.10, 1087a19–20 (the universal colour). 62  DA 3.1, 425b3; 3.3, 428b19–25. Aristotle notes in the second passage that error is most frequent where common perceptibles are involved, although without further explanation. 63 Sometimes this sentence is taken to imply that only the perception of exclusive perceptibles is perception ‘strictly speaking’ (a mistaken construal of the Greek kuriôs), while the other two kinds are called ‘perceptions’ by an extended use of the term. But in general Aristotle does not tend to legislate that one use of a term is correct and the others incorrect or metaphorical; rather, he standardly acknowledges different uses of terms and notes where one is basic or fundamental or primary (kuriôs). Exclusive perceptibles on this reading, then, are not the only genuine perceptibles, but rather the basic or fundamental ones. 64  In contrast with dreams and hallucinations, where we do not perceive anything at all (458b33–459a1).

Perception in Ancient Greek Philosophy    47 to our survival and well-being (Sens. 1, 436b19–437a15).65 But then perceptual content must somehow involve universals as well, even in cases where these are not grasped conceptually. In fact, on Aristotle’s view it must be possible to grasp these contents non-conceptually, since our most basic concepts first arise from earlier perceptual experiences, which are said to ‘implant’ the universal in us (An. Post. 2.19, 100b5), while other animals, though completely without concepts, are still capable of perceptual discrimination.66 Although Aristotle does occasionally speak of the after-effects of sensory stimulation, like after-images (Insomn. 2, 459b7–13), as something perceptible (460b2–3), in general he speaks about phenomenal qualities as belonging to the objects themselves. He regards colours, tones, flavours, odours, warmth, and moisture as public, objective features of the world, external to us, that cause us to perceive them, rather than as properties of our own experiences (Sens. 6, 446b17–26).67 Yet he also seems to think that whenever we perceive, we perceive that we perceive (EN 9.9, 1170a29–b1; Sens. 7, 448a26–30). In one passage, he argues that we accomplish this by means of a ‘common power’ of perception, shared by all the senses, by means of which we are also aware and discriminate the perceptibles of different senses (Somn. 2, 455a15–22).68 But at the beginning of On the Soul 3.2, he offers a more extended discussion and arguments (425b12–25). The interpretation of this passage is controversial, but on the most common reading he argues that this higher-order perception cannot be the function of a distinct power of perception, on pain of infinite regress. On an alternative reading (favoured by Brentano), the argument concerns the activity of perception rather than the power (the Greek aisthêsis being ambiguous between the two). The argument would then be that perceiving that we see or hear cannot be a distinct activity from the original act of seeing or hearing, on pain of an infinite regress. Every act of perception, in addition to being directed at an external object, must also be reflexively directed at itself ‘on the side’ (en parergôi, Metaph. 12.9, 1074b25–26).69

5 Conclusion From even this preliminary survey, it should be clear that an interest in perception specifically, as distinct from other forms of cognition, develops relatively early in Greek philosophy. The Presocratics are preoccupied with getting past the manifold appearances the world takes on in experience to achieve a deeper understanding of the nature of things. Their self-conscious appeal to reason, as a way of sorting out the puzzling and conflicting 65  On Aristotle’s use of krinein for perceptual discrimination, rather than judgement (as it is sometimes translated), see the landmark article by Ebert (1983). 66  Aristotle would thus subscribe to a ‘state’ view of non-conceptual content, rather than a ‘content’ view. For a full exploration and defence of these issues, see my ‘Aristotle on Perceptual Content’ (unpublished). 67 It is worth noting in this context that Aristotle emphatically rejects Democritus’ reduction of perceptible qualities to quantitative features like shape and extension (Sens. 4, 442a29–b26), a criticism that would apply equally to Plato’s Timaeus. 68  For the latter function, see DA 3.2, 426b8–427a16; cf. Somn. 2, 455a12–22; Sens. 6, 448b17–449a20, which constitutes a striking departure from Plato, who argued this function could not be performed by any of the senses, but only by something distinct from all of them (see section 3). For Aristotle’s conception of the ‘common sense’, see Gregoric (2007). 69  For close discussion of these passages and a defence of Brentano’s activity reading, see Caston 2002.

48   Victor Caston elements in our experience, leads naturally to a broad contrast between the deliverances of the senses and what we make of them through reflection and argument. It is not surprising that by the mid-fifth century bce there is increasing attention to the causal mechanisms underlying the different sense modalities and to the features of objects responsible for stimulating our sense organs: for example, the confluence of similar material elements inside and outside the subject in Empedocles; the production of impressions by the object of vision in both Gorgias and Democritus; and the latter’s appeal to geometric and structural properties of an object quite generally to explain the qualitative character of the resulting perceptual experience. Identifying these causes is a natural first step towards determining what precisely the senses can tell us about the world—or cannot, as the case may be. Both the epistemological pessimism we find in Democritus and Protagoras’ optimistic turning of the tables in favour of relativism (if Plato is right) are equally due to reflections on perception as a form of causal interaction. Epistemological concerns are still evident in Plato. But the nature of perception and of perceptible qualities are already coming to be of interest in their own right: what exactly perception’s relation is to the body or to causation more generally; how we should understand the awareness we have of objects and indeed the awareness of perceiving itself; and finally the ontological status of perceptible qualities and their role in explaining the character of perceptual experience. The specific answers that Plato and Aristotle devised had much influence in the subsequent tradition. But it is the framing of the questions that would have enduring value.

References Avotins, Ivars (1980). ‘Alexander of Aphrodisias on vision in the Atomists’. The Classical Quarterly, 30, 429–454. Baltussen, Han (2000). Theophrastus against the Presocratics and Plato: Peripatetic Dialectic in the De sensibus. (= Philosophia Antiqua, vol. 86.) Leiden: Brill. Beare, J. I. (1906). Greek Theories of Elementary Cognition from Alcmaeon to Aristotle. Oxford: Clarendon Press. Brisson, Luc (1997). ‘Plato’s theory of sense perception in the Timaeus: How it works and what it means’. With commentary by Dana Miller. Proceedings of the Boston Area Colloquium in Ancient Philosophy, 13, 147–185. Burnyeat, M. F. (1976). ‘Plato on the grammar of perceiving’. The Classical Quarterly n.s., 26, 29–51. Burnyeat, M. F. (1995). ‘Is an Aristotelian philosophy of mind still credible?’ (A draft). In Martha C. Nussbaum and Amélie Oksenberg Rorty (eds), Essays on Aristotle’s De anima (pp. 15–26). Oxford: Oxford University Press. First paperback edition, including an additional essay by M. F. Burnyeat. Oxford: Clarendon Press, 1992. Caston, Victor (1986). ‘Empedocles’ Theory of Vision’. MA thesis, The University of Texas at Austin. Caston, Victor (1996). ‘Why Aristotle needs imagination’. Phronesis, 41, 20–55. Caston, Victor (1998). ‘Aristotle and the problem of intentionality’. Philosophy and Phenom­ enological Research, 58, 249–298. Caston, Victor (1999). ‘Aristotle’s two intellects: A modest proposal’. Phronesis, 44, 199–227.

Perception in Ancient Greek Philosophy    49 Caston, Victor (2002). ‘Aristotle on consciousness’. Mind, 111, 751–815. Caston, Victor (2005). ‘The spirit and the letter: Aristotle on perception’. In Ricardo Salles (ed.), Metaphysics, Soul, and Ethics: Themes from the Work of Richard Sorabji (pp. 245–320). Oxford: Oxford University Press. Caston, Victor (Unpublished). ‘Aristotle on perceptual content’. Caston, Victor (Unpublished). ‘Receiving form without the matter: Aristotle on the transmission of information’. Cooper, John M (1970). ‘Plato on sense-perception and knowledge (Theaetetus 184–186)’. Phronesis, 15, 123–146. Day, Jane M. (1997). ‘The theory of perception in Plato’s Theaetetus 152–183’. Oxford Studies in Ancient Philosophy, 15, 51–80. Ebert, Theodor (1983). ‘Aristotle on what is done in perceiving’. Zeitschrift für philosophische Forschung, 37, 181–198. Fine, Gail (1988). ‘Plato on perception: A reply to Professor Turnbull, Becoming and Intelligibility’. Oxford Studies in Ancient Philosophy, suppl. vol., 15–28. Frede, Michael (1987). ‘Observations on perception in Plato’s later Dialogues’. In Frede, Essays in Ancient Philosophy (pp. 3–8). Minneapolis: University of Minnesota Press. Fritz, Kurt von (1953). ‘Democritus’ theory of vision’. In E. Ashworth Underwood (ed.), Science, Medicine, and History: Essays on the Evolution of Scientific Thought and Medical Practice, written in honour of Charles Singer, vol. 1 (pp. 83–99). London: Oxford University Press. Ganson, Todd Stuart (2005). ‘The Platonic approach to sense-perception’. History of Philosophy Quarterly, 22, 1–15. Gregoric, Pavel (2007). Aristotle on the Common Sense. Oxford: Oxford University Press. Hussey, Edward (1990). ‘The beginnings of epistemology: From Homer to Philolaus’. In Stephen Everson (ed.), Epistemology (pp. 11–38). (= Companions to Ancient Thought, vol. 1.) Cambridge: Cambridge University Press. Ierodiakonou, Katerina (2005). ‘Empedocles on colour and colour vision’. Oxford Studies in Ancient Philosophy, 29, 1–37. Johansen, T. K. (1998). Aristotle on the Sense-Organs. Cambridge: Cambridge University Press. Kahn, Charles H. (1985). ‘Democritus and the origins of moral psychology’. American Journal of Philology, 106, 1–31. Laks, André (1999). ‘Soul, sensation, and thought’. In A. A. Long (ed.), The Cambridge Com­ panion to Early Greek Philosophy (pp. 250–270). Cambridge: Cambridge University Press. Lesher, J. H. (1994). ‘The emergence of philosophical interest in cognition’. Oxford Studies in Ancient Philosophy, 12, 1–34. Lloyd, G. E. R. (1996). Aristotelian Explorations. Cambridge: Cambridge University Press. McDowell, John (1973). Plato, Theaetetus. Translated with Notes. Oxford: Clarendon Press. Rudolph, Kelli (2011). ‘Democritus’ perspectival theory of vision’. The Journal of Hellenic Studies, 131, 67–83. Rudolph, Kelli (2012). ‘Democritus’ opthamology’. The Classical Quarterly, 62, 496–501. Schirren, Thomas (1998). ‘Aisthesis vor Platon: Eine semantisch-systematische Untersuchung zum Problem der Wahrnehmung’. (= Beiträge zur Altertumskunde, vol. 117.) Stuttgart: B. G. Teubner. Sedley, D. N. (1992). ‘Empedocles’ theory of vision and Theophrastus’ De sensibus’. In William W. Fortenbaugh and Dimitri Gutas (eds), Theophrastus: His Psychological, Doxographical,

50   Victor Caston and Scientific Writings (pp. 20–31). (= Rutgers University Studies in Classical Humanities, vol. 5.) New Brunswick, NJ: Transaction Publishers. Snell, Bruno (1960). The Discovery of the Mind: The Greek Origins of European Thought. Translated by T. G. Rosenmeyer. New York: Harper. (Translated from Die Entdeckung des Geistes, 2nd edn, Hamburg, 1948.) Solmsen, Friedrich (1968). ‘αἴσθησις in Aristotelian and Epicurean thought’. Mededelingen der Koninklijke Nederlandse Akademie van Wetenschappen, AFD Letterkunde, Nieuwe Reeks, 24 (1961), 241–262. Reprinted in his Kleine Schriften, 3 vols, vol. 1 (pp. 612–633). (= Collectanea, vol. 4.) Hildesheim: Georg Olms Verlagsbuchhandlung. Stratton, George Malcolm (1917). Theophrastus and the Greek Physiological Psychology before Aristotle. London: George Allen & Unwin Ltd. Turnbull, Robert G. (1978). ‘The role of the special sensibles in the perception theories of Plato and Aristotle’. In Peter K. Machamer and Robert G. Turnbull (eds), Studies in Perception: Interrelations in the History of Philosophy and Science (pp. 3–26). Columbus, OH: Ohio State University Press. Warren, James (2007). ‘Anaxagoras on perception, pleasure, and pain’. Oxford Studies in Ancient Philosophy, 33, 19–54.

Chapter 2

Perception i n M edieva l Phil osoph y Dominik Perler

1 Introduction: Three problems of perception All medieval philosophers in the Aristotelian tradition agreed that perception provides the foundation for our knowledge of material things: had we no sensory access to them, we would know neither that they exist nor how they exist. Moreover, many medieval authors claimed that perception is also indispensable for our knowledge of non-material things. We would never acquire knowledge of mathematical objects if we did not see instances of, say, triangles and if we were not able to use this perception as our starting point for a process of abstraction. Even our knowledge of God would be impossible if we were utterly unable to perceive the world of creatures—an activity that motivates our reasoning about the first cause of this world.1 Given this tendency to find a starting point for all kinds of knowledge, it is hardly surprising that perception played a crucial role in scholastic debates, especially in the period after 1255 when Aristotle’s works in natural philosophy (among them De anima and De sensu et sensato, which explicitly deal with perception) became part of the university curriculum.2 These debates closely examined the origin of perception, its structure, and its function in epistemic processes. They took place in the context of a faculty psychology, i.e. of a theory that appealed both to sensory and intellectual faculties in order to explain the origin and the content of perception. When dealing with single cases of perception, philosophers in the Latin West focused on three key problems. The first problem concerned the object of perception. What exactly is this object: a material thing, a property of a thing (e.g. colour or shape), the mere appearance of a thing, or some other entity? This question immediately gave rise to a second problem: how are we able to perceive these objects, whatever they are? What cognitive faculties 1 

Thomas Aquinas went so far as to provide an a posteriori proof of God’s existence; see Summa theologiae (= STh) I, q. 2. art. 3, corp. To be sure, not all medieval authors chose this approach. Some, most famously Anselm of Canterbury, attempted to give an a priori proof that does not appeal to perceptual evidence. 2  In 1255, Aristotle’s works in natural philosophy were officially accepted at the University of Paris. On the reception of Aristotle’s writings, see Pasnau 2010, 793–797; on the presence of De anima, see Perler 2008.

52   Dominik Perler and devices are required? And how do all the faculties work together to bring about a perceptual state? These questions inevitably led to a third problem that concerned the reliability of perceptual processes:  why can we be certain that our faculties and cognitive mechanisms enable us to perceive an object as it really is? What entitles us to claim that sense perception provides a robust and trustworthy foundation for our knowledge of the material world? Since this type of knowledge was considered the starting point for all kinds of knowledge, even for our knowledge of mathematical objects and God, it is not surprising that problems of perception opened the door to far-reaching debates in epistemology. At stake in these debates was not only what we know on the basis of perception, but also whether we know anything at all on this basis. This chapter examines the way scholastic authors dealt with the three problems of perception. It goes without saying that it can shed light only on some aspects of a complex debate. It is limited to a discussion of Latin philosophers in the late thirteenth and early fourteenth centuries.3 This is a rather short but highly productive period in medieval philosophy, because it was at this time that various traditional theories became fully available: Aristotelian accounts of perception, Neo-Platonic theories of light, Arabic theories of vision, and ancient sceptical debates that questioned the reliability of sense perception. It should also be noted that this chapter only discusses theories of external perception, leaving aside those dealing with internal perception (sensory self-awareness and inner self-perception).4 Finally, this chapter is confined to philosophical approaches to perception and does not enter into an analysis of scientific debates, for instance in optics and physiology; nor does it examine theological controversies.5

2 The object of perception Inspired by Aristotle, most late medieval philosophers claimed that our acts of perception have two immediate objects: ‘proper sensibles’ and ‘common sensibles’.6 Proper sensibles are properties of material things, perceived by one and only one of the five external senses. Thus, colour is perceived by sight, sound by hearing, and odour by smell. By contrast, common sensibles are properties perceived by two or more senses. For example, the shape or the size of a material thing can be seen as well as touched. Medieval Aristotelians had no doubt that both proper and common sensibles are real properties, present in material things, and not just properties that somehow arise in the perceiving person. They even tried to give an ontological classification of these properties by assigning them to the category of qualities and by emphasizing that they exist in (technically speaking, inhere in) material substances.7 3 For a broader overview that covers both Arabic and Latin discussions, see Knuuttila and Kärkkäinen 2008. 4  On internal perception, see Putallaz 1991, Heller-Roazen 2007. 5  On scientific aspects, see Lindberg 1996; on theological debates, see Denery 2005. 6 See De anima II.6 (418a 11–19). 7 See, for instance, William Ockham, Exp. in libr. Praedicamentorum, cap.  14 (OPh II, 276–285); John Buridan, Quaestiones in Praedicamenta, q. 16 (ed. Schneider 1983, 121). To be sure, not all medieval authors agreed that these qualities necessarily exist in a substance. Inspired by theological debates about

Perception in Medieval Philosophy    53 This account of the immediate objects of perception poses a problem. How can it be that we perceive things and not just loose bundles of properties if all that we immediately grasp are proper and common sensibles? For instance, why do I see a red, round thing and not just the properties redness and roundness when I am looking at an apple? To answer this question, Thomas Aquinas (and after him many other medieval authors) appealed to the inner senses that work on the material provided by the external senses. As soon as sight and touch apprehend redness and roundness, they transmit this information to the common sense, which is located in the brain. Aquinas held that this sense is ‘a certain faculty at which the affections of all the senses terminate’.8 That is, all the properties apprehended by the five external senses come together in this internal sense. Their connection and unification enables the faculty of imagination (phantasia), another internal sense, to come up with a ‘phantasm’, i.e. a sensory image that presents a unified whole. So, I am able to see a red, round thing and not just a loose series of properties because I have a sensory image of something unified. No predication is necessary for this kind of unification. Various properties are merely seen as perfectly cohering, without being conceived as qualities that, technically speaking, inhere in a thing. And the image of all the unified properties is not something I deliberately or even consciously produce. It arises spontaneously as soon as an input stemming from the external senses arrives in the internal senses, and it can be stored and reactivated at a later moment when the apple is no longer present. But why do I see the red, round thing as an apple? Or more generally, why am I able to see something as a thing of a certain type? To answer this question, Aquinas invoked the distinction between ‘sensibles per se’ and ‘sensibles per accidens’.9 Properties like colour and shape are ‘sensibles per se’ that are directly grasped by the external senses and transmitted to the internal ones, without there being any need for an additional faculty that interprets or conceptualizes the sensory input. By contrast, being an apple is a property that is grasped along with the directly apprehended properties as soon as they are interpreted in a certain way. What makes this interpretation possible? The cogitative power, Aquinas affirmed: a special faculty that mediates between senses and intellect.10 It uses the concepts formed by the intellect and applies them to the information provided by the senses. Aquinas called it ‘particular reason’ because it is not the faculty of reason in general, which deals exclusively with concepts and their inferential relations, but a faculty that is concerned with concepts insofar as they are applied to perceived properties. Aquinas’ appeal to this special faculty is significant because it shows that he did not conceive of perception as a purely sensory process. Reason is always involved when we perceive something as such and such. That is why there is a clear difference between brute animals and human beings. Animals also have a common sense and the faculty of imagination. Therefore, they are also able to produce sensory images that present unified things. But they lack the faculty of reason and hence also the use of particular reason that would enable them to apply concepts to what is present in a perceptual situation. Consequently, transubstantiation, some assumed that they can be separated, and others even argued that they can exist on their own; see Pasnau 2011, 179–220. 8 

10 

Sentencia libri De Anima (= SDA) II.13, 119. SDA II.13, 121–122, and STh I, q. 78, art. 4, corp.

9 

SDA II.13, 120.

54   Dominik Perler animals are unable to interpret what they see.11 Thus, a cat sitting in front of an apple is able to produce an image of a coloured thing. But it is utterly unable to see it as an apple because it lacks the concept that would enable it to categorize what it sees. Only human beings, endowed with reason, can go beyond the stage of merely having sensory images: we see unified things and we see them as things of a certain type. Aquinas and many other thirteenth-century authors took it to be unproblematic that the appropriate use of senses and reason enables us to perceive things in the material world. Since proper and common sensibles are properties of real substances, we are always in touch with apples, trees, and many other material things, and we more or less adequately perceive how they are. But can we be certain that these things are in fact our objects of perception? In the early fourteenth century, Peter Aureol raised this question and argued that all we immediately perceive are things with ‘apparent’ or ‘intentional being’ (esse appar­ ens or esse intentionale), which do not exist in nature but are produced by our intellect.12 Aureol adduced cases of sensory illusion to illustrate this fact. When we are travelling on a boat and see moving trees on the shore, we perceive, strictly speaking, only apparent trees and not material ones. Why? The apparent trees clearly have a property, namely being in movement, which the material trees on the shore lack. Similarly, when we see a stick partly submerged in water, we immediately perceive an apparent stick that is distinct from the real one. To be sure, Aureol did not claim that we are, as it were, imprisoned in a world of apparent things and that we never have access to material things. In a normal situation, the apparent and the real thing coincide.13 So, if I see a stick taken out of the water, present in the best possible light, I see it the way it is, namely as an unbent piece of wood. But even then it is, strictly speaking, only the apparent stick I immediately perceive. Whether or not the apparent and the material thing coincide is not something I can tell at first sight. I need to evaluate the perceptual conditions and will be certain about a coincidence or convergence of the two types of things only after having excluded the possibility of a deception. It is clear that this account amounts to a radical redefinition of the objects of perception: nothing but apparent things are our immediate objects, and we can only make reasonable guesses about the relation between these entities and material things. However, Aureol’s position was not widely accepted. His immediate successors, among them Walter Chatton and William Ockham, decidedly rejected it, emphasizing the traditional thesis that material things and their properties are our immediate objects.14 According to Chatton, there is a devastating fallacy in Aureol’s reasoning. Aureol had started by describing an object as a relational thing, i.e. as a thing that is related to a perceiving person, but then turned it into an absolute thing, i.e. a thing that has its own existence. In the logical literature, this was called a ‘relational fallacy’.15 Chatton illustrated it with a 11  Aquinas conceded that animals have an ‘estimative faculty’ that enables them to evaluate things. His example is the sheep that takes the wolf to be dangerous (STh I, q. 78, art. 4). But this is simply a natural reaction and not a conceptual form of evaluation. There is, as it were, a mechanism built into the sheep that inevitably triggers a negative reaction when a certain sensory image is present. 12  Scriptum I.3, sect. 14 (ed. Buytaert 1956, 696–697). 13  Scriptum I.3, sect. 14 (ed. Buytaert 1956, 698). 14 Ockham, Ordinatio I.27, q.  3 (OTh IV, 238–258); Chatton, Reportatio et Lectura, prol., q.  2, art. 2 (ed. Wey 1989, 87–91). On further authors, see Tachau 1988. 15  It was already mentioned by Aristotle in Soph. El. 5 (166b 36–167a 14) and often discussed in medieval logic handbooks, for instance in Peter of Spain’s Tractatus VII, n. 120 (ed. de Rijk 1972, 157–158).

Perception in Medieval Philosophy    55 classical example. If someone were to say ‘Homer exists in an opinion; therefore this person, characterized with a number of specific features, exists as such’, he would first talk about Homer insofar as he is thought about and described by readers of Greek literature, and then falsely conclude that Homer-in-the-mind is a distinct entity. But there is no such entity. All that exists is the real Homer, a person of flesh and blood, and all characterizations apply to this entity. Sensory illusions ought to be explained on the same line. To say that one sees moving trees or bent sticks does not mean that a number of special entities exist. This only amounts to saying that some material things are present under a certain aspect. Consequently, all judgements and descriptions apply to material things only. Thus, ‘There are moving trees’ simply means ‘There are material trees that are present as being in movement’. This special presence is due to the circumstances under which the person is looking at the trees. Should she leave the boat and look at them on the shore, the very same trees would be present as being motionless. This explanatory strategy shows that Chatton argued for the rejection of apparent things by pointing out that one and the same object can be present in different ways and hence can also be described in different ways. Or, technically speaking, there can be different ‘extrinsic denominations’ of the same thing. But types of denominations should not be conflated with types of things. Accepting apparent things in addition to material ones would have devastating consequences. For if we assumed that acts of seeing are only directed at apparent things, we could no longer affirm that we are perceptually related to things in the world. Consequently, we could no longer claim that we acquire knowledge of these things. To avoid this consequence, Ockham and Chatton endorsed the thesis that we directly perceive material things in the world, not a number of inner ‘doppelganger’.16 That is why we do not need to make dubious inferences from internal to external objects. Nor do we need to explain how internal, merely apparent objects can signify or represent external ones. Finally, we do not need to provide special evidence for our certainty about the existence of external things. The mere fact that we directly see them, no matter how many false or misleading descriptions we give, shows that we are in immediate touch with them.

3 The perceptual process The Aristotelian thesis that properties such as colour, size, and shape are the first and most basic objects of perception gives rise to the question of how they can become objects of our perception. What physical, physiological, or psychological processes are required? Since philosophers in the Latin West were strongly influenced by Arabic optics, they mostly discussed this question with respect to vision.17 Their crucial problem was: how do colours

16 Ockham, Ordinatio I.27, q. 3 (OTh IV, 241); Chatton, Reportatio et Lectura, prol., q. 2, art. 2 (ed. Wey 1989, 88). 17  Clear examples are Roger Bacon, De multiplicatione specierum (in Lindberg 1983), and John Pecham, Perspectiva communis (in Lindberg 1970). On the Arabic influence, see Tachau 1988, 3–26, and Denery 2005, 82–100. Although priority was given to visual perception, other sense modalities were not completely neglected; on hearing, see Pasnau 2000.

56   Dominik Perler become objects of visual perception? In their answer to this question they referred to a complex causal process that involves at least three steps. In a first step, colours existing in material things are transmitted through a medium, namely through light or air, to the sense organ. Following al-Kindi, many scholastic philosophers claimed that special entities, so-called ‘species in medio’, are required for this transmission. These are physical entities, propagated through the air, that somehow transport the forms of colours to the eyes and affect them. In a second step, the eyes undergo a change and thereby receive the forms. As a consequence, in a third step additional entities, so-called ‘sensible species’, are produced in the sense organ. As soon as they are combined with species stemming from other sense organs, the perceiver will be able to come up with a complex sensory image of the external thing and see that thing. The analysis of all three steps provoked controversies. In philosophical contexts, steps two and three were closely examined.18 First of all, what kind of change does the sense organ undergo? Thomas Aquinas, following his teacher Albert the Great, gave a clear answer: it is a ‘spiritual change’ that should not be conflated with a natural one.19 In a spiritual change it is just the form and not the matter of the colour that is received in the sense organ. That is why the eyes simply assimilate the form but do not literally become coloured. Thus, a person who is affected by a red apple simply receives the form of redness, but her eyes do not turn red. By contrast, in a natural change the form is received together with matter. Should one paint someone’s eyes with red colour, the eyes would receive the entire form-matter compound and literally become red. For Aquinas, it is of crucial importance that the eyes undergo a mere spiritual change, which makes vision the highest among the five senses. Other senses partly undergo a spiritual change, partly also a natural one. For instance, someone tasting or touching water receives the form of wetness but also literally becomes wet. Aquinas’ opposition of spiritual and natural change may give rise to the impression that he referred to an entirely immaterial process that makes the act of seeing possible. But this impression is misleading, because even the spiritual change takes place in the eyes, which clearly are a material sense organ. A purely immaterial process can only take place in a purely immaterial being, for instance in an angel. Whatever takes place in a material being is bound to material conditions. So, a change that occurs in human eyes is bound to the conditions of these special sense organs, which differ from the conditions to be found in the eyes of a dog or a cat. Aquinas’ point is not that the spiritual change somehow transcends all material conditions and that one could ignore the organ in which it takes place. He rather stressed that there can be two kinds of change inside a material organ: a process that consists in the mere reception of information, and a process that consists in a transformation of the organ itself. A modern comparison may help to clarify this point. A radio playing music receives information from the radio station. The radio clearly is a material thing, and it receives the information through a material medium, namely acoustic waves. It is materially affected when it receives these waves, but it is not materially transformed by them; it does not change its size or shape. It only ‘takes in’ music or speech programmes, and given an inner mechanism, it will broadcast these programmes. Similarly, the eyes are materially affected by light rays that transport the form of a colour, but they are not 18 

Step one gave rise to debates in optics. For an overview, see Smith 1981.

19 See STh I, q. 78, art. 3, SDA I.10, 50, and II.24, 169.

Perception in Medieval Philosophy    57 materially transformed by them; they do not change their own colour. They simply ‘take in’ information about a certain colour, and given their inner constitution, they will make this information present so that a person will be able to see that colour. It would be different if the eyes were painted with the colour. In that case they would be materially transformed because they would receive the entire form-matter compound and thereby be affected in their basic structure—like a radio that would not just receive the speech programmes but also incorporate the air emitted by the speakers.20 But in which way does the information become present once it has been received? An answer to this question amounts to an explanation of step three in the causal process, namely the production of ‘sensible species’. These are special devices that transport forms through the external senses and make them accessible to the inner senses. Were there no species, forms present in external things would never become available and never be apprehended. But what exactly is apprehended: the forms transmitted by the species or the species themselves? At first sight, the answer seems clear. Since species are mere devices in the perceptual process, they are only that by which something is apprehended (the medium quo), not that which is apprehended (the terminus ad quem). And in fact, in an influential passage Aquinas unequivocally held that a species is something ‘in virtue of which sight sees’, not that which is seen.21 It therefore seems clear that species are not apprehended, at least not in a normal situation. Only when we reflect upon the way we make external things perceptually available, we focus on the species and make them our cognitive objects. But even then, they will not be seen or otherwise perceived, but intellectually cognized. Yet, Aquinas’ position is not as clear as it might seem. In a number of passages he remarked that the species are in fact immediately apprehended in a basic act of perception, without there being any reflection. Thus, he spoke about ‘the first thing seen, which is the species of the visible thing existing in the pupil’, and even claimed that there is ‘an apprehensive power that apprehends the sensible species when the sensible thing is present’.22 These passages seem to speak in favour of the thesis that species are the terminus ad quem: one first and foremost apprehends inner species and only secondarily forms that are somehow conveyed by the species. It even seems as if Aquinas committed himself to a ‘veil of species’ theory, similar to the ‘veil of ideas’ theory that was to become prominent in early modern debates. For he did not only claim that the species are the first things we see but also affirmed that they are ‘likenesses’ (similitudines) of external properties.23 This seems to imply that a person who is affected by a red apple apprehends a mere likeness of redness, some kind of inner copy or simulacrum, and that she can only make inferences about the external colour. The real colour seems to be hidden behind the ‘veil of species’. Should Aquinas be committed to this inner-veil theory, he would not only openly contradict his own official position about the first and immediate objects of perception but also pave the way for sceptical attacks. Why are we entitled to claim that we perceive colours and many other properties of external things if all we have immediate access to are our inner ‘sensible species’? Why can we be so sure that there are external properties 20 

For a detailed analysis, see Perler 2002, 42–59, and for a slightly different account Burnyeat 2001. STh I, q. 85, art. 2; similarly, Summa contra Gentiles (=ScG) II.75, n. 1550, 218. 22  In I Sent., dist. 35, q. 1, art. 2, and Quaestiones disputate De Veritate (= QDV) q. 1, art. 11, corp., 35. These passages are thoroughly discussed by Pasnau 1997, 200–208. 23 See STh I, q. 17, art. 2, and q. 85, art. 2. 21 

58   Dominik Perler at all? All we can be certain about are our inner likenesses that are supposed to correspond to or signify external properties. But perhaps there are no external properties. Perhaps we only assume that our inner likenesses relate us to something external. Since we have no immediate access to the properties themselves, we can never verify their existence. Aquinas never worried about these problems. Why not? He did not think that internal likenesses are set apart from external properties. Consequently, he did not assume that these likenesses constitute some kind of veil that prevents us from having access to the external properties. According to his technical terminology, every item that shares the form with something else can be its likeness.24 Thus, a red apple can be the likeness of another red apple because they share the accidental form of redness, or a human being can be the likeness of another human being because they share the essential form of humanity. Likewise, a sensible species can be a likeness of an external colour because they share the sensible form.25 And when one apprehends the species, one grasps the form that is also present in the material thing—no inference is required. ‘Even when something is seen through the likeness of another thing’, Aquinas remarked, ‘it can still happen that someone seeing the thing through the medium considers the thing immediately, without its cognition being turned toward anything else’.26 Why is the cognition not turned to the mere likeness, i.e. to the sensible species? Because even though one apprehends the species, one sees in it and through it the form that also exists in the external thing. The species is a mere medium that makes the form available. (Compare: if you listen to the radio and hear a voice, you can very well say that you immediately hear it. You do not go through inferential steps. The voice is immediately accessible through the medium.) Given the crucial claim that sensible forms can be present both in material things and in perceivers who produce sensible species, Aquinas did not doubt that we have direct, noninferential access to colours, sounds, etc. However, not all medieval authors were so optimistic. Peter John Olivi, who studied in Paris shortly after Aquinas’ death, and William Crathorn, who taught in Oxford around 1330, clearly saw that the species theory can easily be turned into some kind of inner-veil theory.27 One simply needs to give up the thesis about form sharing and assume that the species inside and the sensible property outside the perceiver are two distinct items that have nothing in common. How then can we be certain that we really see the colour and not the species? Crathorn phrased his critique as follows: ‘Someone seeing something white sees at once and without any difference whiteness itself and the species of whiteness. On the basis of the mere fact of seeing, one cannot distinguish between whiteness and the species of whiteness.’28 Imagine a person walking 24 

STh I, q. 4, art. 3. Note that the relation between two red apples or two human beings is symmetrical, whereas that between species and external property is asymmetrical: the species makes the form which it shares with the external colour present, not the other way around. That is why Aquinas adds that we are dealing with a special form of similitudo: the species is ‘the principle leading to a cognition’ of the form it shares with the external property; see QDV, q. 8, art. 11, ad. 3. 26  In IV Sent., dist. 49, q. 2, art. 7, ad. 8 (quoted by Pasnau 1997, 206). 27 Olivi, Quaestiones, q. 74 (ed. Jansen 1926, vol. 3, 122–123); Crathorn, Quästionen, q. 1 (ed. Hoffmann 1988, 102–126). Both are discussed by Pasnau 1997, 236–247, and Perler 2002, 109–127. 28  Quästionen, q. 1 (ed. Hoffmann 1988, 123). 25 

Perception in Medieval Philosophy    59 down a street covered with fresh snow. Why would she be entitled to claim that she sees the colour of the snow? Given that she has a sensible species of whiteness and that this species is also apprehended, even primarily, she could as well say that she merely sees her own species. Of course, she may come up with some causal reasoning, arguing that the species could not have come into existence if it had not been caused by the external colour. But then she would only have inferential knowledge of the colour. And the causal reasoning could always be challenged, because one could always invoke a deviant cause. Could it not be that the omnipotent God caused the species?29 And could it therefore not be that someone had a species of whiteness without there being any external colour? Since this possibility can never be ruled out, a person having a species can never be sure that she is really in touch with an external property. To avoid this absurdity, Crathorn’s teacher Ockham had already called for an ontologically parsimonious explanation. In his view, all one needs to admit is an external thing endowed with a set of properties that affects the sense organs. Given certain natural laws, this change in the external senses immediately triggers the inner senses, thereby producing an act of perception that is immediately directed at the external thing.30 This explanation does not only dispense with sensible species, but with the entire idea of transmitting and receiving forms. To put it in a nutshell: an explanation invoking forms and formal causation was replaced with an explanation that only appealed to efficient causation. Ockham thus paved the way for a break with the traditional explanatory framework—a break that was to become prominent in the early modern period when the Aristotelian idea of assimilating forms was finally rejected. All debates about the perceptual process focused on the cause and the object of an act of perception. But what about the phenomenal experience? Doesn’t seeing something red or tasting something sweet stimulate feeling in a certain way? And does this feeling not call for an explanation? Given the framework of hylomorphism, no medieval author saw a need to introduce special entities (e.g. phenomenal qualities).31 Phenomenal experience is constituted entirely by the formal and material change which a perceiver undergoes. Thus, when I am tasting a piece of sugar, my tongue receives the form of sweetness and is also materially affected by a mixture of moist and dry. This triggers an act of experiencing something sweet—nothing more happens. Of course, this parsimonious explanation presupposes that a hylomorphic change is a very special type of change: we do not only get information about an object when we are affected by it, but we also have some kind of awareness of this information and therefore an immediate experience. While insisting on the immediacy and the non-intellectual character of this experience (brute animals have it as well as human beings), some medieval authors emphasized that special sensible properties are responsible for it. Peter Aureol is a telling example. He pointed out that there is a clear difference between seeing and thinking, even if one deals with one and the same object. In an act of seeing, one cognizes an object ‘under conditions

29 

Crathorn explicitly referred to this possibility in Quästionen, q. 1 (ed. Hoffmann 1988, 124). Reportatio III, q. 2–3 (OTh VI, 64–65 and 114–129). Ockham conceded that an object can even act at a distance, without being in immediate touch with a sense organ, and trigger the sensory faculties; see Reportatio II, q. 12–13 (OTh V, 309). 31  It would therefore be misleading to look for a solution to the famous ‘qualia’ problem in medieval texts. This simply was not a medieval problem; see King 2007. 30 

60   Dominik Perler of quantity’ and therefore has an experience that is lacking in an act of thinking.32 Suppose that you are seeing a red apple in front of you. Why does this seeing feel differently from merely thinking about it? Because you see the apple at a certain distance, at a certain angle, in a certain light, etc. That is, you do not simply grasp redness, but a red thing in a specific situation. Redness is, as it were, enriched by many other properties. Given this richness, seeing the red apple right here in this light feels a certain way. This will be lost in an act of thinking that focuses just on redness and abstracts from all other properties. Aureol’s attempt to explain this crucial difference shows that he was well aware of the phenomenal aspect of perceiving. But he did not invoke special inner qualities to account for it. He rather referred to something external, namely to the complex bundle of sensible properties that are present in a given situation. Of course, these properties are only apparent ones. For Aureol, the immediate objects of perception can never be material things or properties, as has been explained in section two. Therefore, he cautiously remarked that ‘things appear under conditions of quantity’ and that it is this appearance that marks the difference between perceiving and thinking.33 But in a normal situation, apparent things correspond to material ones and even ‘coincide’ with them.34 For instance, I would not perceive something red, present at a certain distance and in a certain light, if I had not been affected by a material thing that is in fact red and in fact present at a certain distance and in a certain light. That is why it is the presence of a rich bundle of external properties that gives rise to the presence of apparent properties and hence also to a perceptual experience.

4 The reliability of perception Every account of the perceptual process, no matter how many physiological or psychological sub-explanations it includes, must address a fundamental problem. Can we ever be sure that it is a reliable process that yields veridical perception? Given their empiricist tendencies, medieval philosophers took this problem seriously. For clearly, only a perceptual process that is in principle reliable provides the foundation for a solid body of knowledge. Should perception constantly mislead us and provide distorted or impoverished information about the material world, our knowledge would stand on shaky grounds. It is therefore hardly surprising that scholastic authors did not only spell out all the steps involved in a perceptual process, but also attempted to explain why we can and even should trust this process. First of all, why should we be confident that we perceive colours, sounds, and other ‘proper sensibles’ the way they really are? Aquinas unmistakably answered: ‘It is proper to sight that it cognizes colour, proper to hearing that it cognizes sound, and proper to taste that it cognizes flavor’.35 Simple and harmless as this statement may seem, it should not be dismissed as a mere reference to the scope of each sense. It is part of an all-embracing 32 

Scriptum I.35, part 1, art. 1 (ed. Friedman 2009, 8). also marks the difference between imagining and thinking; see Scriptum I.35, part 1, art. 1 (ed. Friedman 2009, 8). 34  Scriptum I.3, sect. 14 (ed. Buytaert 1956, 698). 35  SDA II.13, 118. 33  It

Perception in Medieval Philosophy    61 teleological theory.36 For Aquinas, each sense is a capacity that has its natural goal, and if it is appropriately actualized, it unfailingly reaches this goal. Thus, sight is designed to be actualized by the presence of a colour and to bring about an act of seeing that colour. No agent can arbitrarily alter or delete this natural goal. Even God, who could do everything by means of his omnipotence, does not intervene and alter the goal at this or that moment, because doing so would amount to changing the natural order. But it is precisely this order that God chose when creating the world. In fixing a new goal he would thwart his own creation. Given this teleological assumption, Aquinas did not only claim that each sense has its own object, but also that it apprehends this object correctly, at least under normal circumstances. ‘With regards to the proper sensibles’, he affirmed, ‘sense does not have a false cognition, unless this happens by accident as it is seldom the case’.37 The qualifying clause is significant. A sense is not some kind of cognitive automaton that brings about a correct perception in each and every situation. Exceptions are possible. That is why a number of conditions need to be taken into account, among them internal ones (the sensory apparatus needs to be in a healthy state) and external ones (the sensible properties need to be directly present).38 But if the conditions are met, each sense yields the perception it is designed to yield—its veridical character is not to be questioned. Since it only rarely happens that the relevant conditions are not fulfilled, one should not constantly worry whether or not one’s perceptions are correct. Given this teleological picture, it is not surprising that Aquinas and many other medieval authors did not enter into discussions about the famous criterion problem that had been prominent among ancient sceptics.39 How can we ever be certain that our perceptions are correct, the sceptics had asked, if we never possess a criterion that would enable us to check their correctness? All we can do is compile and compare a number of perceptions, but we can never test them from a neutral point of view. That is why it could very well be that some or even most of them are incorrect. For Aquinas, this problem did not arise because he did not see the necessity to test each and every perception. Since our senses are designed to work correctly, the perceptions they bring about can in principle be trusted. Using modern terminology, one could say that someone seeing colours or hearing sounds is in a default position. She does not need to justify the correctness of her perceptions unless there are special circumstances that might impair the functioning of her senses. But what about common sensibles and sensibles per accidens, which are not objects designed to be apprehended by distinctive senses? Aquinas conceded that errors can occur.40 This is most evident in the case of sensibles per accidens. As has been explained in section two, the cogitative power is involved in the grasping of these objects as things of a certain type. Since it is always possible that this power does not apply the appropriate concept (e.g. it may use the concept of pear when being provided with the sensory 36 

On the metaphysical framework of this theory, see Schmid 2011, 35–105. STh I, q. 17, art. 2. 38 In QDV, q. 1, art. 11, 3, and STh I, q. 17, art. 2, Aquinas explicitly mentioned possible failings. A person may be sick so that her tongue interprets sweet things as bitter (a violation of the internal condition), or an object may be present behind a green glass so that its colour is taken to be greenish (a violation of the external condition). 39 They were familiar with this problem thanks to Cicero’s Academica and Augustine’s Contra Academicos. On the reception of ancient debates, see Perler 2006, 15–27, and Lagerlund 2010. 40 See STh I, q. 17, art. 2. 37 

62   Dominik Perler image of an apple), mistakes are possible. But these mistakes are not more serious than other cases of misinterpretation. Like all other natural faculties, the cogitative power is a well-functioning faculty that yields correct states when used under normal conditions. That is why we should not worry about occasional false interpretations that occur under abnormal conditions. We simply need to assess the special conditions under which we mistakenly take a thing, say an apple, to be a pear, and we then need to correct our false interpretation. And here, again, not each and every case is to be tested. In principle, there is a reliability built into the capacity that enables us to form concepts and to apply them to what is present to our senses.41 If one assesses Aquinas’ statements about the reliability of perception against the background of his teleological account of cognitive capacities, it is quite understandable why he did not see a threat in the sceptical challenges. He neutralized them by invoking a general framework that guarantees the appropriate functioning of senses and reason. Consequently, the scenario of global error was no option. However, this optimistic account gave rise to a number of objections. Let me mention two of them that were heatedly debated in the fourteenth century. The first problem concerns the claim that we do not only have reliable perception of single properties, but also of things having these properties. What makes Aquinas so confident that we are correctly able to see a red thing and not just redness? Lurking in the background is the ontological assumption, mentioned in section two, that properties are dependent entities that always exist in substances. So, when perceiving a particular instance of redness, we are also related to the substance in which this colour is present. But is it appropriate to say that we perceive this substance? This is precisely the question raised by Nicholas of Autrecourt, a philosopher who studied and taught in Paris between 1327 and 1340. Launching an attack on all Aristotelians, he claimed that ‘Aristotle never possessed evident knowledge about any substance other than his own soul—taking “substance” as a thing other than the objects of the five senses, and other than our formal experiences.’42 To be sure, Nicholas did not question the assumption that we reliably perceive sensible properties; he was no sceptic about the perceptual foundation of knowledge.43 His point was that we do not perceive substances. We rather infer their existence by arguing that each sensible property must inhere in a substance, a hidden but nevertheless really existing entity. But can we be certain about that? If sensible properties are considered to be real qualities that have their own existence, and if one assumes that they can be taken away from the substances in which they happen to be present (when explaining the sacrament of the altar, many scholastic authors made this assumption, arguing that colour and shape can be separated from the substance of bread), then it is not self-evident that perceiving a sensible property amounts to perceiving a thing having that very property. The alleged thing is merely postulated but not seen.44 41  Concepts concerning the essence of particular things are even unfailingly correct, as Aquinas claimed in STh I, q.  85, art. 6.  On this astonishing thesis, see Kretzmann 1991; on the metaphysical foundation of the reliability thesis, see Perler 2012. 42  Nicholas of Autrecourt, Second Letter to Bernard (ed. de Rijk 1994, 73). 43  He was even a foundationalist, as Grellard 2005 convincingly argued: knowledge always needs to have a firm foundation that consists in ‘formal experience’ (i.e. in the apprehension of logical principles such as the principle of non-contradiction) and in perceptual experience. 44  On fourteenth-century debates on this problem, see Robert 2006 and Pasnau 2011, 124–129.

Perception in Medieval Philosophy    63 There is still another problem that concerns Aquinas’ claim that the natural order is not changed, not even by God. Why should we assume that God never changes the given order? After all, our world is only one of many possible worlds God could create at any moment. And why should the possibility be excluded that he intervenes in this world? After all, miracles show that he does so from time to time. He could do it in such a way that we cannot tell any difference from a natural event. Thus, God could destroy a star in the heavens while maintaining in us the act of seeing that star. William Ockham explicitly mentioned this example, thereby making clear that deviation from the natural order can never be ruled out.45 Yet Ockham did not draw a sceptical conclusion. In his view, we are not deceived. Should the star be destroyed, we would correctly judge that it does not exist. But why should we come up with a correct judgement? Given that God is omnipotent, he could bring it about that there is not the slightest difference between the act of seeing we have when the star is present and the act we have after it was destroyed. Why should the first act give rise to a positive judgement of existence and the second to a negative one? A number of fourteenth-century authors were puzzled by this problem, one of them being Peter of Ailly. He acknowledged that there may be no phenomenal difference between perceptual acts that are caused by immediately present material things and those that are caused by God. Furthermore, he conceded that there is no special cognitive mechanism that makes us automatically produce correct judgements. This led him to the conclusion that we can never be entirely certain about our judgements based on perception. All we can have is ‘conditional evidence’ that should be carefully distinguished from ‘absolute certainty’.46 That is, all we can say is: if everything happens according to the natural order, without any divine intervention, then we have no reason to doubt that our perceptual judgements are correct. By contrast, when we make judgements about logical principles or about our own mental acts, we can be absolutely certain about their correctness. For instance, when we are in a state of fear we can be absolutely certain that the judgement ‘I am in fear’ is correct. No matter what caused this state, a natural event or a divine act, it is a real fact that I am afraid—no conditional clause needs to be added. Peter of Ailly’s opposition of absolute and conditional evidence shows that the distinction between internal and external perception became more and more important in late medieval debates. Only internal perception was considered to be infallible and entirely trustworthy, while external perception was exposed to doubt, despite the general reliability of the cognitive capacities. Why did this doubt arise? Most obviously because of the use of the theory of divine omnipotence as a sceptical scenario: if it is conceivable that the natural order can be suspended at every moment, there can be no absolute trust in our perceptions of material things. It is always possible that they have no natural cause. But there is also a deeper reason for a growing doubt about external perception. Aquinas had still assumed that the objects of perception are, strictly speaking, not material things but the sensible forms of these things, and he had taken for granted that these forms can be transmitted to and received in the perceiver. Peter of Ailly, inspired by William Ockham, no longer spoke about a transfer of forms, but only about a relation of efficient causation: material things affect the senses, thereby triggering cognitive capacities and bringing

45 

46 

Ordinatio, prol., q. 1 (OTh I, 39). Quaestiones I, q. 1, fol. dv. For a discussion, see Perler 2006, 188–191.

64   Dominik Perler about perceptual acts. But if this triggering is all that is required, and if there is no sensible form that needs to be both in the material thing and in the perceiver, then it is only a small step to the hypothesis that there could be all kinds of triggering causes—God or malicious demons as well as material things. To be sure, late medieval authors did not spell out this hypothesis. But in gradually giving up the traditional model of form sharing they paved the way for theories of perception motivated by scepticism.47

References Aquinas, Thomas (1856). In quatuor libros Sententiarum. Parma: Fiaccadori. Aquinas, Thomas (1952). Summa theologiae, (ed.) Petrus Caramello. Rome and Turin: Marietti. Aquinas, Thomas (1961). Summa contra Gentiles, (ed.) Ceslaus Pera. Turin and Rome: Marietti. Aquinas, Thomas (1970). Quaestiones disputatae De veritate, (ed.) Leonina XXII. Rome: S. Sabina. Aquinas, Thomas (1984). Sentencia libri De anima, (ed.) Leonina XLV/1. Rome and Paris: Commissio Leonina and Vrin. Aristotle (1958). Topica et Sophistici elenchi, (ed.) W. D. Ross. Oxford: Clarendon Press. Aristotle (1961). De anima, (ed.) W. D. Ross. Oxford: Clarendon Press. Buridan, John (1983). Quaestiones in Praedicamenta, (ed.) Johannes Schneider. Munich: Verlag der Bayerischen Akademie der Wissenschaften. Burnyeat, Myles F. (2001). ’Aquinas on “Spiritual Change” in Perception’. In Dominik Perler (ed.), Ancient and Medieval Theories of Intentionality. Leiden: Brill, 129–153. Chatton, Walter (1989). Reportatio et Lectura super Sententias, (ed.) Joseph C. Wey. Toronto: Pontifical Institute of Mediaeval Studies. Crathorn, William (?) (1988), Quästionen zum ersten Sentenzenbuch, (ed.) Fritz Hoffmann. Münster: Aschendorff. Denery, Dallas G. (2005). Seeing and Being Seen in the Later Medieval World: Optics, Theology and Religious Life. Cambridge: Cambridge University Press. Grellard, Christophe (2005). Croire et savoir. Les principes de la connaissance selon Nicolas d’Autrécourt. Paris: Vrin. Heller-Roazen, Daniel (2007). The Inner Touch:  Archaeology of Sensation. New  York: Zone Books. King, Peter (2007). ’Why Isn’t the Mind-Body Problem Medieval?’ In Henrik Lagerlund (ed.), Forming the Mind: Essays on the Internal Senses and the Mind/Body Problem from Avicenna to the Medical Enlightenment. Dordrecht: Springer, 187–205. Knuuttila, Simo and Kärkkäinen, Pekka (eds) (2008). Theories of Perception in Medieval and Early Modern Philosophy. Dordrecht: Springer. Kretzmann, Norman (1991). ‘Infallibility, Error, and Ignorance’. In Richard Bosley and Martin Tweedale (eds), Aristotle and His Medieval Intepreters. Canadian Journal of Philosophy, suppl. vol. 17,159–194. Lagerlund, Henrik, (ed.). (2010), Rethinking the History of Skepticism: The Missing Medieval Background. Leiden: Brill.

47  I am grateful to Martin Lenz, Mohan Matthen, Martin Pickavé, and Stephan Schmid for valuable comments on earlier versions of this chapter.

Perception in Medieval Philosophy    65 Lindberg, David (1970). John Pecham and the Science of Optics. Madison, WI: University of Wisconsin Press. Lindberg, David (1983). Roger Bacon’s Philosophy of Nature. Oxford: Clarendon Press. Lindberg, David (1996). Roger Bacon and the Origins of Perspectiva in the Middle Ages. Oxford: Clarendon Press. Nicholas of Autrecourt (1994). His Correspondence with Master Giles and Bernard of Arezzo, (ed.) Lambert M. de Rijk. Leiden: Brill. Ockham, William (1967–1986). Opera Theologica (= OTh), (ed.) Gedeon Gál et  al. St Bonaventure: Franciscan Institute. Ockham, William (1974–1988). Opera Philosophica (= OPh), (ed.) Gedeon Gál et  al. St Bonaventure: Franciscan Institute. Pasnau, Robert (1997). Theories of Cognition in the Later Middle Ages. Cambridge: Cambridge University Press. Pasnau, Robert (2000). ‘Sensible Qualities: The Case of Sound’. Journal of the History of Philosophy, 38, 27–40. Pasnau, Robert (ed.). (2010). The Cambridge History of Medieval Philosophy. Cambridge: Cambridge University Press. Pasnau, Robert (2011). Metaphysical Themes 1274–1671. Oxford: Clarendon Press. Perler, Dominik (2002). Theorien der Intentionalität im Mittelalter. Frankfurt am Main: Klostermann. Perler, Dominik (2006). Zweifel und Gewissheit. Skeptische Debatten im Mittelalter. Frankfurt am Main: Klostermann. Perler, Dominik (ed.) (2008). Transformations of the Soul: Aristotelian Psychology 1250–1650. Leiden: Brill (issue 46.3 of Vivarium). Perler, Dominik (2012). ‘Scepticism and Metaphysics’. In John Marenbon (ed.), The Oxford Handbook of Medieval Philosophy. Oxford: Oxford University Press, 547-565. Peter of Ailly (1490, reprint 1968). Quaestiones super libros Sententiarum. Frankfurt am Main: Minerva. Peter Aureol (1956). Scriptum super Primum Sententiarum, (ed.) M. Buytaert. St Bonaventure: Franciscan Institute. Peter Aureol (2009). Scriptum super primum Sententiarum, (ed.) R. L. Friedman et al. The Peter Auriol Homepage, . Peter John Olivi (1922–1926). Quaestiones in secundum librum Sententiarum, 3 vols., (ed.) Bernardus Jansen. Quaracchi: Collegium S. Bonaventura. Peter of Spain (1972). Tractatus called afterwards Summule Logicales, (ed.) Lambert M. de Rijk. Assen: Van Gorcum. Putallaz, François-Xavier (1991). La connaissance de soi au XIIIe siècle. Paris: Vrin. Robert, Aurélien (2006). ‘Jamais Aristote n’a eu de connaissance d’une substance: Nicolas d’Autrécourt en contexte’. In Stefano Caroti and Christoph Grellard (eds), Nicolas d’Autrécourt et la Faculté des Arts de Paris. Cesena: Stilgraf, 153–174. Schmid, Stephan (2011). Finalursachen in der frühen Neuzeit. Eine Untersuchung der Transformation teleologischer Erklärungen. Berlin and New York: W. de Gruyter. Smith, A. Mark (1981). ‘Getting the Big Picture in Perspectivist Optics’. Isis, 72, 568–589. Tachau, Katherine H. (1988). Vision and Certitude in the Age of Ockham: Optics, Epistemology and the Foundations of Semantics 1250–1345. Leiden: Brill.

Chapter 3

Sk epticism a n d Perception Baron Reed

The history of epistemology has been dominated by engagement with skepticism, particularly through developments in the two main flowerings of that tradition—first in the Hellenistic era and then in the Early Modern period. It is somewhat surprising, then, that skepticism often remains poorly understood. There are several reasons for this. First, much recent discussion of skepticism has been almost entirely anti-skeptical in nature. Second, anti-skeptical epistemologists often argue against the generic ‘skeptic’ without considering the views or arguments advanced by any particular skeptic. Third, anti-skeptical epistemologists often choose as their target a single skeptical argument as if an answer to it were all that needs to be given in responding to skepticism in general. Finally, many of the historical figures who were concerned with skepticism were systematic thinkers. Skepticism often played a role in their broader systems—one that is often missed by epistemologists, who usually have narrower, specialized interests. To proceed in these ways, however, is to miss much of what is most interesting in the skeptical tradition. In what follows, then, I shall try to highlight some of the differences among the major skeptical challenges to perceptual knowledge, while keeping in view their place within the broader philosophical contexts in which they occur. As we shall see, these arguments work by pointing to one or more potential sources of error: that experience can be misleading—either in any particular instance or in general—or that any particular belief can be mistaken, or that the concepts we use to make sense of experience may be misleading. Given the variety of ways in which these arguments work, it will become clear that no single anti-skeptical response can hope to be adequate.

1  Academic criticism of stoic epistemology Although our understanding of the history of skepticism is complicated by the lack of surviving material from early figures like Pyrrho, we do have a clear grasp of the earliest known skeptical arguments.1 Some of these can be found in Cicero’s Academica, which 1 See

Bett (2010) for state-of-the-art scholarship on ancient skepticism, including a thorough bibliography of recent work. See also Thorsrud (2009).

Skepticism and Perception    67 we have in two partial versions.2 In this dialogue, Cicero is recounting recent developments in the Academy in light of the two-centuries-long dispute between the Stoics and the Academics. Although the Academic skeptics claimed Socrates as the original skeptic, it was Arcesilaus (head of the Academy in the middle of the third century bce) who moved the school clearly in a skeptical direction. His arguments targeted the epistemology of the Stoics, whose school had recently been founded by Zeno of Citium. The fundamental element of Stoic epistemology is the cognitive or cataleptic impression: they took it to be the criterion of truth, and they said the sage—who assents only to cognitive impressions—can never go wrong. Zeno initially held that the cognitive impression is one that comes from what is, stamped and impressed exactly in accordance with what is. Arcesilaus then asked Zeno whether a true impression could be just like a false one. Zeno replied that no impression could be cognitive if there could be a false one just like one that comes from what is. Arcesilaus agreed that this would need to be added to the account of the cognitive impression and then set about arguing that no impressions could be cognitive because this last condition could not be satisfied.3 The Academics generally used two different arguments to motivate the line of attack Arcesilaus initiated. The first relies on the existence of pairs of indistinguishable objects, like twins or eggs.4 A rather dramatic example of this sort of cognitive failure occurs when a brood parasite, like a European cuckoo, lays its eggs in the nests of other birds, such as reed warblers.5 To the warbler, the cuckoo egg is indistinguishable from its own—even though, in both cases, the warbler is getting impressions of the eggs exactly in accordance with their size, shape, mottling, etc. Given that the cuckoo chick turns out to be a rather impolite guest, pushing the other eggs and chicks out of the nest, the warbler has every incentive (evolutionary and otherwise) to detect the intruding egg. Yet the cuckoo’s strategy is often quite successful, even though the warbler has ample opportunity to inspect the eggs in its nest. The cuckoo’s ability to deceive the reed warbler indicates that the warbler is unable to know its own egg, even when it is sitting on it. More generally, the fact that a false impression can be just like a true one shows that it isn’t enough for impressions to come from what is, exactly in accordance with what is.6 So long as it is possible for there to be false impressions that are indistinguishable from our best true impressions, none of our impressions can be cognitive. The Stoics replied to this line of argument by saying that nature doesn’t contain pairs of objects that are entirely indistinguishable. If no two objects are completely identical, 2  Cicero (2006/46–4 bce). See the introduction to this translation, by Charles Brittain, for a very helpful overview of Academic skepticism. 3  For this account of the dispute, see Cicero, 2006/46–4 bce: 45 (ii. 77). It is controversial whether Zeno meant to add an additional condition to his account of the cognitive impression or merely intended to clarify what he meant by his initial statement. For more on these interpretive options, see Reed (2002). 4  Cicero, 2006/46–4 bce: 32–35 (ii. 54–58) and 49–50 (ii. 84–86). 5  For more on brood parasitism, see Olivia Judson’s excellent article, ‘Cuckoo! Cuckoo!’, in the New York Times, 1 June 2010. 6  There is an interesting question here regarding the sense in which the warbler’s impression of the cuckoo egg is false. After all, in many respects, she sees it as it is; she is not deluded as to its size or shape or mottled colouring. Nevertheless, the bird apparently sees the egg as being a warbler egg (or as its own egg) and in that sense is mistaken. Some philosophers (e.g. Descartes) would be inclined to treat this as a mistake of judgement rather than as a flaw in the impression itself. Even so, Arcesilaus seems to be right in saying that the impression is inadequate as a basis for knowledge, given that it does not allow the warbler to distinguish between the cuckoo’s egg and its own.

68   Baron Reed then an impression that is ‘craftsmanlike’—i.e. one that reflects all of the object’s characteristics—will indeed be cognitive. But, even if one accepts the Stoics’ version of the Principle of the Identity of Indiscernibles, it is clear that their view places unreasonable demands on the capacity for cognition.7 Ptolemy Philopator, the ruler of Egypt, fooled Sphaerus (one of Zeno’s pupils) with a wax pomegranate; Sphaerus’s reply was that his impression of the pomegranate had not been cognitive but merely reasonable.8 That sort of retreat will be universally required, however, because it will always be possible for there to be two objects that differ only in ways that are imperceptible to humans. The second argument used by the Academics makes use of altered psychological states, like dreams and insanity.9 False impressions, after all, do not need to come from genuinely existing objects. Even if it is granted that no two objects will yield the same impressions, it can still be true that a false but indistinguishable impression can be found for every true impression. The Stoics insisted that the impressions we have in dreams, in drunkenness, and in madness are intrinsically different from those we have while in our right minds. But the Academics replied that all of these impressions are equally assented to, when we have them.10 What is noteworthy about this debate between the Stoics and the Academics is that it is the first time a systematic epistemology—one in which perception plays a central role—meets sustained skeptical criticism. In the end, the Stoics may have made it true by definition that some true impressions are such that there couldn’t be indistinguishable false ones. Chrysippus, the leader of the Stoics in the generation after Arcesilaus, seems to have moved in the direction of saying that the awareness made possible by a cognitive impression includes within itself the object that caused the impression.11 On this way of understanding perception, then, cognition is grounded in a direct awareness of the perceived object. The Stoics have avoided the letter of the Academics’ criticism: the awareness enabled by cognitive impressions is metaphysically different from the awareness given by false impressions because only the former includes an extra-mental object. But it is far from clear that the spirit of the revised view is satisfactory—to the subject, this difference is itself unavailable to consciousness. As we shall see, however, a variant of this sort of answer is one that will be given again by other anti-skeptics in the history of epistemology. 7  What is worse, this principle would be insufficient to solve the problem, even if it were true. Suppose the true and the false impression are discernible in some way; the subject might be able to tell them apart, but that does not mean she could identify which is true and which is false. (I am grateful to Mohan Matthen for this point.) 8  Reported by Diogenes Laertius; see Long and Sedley, 1987: 40F. 9  Cicero, 2006/46–4 bce: 29–32 (ii. 47–53) and 50–52 (ii. 88–90). 10  One might also point out, as the eleventh-century Muslim philosopher Al-Ghazali did, that, even if we reject our earlier dream experiences upon waking, ‘it is possible that a state will come upon you whose relation to your waking consciousness is analogous to the relation of the latter to dreaming’; quoted in Lagerlund, 2010: 11–12. In that case, we will reject our present waking experience, just as we did our dreams. 11  See Reed (2002). Part of the evidence for this claim is a passage from Aetius in which Chrysippus is reported to have provided different accounts for veridical and nonveridical perception, in which they make one aware of ontologically different sorts of objects; see Long and Sedley, 1987: 39B. This is the same sort of account offered by so-called disjunctivists like McDowell (1988).

Skepticism and Perception    69

2  The ten modes of pyrrhonism The Ten Modes were argument forms, perhaps developed by Aenesidemus in the first century bce. They survive in the work of Sextus Empiricus and of Philo of Alexandria.12 The Ten Modes point out ways in which the perceptual beliefs a perceiver has are relative—to species, to individuals, to circumstances, etc. In each of these cases, there will be a disagreement between perceivers who vary in the relevant way. For example, honey will taste sweet to me but bitter to people who have jaundice. In order to know how things really are, the disagreement must be adjudicated. But that judgement cannot come from any of the perceivers who are currently parties to the dispute; that would be question-begging. What is needed is an impartial judge. But any perceiver not currently involved in the dispute will add only another perceptual belief to the disagreement. Her judgement will be no better, and no more impartial, than those of the other perceivers. Hence, these kinds of disagreements cannot be resolved in a way that is not question-begging. There is a wealth of anecdotal information about perceptual relativity gathered in Sextus’s version of the Ten Modes. We hear, for example, about Demophon, Alexander the Great’s waiter, ‘who used to shiver when he was in the sun or the baths, and felt warm in the shade,’ and we learn that ‘the same wine appears sour to people who have just eaten dates or figs, but it seems to be sweet to people who have consumed nuts or chickpeas’.13 This material turned out to be the strongest grounds for the distinction made in the Early Modern period, by philosophers like Galileo, Descartes, and Locke, between (to use Locke’s terminology) primary and secondary qualities.14 The primary qualities—extension (or having spatial dimensions) and motion—are mathematically describable quantities, and our representations of them accurately reflect the qualities as they exist in objects. By contrast, the secondary qualities—such as colours, smells, and tastes—do not seem to admit of mathematical description, and there is nothing in the objects that matches our representations of these qualities. The wine that tastes sour to one person and sweet to another cannot be both. Hence, those divergent perceptual representations of it must depend in large part on the differing circumstances of those perceivers. The philosophers who borrowed from the Pyrrhonists the material on perceptual relativity to motivate the distinction between primary and secondary qualities did not intend to be make a skeptical argument. And yet there clearly are skeptical implications that follow from that distinction. If we grant to Galileo, Descartes, and Locke that material objects are characterized only by the primary qualities, then much of our perceptual experience is misleading. As Pierre Bayle put it, if these philosophers are right, then ‘I know that bodies are not at all as they appear to me’.15 He also recognized that the point can be pushed further: ‘if the objects of our senses appear colored, hot, cold, odoriferous, and yet they are 12  See the translation of Sextus Empiricus’s Outlines of Pyrrhonism in Mates, 1996:  94–110 (book I, section 14); Annas and Barnes (1985) provides both the relevant material from Sextus and from Philo, arranged by mode. 13  Annas and Barnes, 1985: 54 and 80. 14  Locke, 1979/1690: book II, chapter viii. 15  Bayle, 1965/1697: 197 (art. ‘Pyrrho’, rem. B).

70   Baron Reed not so, why can they not appear extended and shaped, in rest and in motion, though they are not so?’ 16 As Berkeley would later argue, we find the same sort of perceptual relativity in our perception of primary qualities as we do in our perception of the secondary qualities.17 So, they are equally doubtful. If the science of the Early Modern period seems to show that perception is unable to reveal the true nature of things, science of our own times has only made the problem starker. Most of the space around us is empty, contrary to how it appears. The world as described by physicists is extraordinarily different from the world as we perceive it.

3  The modes of agrippa Immediately after presenting the Ten Modes, Sextus mentions a set of five modes handed down by ‘more recent Skeptics’ and now usually attributed to Agrippa, about whom nothing else is known.18 Where the Ten Modes are based in an assortment of particular facts about different perceptions, Agrippa’s modes are general argument strategies meant to force beliefs of any sort—perceptual and otherwise—into a problematic structure of justification. Two of the modes, deriving from dispute and from relativity, allow the skeptic to raise a problem with the belief in question. Once the belief has been called into question, there are only three possible ways the believer can defend it; the final three modes come into play depending on which way the believer chooses. Call the target belief B. Suppose she offers another belief, C, in support of B. The skeptic can use one of the first two modes to call C into question. The believer might then defend C by mentioning another belief, D, which can itself be called into question. Either the believer will continue using new beliefs to defend those she has already mentioned, or she will eventually use one of the previously mentioned beliefs again. If the former, the skeptic will use the mode of infinite regress; if the latter, the skeptic will use the mode of circularity. In either case, the skeptic is essentially pointing out that the believer never succeeds in justifying the target belief B because justification never enters the chain of beliefs—it is endlessly deferred, either to an unending series of new beliefs, or to the same beliefs over and over. The final way the believer might defend B is to put forward a belief (either B itself or some other belief offered in support of B) as not needing any further support. In that case, the skeptic will rely on the mode of hypothesis: if the believer can hypothesize, say, C, there is nothing to prevent the skeptic from hypothesizing the denial of C. There is no reason to prefer one to the other. Given the abstract and perfectly general nature of Agrippa’s modes, it is natural to think that they have no special relevance to understanding perception. However, many twentieth-century epistemologists used Agrippa’s modes to argue that the structure of justification has to be foundationalist in nature, and they took perceptual beliefs to be a central component of the foundational level.19 The logic of foundationalism dictates that we must 16 

Bayle, 1965/1697: 197. See also p. 365 (art. ‘Zeno of Elea’, rem. G). Berkeley, 1982/1710: pt. I, sections 14–15. 18  Mates, 1996: 110 (book I, section 15), and Annas and Barnes, 1985: appendix C. 19  This is often called the regress argument for foundationalism. See Price (1932), Lewis (1946), Russell (1948), Chisholm (1977), and Fumerton (1985 and 1995). For a very early version of this sort of view, see Aristotle’s Posterior Analytics, ii. 19 (1993/4th century bce). 17 

Skepticism and Perception    71 identify perceptual beliefs that do not depend on support from other beliefs and yet are not mere hypotheses. Perceptual beliefs that draw on a variety of different experiences— e.g. my belief that most lions are tawny—are not plausible candidates to play this role. But those beliefs that are somehow directly grounded in one’s current perceptual experience can, perhaps, serve as the bottom layer of beliefs in a foundationalist structure: they do not receive justification from other beliefs but do provide it to others. There are many subtle issues that arise in trying to understand what C. I. Lewis called the ‘given element in experience’, which is supposed to ground basic beliefs. Some are metaphysical in nature—e.g., is our experience best understood as consisting of discrete sense-data whose reality is exhausted by their appearance, or should we take experience to be simply properties of the perceiving subject? The more serious problems, though, are epistemological. First, some aspects of our experience are too complex to justify our beliefs. So, how can we make a principled distinction between those perceptual beliefs that are well supported by the relevant experiences and those that are not?20 Second, even if we do draw a principled distinction that allows us to see which perceptual beliefs can be grounded in experience, it seems very unlikely that we will be able to move much beyond those basic beliefs. The examples of foundational beliefs usually given have extremely simple contents—this is blue, or I am being appeared to redly. It is very hard to see how we do or even could use beliefs of that kind to justify beliefs about more interesting objects like tables and chairs or other people. If traditional foundationalism were the only game in town, a skeptical conclusion might seem to be inevitable.21 But many epistemologists have abandoned this sort of foundationalism in favour of one that takes the bottom-level beliefs to be justified in virtue of being reliable, in the sense that they are likely to be true. Reliability, however one understands it, is an externalist property, meaning that the subject who has the belief need not be aware that it is, in fact, reliable. Given this sort of view, there is no reason to limit beliefs at the foundational level to those that conform closely to one’s simple experiences. Beliefs about tables and chairs may turn out to be reliable enough to count as knowledge. Once again, it looks as though the response to skepticism is grounded in something that is unavailable to the subject herself.

4  Descartes’s three arguments In the First Meditation, Descartes offers three arguments for skepticism.22 The first of these—that the senses have deceived him and he should never trust anything that has ever misled him—is not one that he takes very seriously. If he did, he surely would have tried to offer a more substantial reply to it later in the Meditations. The purpose of the first 20 

This is the ‘problem of the speckled hen’, which Gilbert Ryle raised for A. J. Ayer; see Chisholm (1942). See Fumerton (1985 and 1995) for an example of someone who follows the route from foundationalism to skepticism. 22  Descartes, 1984/1641: 12–15 (AT vii 17–23). All three arguments are couched in the first person, and I will follow Descartes in presenting them in that way. Nevertheless, it is helpful to keep in mind that, when Descartes says ‘I’, he is not straightforwardly referring to himself. Rather, he is leaving open space for the reader to follow the meditator’s thoughts. 21 

72   Baron Reed argument is, I think, rhetorical. By first presenting and then immediately discarding the argument, Descartes’s meditator is able to pass himself off as a reasonable person—he’s not someone who will allow himself to be bullied by skeptical arguments. Seeing that the meditator will push back when necessary makes it easier for the reader to follow the path the meditator takes through the Meditations. The same pattern holds when Descartes raises the second of his three skeptical arguments—viz., that he can have the same experiences while dreaming that he has when he is awake. The meditator first considers the possibility that waking experience is intrinsically different from dreams and then rejects it: ‘there are never any sure signs by means of which being awake can be distinguished from being asleep’.23 So far, it looks as though Descartes is largely reprising the argument the Academics used against the Stoics, which worked by calling into question the veridicality of any particular experience a person might have.24 But a careful reading of the entire Meditations shows that Descartes has something else in mind. As this point cannot be fully appreciated without understanding what Descartes is doing in his third skeptical argument, however, let us turn our attention to it. Philosophers often take Descartes’s third argument to rest on the possibility that an evil demon is deceiving him, but this is not entirely correct. It’s true that Descartes does try to encapsulate the argument in the hypothesis that an evil demon is deceiving him, and he does make use of that hypothesis when he brings forth the certainty that he exists in the Second Meditation. But when Descartes introduces the skeptical problem in the First Meditation, he considers first the possibility that he has been created by an all-powerful God and then the possibility that he has come into existence as a matter of random chance. What is really driving his skeptical doubt is the fact that he is fundamentally ignorant of his origin—and of what that origin means for his cognitive abilities. Thinking of this argument as grounded in the evil demon hypothesis also tends to cause confusion in that many philosophers have remarked that it could be updated by changing the possibility of being the victim of an evil demon to the possibility that one is a brain in a vat. But the latter scenario seems to work by calling into question one’s experiences. As illustrated so vividly in The Matrix, the world could be utterly different from the run of experiences one has. Understood in that way, Descartes’s third argument is not very different from the second; in effect, it merely adds the possibility that one might be dreaming all the time. To be sure, Descartes’s third argument does make that addition, but it also goes much further. Notice that, when Descartes begins the argument, he says that ‘since I sometimes believe that others go astray in cases where they think they have the most perfect knowledge, may I not go similarly wrong every time I add two and three or count the sides of a square, or in some even simpler matter, if that is imaginable?’ 25 What Descartes calls into question here is not merely our perceptual experience but our capacity for clear and distinct perception.26 That is, the ideas or concepts we use to make sense of our perceptual

23 

Descartes, 1984/1641: 13 (AT vii 19). is probably why Hobbes accused Descartes of rehashing ‘ancient material’ in the First Meditation; see Descartes, 1984/1641: 121 (AT vii 171). 25  Descartes, 1984/1641: 14 (AT vii 21). 26  For an account of how Descartes can call into question clear and distinct perception without falling into the Cartesian Circle, see Reed (2012). 24 This

Skepticism and Perception    73 experience might turn out to be entirely wrong. It’s not just that I might somehow make a calculation error when adding two and three—the real worry is that the world might not be mathematically describable at all. My fundamental ideas—extension, substance, causation, etc.—might all fail to correspond to anything in reality. The same sort of skeptical worry was developed in a variety of ways by some of the Early Modern skeptics who came after Descartes. For example, Bayle says that, ‘if it were true that the real existence of extension contained contradictions and impossibilities,’ as he has argued in his article on Zeno of Elea, ‘it would be absolutely necessary to have recourse to faith to be convinced that there are bodies’.27 Faith, rather than knowledge, would be the most we could hope for, given the way our ideas impeach themselves. Descartes, of course, thinks that this skeptical problem can be resolved. The path he follows—from the knowledge that he exists to the knowledge that God exists and is not a deceiver—is well known and largely unconvincing to philosophers now. But let us suppose for a moment that it succeeds. God’s guarantee turns out to work differently for clear and distinct perception on the one hand and sense perception on the other. God’s guarantee of clear and distinct perception is perfect because, if we did fall into error through using it, we would have no way of correcting it and God couldn’t fail to be a deceiver. The same cannot be said for most of our perceptual beliefs: they can and should be corrected through the use of clear and distinct perception.28 We are at last in a position to return to the difference between the Academics’ challenge to perception and Descartes’s. Where the former seem to call into question the veridicality of perceptual experiences on an individual basis, Descartes wants to reduce the general epistemic status of perception and remove it from its central position in Aristotelian and Scholastic epistemology. The guarantee he thinks God provides for perception is conditional on our correcting it through the use of clear and distinct perception. Sense perception works well enough for practical purposes, but it is not an adequate way of coming to know the true nature of things—that is the correction that needs to be made. Descartes can manage this sort of limited vindication of perception because he, unlike the Academics, is not a skeptic. It is the combination of his skeptical and anti-skeptical arguments that allows him to manoeuvre perception into the reduced role he thinks it is suited for. Descartes returns to the dream argument at the very end of the Sixth Meditation. His response is rather unsatisfactory—it’s abrupt, inaccurate (in that he now identifies this as the principal reason for doubt, despite the fact that he has devoted far more space to replying to the third argument), and weak. He says that he can ‘now notice that there is a vast difference between’ being asleep and being awake; all he needs to do is to use all of his senses, together with his memory and his intellect, to check the veracity of his perceptions.29 Granted, the difficulties of ordinary life often make this practically impossible, so 27 

Bayle 1965/1697: 377 (art. ‘Zeno of Elea’, rem. H). Bayle sets out the ‘contradictions and impossibilities’ in remark G of this article (pp. 359–372). 28  One exception seems to be the most general perceptual beliefs we have—viz., that there are corporeal things. Descartes says that these objects ‘may not all exist in a way that exactly corresponds with my sensory grasp of them, for in many cases the grasp of the senses is very obscure and confused. But at least they possess all the properties which I clearly and distinctly understand’ (1984/1641: 55 (AT vii 80)). Descartes allows this exception because God has given us a strong natural tendency to believe in mind-independent corporeal objects and no faculty that allows us to correct that tendency (1984/1641: 55 (AT vii 80)). 29  Descartes, 1984/1641: 61–2 (AT vii 89–90).

74   Baron Reed Descartes closes by saying that ‘it must be admitted that in this human life we are often liable to make mistakes about particular things, and we must acknowledge the weakness of our nature’.30 When this ‘discovery’ comes without the support of any argument or investigation, one is tempted to ask why he didn’t just come out with it in the First Meditation. In reality, though, Descartes is simply far less interested in what we may know about particular things—and how well we may know it—than he is in putting science on a more secure footing.31 This is well worth keeping in mind, for two reasons. First, Descartes’s limited goal—and his confidence in his own anti-skeptical arguments—allows him to make the confrontation with skepticism an all-or-nothing affair. He pushes his readers into the depths of despair in the First Meditation. This is not the aim of those who identify themselves as skeptics (e.g., the Pyrrhonists, the Academics, and Montaigne). Second, later epistemologists have tended to follow Descartes in seeing the skepticism/anti-skepticism dispute as one that must end in either of two extreme outcomes—total doubt or the complete vanquishing of skepticism. But they have also turned their focus primarily to ordinary sorts of knowledge, not to the foundations of science. That has both magnified the conflict and made it difficult for many to take the skeptical side of the debate seriously, resting, as it appears to, on the outlandish possibility that an evil demon is deceiving me right now into thinking that I have a human body and am sitting in a chair, etc. To be fair, this is one way of coming to terms with the legacy of skepticism. But it is far from the only or most interesting way to understand it.

5  Moorean common sense If skepticism is the result of carrying the critical reflection characteristic of philosophy to its logical extremes, common sense—as defended by Thomas Reid, G. E. Moore, and others—is the diametrically opposed tendency. Common sense seeks to limit the reach of philosophy, to keep it safely within narrow bounds so that dangerous conclusions can be forestalled or ignored. It is, in that sense, a far more pessimistic approach to philosophy than skepticism is. Moore’s quintessential commonsense reply to skepticism can be seen in his treatment of an argument advanced by Bertrand Russell: Russell’s view that I do not know for certain that this is a pencil or that you are conscious rests, if I am right, on no less than four distinct assumptions . . . And what I can’t help asking myself is this: Is it, in fact, as certain that all these four assumptions are true, as that I do know that this is a pencil and that you are conscious? I cannot help answering: It seems to me more certain that I do know that this is a pencil and that you are conscious, than that any single one of these four assumptions is true, let alone all four.32

30 

Descartes, 1984/1641: 62 (AT vii 90). He is clear at the outset that his goal is to establish something ‘in the sciences that was stable and likely to last’; Descartes, 1984/1641: 12 (AT vii 17). 32  Moore, 1959: 226, emphasis in the original. Moore is responding to Russell (1927). 31 

Skepticism and Perception    75 I’ve left out Russell’s assumptions because it doesn’t really matter to Moore’s argument what they are. As William Lycan would say, the assumptions ‘are only philosophy stuff’.33 They can never be so secure as to overturn the convictions of common sense, to which we are so strongly committed. This response to skepticism, which begins and ends with a simple comparison of some philosophical claims to a commonsense belief, betrays a startling lack of curiosity. As Bryan Frances has pointed out, it allows us to defeat the skeptic ‘without showing just what it is that makes it true that Joe knows he has hands or even showing where the sceptic’s argument has gone wrong. We get the anti-sceptical result without doing any of the work!’ 34 When Moore says that he is more certain that he knows he has a pencil in front of him than he is certain of the truth of any of Russell’s assumptions (or, for that matter, the assumptions used in any skeptical argument), it sounds like he is making a plausible claim. If it is to be an answer to skepticism, though, it is itself more ‘philosophy stuff’, and we need to assess it on those terms. What does it mean to say that he is more certain that he has a pencil? If he could give an epistemological account that shows precisely how the commonsense belief is more certain than the skeptical assumptions, that would be wonderful—but it would be a proper philosophical refutation of skepticism, not one that relies on the simple comparative strategy. If, on the other hand, he cannot explain—philosophically—how he is more certain that he has a pencil, then it is hard to see why the skeptic, or anyone else, should take his claim seriously. The same dilemma can be posed to Moore’s other famous response to skepticism. He holds up a hand and says, ‘Here’s one hand,’ and then he holds up his other hand and says, ‘Here’s another.’ Because hands are things that exist outside the mind, Moore takes himself to have proven that an external world exists.35 If this is a proof, it has to be more than a valid argument, for of course people who remain locked in a disagreement might nevertheless agree that a particular argument is valid. What we need to know is whether the premisses, and therefore the conclusion as well, are true. Can Moore say anything on behalf of the premisses? If he could, he would be offering a proper philosophical response to skepticism. But, if he can’t do this (and, in fact, he doesn’t), it is hard to see how he can legitimately claim to have proven anything. Common sense, in its attempt to bring a premature close to philosophical investigation, is not so much a philosophical outlook as it is an evasion of philosophy.

6  Dogmatism, externalism, and circularity If we are to move beyond Moorean handwaving, we will need to have some way of explaining how the premisses used in responding to skepticism are justified. One possibility is to claim that perceptual experience simply provides justification for one’s perceptual beliefs; 33 

34  Frances, 2005: 167. Lycan, 2001: 41. is the argument Moore gives in ‘Proof of an External World’, also in Moore (1959). Some philosophers have argued that Moore’s target in that paper is idealism rather than skepticism; see Sosa, 2009: ch. 1. Most, however, have regarded it as of a piece with his commonsense reply to skepticism. If necessary, the argument could be strengthened so that it is more obviously epistemological rather than metaphysical. On the strengthened version, his premisses would be that he knows he has hands, and the conclusion would be that he knows there is an external world. 35  This

76   Baron Reed an experience represents the world as being a certain way, and it also justifies one’s belief that the world is that way.36 There are at least two reasons why this view can be called dog­ matism. First, the subject’s justification rests solely on the experience; the subject does not need to be able to cite the experience or anything else as justification for the belief. And, second, the philosophical claim that experience provides this sort of immediate justification is posited but not argued for. Dogmatism about perceptual experience thus threatens to take us into a bad epistemological neighbourhood, where the residents each claim about their own favoured ways of forming beliefs—divine revelation, augury, use of a crystal ball, etc.—that they provide immediate justification. This is a problem to which we shall return. For now, though, let us grant the dogmatist about perceptual experience that it does confer justification on the relevant beliefs. Dogmatism about perceptual experience is an internalist theory, in the sense that it takes justification to stem from the mental states of the subject. One of the major trends in epistemology of the last several decades—and a second way of moving beyond bare Mooreanism—is a move toward epistemological externalism. Views of this sort take justification and knowledge to be grounded in properties that are not internal to the subject—the relevant properties are neither mental states nor easily accessible to the subject’s consciousness. There have been a variety of externalist properties suggested as the ground of justification, including at least the following:  a causal relation obtaining between the belief and its object, the reliability of the process that forms the belief, and the belief’s counterfactual tracking of the truth.37 To take a simple example, suppose that a subject looks out of her window, sees a pine tree, and thereby comes to believe and to know that there is a pine tree nearby. The causal theorist would account for her knowledge by pointing to the complex causal relation that includes the light reflected from the tree to her retinas and the neurological activity that eventuates in the relevant belief. The reliabilist would also require that this process be one that leads the subject to a true belief, not only now, but as a usual matter of course. The tracking theorist, finally, would take the subject’s belief to be knowledge if it is one that would be held in the right circumstances; when there is a pine tree there, she believes it, and when there isn’t she doesn’t.38 It is consistent with any of these forms of externalism that a subject could have a perceptual belief that is justified and counts as knowledge, even though she may not be able to offer any reasons or evidence on its behalf. In that regard, externalism and dogmatism agree. If either dogmatism or externalism were correct, it might seem that the debate with skepticism could be easily resolved. Moore’s belief that he has a hand could be justified in virtue of his perceptual experience of it or in virtue of the reliability of his perceptual belief-forming processes. He may not be able to offer any further defence of it, but at least there will be an account of how he knows the premisses in his argument to be true. This is not, however, the end of the story. The most plausible form of dogmatism holds that perceptual experience provides prima facie justification, where this can be defeated

36 

See Pryor, 2000: 519. See Armstrong (1973), Goldman (1979), and Nozick (1981), respectively. 38  I am ignoring some subtleties here. For example, the causal theorist has to require that the causal relation is not deviant, the tracking theorist pays attention to the method used to form the belief when he evaluates the counterfactual matching of belief with truth, etc. These are important details, but they are largely irrelevant to my purposes here. 37 

Skepticism and Perception    77 by counterevidence.39 The same is true of externalism; the external properties that feature in those views can be defeated when the subject has counterevidence for her belief.40 (Defeaters can themselves be defeated by further evidence. When this happens, the subject’s original justification is restored or replaced with something stronger.) There are several different ways in which counterevidence can provide a defeater for a particular belief.41 Sometimes, the counterevidence indicates that the belief is false. For example, a friend might tell you that it is raining outside, but when you look out of the window you see that it isn’t. Alternatively, the counterevidence might not say anything directly about the truth or falsity of the belief, but it might indicate that the belief is not justified. For instance, a neighbour may tell you that he saw a coyote at the end of the block, but his son informs you that his father can’t see that far without his glasses, which he is not wearing. It remains possible that a coyote really is at the end of the block; even so, you are not justified in thinking this. Finally, counterevidence might indicate that the belief in question may not be justified. It’s not that the subject ought to regard her belief as definitely unjustified—say, because the source is unreliable. Rather, the subject ought to regard the source as too risky to rely upon. For example, you may have believed the results of a recent study that said that eating egg yolks does not significantly raise the risk of a heart attack, but then you learn that the study was conducted by the Poultry Farmers Association. Knowing this last fact does not warrant rejecting the study as unreliable or false, but it would be foolish to rely on the study without seeing independent confirmation of its results.42 The skeptic is now in a position to introduce a defeater for Moore’s belief that he has a hand (or, of course, for any perceptual belief).43 We have seen arguments that show that perceptual experience can be misleading in any particular instance (e.g. the dream argument) or in general (e.g. Decartes’s third argument, grounded in ignorance of one’s own origin and nature); we have also seen arguments that conclude perceptual experience distorts or hides the true nature of things (e.g. Bayle’s use of perceptual relativity and Descartes’s correction of sense perception). These arguments may not positively show that perception is incapable of providing us with justified beliefs, but they do seem to be enough for us to doubt whether our perceptual beliefs are justified. What we need, then, is something that will defeat these defeaters. Only then will our perceptual beliefs count as ultima facie justified and as knowledge. In response to this skeptical challenge, the dogmatist or the externalist may offer a track record argument to establish the reliability of perception. The material for it will be provided by further uses of the subject’s perceptual capacities. Both the dogmatist and the externalist will hold that each resulting belief is justified—in virtue of being grounded in experience or in virtue of having been reliably produced. Having amassed enough 39

  Pryor 2000: 534.   See, e.g., Goldman (1986), Nozick (1981), and Plantinga (1993). The need to add a no-defeater condition to externalist theories was made clear through a series of counterexamples in BonJour (1985: ch. 3), in which a subject has a belief with the requisite externalist property (e.g. reliability) but also has evidence that the belief is false or unjustified. 41  See Lackey, 2008: 44–46, for more on defeaters. 42  For this sort of case, see Reed (2006). 43  See Reed (2006) for this sort of argument. Pryor (2000: 534), says that ‘a priori skeptical arguments do not standardly introduce defeating evidence’ of the sort that he would like to countenance, but he doesn’t justify this stipulation. This is a surprising omission, given how central it is to his view. In any case, typical skeptical arguments are not entirely a priori. Part of what makes the dream argument, for example, compelling is our experience of having vivid, realistic dreams. 40

78   Baron Reed instances of perceptual knowledge, the subject can then inductively infer that perception is a reliable means of acquiring true beliefs. There are two problems with this sort of response. First, the dogmatist and the externalist are warranted in claiming only that these perceptual beliefs have prima facie justification. The skeptic might still argue that the defeater in question applies to all of them. In that case, the track record argument cannot get off the ground because none of the premisses is actually available for use. Second, the response given by the dogmatist and the externalist involves using a belief-forming method to justify itself. But this sort of epistemic circularity undermines the conclusion that the dogmatist and the externalist are trying to reach.44 It would be like asking a used-car salesman if he is honest—an affirmative answer does nothing to settle the question. As I mentioned earlier, there are many different ways of forming beliefs about which one might be dogmatic. The proponents of divine revelation, crystal-ball reading, and so forth might now argue that they, too, can prove that their favoured methods are reliable. After all, when they ask God if he is a reliable guide to the truth, he always says yes! Is the dogmatist about perception, or the externalist who takes perception to be reliable, really no better off than the revelationists and the occultists? At this point, argument seems to give out. There is nothing further that could be said that wouldn’t, at some point, involve us in this sort of epistemic circularity. Still, some epistemologists will say that there is a crucial difference, which we should not overlook. Even though the argument vindicating perception is epistemically circular, it has the virtue of having true premisses and a true conclusion.45 The other dogmatists can’t say the same.46 In the end, how far have we advanced beyond Moore’s commonsense response to skepticism? A more elaborate argument has been provided, but it comes to rest, ultimately, on the same sort of bare assertion that seemed so unsatisfactory in the context of Moore’s shorter proof. In assessing the dispute between skepticism and anti-skepticism, it may be helpful to keep in mind that there is no single conclusion that all skeptics have been driving towards. In the most extreme, and pessimistic, case, the outcome of skepticism is the conclusion that no one knows—or even has reason to believe—anything. But it is also possible to be a more moderate sort of skeptic—one who accepts perception as among the best ways of forming beliefs available to us, even if it cannot be put on as secure a footing as we would like.47 Skepticism understood in this way is not a pessimistic conclusion to philosophical reasoning, but rather a persistent goad to try to carry it further.48

References Annas, J. and Barnes, J. (1985). The Modes of Scepticism. Cambridge: Cambridge University Press. Aristotle (1993/4th century bce). Posterior Analytics (2nd edn), trans. J. Barnes. Oxford: Oxford University Press. 44 

See Fumerton 1995: 173–180, and Vogel (2000) for this complaint. 46  Well, they will say the same. But they’ll be wrong. See Sosa, 2009: 206–208. 47  See Reed (2012). 48  For helpful comments on this chapter, I am grateful to Jennifer Lackey and Mohan Matthen. 45 

Skepticism and Perception    79 Armstrong, D. (1973). Belief, Truth and Knowledge. Cambridge: Cambridge University Press. Bayle, P. (1965/1697). Historical and Critical Dictionary, trans. R. Popkin. Indianapolis: Bobbs-Merrill. Berkeley, G. (1982/1710). A Treatise Concerning the Principles of Human Knowledge. Indianapolis: Hackett. Bett, R. (ed.) (2010). The Cambridge Companion to Ancient Scepticism. Cambridge: Cambridge University Press. BonJour, L. (1985). The Structure of Empirical Knowledge. Cambridge, MA:  Harvard University Press. Chisholm, R. (1942). ‘The problem of the speckled hen’. Mind, 51, 368–373. Chisholm, R. (1977). Theory of Knowledge (2nd edn). Englewood Cliffs, NJ: Prentice-Hall. Cicero (2006/46–4 bce). On Academic Scepticism [Academica], trans. C. Brittain. Indianapolis: Hackett. Descartes, R. (1984/1641). ‘Meditations on first philosophy’. In The Philosophical Writings of Descartes, vol. ii, trans. J. Cottingham, R. Stoothoff, and D. Murdoch. Cambridge: Cambridge University Press. Frances, B. (2005). Scepticism Comes Alive. Oxford: Oxford University Press. Fumerton, R. (1985). Metaphysical and Epistemological Problems of Perception. Lincoln, NE: University of Nebraska Press. Fumerton, R. (1995). Metaepistemology and Skepticism. Lanham, MD: Rowman & Littlefield. Goldman, A. (1979). ‘What is justified belief?’ In G. Pappas (ed.), Justification and Knowledge (pp. 1–23). Dordrecht: Reidel. Goldman, A. (1986). Epistemology and Cognition. Cambridge, MA: Harvard University Press. Lackey, J. (2008). Learning from Words: Testimony as a source of knowledge. Oxford: Oxford University Press. Lagerlund, H. (2010). ‘A history of skepticism in the Middle Ages’. In H. Lagerlund (ed.), Rethinking the History of Skepticism: The missing medieval background (pp. 1–28). Leiden: Brill. Lewis, C. I. (1946). An Analysis of Knowledge and Valuation. LaSalle, IL: Open Court. Locke, J. (1979/1690). An Essay Concerning Human Understanding, ed. P. H. Nidditch. Oxford: Oxford University Press. Long, A. A. and Sedley, D. N. (eds) (1987). The Hellenistic Philosophers, vol. i. Cambridge: Cambridge University Press. Lycan, W. (2001). ‘Moore against the new skeptics’. Philosophical Studies, 103, 35–53. McDowell, J. (1988/1982). ‘Criteria, defeasibility, and knowledge’ (rev. edn). In J. Dancy (ed.), Perceptual Knowledge (pp. 209–219). Oxford: Oxford University Press. Mates, B. (1996). The Skeptic Way. Oxford: Oxford University Press. Moore, G. E. (1959). ‘Four forms of scepticism’. In his Philosophical Papers. London: George Allen & Unwin. Nozick, R. (1981). Philosophical Explanations. Cambridge, MA: Harvard University Press. Plantinga, A. (1993). Warrant and Proper Function. Oxford: Oxford University Press. Price, H. H. (1932). Perception. London: Methuen & Co. Pryor, J. (2000). ‘The skeptic and the dogmatist’. Noûs, 34, 517–549. Reed, B. (2002). ‘The stoics’ account of the cognitive impression’. Oxford Studies in Ancient Philosophy, 23, 147–180. Reed, B. (2006). ‘Epistemic circularity squared? Skepticism about common sense’. Philosophy and Phenomenological Research, 73, 186–197.

80   Baron Reed Reed, B. (2012). ‘Knowledge, doubt, and circularity’. Synthese, 188, 273–287. Russell, B. (1927). An Outline of Philosophy. London: George Allen & Unwin. Russell, B. (1948). Human Knowledge: Its scope and limits. New York: Simon and Schuster. Sosa, E. (2009). Reflective Knowledge: Apt Belief and Reflective Knowledge, vol. ii. Oxford: Clarendon Press. Thorsrud, H. (2009). Ancient Scepticism. Berkeley and Los Angeles: University of California Press. Vogel, J. (2000). ‘Reliabilism leveled’. Journal of Philosophy, 97, 602–623.

Chapter 4

Perception i n E a r ly Moder n Philosoph y Alison Simmons

The senses were subject to considerable scrutiny during the seventeenth and eighteenth centuries (traditionally called the ‘early modern’ period). No early modern philosopher would have denied that the senses are an important source of knowledge about the world, but many worried that they are a systematically misleading source. Consider Malebranche’s ominous warning: I shall teach you that the world you live in is not at all as you believe it to be, because actually it is not as you see it or sense it. You judge on the basis of the relation of your senses to all the objects surrounding you, and your senses beguile you infinitely more than you can imagine . . . there is no precision, no truth in their testimony.1

Descartes before him was less melodramatic but similarly critical:  the senses ‘do not, except occasionally and accidentally, show us what external bodies are like in themselves’.2 It’s not all bad news for the senses, however. Hand in hand with this worry about their ability to show us what the world is really like came an extensive re-examination of almost all aspects of perception. Along the way, the early moderns made important advances in our understanding of the perceptual process, established some of the classic questions with which philosophers and perceptual psychologists wrestled for centuries, and even offered a new vision of the proper function of the senses. Why did the senses come under a cloud of suspicion in the first place? The senses had been eyed cautiously since ancient times: ancient atomists cast colours and flavours into the mind of the perceiver, Plato charged the senses with acquainting us with only shifting appearances, and ancient sceptics challenged the ability of sensory appearances to show us with any certainty what the physical world is really like, or indeed whether there really is one. But something quite dramatic and lasting happened in the early modern period. The rediscovery of ancient writings, and especially ancient sceptical writings, certainly provided one source of renewed concern about the senses.3 An even more pervasive 1 

3 

2  Descartes (1644: II.3). Malebranche (1688: Dialogue I). See Popkin (1979) for an overview of the reception of sceptical writings in the early modern period.

82   Alison Simmons challenge, however, came from developments in natural philosophy or physics, which advanced what I will call the ‘mechanical hypothesis’. Details varied from thinker to thinker, but the basic shared idea was that the physical world is made up of a single kind of stuff, matter, that is (a) fully characterized by a handful of privileged properties including size, shape, position, and local motion, and (b) divisible into insensibly small parts that are characterized by those same properties. Any change in the physical world was to be explained by the motion and impact of variously sized and shaped bodies.4 This conception of the physical world forced a rethinking of almost every aspect of sense perception: the objects of perception; the causal process that gives rise to perceptual experience; the structure of perceptual experience itself; the reliability of the senses for showing us what the world is like; and even the function of the senses. This chapter considers each topic in turn. Although a great many thinkers contributed to the discussion about sense perception in this period, the chapter is limited to philosopher–scientists in Europe who had an especially lasting influence on the topic. It restricts its scope to philosophical questions and debates, leaving aside more technical discussions in optics, anatomy, and physiology, though developments in these areas certainly informed the philosophical discussion. Finally, it focuses on the ‘external’ senses (vision, audition, olfaction, gustation, and touch) to the neglect of the ‘internal’ senses (or bodily senses, like proprioception, kinesthesis, hunger, thirst, etc.), and among the external senses, vision takes pride of place as it did in the period.

1  The objects of perception Early modern philosophers continued to explore the ancient and medieval question how a substance, like a kumquat, can be the object of perception when all we immediately perceive are its sensible properties (its colour, odour, flavour, shape, size, etc.), but two other issues arose that dominated discussions about the object of perception: (a) the distinction between primary and secondary qualities and (b)  the question whether the immediate objects of perception are things or ideas of things. This section examines the primary–secondary quality distinction. Section 4 takes up the issue whether ideas are objects of perception. Boyle and Locke introduced the terms ‘primary quality’ and ‘secondary quality’ into the philosophical discussion in the latter part of the seventeenth century, but Galileo and Descartes made the distinction in the early part of the century.5 The distinction is roughly coextensive with the Aristotelian distinction between common and proper sensibles so far as the lists are concerned: primary qualities include many of the common sensibles (size, shape, position, and local motion and rest); secondary qualities include most of the proper sensibles (colour, sound, odour, flavour, hot and cold). The nature of the distinction, however, is quite different. While both of the Aristotelian common and proper sensibles were 4 

For some classic statements of the mechanical hypothesis, see Boyle (1666 and 1674); Hobbes (1655) and Descartes (1644 and 1664a). 5  See Peter Ross, Chapter 21, this volume.

Perception in Early Modern Philosophy    83 thought to be real properties present in bodies in just the way they appear to be,6 the early modern primary and secondary qualities differ from one another ontologically. Primary qualities were thought to be the fundamental intrinsic properties of body, and so they were present in bodies in just that way they appear to be. Secondary qualities were not. (What they were supposed to be we’ll consider in a moment.) The proposal that there is an ontological difference between a kumquat’s shape and its colour does not suggest itself to perceptual experience: both look to be out there in the kumquat. Arguments for distinguishing their ontologies therefore did not typically rely on introspecting perceptual experience. They piggybacked on arguments for the mechanical hypothesis itself, with its proposal that size, shape, position, and motion are ontologically privileged properties of body that are solely responsible for the movements and interactions of bodies. Some of these arguments for the mechanical hypothesis took the form of a priori conceptual analysis which alleged that size, shape, position, and motion are somehow constitutive of the very concept of body in a way that colour, odour, and the like are not.7 Others insisted on a posteriori grounds that the mechanical hypothesis made for an especially intelligible, simple, or fruitful physical theory.8 Thomas Reid was an interesting exception. He accepted the primary–secondary quality distinction, but thought one could argue for it simply on the basis of introspection. Reflection on our sense-based conception of size and shape, he insisted, shows it to be perspicuous and to inform us what these qualities are ‘in themselves’ while reflection on our sense-based conception of like colour, odour, and the like, he further insisted, shows it to be ‘relative and obscure’, informing us only how these qualities affect us.9 Once size, shape, position, and local motion were given pride of place in the ontology of the physical world, a problem was born about the ontology of the remaining sensible qualities. Just how positively to characterize the ontology of colour, sound, odour, and the like differed from philosopher to philosopher (and sometimes from sentence to sentence within a philosopher). The options included: (a) they are reducible to the (microscopic arrangement of) primary qualities in bodies; (b) they are to be identified with the powers of those (microscopic arrangement of) primary qualities in bodies to produce sensations in the mind of the perceiver; and (c) they are merely sensations in the mind of the perceiver that are produced by the (microscopic arrangements of) primary qualities in bodies. Few thinkers firmly opted for (a), though Descartes and Locke occasionally say things that suggest this reductive view.10 More common were versions of (b) and (c). Locke famously cast secondary qualities as ‘nothing in the objects themselves, but powers to produce various sensations in us by their primary qualities, i.e., by the bulk, figure, texture, and motion of their insensible parts’.11 Boyle and Reid followed Locke in portraying colours, odours, and the like as powers or dispositions of bodies to produce distinctive sensations in human perceivers (and Reid, as I suggested, seemed to think this is what the senses themselves suggest to us).12 Galileo and Hobbes, by contrast, opted for the view that colours, sounds, and the like are simply sensations in the mind of the perceiver. Here is Galileo: ‘[colour, odour, 6  They were distinguished by whether more than one sense modality had access to them. See Dominik Perler, Chapter 2, this volume. 7  See Galileo (1623); Descartes (1644: II.4); Locke (1690: II.viii.9); and Malebranche (1712: I.10). 8  See Descartes (1644: I.69–70 and IV.200–3) and Boyle (1674). 9  Reid (1785: II.17). 10  See Descartes (1637: Discourse 1, 1644: IV.199) and Locke (1690: II.viii.15 and II.viii.17). 12  See Boyle (1666) and Reid (1764: VI.4, 1785: II.17). 11  Locke (1690: II.viii.10).

84   Alison Simmons flavours, and sound] which are supposed to be qualities residing in external objects have no real existence save in us, and outside ourselves are mere names’.13 However unsettled the ontology of secondary qualities was in the period, two commitments were clear and common: (a) secondary qualities like colour and sound are not in physical objects in the way they sensorily appear to be, and (b) according to most parties, they depend as much on the perceiver as on the body to which they are attributed.14 To put the point in somewhat different language:  primary qualities are objective features of the physical world, while secondary qualities are in some sense subjective. Berkeley was a rare opponent to the primary–secondary quality distinction, which he considered both philosophically indefensible and an affront to common sense. His most memorable (if unconvincing) argument against the distinction came in the form of a simple challenge: try to conceive a body that has size and shape without conceiving it to have any colour or tactile qualities. He trusted we will find that we cannot, that the distinction is therefore inconceivable, and that it rests on a false abstraction of the mind.15 Both colours and shapes, he insisted, are ontologically on a par. Curiously, and much to the consternation of later philosophers, he defended this commonsense view not by returning colours and the like to a mind-independent world of bodies, but rather by drawing shapes and sizes into the mind alongside colours: all the sensible qualities (and bodies themselves, for that matter), Berkeley argued, exist as mind-dependent ideas (or, in the case of bodies, collections of ideas).16 Few followed him in this thesis.

2  The origins of perception: Sensory processing Just as the early moderns replaced the Aristotelian conception of the physical world and so objects of perception, so they replaced their account of how it is that we come to perceive it. The task for both was to explain how sensible properties out in the world are causally responsible for sense perceptual experiences in perceivers, a process that often occurs over a considerable distance. On the Aristotelian view, sensible species that in some way resemble the sensible properties of bodies are propagated through the medium and received by the sense organs of a sentient perceiver thereby ‘informing’ her experience of the world.17 Descartes explicitly rejected the species theory: the process, he wrote, cannot involve ‘images transmitted by objects to the brain’.18 Hobbes is downright hostile: ‘the 13  Galileo (1623). See also Descartes (1641: 6th Replies, 1644: I.71); Hobbes (1655: XXV.3 and 10, 1658: II.9); and Locke (1690: II.viii.19). 14  If there are genuine adherents to the reductionist position (a), they may say that the orange colour of the kumquat does not depend on the perceiver (the orange colour is nothing but, say, the having of a certain surface texture that can be cashed out in terms of size, shape, position, and motion), but even the reductionist will say that the appearance of the colour that we associate with the word ‘orange’ is dependent on the distinctive sensations that the kumquat produces in the perceiver. 15  Berkeley (1710, §10). 16  See Wilson (1982) for a discussion of the mind-dependence of sensible qualities in Berkeley. 17  See Dominik Perler, Chapter 2, this volume. For a more detailed discussion of this process, see Simmons (1994). 18  Descartes (1637: Discourse 4 and 1; 1641: 6th Replies; 1644: IV.198).

Perception in Early Modern Philosophy    85 introduction of species . . . passing to and fro from the object, is worse than any paradox, as being a plain impossibility’.19 The problem stemmed from the mechanical hypothesis: if bodies operate only by local motion and impact, then the production of, say, an orange species in the medium or eye is unintelligible; no amount of pushing or turning or jiggling of variously sized and shaped particles of matter is going to result in the production of something orange. Species had to go. The early moderns replaced the species theory with a thoroughly mechanical theory. Instead of species of colour and sound propagated through the medium, they proposed the impact of (insensibly small) bodies in motion. Hobbes offered a nice schematic account of the auditory processing of a ringing bell: . . . the clapper hath no sound in [the bell], but motion, and maketh motion in the internal parts of the bell; so the bell hath motion, and not sound, that imparteth motion to the air; and the air hath motion, but not sound; the air imparteth motion by the ear and nerve unto the brain; and the brain hath motion but not sound . . .20

The explanatory rules here are clear: from object to brain there is nothing but the local motions of bodies.21 A critical moment in early modern theorizing about the sensory process was Kepler’s discovery in 1604 that the function of the lens (or ‘crystalline humor’ as it was called) is not to sense, but rather to refract the light coming into the eye in such a way that all the rays of light coming from one point on a focal object are reassembled at a single point on the retina, resulting in a two-dimensional (upside-down and backward) image of the object on the retina.22 The role of the retinal image, and the puzzle about how the proper orientation and the three-dimensional properties of the object are recovered in perceptual experience, became central questions in the study of vision.23 Descartes accepted Kepler’s account of the lens and retinal image.24 Indeed he enthusiastically gives instructions on how to demonstrate it to ourselves with ‘the eye of a freshly dead human being—or failing that, the eye of an ox or some other large animal’.25 Descartes put the retinal image to work in his mechanical account of sensory physiology, speculating that the retinal image is reproduced in the brain by the motion of filaments in the optic nerve that connect the retina to the brain: when filaments jiggle on the retina they simultaneously jiggle at the other end on the ‘inner surface’ of the brain; in so doing they open pores in a pattern matching the retinal image. The open pores that constitute that brain image in turn draw animal spirits—tiny fast-moving bits of matter that perpetually flow from the pineal gland at the centre of the brain—so that the spirits trace yet another replica of the retinal image on the 19 

Hobbes (1658: II.4). See also Malebranche (1712: III.ii.2) and Reid (1784: II.8). Hobbes (1658: II.9). 21  See Descartes (1644:  IV.198); Locke (1690:  II.viii.11–13); Malebranche (1712:  I.11); and Reid (1785: II.2–3). 22  Kepler (1604: 5.3). 23  Berkeley, for instance, noted: ‘the solution of this knot about inverted images seems the principal point in the whole optic theory, the most difficult perhaps to comprehend, but the most deserving of our attention, and, when rightly understood the surest way to lead the mind into a thorough knowledge of the true nature of vision’ (1733: §52). 24  He further noted that the lens ‘accommodates’ to distance by changes in its shape as one focuses on nearer or further objects, thereby serving as an important cue to the object’s distance. 25  Descartes (1637: Discourse 5). Malebranche repeats the instructions at (1712: I.12). 20 

86   Alison Simmons surface of the pineal gland.26 An image of the object is thus transmitted mechanically from retina to brain to pineal gland.27 Although Descartes occasionally spoke as if the mind sees objects by inspecting these retinal and pineal images,28 he quite emphatically insisted in his Dioptrics that the mind in no way sees objects by inspecting images on the retina or in the brain ‘as if there were yet other eyes within our brain with which we could perceive’ them.29 It is rather that the motions of the filaments in the brain, and the flow of animal spirits from the pineal gland, cause our perceptual experience of the object.30 Writing more than a century later, Reid rejected Descartes’ idea that the retinal image is reproduced further back in the brain (he was dubious that anyone had any idea what was going on in the brain), but he continued to insist, with Descartes, that the mind in no way sees objects by inspecting images of them on the retina: ‘No man ever saw the pictures in his own eye, nor indeed the pictures in the eye of another, until it was taken out of the head and duly prepared.’ 31 The retinal image, and any images further back in the brain, were thought to be links in the mechanical causal chain. The million-dollar question, of course, is: what happens next? How do we get from local motions in the brain to a conscious perceptual experience of a bright orange, tangy, ovoid kumquat on the table three feet away? The question is really threefold: (a) how do we get from motions to conscious experiences in general (from something physical to something mental), (b) how do we get from local motions to colours and sounds in the case of secondary quality perception in particular, and (c) how do we get from local motions that constitute a two-dimensional image of the object in the head to a perception of three-dimensional objects outside the head and at a distance from us? The first two questions land us squarely in the mind–body problem. The third is a topic for perceptual psychology, and so will be considered in the next section. The problem how motions in the brain give rise to conscious perceptual experiences in the mind is clearest for Descartes. According to his dualism, mind and body are distinct and utterly heterogeneous substances:  the mind is an immaterial, consciously thinking and perceiving thing while the body is a material and unconscious thing devoid of thought and perception. The mystery is how two things that are so different could have any causal commerce with each other. Materialists didn’t have it any easier: it’s no more obvious how motions in the brain constitute conscious perceptual experiences than it is how they cause them in an immaterial mind.32 Unfortunately, the early moderns did not do much to illuminate this crucial step. Descartes’ treatment was typical: ‘we know that the nature of our soul is such that different local motions are quite sufficient to procure 26 

Descartes (1664b: §67). For an excellent introduction to Descartes’ sensory physiology, see Hatfield (1992). 28  Descartes (1664b: §70, 1641: Meditation 6). 29  Descartes (1637: Discourse 6). 30  See Wilson (1991) for a discussion of these two ways of reading the relationship between pineal image and mind. 31  Reid (1764: VI.12); see also Reid (1785: II.4). 32 Hobbes suggested that conscious perceptual experiences are constituted by a kind of outward directed resistance to motions coming into the brain from the external world: ‘from the brain, [the motion] reboundeth back into the nerves outward, and thence it becometh an apparition without, which we call sound’ (Hobbes, 1658: II.9; see also Hobbes, 1655: XXV.2). It’s not at all clear that this is an improvement on the dualist’s response. 27 

Perception in Early Modern Philosophy    87 all the sensations in the soul’.33 He added that God established a psycho-physiological law (he called it an ‘institution of nature’) joining types of brain motions with types of sensations in the mind,34 but that still doesn’t tell us how the causal exchange occurs.35 The early modern period was not without creative metaphysical ways around the problem of mind–body interaction:  Malebranche’s occasionalism (which was prevalent among the Cartesians) limited all causal efficacy to God, so that the causal exchange between mind and body, like all causality in the created world, was understood to be powered by God;36 Spinoza’s parallelism asserted that mind and body were not separate substances after all, but two expressions a single substance (God or Nature) and that their relation is not causal but representational;37 and according to Leibniz’s pre-established harmony, God set things up so that the internal (and internally caused) events in the mind would be cosmically coordinated with the internal (and internally caused) events in the body.38 Berkeley took Malebranche a step further and held that God directly causes ideas of bodies in us without the need for any extra-mental bodies existing at all.39 Most philosophers, in other words, backed away from saying there is a straightforward causal interaction between mind and body. In response to the second question how motions in the brain result in sensations of colour, flavour, and the like that bear no resemblance to anything in objects or the brain, the early moderns tended to deny that this creates any special problem by pointing out that physical causes produce mental effects that bear no resemblance to them all the time: the written word ‘aardvark’ results in our imagining a critter with a long nose; a blow to the eye results in seeing stars; and a knife slicing flesh results in pain. These things don’t give us pause, so why should we be puzzled at local motions giving rise to bright orange visual sensations and tangy flavour sensations?40 We are, once again, offered no real insight into how this transformation from motions to colours and flavours is supposed to work, and we are left with an explanatory gap. A handful of philosophers, like Locke and Reid, who were especially modest in their estimation of the range of human knowledge, conceded the explanatory gap between mind and body. Reid, for example, wrote: how are the sensations of the mind produced by impressions upon the body? Of this we are absolutely ignorant . . . there is a deep and a dark gulf between [mind and body] which our understanding cannot pass; and the manner of their correspondence and intercourse is absolutely unknown.41

Since intelligibility and explanatory success were meant to be precisely the advantages that the mechanical philosophy had over Aristotelian physics, this concession made at the 33 

34  Descartes (1641: Meditation 6, 1637: Discourse 6). Descartes (1644: IV.198). had a similar view but acknowledged the explanatory gap: ‘we must often be satisfied with knowing that certain things are connected, and invariably follow one another, without being able to discover the chain that goes between them. It is to such connections that we give the name of laws of nature’ (1764: VI.12). 36  See Malebranche (1688: Dialogue IV.10). 37  See Spinoza (1677). 38  See Leibniz (1695). 39  See Berkeley (1710: §26). 40  See, e.g. Descartes (1644: IV.197) and Locke (1690: Essay II.viii.13). Of course, the natural response is that these phenomena should give us pause! 41  Reid (1764: VI.21). See also Reid (1785: II.4) and Locke (1690: Essay IV.iii.13). 35  Reid

88   Alison Simmons body–mind junction was significant. Berkeley did not miss the opportunity to point out exactly that.42

3  The structure of perceptual experience Once in the mind, there is still work to be done to get us to perceptual experience. Descartes famously distinguished three ‘grades of sensory response’: (a) motions in the sense organs and brain, (b) sensations, which are the immediate result in the mind of those motions, and (c) a host of judgements that embellish those sensations in a variety of ways.43 Why suppose that judgements are involved in perception? After all, it doesn’t feel like I am making any judgements when I look at the trees out my window. I just open my eyes, turn my head, and I see them. The trouble stems from the fact that everyone in the period granted that the sensations we receive from the world are impoverished by comparison with the perceptual experience we actually have of it. Visual sensations, for example, were thought to amount to a series of kaleidoscopic images of two-dimensional colour patches. What we see, however, are three-dimensional objects of constant size, shape, distance, and colour. Visual experience must therefore have a more complex structure than meets the eye: it is, the early moderns proposed, determined by a combination of sensations received from without the mind and judgements produced from within it. Descartes’s account of the judgemental component of perceptual experience was a bit of a hodge-podge: it included judgements that attribute colours and flavours and the like to bodies, judgements that flesh out the three-dimensionality of visual objects, judgements that provide size and shape constancy, judgements by which objects appear to be ‘outside’ us, and also the epistemologically precarious judgements that things in the world are as they sensorily appear. He also rather implausibly suggested that while in adulthood we make all these judgements so habitually that we don’t notice them, we originally made them deliberately.44 Malebranche cleaned up the Cartesian picture by separating what he called ‘natural’ judgements that affect the way the world perceptually appears to us from ‘free’ judgements that result in beliefs about how things are in the world, for example, that they are as they appear.45 Only the latter free judgements, he thought, involve an act of will and result in beliefs for which we are epistemologically responsible, since they are the only ones we have any control over. Natural judgements that result in perceptual experience itself, he proposed, are hard-wired into our nature: that colours appear to be on the surfaces of objects and that bodies appear to have three dimensions not two are the result of judgements that occur in us ‘independently of us and even in spite of us.’46 That judgements contribute to perceptual experience was generally accepted. The nature of those judgements, however, was hotly debated. The debate centred largely on spatial perception in vision, for the problem to solve in this case was both clear and pressing: how is it that from two-dimensional retinal and sensory images we come to see three-dimensional 42 

For discussion, see Wilson (1982). Descartes (1641: 6th Replies). For a similar breakdown of the process, see Malebranche (1712: I.9). 44  See Descartes (1641: 6th Replies, 1644: I.71). 45  See Malebranche (1712: I.10 and I.14). 46  See Malebranche (1712: I.7, I.9, I.11, and I.14). 43 

Perception in Early Modern Philosophy    89 objects? Berkeley opened his hugely influential work, An Essay Toward a New Theory of Vision (1709), with a puzzle about distance perception in particular: 2. It is, I think, agreed by all that Distance, of itself and immediately, cannot be seen. For, distance being a line directed endwise to the eye, it projects only one point in the fund of the eye [the retina], which point remains invariably the same, whether the distance be longer or shorter. 3. I find it also acknowledged that the estimate we make of the distance of objects considerably remote is rather an act of judgement . . . than of sense.47

Everyone agreed that if the retinal image did not contain information about distance then any sensation produced in the mind as a result of it could not either.48 Judgements must fill in the distance. The Cartesians are routinely thought to cast these judgements as innate to the mind (witness Malebranche’s description of them as ‘natural’) and as intellectual in nature: we calculate the distance of an object ‘as if by a natural geometry’, Descartes famously wrote; thus, for example, from the knowledge we have of the distance between our eyes and their angular convergence on an object, we calculate by a process of reasoning the distance of the object by angle-side-angle.49 Berkeley, by contrast, argued that the judgements in question are learned not innate, and associative not intellectual: we immediately perceive distance only through touch (by reaching for or walking toward the object), and thus we must learn to ‘see’ distance by associating our visual sensations of an object with tactile perceptions of its distance; distance perception is an intermodal phenomenon and geometry has nothing to do with it.50 This classic portrayal of the debate does an injustice to the Cartesians, who in fact proposed many means by which we perceive distance, some purely psycho-physiological (and so involving no judgements at all), some involving learned associative judgements, and only occasionally ones that smack of innate geometrical reasoning.51 There is nevertheless a real disagreement between them over whether vision needs to be supplemented by touch in order for visual objects to be represented at a distance, and this debate had repercussions into the twentieth century.52 Reid was another important figure in the debate about the structure of perceptual experience. He rejected an important assumption shared by the Cartesians and Berkeley alike: that judgements effectively finish the representational job begun by sensations to provide us with a full-blooded perceptual experience of the world. First, Reid drew a sharp distinction between sensation and perception. Sensation, he proposed, is a wholly 47 

Berkeley (1709: §§2–3). But see below, fn. 51, and Hatfield (1992) for a possible exception in Descartes. 49  See Descartes (1637: Discourse 6; 1641: 6th Replies; and 1666: §48). See also Malebranche (1712: I.9). 50  Berkeley (1709: §45). 51  Even the ‘natural geometry’ in Descartes was sometimes simply a metaphor to describe a purely psycho-physiological process that operates ‘as if’ our brains were calculating by a kind of natural geometry. For his part, Malebranche was crystal clear that the ‘natural geometry’ is part of the system of ‘natural judgments’ hard-wired into the mind so that it involves no actual reasoning (Malebranche, 1712: I.9). For a helpful discussion of the many Cartesian cues to distance, including the natural geometry, see Hall’s commentary in the translation of Descartes (1664b), Hatfield (1992), Simmons (2003b), and Wolf-Devine (1993). 52  For a helpful review of the early modern debate, and a detailed discussion of Berkeley’s side of it, see Atherton (1990). For a discussion of the debate over the course of 300 years, see Degenaar (1996). 48 

90   Alison Simmons non-representational mental state that has no object but only distinctive qualitative character.53 Perception, by contrast, is a mental state that always has an object and that involves both a conception of the object and an irresistible belief in its present existence.54 The two mental states are not two stages in the building of a sensory representation of the world, but two fundamentally different kinds of mental state that are confused together in our ordinary perceptual experience of the world. Second, Reid thought that the transition from having a sensation to perceiving an object occured not by any kind of innate reasoning (contra the Cartesian account of distance perception) and not by learned associations (contra Berkeley’s account of the same), but simply, if mysteriously, ‘by the constitution of our nature’.55 Sensations, he proposed, are nothing but ‘natural signs’ of the properties of bodies that never bear any resemblance to their objects, but that trigger perceptions of those properties ‘by a kind of natural magic’.56 The resulting perceptions are ‘original perceptions’, which Reid distinguished from ‘acquired perceptions’ which depend on learned associations between one original perception and another, as when I ‘see’ that the bag of groceries is heavy.57 On the topic of spatial perception in particular, he granted Berkeley that it is an acquired perception: we must learn to see spatial properties through associations between original perceptions of visual figure (which are always only two-dimensional) and original perceptions of tangible figure (which is three-dimensional).58 The lively debate about spatial perception touched on another famous debate that surfaced in this period: the ‘Molyneux problem’. William Molyneux, an Irish philosopher, posed the following problem to Locke: suppose a man born blind is acquainted by touch with a globe and a cube of similar size and made of the same metal; take the globe and cube away; restore the man’s sight; can he on the basis of sight alone determine which object is the globe and which the cube? Although there are differences in the details, Locke and Berkeley both answered no: it takes experience to associate the look of the objects with the feel of their shapes.59 Leibniz, in a ‘Cartesian’ sounding moment, answered yes: both vision and touch give us access to an innate intellectual geometry, and once that is in place the patient can (at least in principle) visually discern the sphere and cube ‘by applying rational principles’, viz., geometry, to his new visual sensations; there is no need to associate the visual and the tactile here.60 Reid took on the problem too, but gave different answers in different places depending on slightly different construals of the Molyneux question: for a newly sighted blind boy not steeped in the principles of mathematics, he agreed with Berkeley 53 

See Reid (1785: I.1 and II.16, 1764: VI.20–21). See Reid (1785: I.1, II.5, and I.16, 1764: VI.20). Malebranche is often thought to have anticipated Reid’s distinction between sensation and perception (see Nadler, 1994; Jolley, 1995; and even Reid, 1785 II.7; but cf. Simmons). 55  Reid (1764: VI.12). 56  Reid (1764: 5.3, VI.21 and 6.24, 1785: II.16). 57  Reid (1764: VI.20). 58  Reid (1764: VI.3 and VI.21–22; 1785: II.19 and 21). His account is complicated by the fact that he thought our original perceptions of visible figure themselves skipped the sensational stage, proceeding directly from impressions in the eye to original perceptions of (two-dimensional) shapes. Moreover, contrary to Berkeley, who took visual and tactile figure to be heterogeneous properties, Reid insists that our original visual perceptions of figure are homogeneous but incomplete or ‘partial’ perceptions of the same properties perceived completely by touch (see Reid 1785, II.19). 59  Locke (1690:, II.ix); Berkeley (1709: §§41 and 110); and Berkeley (1710: §43). 60  Leibniz (1704, II.ix). 54 

Perception in Early Modern Philosophy    91 that the boy would not be able to distinguish the sphere from the cube and that discerning three-dimensional shapes through vision typically depends on cross-modal associational learning;61 for a sophisticated mathematician, however, he sided with Leibniz, arguing that she could figure out the shapes by applying the principles of mathematics to what is presented in visual sensation.62

4  A veil of ideas? So far we have focused on the question of how perceptual experience comes about. Let’s turn to perceptual epistemology: what is perception like as a source of knowledge about the world? There are two main questions to tackle here: (a) did the early moderns think that things or ideas of things are the proper objects of perception and (b) do the senses yield any useful knowledge about the world? This section treats the first question; the next and final section treats the second. It used to be taken for granted that the early moderns were committed to a ‘veil of ideas’ theory of perception according to which all we immediately see, hear, and smell are ideas that represent objects and their properties, and from which we can only infer the existence of objects and properties that lie on the other side of the ideational veil.63 Ideas, on this view, are both ontological and epistemological intermediaries standing between perceiver and world. The trouble with such a theory of perception is that it invites external world scepticism: if all I immediately perceive are ideas, then how can I be sure there is anything on the other side? It is also an affront to common sense: when I say that I see a vase of lilacs on the table, what I take myself to be in perceptual contact with is a physical vase of lilacs and not a mental representation of it. The evidence that the early moderns committed themselves to a veil of ideas theory is considerable: Descartes opened his Meditations on First Philosophy (1641) with a battery of sceptical arguments involving illusions, dreams, and a malicious demon that question our sensory access to a mind-independent world; a systematic disparity between sensory appearance and physical reality is built into the mechanical hypothesis suggesting a distinction between what we see and what there is; talk of ‘ideas’ was everywhere in the texts; talk of what is immediately perceived and what is only mediately perceived (or judged) was common; Berkeley went so far as to suggest that kumquats and their kin are themselves nothing but collections of ideas; and Reid charged almost every one of his predecessors with holding the veil of ideas theory that culminated in Berkeley’s idealism.64 There is, nevertheless, good reason to resist this reading of the early moderns. Ideas entered the theory of perception on behalf of explaining how it is that we perceive things 61 

Reid (1764, VI.3). Reid (1764: VI.7 and VI.11). Reid thought that visual and tangible figure were inter-derivable, since they are not, contra Berkeley, heterogeneous properties. For a helpful discussion of Reid’s complex answers to the problem, see Nichols (2007: ch. 9). 63  This reading of the early moderns has been around since Reid (1764 and 1785), but it was reintroduced with vigour in the twentieth century by Bennett (1971) and Rorty (1979). 64  The only philosopher (from Plato to Hartley) that Reid hesitates to attribute the veil theory to is the Cartesian philosopher Antoine Arnauld. See Reid (1785: II.13). 62 

92   Alison Simmons like lilacs. Any theory of perception has to work within certain constraints. For most of the early moderns those constraints included (a) no action at a distance, so information about the lilacs has to get to the perceiver somehow; (b) immaterial minds do the perceiving, so information about the lilacs ultimately has to get into the mind in an immaterial form;65 and (c) the world consists of matter in motion, so something has to account for the disparity between the way the lilacs physically are in the world and the purple, fragrant way they appear.66 Given these constraints, ideas might be thought of as immaterial carriers of information that enable the human mind to perceive things like lilacs in the colourful and fragrant way that it does. If that’s right, then early modern ideas were doing much the same work that Aristotelian species did, serving not as the objects of perception but rather as the means of perceiving objects in the way that we do.67 One way of arriving at this alternative, and increasingly popular, reading of the texts is to contextualize the term ‘idea’.68 It is clear that ideas are supposed to be mental, and so, for most early moderns, immaterial. It is also clear that we cannot think or perceive without them and that they are in some sense representations of objects. But are they mental objects? In his mature work, Descartes distinguished two ways to understand the term ‘idea’: (a) as an act of thinking or perceiving and (b) as a representation of an object.69 What is important is that these are two aspects of one and the same mental state and not two distinct mental items that stand to each other as act to object. The Cartesian Antoine Arnauld made this point emphatically: ‘I . . . take the idea of an object and the perception of an object to be the same thing.’ 70 If that’s right, then perceptions are themselves representations of objects; they are not directed to representations of objects. Properly speaking we do not perceive ideas; we have ideas; and in having them we perceive objects. Malebranche, by contrast, explicitly took ideas to serve as objects of perception: we have to perceive ideas if we want to perceive lilacs, for there is nothing representational about our own mind to make lilacs present to it. Malebranchean ideas, however, were purely intellectual representations residing in the mind of God, and nothing like the epistemologically private sensory images at play in the ‘veil of ideas’ theory. When he said that sense perception involves the perception of ideas, he had in mind that there is something intellectual at the core of it, and that there is something outside our minds to which all our perception is directed when we perceive an object.71 Interestingly, in the very public debate between Arnauld and Malebranche on the nature of ideas, each accused the other’s conception of ideas as falling prey to a scepticism-inducing veil between perceiver and world, and each prided himself on avoiding any such thing.72 65 

66  Berkeley was an exception to (c). Hobbes, a materialist, was an exception to (b). challenges to the ‘veil of ideas’ reading of the early moderns, see O’Neil (1974), Arbini (1983), Yolton (1984), Nadler (1994), Yolton (1996), Lennon (2001), and Bolton (2004). For some interpretive push back, see Chappell (1994) and Wilson (1994). 68  For a helpful overview of the many meanings and uses of the term in the period, see Yolton (1996, ch. 2). 69  He gives different labels to them in different places: ideas considered ‘materially’ and ‘objectively’ (Descartes, 1641:  Preface to the Reader); ideas considered ‘formally’ and ‘objectively’ (Descartes, 1641: Meditation 3); ideas considered ‘materially’ and ‘formally’ (Descartes, 1641: 4th Replies); and without any explicit labels (Descartes, 1644: I.17). 70  Arnauld (1683: ch. 5). 71  For discussion, see Jolley (1990: ch. 4); Nadler (1994); and Wahl (2004). 72  For discussion of this aspect of the debate, see Simmons (2009). 67  For

Perception in Early Modern Philosophy    93 Locke initially looks committed to the veil: the mind, he wrote, ‘hath no other immmediate object but its own ideas’73 and ‘’Tis evident, the Mind knows not Things immediately but only by the intervention of the Ideas of thing.’ 74 But then again he also wrote, like Arnauld, that having ideas and perceiving things amount to the same thing 75 and he vehemently rejected Malebranche’s reification of ideas as objects distinct from the perceiving mind.76 It is possible that in saying that ideas are the immediate objects of the mind, Locke was simply pointing out that our access to objects comes not by the objects hurtling themselves into the mind, but rather by way of ideas, that is, by our perceiving them.77 As for Berkeley, he insisted that he was ‘not changing things into ideas, but rather ideas into things’.78 In saying this he was trying to distance himself precisely from the veil theory: we immediately perceive ideas, but since those ideas constitute things like lilacs there is no veil between mind and world; ideas only introduce a veil when there is something else lurking behind them (like collections of insensibly small bits of [mind-independent] matter).79 Clearly the notion of an idea was not fixed in the period. But far from conceiving ideas as epistemological barriers to the world, the early moderns seem to have taken them to be an essential means of access to it (or, in Berkeley’s case, as parts of it) and seem to have been staunchly committed to avoiding the implications of any veil theory.

5  Sensory epistemology How, then, does perception fare as a source of knowledge in the early modern period? In the Aristotelian tradition, the senses were the starting point for our knowledge of both the existence and the nature of the physical world.80 The early moderns largely agreed that the senses are the source of our knowledge that a physical world exists. They took external world scepticism seriously, but responded to it with a variety of arguments for the existence of a physical world based on one or another feature of perceptual experience. Only Reid refused to give an argument, saying instead that our sense-based belief in the physical world is at once ‘unaccountable’ and unassailable.81 Most conceded to the sceptic, however, that the conclusion is not known with absolute certainty.82 Berkeley, 73 

Locke (1690: IV.i.1). 75  Locke (1690: II.i.9). 76  Locke (1706). Locke (1690: IV.iv.2). 77  For a representation of the interpretive dispute, see Chappell (1994); Lennon (2001); and Bolton (2004). 78  Berkeley (1713: Dialogue 3). 79  Berkeley took collections of insensibly small bits of matter to be just mere collections of ideas that are reliably correlated with collections of, in this case, lilac ideas, and not as something lurking behind the sensory appearances. 80  They were also the starting point for our knowledge of immaterial things like the soul and God (see Dominik Perler, Chapter 2, this volume). The early moderns had mixed views concerning our knowledge of immaterial things: some (like Descartes) allowed for purely intellectual knowledge of them that is independent of the senses; some (like Locke) adopted the posture of modesty about our ability to have genuine knowledge of immaterial things, though nonetheless offered arguments for the existence of God; some (like Berkeley) introduced a new category of cognition (cognition by ‘notion’) to talk about the knowledge we have of immaterial things; and some (like Hume) purported to have no idea (literally) what is meant by such terms. 81  Reid (1785: II.20). 82  For some of these discussions, see Descartes (1641: Synopsis and Meditation 6); Arnauld (1683: ch. 28); Locke (1690: IV.ii.14); Malebranche (1712: I.10 and Elucidation 6); and Reid (1785: II.20). 74 

94   Alison Simmons as usual, was an exception in thinking that the senses give us conclusive evidence for the existence of a physical world, but no evidence whatsoever for the existence of a mind-independent physical world. He was as concerned as the others with scepticism, but found a decisive means for refuting (or undermining) it in idealism. (Of course, many thought that Berkeleyean idealism amounted to a simple acceptance of the sceptic’s conclusion.) Where the early moderns departed sharply from their predecessors was in denying that the senses are reliable guides to the nature of the physical world. It is not that they thought the senses show us nothing about the physical world, but what they show us is limited and qualified. The early moderns generally agreed that our perception of primary qualities like size and shape shows us something about what the world is like, but there are qualifications: it is subject to occasional errors about particulars (square towers look round from a distance and straight sticks in water look bent); it is markedly perspectival (coins look perfectly round when viewed from above, but in some sense look elliptical when viewed obliquely); it is relational (what looks to be to your left looks to be to my right); and it is limited (we can’t see anything smaller than a mite or very far away). These caveats worried Malebranche a great deal: ‘the judgments we form on the testimony of our eyes concerning extension, figure, and motion are never exactly true’.83 Even Malebranche, however, allowed that our perception of primary qualities ‘include some measure of truth’.84 It represents to us the sorts of properties that really are out there in the world, even if any particular representation inevitably contains something false or misleading about it. Secondary quality perception is another matter. Locke famously argued that while our sensory ideas of primary qualities ‘resemble’ the qualities in the world that cause them, our sensory ideas of secondary qualities do not.85 Berkeley retorted that nothing mental can resemble anything physical (what could they possibly have in common?), but it seems clear that what Locke had in mind was that our perceptual experience of size, shape, position, and motion shows us (at least in general) what these properties are like in bodies, whereas our perceptual experience of colours, sounds, smells, flavours, and hot and cold does not show us what these qualities are like in bodies. Not even in general. Colour vision may show us that the surface of a lemon is different from the surface of a lime, but it does not reveal the true nature of that difference; that is, it does not show us what that difference consists in physically on the surface of the fruits. Descartes put it this way: ‘If someone says he sees color in a body . . . this amounts to saying that he sees . . . something there of which he is wholly ignorant, or in other words, that he does not know what he is seeing.’ 86 His persistent characterization of secondary quality perception as ‘obscure and confused’ underscored this point. Reid agreed with his predecessors on this point: our senses give us a distinct conception of primary qualities and ‘inform us what they are in themselves’ while they give us only ‘a relative and obscure notion’ of secondary qualities and ‘as to what they are in themselves, our senses leave us in 83 

84  Malebranche (1712: I.10). Malebranche (1712: I.10). Locke (1690: II.viii.15). Descartes and Malebranche similarly spoke of a lack of resemblance between mind and world in the case of colour, odour, sound, etc. (see Descartes, 1641: Meditation 6, 1664a: ch. 1, and Malebranche, 1712: I.12). 86  Descartes (1644: I.68). 85 

Perception in Early Modern Philosophy    95 the dark’.87 Only Berkeley thought our perception of secondary qualities quite true to the nature of reality. It should come as no surprise, then, that so many of the early moderns treated the senses as epistemic troublemakers. Because we typically believe what we see, hear, smell, taste, and feel, we wind up with a lot of false beliefs. On instinct, we believe that pineapples are yellow in just the way they appear to be; that where we see no bodies there are no bodies; that the sun rises and sets while the earth remains still; and that the stars are small and nearby. These are all false beliefs, and it takes something other than unaided sense perception to get us to appreciate the truth of the matter: pineapples may be yellow but not independently of their effect on colour vision; there are insensibly small bodies all over the place; the sun is stationary while the earth rotates; and the stars are very large and very far away. Even once we learn the truth, it is difficult to resist our habitual sense-based beliefs: Descartes notes that even once we study astronomy, it is hard to maintain that belief that stars are large and distant when we actually look at them.88 It is the prevalence and persistence of these false sense-based beliefs that prompted Descartes’s full-scale sceptical attack on the senses at the opening of the Meditations and Malebranche’s exhaustive and lengthy inquisition of the senses at the start of the Search After Truth. Their advice is to withdraw from the senses and rely instead on the deliverances of the intellect in our search for truth about the nature of the physical world. As an empiricist, Locke was friendlier to the senses, taking them as an essential starting point for knowledge, but even he thought the knowledge we can reap from them about the nature of the physical world is extremely limited by the ‘dull and narrow information’ we receive from our ‘not very acute ways of perception’.89 His advice was not to turn to the intellect (since he didn’t think it could do anything other than manipulate sensory ideas), but rather to ‘look a little into the dark side, and take a view of our ignorance’ 90 and to recognize with modesty that ‘we are not capable of a philosophical knowledge of the bodies that are about us’.91 Even Reid, a self-appointed apologist for the senses, concedes that the senses get us into epistemic troubles when we make hasty judgements on their basis.92 All of this raises a question: if the senses lead us into false beliefs about the world, then why on earth do we have them? It can’t be an unfortunate accident. In the theological context of the period, God created us and gave us our senses. What was he thinking? What kind of benevolent creator would equip his creatures with such distorting lenses on the world? The early moderns had an interesting answer: God gave us senses not to show us the true nature of the physical world, but rather to help us to get around safely in the world. As Malebranche put it: ‘the senses were not given to us to know the truth about things in themselves, but only for the preservation of our body’.93 The early moderns thus reconceived the very function of the senses. According to Aristotelian epistemology, the senses are something like under-labourers to the intellect, providing it with the raw materials for knowledge about the nature of the physical world. The early moderns reconceived them as guides to survival. Whatever disagreements the early moderns had on the details 87 

Reid (1785: II.17). See Descartes (1644: I.72 and 1641: 6th Replies). See also Malebranche (1712: I.14) and Reid (1785: II.22). 89  Locke (1690: IV.iii.6). 90  Locke (1690: IV.iii.22). 91  Locke (1690: IV.iii.29). 92  Reid (1785: II.22). 93  Malebranche (1712: I.5). 88 

96   Alison Simmons of sensory processing and the structure of sense perception, they all agreed on this. Even Berkeley, who disagrees with so much of what his predecessors say about perception, agreed that the function of the senses is to facilitate bodily self-preservation: through them ‘we are instructed how to regulate our actions in order to attain those things that are necessary to the preservation and well-being of our bodies, as also to avoid whatever may be hurtful and destructive of them.’94 With this in mind, let’s think again about the senses as sources of knowledge about the physical world. They may do a messy job of showing us the fundamental nature of physical reality, but if their job is to guide us safely through the world, what they need to show us is how it pertains to our bodily well-being. When I’m thirsty, I need to know not that the glass of milk is situated at a certain latitude and longitude but whether it is within reach of my hand. I need to know not that it has a certain physical constitution but whether it is good to drink. The senses reveal precisely these sorts of things to me: the glass of milk looks to be within arm’s reach to my right and smells fresh not sour, so I can drink it. The senses, we might say, provide a self-interested or even ‘narcissistic’95 view of the world: if I’m sick, that same glass of milk may well taste terrible, as well it should since milk is not what I need at the moment. The way the Cartesians put this point was by saying that the senses represent the world not ‘as it is itself’ but ‘as it is related to and can benefit or harm my body’.96 Note that this holds of both primary and secondary quality perception: the spatial properties of the glass of milk are represented egocentrically and perspectivally, and its secondary qualities (like its taste) as ‘agreeable’ or ‘disagreeable’.97 Both are helpful in guiding action. Locke went so far as to suppose that our senses are perfectly fitted ‘to the conveniences of life and the business we have to do here’, so that if we were given more acute sense organs, like ‘microscopical eyes’, that show us more of the detail of the physical world, it would only be to our detriment.98 Reid concurred, insisting that ‘by diminishing or increasing [the acuity of our senses] we should not mend but mar the work of Nature’.99 (Reid thought that our acquired sensory appreciation of fine wine and gourmet food, for instance, constituted such an increase that inevitably leads to a more miserable life.) When viewed as guardians of the body, the epistemological criticism of the senses is replaced with accolades. Descartes wrote that in matters concerning our self-preservation the senses ‘report the truth much more frequently than not’.100 Even Malebranche wrote that they are ‘faithful witnesses’ concerning what’s good for the body; that they are ‘accurate and precise’ in informing us about the relations between our own body and other 94  Berkeley (1709: §147). In other figures, see Descartes (1641: Meditation 6); Locke (1690: II.xxiii.12); and Reid (1785: II.16, 20, and 22). 95  See Akins (1996). 96  Descartes (1644: II.3) and Malebranche (1712: I.6, I.10, I.18 and Conclusion First Three Books, 1688: Dialogues IV.13–14 and XII.2). 97  See Descartes (1641: Meditation 6); Malebranche (1712: I.5); and Reid (1785: II.16 and II.21). Descartes went so far as to say that even colour perception represents things as agreeable or disagreeable (green, he suggested is the most agreeable colour). Malebranche and Reid would have none of that, and instead added a third category of ‘indifferent’ sensations that serve to help us readily distinguish objects. For a more detailed discussion of the self-interested nature of sensory representation in Descartes and Malebranche, see Simmons (2003a and 2008). 98  Locke (1690: II.xxiii.12). 99  Reid (1785: II.21). 100  Descartes (1641:, Meditation 6), emphasis mine; see also 6th Replies.

Perception in Early Modern Philosophy    97 bodies; and that they lead to ‘quite correct’ judgements concerning the preservation of the body.101 Reid insisted that they ‘neither require nor admit of improvement’ in this area.102 If the senses get us into epistemological trouble (i.e. false beliefs), it is because we use them hastily and improperly to construct theories about the nature of the physical world when they are designed to be guides to action.103 The problem is not so much with the senses as with our misuse of them. The scrutiny to which the senses are subject in this period, then, should be read not as an indictment against their epistemological credibility, but rather as part of an effort to recast their role in our cognitive economy.

References Akins, Kathleen (1996). ‘Of Sensory Systems and the "Aboutness" of Mental States’. Journal of Philosophy, 93, 337–372. Arbini, Ronald (1983). ‘Did Descartes have a Philosophical Theory of Sense Perception?’ Journal of the History of Philosophy, 22, 317–337. Arnauld, Antoine (1683). Des vrayes et dees fausses idées. Cologne. Translation: On True and False Ideas. Translated by E. J. Kremer. Lewiston: The Edwin Mellen Press, 1990. Atherton, Margaret (1990). Berkeley’s Revolution in Vision. Ithaca, NY: Cornell University Press. Bennett, Jonathan (1971). Locke, Berkeley, Hume: Central Themes. New York, Oxford: Clarendon Press. Berkeley, George (1709). An Essay Towards a New Theory of Vision. Dublin. Berkeley, George (1710). Treatise concerning the Principles of Human Knowledge. Dublin. Berkeley, George (1713). Three Dialogues between Hylas and Philonous. London. Berkeley, George (1733). New Theory of Vision Vindicated and Explained. London. Bolton, Martha (2004). ‘Locke on Sensory Representation’. In R. Schumacher (ed.), Perception and Reality: From Descartes to the Present (pp. 146–167). Paderborn: Mentis. Boyle, Robert (1666). Origin of Forms and Qualities. Oxford. Boyle, Robert. (1674) About the Excellency and Grounds of the Mechanical Hypothesis. London. Chappell, Vere (1994). ‘Locke’s Theory of Ideas’. In V. Chappell (ed.), The Cambridge Companion to Locke (pp. 26–55). New York: Cambridge University Press, 1994. Degenaar, Marjolein (1996). Molyneux’s Problem: Three Centuries of Discussion of the Perception of Forms. Translated from the Dutch by M. Collins. Boston: Kluwer. Descartes, René (1637). La Dioptrique, published with his Discours de la method. Leiden. Descartes, René (1641). Meditationes de prima philosophia, published along with six sets of objections and the author’s replies. Paris. Descartes, René (1644). Principia Philosophiae. Amsterdam. References to book and section as I.1. 101 

Malebranche (1688: Dialogue 1 and Dialogue 4); see also Malebranche (1712: I.12, I.20, and Conclusion of the First Three Books). 102  Reid (1785: II.21). 103  That is not to say that the senses are useless in constructing a theory of the physical world. Even for a rationalist like Descartes, they have an important role to play in scientific observation and experiment: the intellect determines the nature of the physical world in general, and offers up possibilities for the way the world might be, but the senses are needed to determine which among the possibilities are actual. See Hatfield (1986).

98   Alison Simmons Descartes, René (1664a). Le Monde de M. Descartes ou le traité de la Lumière. Paris. Originally written before 1637, but only published posthumously. Descartes, René (1664b). L’Homme. Paris. Originally written before 1637, but only published posthumously. Translation: Treatise on Man. T.S. Hall. Cambridge, MA: Harvard University Press, 1972. References are to section numbers in the French edition, which is reproduced in Hall. Galilei, Galileo (1623). Il Saggiatore. Rome. Translation: The Assayer in The Controversy on the Comets of 1618. Translated by S. Drake and C. D. O’Malley. Philadelphia: University of Pennsylvania Press, 1960. References are to pages in Drake and O’Malley. Hatfield, Gary (1986). ‘The Senses and the Fleshless Eye: The Meditations as Cognitive Exercises’. In A. Rorty (ed.), Essays on Descartes’ Meditations. Berkeley: University of California Press: 45–79. Hatfield, Gary (1992). ‘Descartes’s physiology and its relations to his psychology’. In J.  Cottingham (ed.), The Cambridge Companion to Descartes (pp. 335–370). New York: Cambridge University Press. Hobbes, Thomas (1655). Elementorum philosophiae section prima De Corpore. London. References are to chapter and section as I.1. Hobbes, Thomas (1658). Elementorum philosophiae section secunda De Homine. London. References are to chapter and section as I.1. Jolley, Nicholas (1990). The Light of the Soul: Theories of Ideas in Leibniz, Malebranche, and Descartes. Oxford: Clarendon. Jolley, Nicholas (1995). ‘Sensation, Intentionality, and Animal Consciousness: Malebranche’s Theory of the Mind’. Ratio (New Series), 7, 128–142. Kepler, Johannes (1604). Ad vitellionem paralipomena. Frankfurt. Translation: Optics: Paralipomena to Witelo & Optical Part of Astronomy. Edited and translated by W. Donahue. Santa Fe, NM: Green Lion Press, 2000. References are to chapter and section as 1.1. Leibniz, Gottfried (1695). ‘System mouveau de la nature et de la communication des substances, aussi bien que de l’union qu’il y a entre l’ame et le corps’. Journal des savants. Published anonymously. Leibniz, Gottfried ([1704]/1765). Nouveaux essays sur l’entendement humain. Amsterdam and Leipzig. Leibniz wrote the text in 1704, but suppressed publishing it when he heard of Locke’s death that year; it was published posthumously in 1765. References are to book, chapter, and section as I.i.1. Lennon, Thomas (2001). ‘Locke and the Logic of Ideas’. History of Philosophy Quarterly, 18(2), 155–177. Locke, John (1690). An Essay Concerning Human Understanding. London. References are to book, chapter, and section as I.i.1. Locke, John (1706). ‘An examination of P. Malebranche’s opinion of seeing all things in God’. In P. King (ed.), Posthumous Works of Mr. John Locke. London. Malebranche, Nicolas (1688). Entretiens sur la métaphysique et la religion. Paris. Translation: Dialogues and Metaphysics and Religion. Translated and edited by N. Jolley and D. Scott. Cambridge: Cambridge University Press, 1997. Malebranche, Nicolas (1712.) De la recherche de la vérité. Où l’on traitte de la nature de l’esprit de l’homme, et de l’usage qu’il en doit faire pour eviter l’erreur dans les sciences. 6th and final edition. Paris. First published in 1674–1675. Translation: The Search After Truth. Translated and edited by T. Lennon. Columbus, OH: Ohio State University Press, 1980. References to book, (part where applicable), and chapter as I.i.1.

Perception in Early Modern Philosophy    99 Nadler, Steven (1994). ‘Malebranche’s Theory of Perception’. In E. Kremer (ed.), The Great Arnauld (pp. 108–128). Toronto: University of Toronto Press. Nichols, Ryan (2007). Thomas Reid’s Theory of Perception. New York: Oxford University Press. O’Neil, Brian (1974). Epistemological Direct Realism in Descartes’ Philosophy. Albuquerque: University of New Mexico Press. Popkin, Richard (1979). History of Skepticism from Erasmus to Spinoza. Berkeley, CA: University of California Press. Reid, Thomas (1764). An Inquiry into the Human Mind on the Principles of Common Sense. Edited by D. R. Brookes. University Park: Pennsylvania State University Press, 1997. References are to chapter and section as I.1. Reid, Thomas (1785). Essays on the Intellectual Powers of Man. Edited by D. R. Brookes. University Park, PA: Pennsylvania University Press, 2002. References are to essay and chapter as I.1. Rorty, Richard (1979). Philosophy and the Mirror of Nature. Princeton: Princeton University Press. Simmons, Alison (1994). ‘Explaining Sense Perception: A Scholastic Challenge’. Philosophical Studies, 73, 257–275. Simmons, Alison (2003a). ‘Spatial Perception from a Cartesian Point of View’. Philosophical Topics, 31(1&2), 395–423. Simmons, Alison (2003b). ‘Descartes on the Cognitive Structure of Sensory Experience’. Philosophy and Phenomenological Research, 67(3), 549–579. Simmons, Alison (2008). ‘Guarding the Body: A Cartesian Phenomenology of Perception’. In P. Hoffman, D. Owen, and G. Yaffe (eds), Contemporary Perspectives on Early Modern Philosophy: Essays in Honor of Vere Chappell (pp. 81–113). Buffalo: Broadview Press. Simmons, Alison (2009). ‘Sensation in a Malebranchean Mind’. In J. Miller (ed.), Topics in Early Modern Philosophy of Mind (pp. 105–129). Dordrecht: Springer. Spinoza, Baruch (1677). Ethica: Ordine Geometrico demonstrata, et in quinque partes distincta. Amsterdam. Wahl, Russell (2004). ‘Malebranche—The Senses, Representation, and the Material World’. In R. Schumacher (ed.), Perception and Reality: From Descartes to the Present (pp. 108–121). Paderborn: Mentis. Wilson, Margaret (1982). ‘Did Berkeley Completely Misunderstand the Basis of the Primary– Secondary Quality Distinction in Locke?’ In C. M. Turbayne (ed.), Berkeley: Critical and Interpretive Essays (pp. 198–223). Minneapolis: University of Minnesota Press. Wilson, Margaret (1987). ‘Berkeley on the Mind-Dependence of Colors’. Pacific Philosophical Quarterly, 68(3–4), 249–264. Wilson, Margaret (1991). ‘Descartes on the Origin of Sensation’. Philosophical Topics, 19(1), 293–323. Wilson, Margaret (1994). ‘Descartes on Sense and "Resemblance"’. In J. Cottingham, Reason, Will, and Sensation: Studies in Cartesian Metaphysics (pp. 209–228). Oxford: Clarendon. Wolf-Devine, Celia (1993). Descartes on Seeing: Epistemology and Visual Perception. Carbondale, IL: Southern Illinois University Press. Yolton, John (1984). Perceptual Acquaintance from Descartes to Reid. Minneapolis: University of Minnesota Press; Oxford: Blackwell. Yolton, John (1996). Perception and Reality: A History from Descartes to Kant. Ithaca, NY: Cornell University Press.

Chapter 5

Perception i n Phil osoph y a n d Psychol ogy i n the 19th a n d E a r ly 20th Cen tu r ies Gary Hatfield

The latter nineteenth century and the first decades of the twentieth century was a period of intense investigation of sensory perception in Germany, Great Britain, and then the United States. New experimental techniques were applied to the study of perception, and there was lively debate within philosophy about the objects of perception, the character of perceptual knowledge, and the structure of the perceptual act. In sensory physiology and sensory psychology, psychophysical methods seemed to allow states of the soul itself to be measured. More generally, laboratory control was established over aspects of sensory perception, especially colour vision, spatial perception, and auditory perception. Investigators such as Wilhelm Wundt (1862, 1874), Hermann Helmholtz (1867), Ewald Hering (1868, 1874), and William James (1890) offered theoretical syntheses or overviews. Philosophically inclined scientists, including Helmholtz (1878) and Ernst Mach (1886), explored the implications of sensory physiology and psychology for the theory of knowledge, and they were answered by NeoKantians seeking to preserve some questions for philosophy. In Britain, scientifically informed philosophers, such as William Hamilton (1861) and John Stuart Mill (1865), debated questions about our knowledge of an external world. These debates sparked an explosion of philosophical argumentation about perception in Britain from 1890 on, which criss-crossed the Atlantic in the first decades of the new century. These discussions concerned not only whether we have knowledge of a mind-independent reality, but especially how such knowledge is constituted, what its objects might be, and whether such objects are directly as opposed to indirectly perceived. These empirical advances and philosophical discussions did not arise spontaneously or without precedent. The topic of perception had enjoyed attention throughout the seventeenth and eighteenth centuries and into the nineteenth, from both philosophers and natural philosophers, many trained as physicians. From this earlier work, the new experimentalists and the theorists of the latter nineteenth century inherited a complex

Perception in Philosophy and Psychology    101 of empirical questions, theoretical ideas, and philosophical problems. These concerned whether spatial perception is innate or learned, whether the fundamental processes in the psychology of vision involve calculative judgement or bare association, epistemological problems concerning perception of an external world, the distinction between primary and secondary qualities, and the interaction of such issues with theories of the relation between mind and body. This chapter begins with a sketch of the empirical, theoretical, and philosophical background, focusing on visual perception. It then considers in depth German sensory physiology and psychology in the nineteenth century and its reception. It offers a brief look at the interaction between perceptual theory and philosophical issues in epistemology and the metaphysics of mind in Britain and America, followed by an overview of psychological theories of perception in the early twentieth century and the Gestalt reaction, culminating with J. J. Gibson.

1 Philosophy and psychology of perception before 1850 Seventeenth-century discoveries set a new framework for theories of visual perception. Kepler’s discovery of the retinal image demanded a new physiology of visual stimulation and Newton’s discovery of the spectral composition of light radically altered the physics of colour vision. Kepler showed how a point-for-point, two-dimensional perspective image is cast upon an opaque surface in the eye. His theory replaced a ‘quasi-optical’ conception of processes in the optic nerve, in which Aristotelian ‘forms’ of light and colour in a two-dimensional arrangement are transmitted along a hollow optic nerve filled with translucent fluid. Kepler retained an ontology of forms and qualities but was undecided whether the image is sensed in the eye or conveyed into the brain and sensed there (Kepler 1604/2000, ch. 5.2).1 As the nerves came to be viewed mechanistically (and, subsequently, electrically or chemically), theorists had to describe how light (or other forms of sensory stimulation) could affect the nerves and how nerve activity that enters the brain results in a sensation or other sensory experience. Newton’s discovery in the 1660s of spectral composition—that white light is composed of component rays having differing refrangibility, which yield the various colours of the rainbow—gave a new physical basis for a theoretical outlook that was already gaining ground: that physical light is to be conceived as a mechanistic process that produces colour sensations as a subjective response in perceivers (see Newton 1704). A related view had been expressed as the distinction between primary and secondary qualities by Boyle and Locke (and, without using those terms, by Galileo and Descartes). Newton’s work added new knowledge of the physical characteristics of light and of their relation to the perceptual experience of colour.2 1 

2 

On Kepler’s optical theory and previous theories, see Lindberg (1976) and Hatfield and Epstein (1979). On early modern distinctions between primary and secondary qualities, see Nolan (2011).

102   Gary Hatfield These findings were accommodated within a larger framework of visual theory. Since antiquity, the science of optics had been a complete theory of vision, applying geometrical analysis not only to optical stimulation but also in accounts of size and distance perception. During the seventeenth century, debates arose concerning whether distance perception is acquired or innate, positions later dubbed ‘empirism’ and ‘nativism’. During the eighteenth and early nineteenth centuries, this discussion was incorporated into the medical and psychological literatures (Hatfield 1990, chs. 2–4). Philosophers, especially Descartes, Berkeley, and Reid, produced natural philosophical works on vision that engaged this issue and others, such as whether the processes underlying vision are fundamentally associational or include an unnoticed act of judgement or calculation. Generally, participants in these debates drew a distinction between an immediate object of vision—characterized as ‘sensation’ by some and consisting of a two-dimensional array of colours—and a percep­ tion that arises through associational or judgemental processes and includes an experience of distance.3 Some theorists, such as Descartes (1637, disc. 6), posited innate physiological mechanisms that directly yield an experience of distance (the third dimension). But the majority view in the eighteenth century was that the original and immediate product of visual stimulation is a two-dimensional array of colours reproducing the spatial structure of the retinal image.4 Philosophers raised questions about the ontology of sensory experience and about the relation between such experience and an external, material world. The proper interpretation of the resulting philosophical theories is a matter of ongoing debate. In my estimation (Hatfield 2009a), Descartes viewed all sensory ideas, including, in vision, the experience of both spatial properties and colour, as intrinsically representational. As had been usual since Aristotle, he considered sensory perception as functioning to preserve the health of the animal by allowing for bodily goods and evils to be detected and approached or avoided. Notoriously, he did not hold sensory experience to be the paradigm of knowledge (which was intellectual knowledge, including the purely intellectual contemplation of essences), but he did regard it as good enough for bodily preservation and as a source of observational knowledge in natural science. It is controversial whether Descartes was a critical direct realist, who held that we directly perceive external objects through sensory ideas, or a representative realist, who held that we perceive our ideas and infer external objects from them. This question is also disputed for Locke, but the grounds for regarding him as a representative realist may be stronger.5 Other positions in the metaphysics and epistemology of sensory perception were legion. Leibniz regarded body (matter) as a well-founded phenomenon, with well-foundedness consisting in the agreement of perceptual representations among monads, the individual substances 3 

On the notion of immediate or direct objects of vision, see Perler, Chapter 2, and Simmons, Chapter 4, in this volume. 4 On Descartes’ various accounts of distance perception, including a direct psychophysiological account tied to accommodation and convergence, see Hatfield (1992) and Wolf-Devine (1993). On theories of distance perception more generally, see Boring (1942), chs. 7–8; Pastore (1971), chs. 2–7; and Hatfield (1990), ch. 2. 5  On epistemological direct realism in Descartes, see O’Neil (1974) and Hoffman (2002). Whether Locke counts as a representative realist depends on the criterion. If it suffices to hold that a three-dimensional visual world is inferred from a two-dimensional sensation or sensory idea, Locke (1690), II.10, meets the criterion; if representative realism requires positing ideas as third things, distinct from minds, then the case is by no means clear (Rogers 2004).

Perception in Philosophy and Psychology    103 with which he populated his universe. Notoriously, monads do not have causal or other relations to one another and are not in space; rather, space is in them as a phenomenal structure. Berkeley supported a clearer and purer idealism, in which only minds, their ideas, and God exist; spatial structures exist only as objects of perceptual experience. Hume adopted an attitude of sceptical naturalism, in which our only sure knowledge is of sensory and emotive impressions and ideas, although he countenanced a natural belief in persisting bodies beyond the impressions. Kant famously limited knowledge to a phenomenal realm, caused by unknowable ‘things in themselves’ that appear to us according to our modes of perception but cannot be known as they are in themselves.6 These various positions (excluding Leibniz and Kant) were examined by Thomas Reid (1785), who contended that Berkeley’s idealism and Hume’s scepticism rested on a shared mistake. Reid read the major philosophers from Descartes to Hume as erroneously committed to a representative theory of perception. In his view, Berkeley and Hume simply revealed that any attempt to infer an external world from behind a veil of perception must fail. Reid offered instead a common-sense realism, in which perceivers naturally believe in and perceive a world of objects in three-dimensional space (natural belief supplants inference). Reid’s diagnosis, its interpretation, and its assessment were closely discussed in the nineteenth century, by the Scottish philosopher-psychologists Thomas Brown and William Hamilton, whose disagreements were examined by John Stuart Mill (1865). Brown rejected Reid’s diagnosis because it foisted an implausible form of representative realism onto figures such as Locke, who, in Brown’s view, spoke only of perceptions and their objects and did not interpose ideas as third things; for Brown’s Locke, ideas are perceptions (1820, 2: 8), a position he assimilates to Reid’s. In contrast, Hamilton interpreted Reid as saying that the mind is in direct and intuitive relation to the external world, unmediated by any mental state; consciousness takes an external entity directly as its object. For Hamilton (1861, 2: 130), this object was, in vision, the light on the retina. Finally, Mill (1865) argued instead that sensations are the immediate object of perception and that beliefs in external objects are in fact psychologically derived beliefs in ‘permanent possibilities of sensation’. Kant’s (1781, 1783) distinction between appearances and things in themselves was closely scrutinized in Germany. Even during Kant’s lifetime, critics complained about the role of the thing in itself in his philosophy, some finding it an unnecessary and unwelcome posit (and so, endorsing idealism proper, as with Fichte), others claiming that more could be known about the thing in itself. In the early decades of the nineteenth century, the philosophers Johann Friedrich Herbart and Jakob Friedrich Fries contended that the thing in itself, or a reality beyond perception, could be known (Hatfield 1990, ch. 4). During the nineteenth century, sensory physiology and sensory psychology in Germany was heavily influenced by Kant. His claim (1781, 1783) that space and time are a priori forms of sensibility, which condition all possible human experience, was given a psychological and naturalistic interpretation. For Kant, an a priori form of intuition need not be regarded as innate because it could unfold with experience.7 He invoked such forms in philosophical

6  On epistemological aspects of theories of perception from Descartes to Kant, see Yolton (1984, 1996); on Descartes to Reid, see also Simmons, Chapter 4, in this volume. 7  On Kant’s notion of a priori forms of intuition and their relation to notions of innateness and to spatial knowledge, see Falkenstein (1990); Hatfield (1990), ch. 3; 2006; and Kitcher (1995).

104   Gary Hatfield arguments about the grounds for knowledge, framed within his ‘transcendental philosophy’. Sensory physiologists and psychologists rendered questions about the status of spatial perception into empirical questions about the innateness of spatial representation. Johann Georg Steinbuch and Caspar Theobald Tourtual offered physiological and psychological theories to explain how spatial representation arises. Steinbuch (1811) espoused a radical empirism, according to which perceivers first acquire the ability to represent spatial structures and then to see things as arrayed in space through processes developed in early experience. Tourtual (1827) offered a nativist account of the origin of spatial representation and of three-dimensional visual perception. Some authors also naturalized the question of whether things in themselves can be known. Steinbuch in particular held that his account, in which spatial perception is acquired through causal interaction with external spatial objects so as to establish a correspondence between spatial perception and real spatial objects, could support the claim that we know things in themselves as they are. Among philosophically inclined scientists, the question of whether things in themselves are knowable continued through the nineteenth century, some finding them unknowable (Helmholtz 1878) and others holding that, because they would be unknowable, they are not needed (Mach 1886). The desire to avoid positing unknowable things in themselves was echoed in British thought.

2 German sensory physiology and psychology The nineteenth century was a golden age for sensory physiology and psychology, especially regarding vision, but also hearing and touch. Research blossomed after 1850, when Helmholtz, Wundt, Hering, G.  E. Müller, and others worked.8 German philosophical writers were aware of this work, whether they considered it to have strong implications for philosophy (as did Mach) or not (the feeling of NeoKantians such as Cohen and Natorp; see Edgar 2008). Scientific investigation of the senses explicitly considered theoretical questions about the relation between nerve activity and sensation, and the processes by which sensations (or elemental sensory representations) are combined to yield perceptions. Empirical techniques gained sophistication, as physicists and physiologists adapted or created instrumentation to allow precise measurement of subjects’ responses to stimuli. The best known are the psychophysical methods of E. H. Weber and Gustav Fechner, which include several experimental paradigms (reviewed below). Theoretically, a basic question concerned the relations among the physical properties of the stimulus, the inception and transmission of nerve activity, and the production of elementary sensations or representations. Although knowledge of the eye’s optical properties continued to be refined, the stimulus to vision was taken to be the retinal image. Earlier theorists had known that the images differ between the two eyes and that these differences are relevant for depth perception, but in the 1830s Wheatstone and Brewster

8 

On these figures, see Hatfield (1990), ch. 5; Turner (1994); and Heidelberger (2004).

Perception in Philosophy and Psychology    105 demonstrated that binocular disparity yields a powerful depth effect. Stereoscopic vision quickly became a major research topic in German sensory physiology.9 Another major topic concerned eye movements, with some theorists holding that the visual system uses eye motion to ‘measure’ visual space. As regards light, the physical agent of retinal stimulation, its wave or particle status was debated (waves were winning), but the basics of Newtonian spectral analysis were widely accepted, Goethe’s (1810) efforts to the contrary notwithstanding.

Nerve–sensation relations and spatial perception In psychological theories of vision, a crucial theoretical choice concerned the conception of the nerve–sensation juncture. Nineteenth-century theorists inherited the standard eighteenth-century conception that the primitive sensation of vision is a two-dimensional correlate of the retinal image. This was variously conceived. The most commonly accepted eighteenth-century position supposed that the two-dimensional sensation arises because the separate nerve fibres running from the retina into the brain retain their order. They project into the brain retinotopically, with each nerve producing a punctiform elemental sensation; these sensations are collectively experienced to have the same spatial order as do the nerve fibres (e.g. Gehler 1787–1796, 4: 11–12). Hence, they constitute a two-dimensional phenomenal image structure, which is what infants experience. Subsequently, as a result of learning to ‘interpret’ the various sources of information about depth and distance—including accommodation of the lens and convergence of the eyes (muscle cues), known size in conjunction with image size, awareness of continuous sequences of ground intervals, and atmospheric perspective and the clarity of details—this two-dimensional image is transformed (via unconscious or unnoticed psychological operations, whether associative or judgemental) into an experience of objects at a distance with a shape and size in three-dimensional space (Hatfield 1990, 35–44). Although this conception of the psychophysiological relations between nerves and sensations was standard fare in textbooks, another theory was proposed by the prominent physiologist Johannes Müller. To this standard theory he added the possibility that the retinal image may be ‘felt’ in its two-dimensional form at the retina and that this feeling may be transmitted via the nerves into the brain (Müller 1833–1840, 2: 350). Other theorists denied that the spatial order of the nerves, either in the retina or in the brain, could in itself account for the spatial order of vision. According to them, the mere spatial order of the nerves cannot determine the spatial order of sensations. Such theorists accepted that each nerve fibre produces a single sensation of colour, but they held that such sensations are intrinsically without spatial order, in just the way (they sometimes asserted) that tones can be heard with different pitches but without spatial location. The radical empirist Steinbuch (1811) held that a two-dimensional visual representation is first achieved through learning. The nativist Tourtual (1827) held that unordered sensations are, by means of ‘specific signs’ that mark the sensations of each nerve fibre, ordered into a two-dimensional representation according to an innately given law, and that depth 9  On early work on binocular vision, see Wade (1983, 2003); on early work in Germany, see Turner (1994), ch. 2.

106   Gary Hatfield and distance arise through a mixture of innate and learned factors. The physiologist and philosopher Hermann Lotze (1852) initially adopted a position similar to Tourtual’s (except that he called the nerve-specific markers ‘local signs’ and had the third-dimension arise entirely through learning), but he later endorsed an empiristic theory according to which perceivers must learn to localize sensations by ‘measuring’ positions through eye-movements and bodily motions, first for two dimensions and then for three (1886, 58–59).10 Despite their differences, these theorists agreed that a two-dimensional image constitutes a stage in the psychological process of visual perception (or does at some point during development). By contrast, the two major German visual theorists of the final third of the century, Helmholtz and Hering, saw no need for such a representation. Helmholtz, like Steinbuch, was a radical empirist, and he shared the assumption that individual visual nerves yield individual sensations that are not originally ordered in space. Unlike Steinbuch, he found no reason to posit a two-dimensional planar image as a representational stage: although ‘most physiologists have regarded it [a planar image] as the kind of vision which results most directly from sensation’ and have ‘looked upon ordinary solid vision as a secondary way of seeing things’, Helmholtz held that ‘solid vision’—that is, the three-dimensional perception of things in a direction at a distance—is the primary mode of representation (1868/1995, 185). For purposes of exposition, he allowed that one might speak of perceiving a ‘surface’ in the field of view. However, although perception of direction may be indefinite about distance, that fact does not call for a planar representation (whether the plane be flat or spherical). In actual perception, direction and distance are joined (1867/1924–25, 3: 235). Helmholtz’s nativist counterpart, Hering, also held that three-dimensional perception, or perception of things as in relief, is basic; but he attributed it to innate factors that are only fine-tuned through learning (Turner 1994, 65–66). The debate between Helmholtz and Hering and their followers over whether spatial perception is innate or learned raged on into the twentieth century.

Psychophysics and size constancy The development of psychophysics by Weber and Fechner is among the best-known achievements of German sensory psychology. The most widely discussed aspect of this work, which has become emblematic of it, is the empirical finding that just discriminable changes of intensity arise with a constant ratio of difference between the intensities of stimuli, a relation that holds across a wide variety of stimulus types. Weber obtained such ratios when he asked subjects to compare different weights and to judge the smallest perceptible differences between the pitches of tones (among other tasks). Reviewing this work, Fechner (1860) formulated ‘Weber’s law’, according to which the proportional relations between stimuli needed to produce a ‘just noticeable difference’ (or jnd) are constant (where R is the Reiz, or physical stimulus, ΔR/R = constant, for the jnd). In other words, the stimulus differences between just discriminable pitches are not

10 

On these theorists, see Hatfield (1990), ch. 4.

Perception in Philosophy and Psychology    107 absolute intervals but vary proportionately. Similarly, with weights there is no set amount (for example, 1 gram) that produces the least discriminable difference. We might barely discriminate a 4.0-gram from a 3.9-gram weight (absolute difference, 0.1 gram) but be unable to discriminate a 39.9-gram weight from a 40.0-gram weight (absolute difference, 0.1 gram). We should be able just to discriminate a 39-gram weight from a 40-gram weight, because the proportion 39/40 is preserved. Fechner transformed Weber’s law into Fechner’s law by assuming that each jnd differs in felt quality or intensity by the same amount as any other jnd and by assigning a value of 1 unit to any physical stimulus at the threshold of detection. Fechner’s law states that the magnitude of sensation (S) is equal to the logarithm of the stimulus times a constant (S = k log R).11 Fechner’s efforts spurred other quantitative work on sensation and perception, facilitating the declaration of a ‘new psychology’ founded on quantitative experimental methods. The best known of these is the ‘method of limits’, which seeks to establish the discriminable intervals (jnds) by regularly varying the intensity (or other stimulus dimension) upwards or downwards until the threshold of sensitivity is crossed. But Fechner offered other methods that also were influential. He described a ‘method of right and wrong cases’, which determines the threshold of stimulus sensitivity and the value of just-discriminable intervals by presenting stimuli randomly rather than in an orderly progression, as with the first method. Fechner’s third method, the ‘method of average error’, became widely adapted (with some modifications) in work on perception. In this method, a standard stimulus is presented and the subject’s task is to match a comparison stimulus to it so that they look the same (are phenomenally indistinguishable). In Fechner’s original conception, this would be done by continuously varying a comparison stimulus until a subjective (apparent) match is obtained. In studying spatial perception, the apparent spatial attributes of the standard are matched to a comparison stimulus. Thus, a subject might be presented with a horizontal white line of a certain length (say, 50 mm) and asked to adjust the length of a second white line off to the side so as to match the first one (Titchener 1905, 1: 70). After 100 trials, the subject’s deviations from the physical value are averaged, yielding the ‘constant error’ (which could be zero or another value, depending on how accurate the subject is). The experimenter also calculates a measure of the average variable error. The first value concerns how close the subject comes to making a physical match between the two stimuli, the second measures the variability of the subject’s responses, that is, the consistency among the settings. If a subject always achieved a perfect match, both error values would be zero. If the subject’s matches varied greatly, sometimes underestimating and sometimes overestimating, the constant error might still be small but the variable error would be large. The study of size constancy shows a trend away from the method of limits toward the method of average error and its descendants. Fechner had noted that perceived size does not vary directly with visual angle but has a tendency to remain constant despite moderate increases in the distance to the object, a phenomenon known as ‘size

11  Accounts of Fechner’s work, its relation to Weber, and its reception, may be found in Titchener (1905); Woodworth (1938), chs. 17–18; Boring (1942), 34–45; and Heidelberger (2004), ch. 6.

108   Gary Hatfield constancy’. Indeed, this observation is found frequently in the optical literature (e.g. in Ptolemy, Ibn al-Haytham, and Descartes) and was widely repeated in the nineteenth century (Ross and Plug 1998). In Wundt’s lab, Götz Martius (1889) studied the problem using psychophysical methods. Subjects matched standard rods of 20, 50, and 100 cm, viewed at 50 cm, to comparison stimuli placed at 300 and 575 cm. Martius varied the comparison stimuli by small increments (as in the method of limits) until a match was obtained. At 300 cm, subjects chose a size slightly larger than the standard as a match, and at the still farther distance they selected a somewhat larger comparison stimulus. From this it can be inferred that distant comparison objects that were equal in physical size to the nearby standard would look slightly smaller than that standard (hence a larger comparison object was needed to match phenomenally the nearby standard). The subjects came nowhere near to matching the retinal sizes or visual angles of the standard and comparison stimuli, which would require greatly enlarged comparison settings, as the visual angles subtended by comparison stimuli of equal physical size to the standard would be, respectively, 1/6 and less than 1/11 of that of the standard (so that, in order to match the standard in visual angle, the nearer of the comparison stimuli would need to be six times as large as the standard). Instead, their responses were closer to ‘size constancy’, that is, to matching a distant comparison to the objective size of the nearby standard. Subsequent authors adopted methods related to the method of average error, in which subjects adjust the comparison to match a standard. Franz Hillebrand (1902) investigated the orientation required of cords lying on a table to make them appear parallel to one another for a subject viewing them from one end. Here, the phenomenal parallel is an assumed standard supplied by the subject. In order to obtain a structure that appeared phenomenally parallel, subjects made the cords diverge. Hillebrand repeated the experiment with many threads hung vertically to yield phenomenal walls and had subjects adjust the walls so that they appeared parallel. Again, they were set to diverge with distance from the subject’s vantage point. The British psychologist Robert Thouless (1931, 1932) examined shape perception by having subjects make drawings of a standard circle or diamond that was rotated in depth, or match the standard to one of a series of nearby comparison shapes. Subsequent experiments on size and shape constancy in Britain and the United States provided variations on these themes, with subjects adjusting the comparison to match a standard or matching the standard to one of a series of comparison sizes or shapes (Epstein and Park 1963; Wagner 2006, 103). The utilization of such methods in studying size perception and other domains of sensory experience amounts to a form of controlled introspection that remains in use today.12

Colour matching and colour theories When Newton established that white light is composed of various spectral colours (separable by a prism), he opened the door to questions about how colours are formed by mixing spectral lights (or by mixtures of mixtures). Various eighteenth-century authors, predating

12 

On various types of introspection, see Titchener (1912) and Hatfield (2005).

Perception in Philosophy and Psychology    109 Thomas Young, speculated that all colours can be formed by mixing three primaries. Just after 1800, Young proposed red, yellow, and blue as primaries, but subsequently altered this list to red, green, and violet (Kaiser and Boynton 1996, 18–22).13 In the study of light, psychophysical methods can be applied to some stimulus relations, including changes of intensity. It had long been conjectured (Bouguer 1760/1961, 51) that discriminable changes in light intensity follow a proportional structure like that encoded in Weber’s law. For light intensity, the concept of altering the physical intensity and noting how the perceived intensity responds is analogous to other domains of psychophysics, in which one charts the relation between physically defined dimensions of variation and perceived values. The method of limits can also be applied to changes along the spectrum, by asking how far two spectral lights must be separated (in ‘refrangibility’ or, in modern terms, wavelength) to be perceived as different. With colour mixture, the logic of measuring the relation between a physically specified dimension of variation and a perceived value breaks down. In the context of nineteenth-century investigations (prior to any physical isolation and direct measurement of cone-pigment sensitivities), there was no prior basis for conjecturing what should happen when lights are mixed. The relevant dimensions of variation are not given by physics (as with intensity), but must themselves be discovered psychophysically. Young’s conjecture that there are three types of sensitive element in the retina that respond best to his three primaries (receptor trichromacy) was based on the empirical result that the primaries can be used to mix (most) other colours. Near the time of the advent of psychophysics, Helmholtz, Hermann Grassmann, and James Clerk Maxwell established laws of colour mixture (Boring 1942, ch. 4; Kaiser and Boynton 1996, chs. 1, 5). They showed, with some known exceptions, that any spectral light or mixture of lights can be matched by a mixture of three suitably chosen primaries. Which primaries are suitable, and how they have to be mixed in order to match a given light, is entirely an empirical matter. On the basis of subjects’ responses, these investigators formulated tables revealing laws of colour mixture. Accordingly, the concept of constant error has no meaning in relation to the physical properties of light that enter colour mixtures. Physical facts about light do not predict that mixtures of red and green light yield the perception of yellow. Thus, there is no meaning (prior to the establishment of an empirical law) to saying that the perceiver is in error, or not, in responding to the physical mixture as yellow; yellow is the ‘correct’ value only relative to a certain type of perceiver. Indeed, for much of evolution, mammals were dichromats and responded in a different manner to mixtures of spectral lights. Consequently, experiments in colour mixture are episodes of discovering the perceptual response characteristics of particular types of subjects. In this sense, colour is a subjective (subject-based) response—which is not incompatible with the objectivity of colour as a property of lights and objects (Hatfield 2003). For normal human trichromats, the average responses to various colour mixtures were worked out with great precision. As usual, the variable error (the distributed differences among one subject’s response to repeated stimulation, or across different subjects) is simply a measure of consistency of response. For colour-matching experiments, the variable error is remarkably small.

13  On these topics, see also Akins and Hahn, Chapter 22, this volume, on colour, and Ross, Chapter 21, this volume, on primary and secondary qualities.

110   Gary Hatfield In the latter half of the nineteenth century and well into the twentieth century, two different accounts of the physiology and psychology of colour vision vied for acceptance. The first, a psychological trichromacy theory, was made prominent by Helmholtz. According to this theory, experienced colours are the product of three types of sensations that are combined unconsciously to yield a perceived colour. One type of sensation corresponds to each of the three types of colour-sensitive elements in the human eye. Helmholtz postulated sensations of red, green, and violet (1868/1995, 158–63). Experienced colours arise from a mixture of the phenomenal characters of the three primary sensations; ‘sensation’ must here, as usually in Helmholtz, be regarded as a phenomenally characterized psychological state, not as mere neural activity. Phenomenal blue is a mixture of the phenomenally characterized sensations of green and violet, and yellow is a mixture of the sensations of red and green. Hering raised phenomenological objections against this theory, leading to his opponent-process theory. He noted that, phenomenally and psychologically, yellow seems to be a primary colour, on a par with red, blue, and green (Hering 1905–11/1964, 41–50). Yellow does not seem to be a mixture of green and red; indeed, it is difficult to see how it could be regarded as such, phenomenally. Hering therefore posited that there are four types of receptors involved in colour vision (‘chromatic’ colour vision, leaving aside black and white) that feed into two physiological channels, a red–green channel and a blue–yellow channel. Each channel responds in an ‘opponent’ manner: the red–green channel may produce either red or green, but not both, which means that it can be physiologically driven toward red or green. When balanced, it produces no effect, and the chroma is determined by the other channel (blue or yellow). These channels can interact to yield the physiological basis for various experienced colours: if a red-process in the one channel interacts with a yellow in the other, phenomenal orange results. This does not come about through a mixture of phenomenally characterized sensations, but through a physiological combination that then produces an experience of orange (Hering 1905–11/1964, ch. 10; Turner 1994, ch. 7). The Hering and Helmholtz schools confronted one another well into the twentieth century (Turner 1994, chs. 10–11, 14; Hatfield 2009b). Today’s handbooks portray a resolution to this controversy through ‘two stage’ or ‘zone’ theories (Kaiser and Boynton 1996, 24–25). In such a theory, Helmholtz gets credit for being right about the three cone-types (retinal receptor trichromacy), while Hering’s opponent theory describes subsequent processes that underlie visual experience. There is something correct about this picture, and even Hering (1905–11/1964, 48 n. 2) seems to imply that such a division might allow some parts of the two theories to coexist. Historically speaking, however, this cannot count as ‘both theories being right’. For the theories to coexist, the Helmholtz theory must concede that the trichromatic processes are merely physiological, feeding into subsequent opponent processes; hence, the individual receptor types do not produce three fundamental phenomenally characterized sensations that are then mentally combined to yield a perceived colour. For the Hering school, this means that a fundamental tenet of Helmholtz’s theory, his generation of all hues by combining three basic sensations, must be abandoned in favour of Hering’s physiological theory (Hurvich and Jameson 1951; Turner 1994, 229). There are other dimensions of thought in German sensory psychology and related philosophical works, including the rise of the phenomenological approach of Franz Brentano (1874) and Mach’s (1886) analysis of sensations. These approaches will be regarded through their British and American receptions.

Perception in Philosophy and Psychology    111

3 Perception in British and American philosophy and psychology Nineteenth-century British writings on perception continued the controversy between Hume and Reid over the belief in and perception of an external world. Most authors accepted Berkeley’s theory that the immediate object of vision is a two-dimensional correlate of the retinal image, and that the perception of depth and distance by sight is acquired through interaction with touch (but Abbott 1864 rejected both tenets). The theory that touch educates vision was further refined by British thinkers through the development of the concept of the muscle sense as a sixth sense beyond the traditional five. Thomas Brown provided an early statement of this theory (Scheerer 1987). He ascribed the origin of the idea of extension not to touch or vision, but to the infant’s experience of moving its arm in three dimensions and feeling, through an awareness of muscle-induced motions, the three-dimensionality of the limb’s path. Brown thereby proposed an empirism as radical as that of Steinbuch or Helmholtz. He pre-dated Helmholtz in foregoing construction of a two-dimensional image in sensation. While acknowledging that, since Berkeley, theorists had ‘universally supposed’ that superficial extension, or visible figure, is immediately available to sight and subsequently serves as the basis for learning to see distance, Brown contended that we learn to see in three dimensions without passing through a stage with a two-dimensional image (1820, 2: 66–97). Brown also speculated that, through the surprise engendered when the usually free motion of an infant’s limb is resisted by an external object, the infant acquires the conception of and belief in an external world (1820, 1: 511–517). Alexander Bain (1855), in one of the first works of the ‘new psychology’ in Britain, offered an account of spatial vision and the belief in an external world bearing similarity to Brown’s theory. The problem of the external world was extensively discussed in Britain throughout the second half of the nineteenth century. Hamilton (1861), intending to support Reid (though perhaps misinterpreting him), held that in perceptual consciousness we are directly aware of both the act of perception and a non-mental object of that act. In the case of vision, we have seen that he regarded the retinal image itself, as a physical image of light, to be the immediately discerned external object. He dubbed his position an ‘intuitive’ theory of perception (1861, 2: 66–71), by contrast with the ‘representative’ theory he (with Reid) ascribed to Locke (ibid., 53–59). He also called it a ‘natural realism’ (ibid., 65). Although challenged by Mill (1865), Hamilton’s position was repeated with some variation by the Oxford philosophers Thomas Case (1888) and L. T. Hobhouse (1896). The notion that perception (as cognitive) is structured so as to include an act directed upon a distinct object became widely accepted, even if divorced from Hamilton’s ‘intuitive’ natural realism. The act–object structure was taken to embrace all mental phenomena by Brentano (1874/1995, 89–91), who was a close student of Hamilton’s writings, and whose writings in turn attracted the attention of G. F. Stout (1896). The early sense-data theories of Moore and Russell accepted an act–object structure, while rejecting Hamilton’s ‘natural realism’ and adopting, at certain times at least, a representative theory of perception.14 14  On the problem of the external world in British philosophy from Brown to Russell, see Hatfield (2013b).

112   Gary Hatfield The question of whether perception is direct or mediated was widely discussed by British and American philosophers in the early decades of the twentieth century. The positions they held included: (1) naïve direct realism, which held that the immediate objects of perception are external material things (Alexander 1909–10, 2; Cook Wilson 1926, 780); (2) representative realism, which in a standard sense-data version rendered an interposed third thing as the object (Russell 1912); (3) neutral monism, which reduced both mind and body to constructions out of neutral particulars (James 1904; Russell 1921); and (4) critical direct realism, which regarded perceptions as mental states that are not themselves the objects of perception but are the means by which we become directly aware of external objects (Sellars 1920, 1961).15

4 Psychology of perception after 1900 In the nineteenth century, the psychology of visual perception witnessed a great atomizing tendency, toward positing non-spatial colour sensations as the primitive sensations in vision.16 From Steinbuch to Helmholtz, this outlook reigned. Hering (1868), Mach (1886), and James (1890) started a counter-reaction, arguing that spatiality is originally given in vision. The atomizing account was paired with another theoretical tendency, which was to see visual spatial perception as the constructed product of unconscious or unnoticed processes of association. Early in the twentieth century, the Gestalt psychologists mounted an ever more effective attack on this unholy pair. Köhler (1913) and subsequently Koffka (1935, 84–87) insisted that the associational processes were only needed because of the hypothesis of atomic sensations, which was itself allied to a particular conception of the relation between nerves and phenomenal sensations: a one-fibre, one-sensation view that they labelled the ‘constancy hypothesis’.17 In place of this web of ideas, they constructed a theory in which three-dimensionality is the primary mode of visual experience (there is no two-dimensional-image stage); visual experience tends toward organization (as in figure– ground structures, or grouping of proximate or similar items); and these aspects of visual experience are produced by (or are identical with) brain processes that are ‘isomorphic’ in structure with the experiences (Koffka 1935; Köhler 1947). The Gestaltists also emphasized that perception tends to track objective properties of things, as in size constancy. They refused to treat the stimulus to vision as a coherent (unified) two-dimensional image, 15  On sense-data, perception, and various ‘realisms’ from 1860 to 1950, see Hatfield (2013a). Price (1932, ch. 3) called naïve realists such as Alexander and Cook Wilson ‘modified naïve realists’ because they took into account perceptual relativity while affirming that the perceiver immediately apprehends objects at a distance. Mach (1886) is not included among the neutral monists, as his restriction to phenomenal elements was epistemic, whereas James (1904) and Russell (1921) proposed a fundamental metaphysics of ‘neutral stuff’ or ‘momentary particulars’. 16  This psychological atomism can be found earlier in Hume (1739–40), bk. 1, pt. 2, sec. 3. 17  Here, the term ‘constancy’ describes the relation between an isolated neural response to a stimulus and the resultant sensation; its connotation is opposite to that of ‘size constancy’, in which the visual system’s global response tracks the properties of external objects rather than those of local proximal stimulation. For this reason, Gilchrist (2012, 107)  suggests renaming the constancy hypothesis as ‘the doctrine of local determination’.

Perception in Philosophy and Psychology    113 but rather regarded it as a mosaic of independent light intensities that individually interact with neural processes but are not themselves perceived. Stimulation from the eyes conditions central neural processes that produce an ordered perceptual world in three dimensions. Order arises only in perception; it is not given in the mosaic. The final assault on the notion of a static retinal image as the stimulus for vision, and of a processing stage that consists of a two-dimensional representation of the visual field, came through the work of J. J. Gibson, himself a fan of the Gestaltists. Gibson (1950) contended that perception of a visual world in three dimensions is the primary and normal mode of perception. There is no two-dimensional stage of processing; the two-dimensional visual field is an atyptical experience that arises from adopting a particular viewing attitude, sometimes called the ‘painter’s attitude’. Considered as a perceptual system, the visual system is built to track the three-dimensional visual world. It does so by responding to dynamic patterns of change within the optic array (Gibson 1950, 1966). Gibson argued that associative or cognitive processes are not needed to respond to the higher-order, complex features of the optic array, as these features are rich enough to specify directly the three-dimensional visual world. Gibson’s outlook is controversial, especially his denial of the need for psychologically interesting mechanisms to respond to the optic array (he granted the need for physiological mechanisms of reception). But however one reacts to that aspect of his theory, the notion that the stimulus to vision is a complex and dynamic pattern of energy, as received by a visual system that includes mobile eyes and a mobile body, has entered the mainstream of visual theory. The notions of a static two-dimensional image and of spatially atomized sensations have been surpassed. The closest counterparts to the latter are the many specialized detectors with small ‘receptive fields’, such as disparity detectors, edge detectors, or motion detectors, that encode retinal stimulation. But even here, the problem of perception lies in understanding how the pattern of activation in locally responsive neurons can be synthesized to yield a global representation of surfaces at a distance, as in Marr’s (1982) 2½ D sketch. The problem of how to theorize the processes that respond to these mechanisms as they encode dynamic patterns of optical stimulation is ongoing.18 Still, the old idea that perception begins from a static 2D image is a thing of the past. From dynamic patterns of information, we see a world of three dimensions, organized into discrete regions according to Gestalt figure–ground relations and through processes of object-recognition. The landscape of visual theory is transformed, which should mean that the philosophical landscape includes new territories and possibilities.

References Abbott, Thomas K. (1864). Sight and Touch: An Attempt to Disprove the Received (or Berkeleian) Theory of Vision. London: Longman, Green, Longman, Roberts, and Green. Alexander, Samuel (1909–10). ‘On Sensations and Images’, Proceedings of the Aristotelian Society, 10, 1–35. 18 

For a survey of recent visual theories, including the legacy of Gestalt, ‘constructivist’ (judgmental or associationist), and Gibsonian approaches, see Palmer (1999), chs. 1–2; for an appreciation of major theoretical trends in relation to Koffka and the Gestaltists, see Epstein (1994).

114   Gary Hatfield Bain, Alexander (1855). The Senses and the Intellect. London: Parker. Boring, Edwin G. (1942). Sensation and Perception in the History of Experimental Psychology. New York: Appleton-Century-Crofts. Bouguer, Pierre (1760). Traité d’optique sur la gradation de la lumière. Paris:  Guerin & Delatour. Translation: Pierre Bouguer’s Optical Treatise on the Gradation of Light, (trans.) W. E. Knowles Middleton. Toronto: University of Toronto Press, 1961. Brentano, Franz Clemens (1874). Psychologie vom empirischen Standpunkt. Leipzig: Duncker and Humblot. Translation:  Psychology from an Empirical Standpoint, (trans.) Antos C. Rancurello, D. B. Terrell, and Linda L. McAlister. London: Routledge, 1995. Brown, Thomas (1820). Lectures on the Philosophy of the Human Mind, 4 vols. Edinburgh: Tait. Case, Thomas (1888). Physical Realism, Being an Analytical Philosophy from the Physical Objects of Science to the Physical Data of Sense. London: Longmans, Green. Cook Wilson, John (1926). ‘Letter in criticism of a paper on primary and secondary qualities’. In Statement and Inference, with Other Philosophical Papers, 2 vols. Oxford: Clarendon Press, 764–800. Descartes, René (1637). La Dioptrique, published with his Discours de la méthode. Leiden: Maire. Edgar, Scott (2008). ‘Paul Natorp and the Emergence of Anti-Psychologism in the Nineteenth Century’. Studies in History and Philosophy of Science, 39, 54–65. Epstein, William (1994). ‘ “Why do things look as they do?”: What Koffka Might have Said to Gibson, Marr, and Rock’. In Stefano Poggi (ed.), Gestalt Psychology: Its Origins, Foundations and Influence. Florence: Olschki, 175–189. Epstein, William, and Park, John N. (1963). ‘Shape Constancy: Functional Relationships and Theoretical Formulations’. Psychological Bulletin, 60, 265–288. Falkenstein, Lorne (1990). ‘Was Kant a Nativist?’. Journal of the History of Ideas, 51, 573–597. Fechner, Gustav Theodor (1860). Elemente der Psychophysik. Leipzig: Breitkopf und Härtel. Partial translation: Elements of Psychophysics: Volume 1, (trans.) H. E. Adler. New York: Holt, 1966. Gehler, Johann Samuel Traugott (1787–96). Physikalisches Wörterbuch, oder Versuch einer Erklärung der vornehmsten Begriffe und Kunstwörter der Naturlehre, 6 vols. Leipzig: Schwickert. Gibson, James J. (1950). The Perception of the Visual World. Boston, MA: Houghton Mifflin. Gibson, James J. (1966). The Senses Considered as Perceptual Systems. Boston, MA: Houghton Mifflin. Gilchrist, Alan (2012). ‘Objective and Subjective Sides of Perception’. In Gary Hatfield and Sarah Allred (eds), Visual Experience: Sensation, Cognition, and Constancy. Oxford: Oxford University Press, 105–121. Goethe, Johann Wolfgang von (1810). Zur Farbenlehre. Tübingen: Cotta. Translation: Goethe’s Theory of Colours, (trans.) Charles Lock Eastlake. London: Murray, 1840. Hamilton, William (1861). Lectures on Metaphysics, (ed.) Henry L. Mansel and John Veitch, 2nd edn, 2 vols. Edinburgh: Blackwood. Hatfield, Gary (1990). The Natural and the Normative: Theories of Spatial Perception from Kant to Helmholtz. Cambridge, MA: MIT Press. Hatfield, Gary (1992). ‘Descartes’s Physiology and its Relation to his Psychology’. In John Cottingham (ed.), Cambridge Companion to Descartes. Cambridge: Cambridge University Press, 335–370. Hatfield, Gary (2003). ‘Objectivity and Subjectivity Revisited: Colour as a Psychobiological Property’. In Rainer Mausfeld and Dieter Heyer (eds), Colour Perception: Mind and the Physical World. Oxford: Oxford University Press, 187–202.

Perception in Philosophy and Psychology    115 Hatfield, Gary (2005). ‘Introspective Evidence in Psychology’. In Peter Achinstein (ed.), Scientific Evidence: Philosophical Theories and Applications. Baltimore: Johns Hopkins University Press, 259–286. Hatfield, Gary (2006). ‘Kant on the Perception of Space (and Time)’. In Paul Guyer (ed.), Cambridge Companion to Kant and Modern Philosophy. Cambridge: Cambridge University Press, 61–93. Hatfield, Gary (2009a). ‘The Sixth Meditation: Mind-Body Relation, External Objects, and Sense Perception’. In Andreas Kemmerling (ed.), Meditationen über die Erste Philosophie. Berlin: Akademie, 123–146. Hatfield, Gary (2009b). ‘What Can the Mind Tell Us about the Brain? Psychology, Neurophysiology, and Constraint’. In Perception and Cognition: Essays in the Philosophy of Psychology. Oxford: Clarendon Press, 434–455. Hatfield, Gary (2013a). ‘Perception and Sense Data’. In Michael Beaney (ed.), The Oxford Handbook of the History of Analytic Philosophy. Oxford: Oxford University Press. Hatfield, Gary (2013b). ‘Psychology, Epistemology, and the Problem of the External World: Russell and Before’. In Erich Reck (ed.), The Historic Turn in Analytic Philosophy. London: Palgrave Macmillan, 171–200. Hatfield, Gary and Epstein, William (1979). ‘The Sensory Core and the Medieval Foundations of Early Modern Perceptual Theory’. Isis, 70, 363–84. Heidelberger, Michael (2004). Nature from Within:  Gustav Theodor Fechner and His Psychophysical Worldview, (trans.) Cynthia Klohr. Pittsburgh, NJ:  University of Pittsburgh Press. Helmholtz, Hermann von (1867). Handbuch der physiologischen Optik. Leipzig: Voss. As republished in the 3rd German edn, 3 vols. Leipzig: Voss, 1910. Translation: Helmholtz’s Treatise on Physiological Optics, (ed. and trans.) James P. C. Southall, 3 vols. Rochester, NY: Optical Society of America, 1924–25. Page citations are to the 3rd German edn; these numbers are shown in the Southall translation. Helmholtz, Hermann von (1868). ‘Die neueren Fortschritte in der Theorie des Sehens’. Preussische Jahrbücher, 21, 149–170. Translation: ‘Recent Progress in the Theory of Vision’, in Helmholtz (1995), 127–203. Citations are to the translation. Helmholtz, Hermann von (1878). Die Thatsachen in der Wahrnehmung. Berlin: Hirschwald. Translation: The Facts in Perception, in Helmholtz (1995), 342–380. Helmholtz, Hermann von (1995). Science and Culture: Popular and Philosophical Essays by Hermann von Helmholtz, (ed.) David Cahan. Chicago, IL: University of Chicago Press. Hering, Ewald (1868). Die Lehre vom binocularen Sehen. Leipzig: Engelmann. Translation: The Theory of Binocular Vision, (trans.) Bruce Bridgeman. New York: Plenum Press, 1977. Hering, Ewald (1905–11). Grundzüge der Lehre vom Lichtsinn. Leipzig:  Engelmann. Translation: Outlines of a Theory of the Light Sense, (trans.) Leo M. Hurvich and Dorothea Jameson. Cambridge: Harvard University Press, 1964. Hering, Ewald (1874). Zur Lehre vom Lichtsinne. Vienna: Gerold’s Sohn. Hillebrand, Franz (1902). ‘Theorie der scheinbaren Grösse beim binokularen Sehen’. Denkschrift der Kaiserlichen Akademie der Wissenschaften Wien, mathematischnaturwissenschaftliche Classe, 72, 255–307. Hobhouse, L. T. (1896). Theory of Knowledge. London: Methuen. Hoffman, Paul (2002). ‘Direct Realism, Intentionality, and the Objective Being of Ideas’. Pacific Philosophical Quarterly, 83, 163–179. Hume, David (1739–40). Treatise of Human Nature. London: John Noon.

116   Gary Hatfield Hurvich, Leo M. and Jameson, Dorothea (1951). ‘The Binocular Fusion of Yellow in Relation to Color Theories’. Science, 114, 199–202. James, William (1890). Principles of Psychology, 2 vols. New York: Holt. James, William (1904). ‘Does “Consciousness” Exist?’, in Journal of Philosophy, Psychology and Scientific Methods, 1, 477–491. Kaiser, Peter K. and Boynton, Robert M. (1996). Human Color Vision, 2nd edn. Washington DC: Optical Society of America. Kant, Immanuel (1781). Kritik der reinen Vernunft. Riga: Hartnoch. Kant, Immanuel (1783). Prolegomena zu einer jeden künftigen Metaphysik. Riga: Hartnoch. Kepler, Johannes (1604). Ad vitellionem paralipomena. Frankfurt:  Marnium & Aubrii. Translation: Optics: Paralipomena to Witelo and Optical Part of Astronomy, (ed. and trans.) William H. Donahue. Santa Fe, NM: Green Lion Press, 2000. Kitcher, Patricia (1995). ‘Revisiting Kant’s Epistemology: Skepticism, Apriority, and Psychologism’. Noûs, 29, 285–315. Koffka, Kurt (1935). Principles of Gestalt Psychology. New York: Harcourt, Brace. Köhler, W. (1913). ‘Über unbemerkte Empfindungen und Urteilstauschungen’. Zeitschrift für Psychologie, 66, 51–81. Translation: ‘On Unnoticed Sensations and Errors of Judgment’, (trans.) H. E. Adler, in Selected Papers of Wolfgang Köhler, (ed.) Mary Henle, 13–39. New York: Liveright, 1971. Köhler, W. (1947). Gestalt Psychology: An Introduction to New Concepts in Modern Psychology. New York: Liveright. Lindberg, David C. (1976). Theories of Vision from al-Kindi to Kepler. Chicago, IL: University of Chicago Press. Locke, John (1690). An Essay Concerning Human Understanding. London: Bassett. Lotze, Rudolph Hermann (1852). Medicinische Psychologie, oder, Physiologie der Seele. Leipzig: Weidmann. Lotze, Rudolph Hermann (1886). Outlines of Psychology, (trans.) George T. Ladd. Boston: Ginn. Mach, Ernst (1886). Beiträge zur Analyse der Empfindungen. Jena:  Fischer. Translation: Contributions to the Analysis of Sensations, (trans.) C. M. Williams. La Salle, IL: Open Court, 1897. Marr, David (1982). Vision: Computational Investigation into the Human Representation and Processing of Visual Information. San Francisco, CA: Freeman. Martius, Götz (1889). ‘Ueber die scheinbare Grösse der Gegenstände und ihre Beziehung zur Grösse der Netzhautbilder’. Philosophische Studien, 5, 601–617. Mill, John Stuart (1865). An Examination of Sir William Hamilton’s Philosophy. London: Longman, Green, Longman, Roberts & Green. Müller, Johannes (1833–40). Handbuch der Physiologie des Menschen. Coblenz: Hölscher. Newton, Isaac (1704). Opticks, or a Treatise of the Reflexions, Refractions, Inflexions and Colours of Light. London: Smith and Walford. Nolan, Lawrence (ed.) (2011). Primary and Secondary Qualities: The Historical and Ongoing Debate. Oxford: Oxford University Press. O’Neil, Brian (1974). Epistemological Direct Realism in Descartes’ Philosophy. Albuquerque, NM: University of New Mexico Press. Palmer, Stephen E. (1999). Vision Science:  Photons to Phenomenology. Cambridge, MA: MIT Press. Pastore, Nicholas (1971). Selective History of Theories of Visual Perception:  1650–1950. New York: Oxford University Press.

Perception in Philosophy and Psychology    117 Price, H. H. (1932). Perception. London: Methuen. Reid, Thomas (1785). An Inquiry into the Human Mind, 4th edn. Edinburgh: Bell and Creech. Rogers, G. A. J. (2004). ‘Locke and the Objects of Perception’. Pacific Philosophical Quarterly, 85, 245–254. Ross, Helen E. and Plug, Cornelis (1998). ‘The History of Size Constancy and Size Illusions’. In Vincent Walsh and Janusz Kulikowski (eds), Perceptual Constancy: Why Things Look As They Do. Cambridge: Cambridge University Press, 499–528. Russell, Bertrand (1921). Analysis of Mind. London: Allen and Unwin. Russell, Bertrand (1912). Problems of Philosophy. London: Williams and Norgate. Scheerer, Eckart (1987). ‘Muscle Sense and Innervation Feelings: A Chapter in the History of Perception and Action’. In Herbert Heuer and Andries F. Sanders (eds), Perspectives on Perception and Action (pp. 171–194). Hillsdale, NJ: Erlbaum. Sellars, Roy Wood (1920). ‘Knowledge and its Categories’. In Durant Drake (ed.), Essays in Critical Realism (pp. 187–219). London: Macmillan. Sellars, Roy Wood (1961). ‘Referential Transcendence’. Philosophy and Phenomenological Research, 22, 1–15. Steinbuch, Johann Georg (1811). Beytrag zur Physiologie der Sinne. Nurnberg: Schragg. Stout, G. F. (1896). Analytic Psychology, 2 vols. London: Swan Sonnenschein. Thouless, Robert H. (1931). ‘Phenomenal Regression to the Real Object, I’. British Journal of Psychology, 21, 339–359. Thouless, Robert H. (1932). ‘Phenomenal Regression to the “Real” Object, II’. British Journal of Psychology, 22, 1–30. Titchener, Edward Bradford (1905). Experimental Psychology:  A  Manual of Laboratory Practice, Vol. 2: Quantitative Experiments. London: Macmillan. Published in two parts. Titchener, Edward Bradford (1912). ‘The Schema of Introspection’. American Journal of Psychology, 23, 485–508. Tourtual, Caspar T. (1827). Die Sinne des Menschen in den wechselseitigen Beziehungen ihres psychischen und organischen Lebens:  Ein Beitrag zur physiologischen Aesthetick. Münster: Coppenrath. Turner, R. Steven (1994). In the Eye’s Mind: Vision and the Helmholtz–Hering Controversy. Princeton, NJ: Princeton University Press. Wade, Nicholas J., (ed.) (1983). Brewster and Wheatstone on Vision. London: Academic Press. Wade, Nicholas J. (2003). Destined for Distinguished Oblivion: The Scientific Vision of William Charles Wells (1757–1817). New York: Kluwer. Wagner, Mark (2006). Geometries of Visual Space. Mahwah, NJ: Erlbaum. Wolf-Devine, Celia (1993). Descartes on Seeing:  Epistemology and Visual Perception. Carbondale, IL: Southern Illinois University Press. Woodworth, Robert (1938). Experimental Psychology. New York: Henry Holt. Wundt, Wilhelm (1862). Beiträge zur Theorie der Sinneswahrnehmung. Leipzig: Winter. Wundt, Wilhelm (1874). Grundzüge der physiologischen Psychologie. Leipzig: Engelmann. Yolton, John W. (1984). Perceptual Acquaintance from Descartes to Reid. Minneapolis, MN: University of Minnesota Press. Yolton, John W. (1996). Perception and Reality:  A  History from Descartes to Kant. Ithaca, NY: Cornell University Press.

Chapter 6

Sense-Data Paul Snowdon

The term ‘sense-datum’ entered the language of philosophy towards the end of the nineteenth century, and employments of it by Royce and William James (in 1882 and 1890 respectively) are cited, in dictionaries, as early examples of its use. It was then taken up by Russell and Moore and became a part of standard philosophical terminology, retaining a central place in the vocabulary employed by philosophers of perception ever since. Despite holding this central place the term ‘sense-datum’ has had a somewhat chequered career. It has had, or perhaps it is useful to think of it as having had, three main interpretations. According to the first two, we are to understand ‘sense-datum’ as standing for an object, of some kind or other. These two attitudes might be divided into a dominant and a less dominant interpretation. On the dominant interpretation the words were linked to a particular conception of the objects of perceptual experience (or the objects involved in perceptual experience), a conception which had existed amongst philosophers (and scientists) for a long time before this particular terminology emerged. In earlier times this conception had been expressed using different terms, notably in the use of the word ‘idea’ to stand for what we (directly) perceive. On what I shall call the less dominant object interpretation, the term ‘sense-datum’ was used to express a supposed conception of an object that it is undeniably present in perception, the only question being what kind of object it is. People using the term in this second way quite often ended up ultimately agreeing or being close to agreeing with those who used it in the first way, but at least they reserved the option of using the term ‘sense-datum’ in a positive way without ending up affirming the traditional view. Moore, who championed this second use, spent his entire philosophical life wondering whether to take this option (or something like it) or not.1 Towards the middle of the century the third usage emerged, associated with A. J. Ayer. According to this usage it is somehow beneficial to employ the terminology of ‘sense-datum’ as part of a stipulated re-expression of appearance claims, where its employment in such a re-expression does not signal the postulation of entities of any kind whatsoever. The principal question that this last development raised was what advantage for philosophy was generated by such a linguistic stipulation or recommendation. I shall describe these different employments in a little more detail below. These second two moves away from 1 

Moore’s version of what I am calling the less dominant interpretation is described in section 3.

Sense-Data   119 the dominant interpretation are both attempts to reduce the theoretical commitments of ‘sense-data’ talk. Very roughly, in the first half of the twentieth century the dominant research strategy in the philosophy of perception was the development of approaches to perception centred on what we might call the postulation of sense-data, by philosophers such as Russell, Moore, Broad, Price, and Ayer. In the second half of the century the tide turned and the dominant research goal was to think about perception in a way that avoided their postulation—an approach endorsed and developed by Wittgenstein, Austin, Ryle, Armstrong, and Pitcher, amongst many others.2 As with all tides, there have been those swimming against this later one, such as Frank Jackson, Brian O’Shaughnessy, and Howard Robinson, just as there in fact had been those who swam against the earlier tide as well. The debates about this type of theory are very familiar to anyone who has worked on the philosophy of perception, and it is unlikely that anything significantly new can be said about them. My hope here is to present and structure this rather familiar material in a way that illuminates and clarifies these debates. Let us begin, then, by outlining the all too familiar and very long-standing model, or theory, to which the sense-datum terminology has been dominantly assigned.

1  The dominant sense-datum model The types of occurrence to start with are those regular events which we naively think of as events of perceiving the world, say, seeing the book you currently think you are seeing. We can here, in our choice of example, but also explicitly, register the fact that philosophers have tended to think primarily about vision when they consider perceptual experience, a practice I shall follow initially. Now, we, normal people, think of that event as one which enables us to pick out, or discern, an object—the book—which is a regular, three-dimensional external object. That is the object which the occurrence enables us to scrutinize and focus on. It is also thought of as a public object, in the sense that it is there for others also to perceive and see. It is part of our shared and communally perceivable environment. But according to the model of this event that philosophers accepted it actually, and in truth, involves the subject standing in a mental or psychological relation which was called

2  As a rough piece of history we can say that once the opposition to sense-data became a common shared assumption, the first response was to be fairly untheoretical about perception and simply oppose the sense-datum account, a description that applies to Austin, and perhaps Wittgenstein. Once the theorizing ambitions returned an early approach was that of the belief theorists. It is obvious that the dominant constraint on that sort of theory was the avoidance of sense-data; these were avoided by taking the psychological primitive in their analysis to be belief, a state the presence of which does not seem to require sense-data. The second advantage of belief is that it is a state with content, and hence a state which promises the possibility of grounding the sort of content that appearances involve. A crucial drawback to basing an analysis on belief is that belief seems to be a psychological state which can be present without involving experiences, whereas perception seems to be an experience. It is therefore not surprising that the next idea to emerge was an analysis of perception based around a distinctive experience-involving contentful state.

120   Paul Snowdon apprehending, or perceiving, or directly perceiving, or being acquainted with (a relation clearly patterned on that of seeing itself, as we understand it) to a quite different sort of object, to which the name ‘sense-datum’, once it emerged, was assigned.3 What is important is the theoretical conception of this postulated type of object or item. Now, by a theoretical conception of an object is meant the general properties it is supposed to possess and the fundamental conditions or modes of existence it has according to the theory. In the case of sense-data, the item was thought of as possessing certain sensible qualities—in the case of visual experience, it possessed colour, and given the overall structure of colours it also exhibits features such as lines and shapes. In fact, the best way to think of them in this sort of case is as picture-like objects—objects that possess the basic properties that pictures have. (I shall argue later that the existence of actual pictures and our familiarity with them is an important psychological source of the long-standing attraction of such ways of thinking.) However, their mode of existence is not like that of real pictures in the world. They are thought of as not being in public space, but as having a subjective or mental existence. Classically, this was captured in Berkeley’s slogan that their ‘esse’ (being) was ‘percipi’ (to be perceived). Along with this conception of their mode of existence went the idea that sense-data are private to a subject—each subject when having such experiences has his or her own sense-data. It should be clear that a theory with this structure can be found in much earlier philosophical theorizing about perception, in periods when the sense-datum terminology had not yet emerged. Thus, it seems reasonable to interpret the following passage in Locke as basically expounding the model just sketched. In his famous discussion of primary and secondary qualities Locke says: Whatsoever the Mind perceives in it self, or is the immediate object of Perception, Thought or Understanding, that I call Idea . . . Let us suppose at present, that the different Motions and Figures, Bulk and Number of such Particles, affecting the several organs of our Senses, produce in us those different sensations, which we have from the Colours and Smells of Bodies, v.g. that a Violet . . . causes the Ideas of the blue Colour. . .  Flame is denominated Hot and Light; Snow White and Cold; and Mana white and Sweet from the Ideas they produce in us. Which qualities are commonly thought to be the same in those Bodies, that those Ideas are in us, the one the perfect resemblance of the other, as they are in a Mirror. . .4

It is, of course, a matter of dispute how best to interpret this famous passage, but it seems Locke’s view is that we directly perceive ideas, which are inner mental items, the type of 3 Russell

introduced the terminology of acquaintance, but that was an odd appropriation of an expression in ordinary language. Russell means it to stand for a relation to an item in virtue of which the subject can, when it holds, scrutinize and attend there and then, to the item. But in normal speech I can be acquainted with an object at a time without at that time being able to attend to it. I am currently acquainted with many people I am not able to concentrate on now. 4  Locke (1975), Bk 2, ch 8 extracted from ss 13 and 15. A complication in the terminology here and one that comes out in the passage quoted is that Locke uses the term ‘idea’ to stand for a type of item present to the mind in both perception and thinking. This reflects his assumption that we should model both occurrences along what I call ‘act/object’ lines. By using the same term, ‘idea’, to cover both cases Locke invited the question, later discussed by Hume, as to what the difference is between experiences which are perceptual and those which are thoughts. Locke failed to face up to this issue, whereas it stared Hume in the face. Despite that insight, Hume’s answer, encoded in the dual terminology of ‘impressions’ and ‘ideas’, is hardly satisfactory.

Sense-Data   121 item present when a sensation is felt, and that this item presents to the percipient such qualities as whiteness and blueness. Locke is concerned to emphasize that ordinary people think that the sensible quality presented by and so belonging to the idea mirrors (or resembles) the same quality in the causing object, but they are, according to him, wrong to think this.5 It is surely clear that Berkeley would have said the same. Hume is slightly more complicated because of his scepticism about subjects, but his characterization of impressions would have attributed to them the same sort of features. Impressions are for him, as it were, independent picture-like images somehow involving consciousness. This conception persisted well into the last century and here at its beginning is Russell speaking along very similar lines. ‘Let us give the name of “sense-data” to the things that are immediately known in sensations: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name “sensation” to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation.’6 Russell’s way of speaking is somewhat different but the model being proposed is surely the same. It is obvious that many other examples of the expression of this model could be cited.

2  Some aspects of the dominant model Four aspects (out of a number of important ones) of this general approach merit noting immediately. The first is that proponents of the theory or model tended to regard it as deeply revisionary of ordinary opinion. The idea is that ordinary people think of the events they conceptualize as perception of the public world as having a certain structure—the public object, as it were, enters or gains access to the consciousness of the percipient. This conception is labelled naive realism, reflecting the conviction that it is the theory of the naive. The espousal of the new picture is then often regarded as an instance of commonsense thinking being superseded by what is, in a sense, a scientifically and properly worked-out account. In the marvellous terminology of Sellars the new theory represents the triumph of a scientific image over the manifest image. It needs adding that not all proponents of sense-data viewed matter that way, for example Moore did not. The second aspect is that in its general structure it is what philosophers have called an ‘act-object’ theory. It analyses the experiential occurrence as consisting of an object, the sense-datum, with its features, and a mental relation towards that object, which relation can be called an ‘act’. This helpful terminology should not, of course, be read as committing the model to treating the so-called act as being an active doing by the subject, an exercise of the subject’s (voluntary) agency. Once this structure has been noted it becomes a major question whether it is obligatory to adopt an account of the nature of such experiences with this structure. But this is a more general issue than simply whether the experiences we tend to think of as perceptual should be so analysed. Should we think of experiences in general this way—including experiences of pain, after-images, and itches? Are we constrained to 5 

It is highly questionable whether Locke characterizes the naive view accurately here. The naive view is not so much a resemblance view, as the view that what is presented as coloured is the external object. 6  Russell (1912: 12).

122   Paul Snowdon apply it completely generally? Must we think, for example, of a pain as an object that we apprehend when we feel a pain? This is an aspect of the sense-datum theory that obsessed the later Wittgenstein. The third thing to note is that there is a sense in which this model is not, strictly speaking, a theory of perception at all. The reason for saying this is that built into the theory itself is a postulated relation, expressed in such terms as ‘apprehending’ or ‘directly perceiving’, which seems to be more or less equivalent to a relation of perceiving. No analysis or decomposition is offered of this relation. It is, within the model at least, a primitive basic component which the analysis relies on. It can be said that the theory is a theory about the objects of perception. It certainly says what we (directly) perceive. But it clarifies things, I want to suggest, to regard the model as more correctly described as a theory of appearance. The idea is that when subjects have such experiences (which we think of as perceptual) certain appearance facts obtain, such as we would report by saying: ‘It looks to the subject as if there is a red round tomato.’ The fundamental explanatory role of the model is to decompose such facts into an act-object state of affairs, in which the nature, or as one might say, the content, of the appearance is explained by assigning as qualities to the object, the sense-datum, ones which ground or yield that appearance. In the case in question it would postulate that the sense-datum is actually red and that the red patch exhibits a round shape. It is obvious that such a model cannot in any straightforward way account for the truth of the appearance as being of a tomato, since the sense-datum cannot itself be a tomato. To explain that aspect of appearance facts needs more to be built into the account, or perhaps the development of a more sceptical attitude to the idea that appearances can really involve a tomato aspect. The fourth aspect of the theory to mention here is that in order for this model to work as a theory of appearance the central relation between the subject and the postulated item has to be thought of as one which is, in a sense, perfectly transparent. That is, in the obtaining of the relevant relation, the postulated ‘act’, the properties or qualities that the sense-datum has must be revealed without any distortion or subtraction or addition, since if what we might call the generation of illusions about the nature of the sense-datum were possible the basic model would not in any determinate way generate appearances at all. Thus given that possibility of an illusion to be told that the experience consisted of an apprehending of a red patch would merely generate the further question: yes, but how did the red patch appear? Red, or perhaps another colour?

3  Moore’s interpretation of sense-data I have tried to present what I am calling the dominant employment of the sense-datum terminology, as a term standing for an element in a theory of (perceptual) experience, and to draw attention to some aspects of that theory. I shall now briefly sketch the first of the two less dominant uses, the one particularly associated with G. E. Moore. In Moore’s use it is taken to be simply totally obvious that there are sense-data. In the dominant use, in contrast, it is taken that the introduction of sense-data into our theory requires arguments and a defence. Moore’s attitude is that there is a way to introduce the terminology of sense-data which means that no one would deny there are sense-data—that is as obvious

Sense-Data   123 as the fact that there are experiences at all. How can this be? Moore’s assumption is that to have an experience is to be in a position, there and then, to pick out some presented item—a sense-datum. The only real question is: what sort of item is the undeniably or obviously present (or presented) object? That is the question that needs arguments to settle it. There is not the space in this chapter to investigate Moore’s use of the term ‘sense-datum’ at any length, but I  wish to make three observations about it. First, in one way the difference between Moore’s type of use and the dominant one can be regarded as simply a difference in terminological packaging. Moore assumes there is obviously an object presented to the subject, or apprehended by the subject, and labels it a sense-datum, but then he argues for a certain characterization of it, which could be, even if it actually is not, precisely the same as that built into the employment of the term ‘sense-datum’ by the dominant use. And the person arguing for the existence of sense-data, understood in the dominant way, will in effect assume there is an object present within the experience, a fact that Moore employs the term ‘sense-datum’ to record. Moore, for reasons of his own, does not accept that the object depends for its existence on being apprehended or sensed, and so does not actually believe that sense-data understood in Moorean usage are sense-data understood in the dominant use.7 This is, however, unconnected with his use of ‘sense-data’. Second, Moore evidently thought that all experience involves the presentation of an object to a subject. This assumption sustained his conviction that one can discern an object, the sense-datum, within the experience. This assumption is, however, not evidently true at all. It is a significant question whether experience is like that.8 This means that Moore is not entitled to his supposedly ‘non-theoretical’ sense-data. Third, Moore’s idea is that it is obvious that there is an object but its nature remains to be determined. Evidently if he thinks this he must be very cautious about characterizing the object. Since he does not know what kind of object it is, how does he know what the experience entitles him to say about it? Moore is not in fact cautious enough, and when he argues that, say, the sense-datum is not the surface of a physical object he relies on assumptions about its character which he is not entitled to make, unless he already knew that it was not a surface. For example, in thinking about double vision Moore simply assumes there are two objects, two sense-data, when maybe there is only one object seen twice, and hence only one sense-datum. Moore falls into the two traps that his approach sets him. The first is that it rests on a general theory and is not truly a-theoretical, and the second is that he does not preserve his neutrality when he characterizes sense-data.

4 Ayer’s use In 1940 A. J. Ayer published his book The Foundations of Empirical Knowledge. Perhaps the chief importance of this book now is that it became the target of Austin’s famous criticisms of sense-data. However, Ayer’s own aim was to give an account of our perception-based 7 

This is the main point of Moore’s highly influential and famous, but also rather obscurely argued, Refutation of Idealism. 8  In section 7 I shall argue that the assumption is actually false.

124   Paul Snowdon knowledge of our environment (so-called ‘empirical knowledge’). In the early stages of his argument Ayer endorses an employment of the terminology of ‘sense-data’, according to which it is not a terminology the use of which involves novel (or indeed, any) ontological commitments. It simply represents a ‘new verbal usage’.9 This is how Ayer puts it: In order to avoid these ambiguities, what the advocates of the sense-datum theory have done is to decide both to apply the word ‘see’ or any other words that designate modes of perception to delusive as well as to veridical experiences, and at the same time to use these words in such a way that what is seen or otherwise sensibly experienced must really exist and must really have the properties that it appears to have. . .  This procedure is in itself legitimate; and for certain purposes it is useful. I shall adopt it myself. But one must not suppose that it embodies any factual discovery. . .  What he is doing is simply to recommend a new verbal usage. He is proposing to us that instead of speaking, for example, of seeing a straight stick which looks crooked . . . we should speak of seeing a sense-datum which really has the quality of being crooked . . .10

Ayer himself credits G. A. Paul with bringing out that we should understand the introduction of ‘sense-data’ talk as merely a new ‘verbal usage’. How should we view this development? Ayer’s attitude represents, I think we can first say, a complete misunderstanding of Paul’s point in his famous and influential paper.11 Paul’s point was that in the philosophical tradition in which sense-data were talked about—a tradition of which he had had first-hand knowledge during his period in Cambridge—the proponents of such talk, as he puts it, ‘have not spoken as if what they were doing was introducing merely an alternative way of saying this same thing over again, but as if the new sentence which they substitute were in some way nearer the facts’.12 Despite them not thinking this, it is Paul’s view that a scrutiny of their new terminology and how they use it reveals it cannot be ‘nearer to reality’. Paul’s attitude is, then, at bottom a criticism of the proponents of sense-data. Now, my interest here is not in assessing the force of Paul’s critical argument, but in noting that what was in Paul’s hands meant to be a criticism is taken by Ayer to be a characterization of a favourable way of understanding the endorsement of ‘sense-data’ talk as a positive but purely linguistic proposal.13 Further, it is quite clear that Ayer’s approach is inviting trouble. It seems obvious that if there is a tradition of theorizing in which a technical term, ‘sense-datum’, is taken to stand for an object of some kind, it will be hard to maintain the attitude that a new usage is being proposed according to which it has no such semantic role. There is surely a danger that the old understanding will enter how the new talk, in its argumentative context, is taken. It seems a rather imprudent proposal. And, sure enough, we find Ayer almost immediately saying things that betray such a misunderstanding. Thus Ayer himself says that the new terminology commits itself to the idea that ‘what is seen or otherwise sensibly experienced must really exist and must really have the properties that it appears to 9 

Ayer (1940: 25). Ayer (1940: 24–25). I have left out parts of the two paragraphs in the quotation. 11  See Paul (1936)—page references to the reprint in Flew (1960). 12  Paul (1936: 107). By this ‘same thing’ Paul means something along the lines of: that stick looks bent. 13  Paul’s general approach is clearly inspired by Wittgenstein’s attitude to sense-datum talk. It is a mark of the significance of Paul’s article on sense-data that Flew chose to reprint it in a collection published in 1960, twenty-four years after it came out. 10 

Sense-Data   125 have’.14 But this seems to be a total misunderstanding of his own proposal. When the user of the new language re-expresses what he or she would have said in the words ‘that looks bent’ by using the words ‘I see a sense-datum that is bent’ they are not committing themselves to something which ‘really has’ the property of being actually bent. The word ‘bent’ in the new usage can occur in true sentences without there being anything that is actually really bent, at least, insofar as it can so occur in the former locution. The coupling of the term ‘bent’ with ‘sense-datum’ shows that it can have a role in a true sentence without anything being really bent, just as it can in such a sentence as ‘S thinks that is bent’. So Ayer immediately falls into the very trap his proposal is setting. We can also ask what the point is supposed to be. Ayer explains how he sees it in these words: ‘since in philosophizing about perception our main object is to analyse the relationship of our senseexperiences to the propositions we put forward concerning material things, it is useful for us to have a terminology that enables us to refer to the contents of our experiences independently of the material things that they are taken to present. And this the sense-datum terminology provides.’ 15 It is clear, though, that this is a mistake. The new language can only be understood on the basis of knowing what the translation rules are from the new sentences to old sentences. This means that the new terminology cannot provide ways of talking about experience which are more independent of material object notions than the original sentences were. There cannot then be any advantage in employing it for philosophical purposes. Rather, the new terminology will disguise or hide what those relations are. Ayer’s third way with the ‘sense-datum’ terminology, then, seems like other recent ‘third ways’ of speaking, to represent a bad way.

5  Epistemology and ontology Before investigating the arguments in favour and those against the dominant model, something needs to be said about the main focus of the model. The need arises because the chief function (for us) of perception is to gain information about the world (and ourselves). Perception centrally has an epistemological role. This means that philosophical investigations of perception can be motivated by a desire to understand how it yields the information that it does for us, or a desire to understand what the structure of the perceptual relation itself is. In current jargon the latter interest is sometimes called ‘metaphysical’. Now, it seems true to me to say that these two roles have often been confused in the discussion of philosophers. This confusion, if it has occurred, is perennial, but it has been fostered by the use of the term ‘sense-datum’ which is normally taken to stand for a postulated object, but by talking of a ‘datum’ people are encouraged to think it stands for something fact-like that can be learnt or discovered. Once this distinction is blurred confusion breaks out. We can, I think, illustrate this by looking at selections from a passage of Ayer’s. In this passage Ayer is not presenting an argument but is, rather, introducing what he calls the ‘problem of perception’ to the reader. Here is what Ayer says about the problem.

14 

Ayer (1940: 24).

15 

Ayer (1940: 26).

126   Paul Snowdon The problem of perception, as the sceptic poses it, is that of justifying our belief in the existence of the physical objects which it is commonly taken for granted that we perceive. In this, as in many other cases, it is maintained that there is a gap, of a logically perplexing kind, between the evidence with which we start and the conclusions that we reach. . .  The starting point of the argument is, as we have seen, that our access to the objects whose existence is in question must be indirect. In the case of perception, however, it may be well be doubted whether this premise is acceptable. . .  It is certainly not obvious that there is any question here of a passage from one type of object to another. Nevertheless, a great many philosophers have held that this was so. . .  Taking the hard data to be securely known, they have regarded the existence of physical objects as being relatively problematic. . . . What, according to them, is immediately given in perception is an evanescent object called an idea, or an impression, or a presentation, or a sense-datum, which is not only private to a single observer but private to a single sense.16

There are two sorts of oddities, it seems to me, in this passage. One sort are the remarks which, considered on their own, are problematic. For example, Ayer seems to think that the problem of perception is the question as to how we can justify our belief in external objects. Now, that question, or problem, is not posed by the sceptic. It can be asked by anyone. Ayer also talks about ‘the argument’, but it remains unclear as to what, at this stage, the role of any argument is. Does Ayer mean an argument designed to show that there is no justification, or to show that there is something we can think of as our evidence which itself is not a claim about external objects? However, the second, more general oddity, in this passage as a whole, is that no clear conception of the problem of perception emerges. Thus, it is clear that Ayer thinks the problem of perception is an epistemological problem, a problem about justifying a certain class of beliefs. Now, as has been pointed out, Ayer regards the background here as an argument, but it has to be wondered why, if the argument is thought of as promoting the view that there is no justification, any such argument needs to rest on the claim that ‘access to [external] objects’ must be indirect? Indeed, what does that mean? If ‘access’ means way of knowing then presumably the notion of indirectness simply means that knowledge of the relevant facts is based on evidence of a different kind. In that sense the idea that the sceptical argument requires indirectness seems correct but trivial. But Ayer seems to assume that it must involve the idea of a passage, of some sort, from one kind of object to other. What does that mean—and why is it required? And that idea of indirectness then gets aligned to the postulation of a new kind of object—a sense-datum. It seems, on the contrary, obvious that epistemological indirectness does not require this other sort of indirectness. It remains problematic too whether the epistemological indirectness itself follows from the other sort of indirectness. Standing back from Ayer’s introduction, it seems clear that he writes as if there is some sort of argument about perception the interest of which is that it creates an epistemological problem. But no clear idea is presented as to what the epistemological problem really rests on—does it rest on the soundness of the object introducing argument or not?—nor is there any clear recognition that there are two very different notions of ‘indirectness’ involved, nor does Ayer indicate that the introduction of ‘objects’ might be interesting for other reasons or be motivated by 16 

Ayer (1956: 84–85). The quotation in the text draws on three paragraphs from Ayer’s text.

Sense-Data   127 quite different considerations. I think myself that no clear impression of a problem and its interlocking parts is created in this passage. This passage, I am suggesting, is confused. But this allegation has another significance for the sense-datum debate. One important question about the contribution of Austin to the sense-datum debate is to what extent he properly uprooted the approach. Now, one aspect of that issue is the extent to which the people he identified as his opponents and whom he intellectually stalked are the best supporters of the model. It weakens Austin’s contribution if the people he destructively criticizes are not exemplary defenders of the theory. It is, of course, primarily Ayer that Austin criticizes. The worry is that Ayer is himself too mired in confusion to be the best exponent to criticize. There are two important respects in which Ayer is not a good target. The first is that his discussion exhibits the lack of clarity between epistemology and ontology as, I hope, brought out above. The second is that he operated with the notion of sense-datum talk as useful without regarding sense-data as entities—what I called the third way with sense-data. Now this is, as I have argued, a bad approach. That Ayer exhibits both confusions considerably weakens his role as the principle target in Austin’s attempted destruction of the problem of perception.

6  Arguments for the dominant model The standard arguments in favour of the dominant model can be thought of as having a two-part structure. The first part takes a limited range of cases and argues or claims that the model applies to them. The second stage generalizes the conclusion to all cases. These arguments are usually named on the basis of the limited range of cases in the first part. One famous argument—the argument from illusion—takes them as the basic case, and another, the argument from hallucination, generalizes from hallucinations. Arguments with this structure are pervasive in the philosophy of mind.17 Now, these arguments in the philosophy of perception face basically two questions. The first question is whether the claim that the model applied to the basic cases is well supported. The second question is whether the generalizing step is legitimate. With these questions in mind, consider first the argument from illusion. The notion of an illusion as it is used here is that of a case where an object is, as we say, perceived but looks in some way how it is not. The case that was often chosen is that of a straight stick partly seen in water; the stick looks bent but is straight. Why was this case (or type of case) considered interesting? The answer is that it is being used to show that there is a sense-datum, with certain qualities and its ontological status, of which the subject is aware. It can do this if the case enables us to recognize the presence of such an object. Basically, it works by eliciting the acknowledgement that there is something that is bent, which cannot be the external object, which is, of course, agreed not to be bent, and which is within the subject’s range of awareness. The acknowledged presence of the thing, exhibiting bentness, requires the introduction into the model of what is happening of an object distinct from the physical object. Now, it would in fact require extra argument to

17  One interesting example is the pattern of argument aimed at showing that all bodily action involves trying. This first argues that there is trying in the case of failure and then generalizes that claim to all cases.

128   Paul Snowdon show that the postulated object has to have the nature of a sense-datum, but an equally serious question is why a case like this requires us to postulate a bent entity at all. There are two ways of thinking about this. One is that it is simply obvious to the subject (and hence to the theorist) that there is something bent. This claim, however, invites the response of asking why this fact is obvious. The counter-suggestion is that it is obvious that it looks as if there is something bent, but it is not obvious that anything is actually bent. That dialogue, it seems, to me, stops that argument in its tracks. We should also invite anyone who is tempted to claim this is obvious to weigh up the consequences of accepting that conclusion. If something is, say, bent in that occurrence then we have to locate somewhere a bent thing, and that commitment is serious and difficult to fulfil. These considerations need weighing up by anyone who finds the ontological claim obviously true. The second way to look at the conviction that something is bent is that it is the result of an application of a plausible general principle that might be expressed thus; if something looks F then there is something that is F. This general principle is called, by Howard Robinson, the Phenomenal Principle.18 However, invoking a principle merely invites the response of asking why that should be accepted. Further, the current principle is nowhere near the truth. No one would agree that if someone looks old then there must be something old. Considered either way, as evident truth or application of a principle, there is no warrant to introduce the entity in a correct account of such cases.19 This means, I  suggest, that the legitimacy of the spreading (or generalizing) step in the case of the argument from illusion can be left uninvestigated. But the same problem faces the argument from hallucination as it is employed to support the general truth of the sense-datum theory. The issue is why the treatment of the base case of hallucination as involving sense-data is legitimate. If one hallucinates, say, a bent stick, we cannot, of course, treat that as was proposed for the illusion of a bent stick case, as, namely, a straight stick looking bent. However, that does not mean that we need to regard it as involving a bentness-presenting sense-datum, unless we already subscribe to something like the Phenomenal Principle, which we have been given no reason to do, or because it is simply thought to be obvious that there is a bent entity present to the subject’s consciousness, which idea is no more obviously correct in this case than the illusion case. In some other cases that have been appealed to as the ground for introducing sense-data into the account of the base case they have not been based on the straightforward idea of trying to locate an entity bearing a property which is in some sense in the appearance, but rather because it is felt there are two entities within the subject’s consciousness, but only one physical object, for example in the case of seeing double. However, such cases can be treated without invoking sense-data. One way is to regard double vision as simply a double sighting of a single entity, hence no new entity needs postulating. Alternatively, if it is thought that that account is deficient, then one can treat what one might think of as one of the sightings, or maybe, both, as experiences having a structure akin to that involved in hallucination, whatever that is. I am proposing that there is no cogent way to introduce sense-data into any of the base cases, and so there is no interim conclusion about sense-data that can be generalized across 18 

See Robinson (1994: ch. 2). A fuller analysis of the argument from illusion with a different emphasis from the present analysis can be found in Snowdon (1992). 19 

Sense-Data   129 all cases. Two things need adding. First, the generalizing case itself is plainly dubious in the case of the argument from hallucination. Austin’s lovely example of seeing a lemon and seeing a lemon-like bar of soap bring out that the fact that subjects cannot tell (if they in fact cannot) that a hallucination is not a perception simply on the basis of the experience itself does not imply that the two occurrences are not of quite a different nature.20 Second, even if these standard cases—such as illusions and hallucinations—do not yield any support for the sense-datum theory, it does not follow that reflection on them does not yield significant conclusions about perception.

7  Problems for the dominant model The tide swung against the dominant model in the middle of the twentieth century. One important development in philosophy around the time of the Second World War was the emergence of what might be called theories of ‘anti-theory’. By that I mean the conviction shared by both the approaches of Wittgenstein and Austin that philosophy should not engage in strong positive theorizing. It is not entirely easy to say why these influential philosophers accepted this idea, but both of them took what I have been calling the dominant model as an example of bad positive philosophizing. Austin’s Sense and Sensibilia is a more or less totally negative engagement with the dominant model in which he displays his massive talents as a critic. Wittgenstein hammered away at the model repeatedly in his discussion of philosophy of mind.21 Although the philosophy of anti-philosophy did not last it did leave as its legacy the abiding conviction that the sense-datum theory was not a good theory. Moreover, one very fundamental conviction of the philosophy that succeeded it was a commitment to materialism, and the sense-datum model did not fit that approach. Sense-data as characterized in the theory did not seem to be entities that a materialist could countenance. This shift cemented the fate of the model. An important point to note at this stage is that although there is a branch of philosophy called ‘the philosophy of perception’ its own proper home is as a branch within the philosophy of mind. Perception is simply a very basic and central psychological phenomenon. In many ways the fundamental constraints that shape our thinking here have to be those which are central to our understanding of the mind generally. And it is quite clear that no proper psychological theory can postulate an unanalysed psychological relation with mysterious properties at the heart of its analysis of any psychological phenomenon. These are remarks about intellectual history and basic assumption, which are, I hope, illuminating. But I want to develop what I think of as another real problem for the theory.

20  Austin’s

example blocks basing the generalizing step (in the argument from hallucination) on anything like subjective similarity or indistinguishability. More recently, the generalizing step has been grounded in causal considerations (see Robinson, 1994: ch. 6). The attitude to that development implied by the present argument is that his strengthening, should it be a strengthening, cannot aid the case for sense-data, since they do not get into a correct account of the base cases. It might, however, aid the derivation of other conclusions based on hallucinations. 21  I have tried to analyse Wittgenstein’s views in Snowdon (2011).

130   Paul Snowdon I have suggested that the sense-datum theory is best thought of as a theory of appearances. Now, when we focus on appearance reports it seems quite appropriate to talk of the content of an appearance. Thus, if I say that it looks to S as if there is a red patch I can gloss that report as saying that the content of the appearance is that there is a red patch. This is as natural as saying, as practically all philosophers do, that the content of the belief that P is (that) P. This allows us to say that what the sense-datum model offers is a theory of the content of appearances. But the structure of the theory can be conveyed using a terminology, that of content and vehicle, that has recently emerged and which is, I suggest, very helpful.22 We can talk of the sense-datum as the vehicle, the item, to which properties are being ascribed to generate the content of appearance. The idea is that the properties of the vehicle match and explain the content. Now given the commitments of the model under investigation to the idea of the transparency of the psychological relation, the act bearing on the object, it follows that there is a tight relation between the content and the postulated vehicle. Roughly, any element in the content of the appearance must correspond to the presence of a corresponding quality or feature belonging to the vehicle, otherwise that aspect of content has not been explained, and any quality of the vehicle must have a corresponding role in the content, otherwise the ‘act’ has lost its transparency. This leads to two enormous difficulties for the model. The first is that there are properties ascribed to the object that are not mirrored in appearance. Thus the vehicle is supposed to be private, inner, and dependent for its existence on awareness, but no one would suggest that in normal appearances anything is present corresponding to those aspects. Now, the obvious reply to this is to suggest that some aspects or properties of the sense-datum are ‘conveyed’ or ‘captured’ by the transparent act, whereas other, for example the ontological status of the entity, are not. There is no simple way to block this proposal. But, first, not all ‘sense-datum’ theorists do draw this distinction.23 Second, such a distinction cannot just be asserted but needs properly explaining, and it remains unclear what that explanation would be. What is going on here is that the theorist simply assumes they can draw a distinction which does apply to ordinary perception, that is the distinction between the features or aspects of things that perception acquaints us with and those that it does not. But the explanation of that distinction rests on assumptions about the nature and processes involved in ordinary perception which cannot be drawn on when thinking about the pure apprehending relation. More important, though, is that there are, or seem to be, properties of appearance which are not mirrored by matching qualities in the object. One very interesting case is that of what might be called the indeterminacy of appearance. Consider the following case. I can see, as we would say, two lines, A and B, on a surface in front of me. Imagine 22  This terminology is now popular and its employment widespread but a very helpful exposition of it can be found in Millikan (1991). 23  See for example Hume (1964), Bk 1, Pt 4, s 2, p. 185. As Hume puts it: ‘Add to this, that every impression, external or internal, passions, affections, sensations, pains, and pleasures, are originally on the same footing; and that whatever other differences we may observe among them, they appear, all of them, in their true colours, as impressions or perceptions.’ The last part of this sentence is, in effect, endorsing the implication of the model that since they are impressions they exhibit their status as impressions.

Sense-Data   131 that A and B are quite far apart. I look at the lines carefully, but there and then I could not say whether the lines are equal in length or different. If they are different I cannot say which is longer. How should we describe the appearances in such a case? Since, however carefully I attend, I cannot tell what the relation is between the lengths of the lines, it seems to me that the correct appearance or looks judgement is that A and B do not look to be the same length, but they also do not look to be different lengths. Put simply, in appearance A and B are neither the same nor different. We can put this by saying that there is an indeterminacy in the perceptual appearance; appearances leave their relative lengths indeterminate. Now, since it is important in developing this criticism that the indeterminacy of appearance claim is granted, it is helpful to compare appearances with the case of belief and with the case of the objects themselves. It is clear, surely, that the beliefs of a single subject might be described as being indeterminate about the relative lengths of A and B. This would be the case if the believer believed that A and B both have lengths but he or she had no further beliefs about their lengths. It can thus be indeterminate according to a belief system what their relative lengths are. If we think, though, about the lines themselves we would be inclined to say that it cannot be indeterminate in fact how their lengths are related. Either A is longer, or B is longer, or they are the same length. We have, therefore, no indeterminacies in the world (at this level) but we can have indeterminacies of content within belief systems (or theories). The question is into which category do episodes of perceptual appearing belong. Now it clearly does not settle this question to point out that perceptual episodes are natural physical episodes and hence are determinate occurrences. The same is true, we can say, of belief and of speech, cases where content can be indeterminate. Basically, the rule, I  suggest, is that if an appearance (in a perceptual episode) does not enable the subject to come to an opinion as to whether a claim P is true or not, given the ability to concentrate and take their time (and told to take nothing else into account other than how things appear), then it cannot be correct to characterize the appearance as being one as of P’s being true. Thus, if in an appearance to a subject the subject simply cannot estimate which of two objects is further away, we conclude that neither of the objects looks to the subject further away. I am suggesting that that is a basic principle (or close to a basic principle) of appearance ascription. If that is accepted the sense-datum model itself faces a deep problem. Given that the act or psychological relation is itself purely transparent, and given that the actual lines on the internal vehicle have to be determinately related, it cannot be that there is an indeterminacy in appearance. Although the language that has been employed to express this criticism is located in current theories of mind the point being made is one that proponents of act/object analyses of mental phenomena have been grappling with for centuries. It is precisely this type of problem that proponents of imagistic or idea-based theories of thought and language understanding, such as Locke, Berkeley, and Hume, faced in the seventeenth and eighteenth centuries. Berkeley’s key insight in his dispute with Locke about abstract ideas is that single determinate images cannot be the vehicles for general thought. His question is: how can the presence before the mind of a determinately coloured red image ground that relatively indeterminate thought that something is, simply,

132   Paul Snowdon red?24 This problem struck these thinkers in relation to the content of thought (and language) because the generality of thought is hard to miss, whereas, what we might call the generality of perception (and experience) is not quite so obvious. What is the correct response to this problem? The correct response, I want to suggest, is to abandon the act/object structure as the form of the analysis of experience. In fact we can then employ what is called an adverbial analysis. In effect that name stands for nothing more definite than approaches which do not treat it as involving an object and an act. It should not be thought, though, that this means no experiences have an act/object structure, but when they do the act component ought not to be thought of as transparent in the sense that it reveals in a perfect way the character of the object.25 It is essential that we think of such cases, if we wish to acknowledge them, involving an ‘act’ that permits illusions and distortions. There are two other, and related, problems with the model that I wish to highlight. I have been concentrating in the discussion and exposition of the sense-datum theory on the visual case, as is standard with that model, and I want to continue to do so in order to make the next point. When sense-datum theorists think about visual experience they deny that in it things look to be located in three-dimensional space.26 No object can strictly look to be behind or further away than another. Here for example is Locke struggling with the problem: So that from that, which truly is variety of shadow or colour, collecting the figure, it makes it pass for a mark of Figure, and frames to it self the perception of a convex Figure, and an uniform colour; when the Idea we receive from thence, is only a Plain variously colour’d, as is evident in Painting.27

In fact, in this passage Locke is trying to be true to his sense of the manifest character of visual experience, which is that it is three dimensional, but also to be true to what his model fundamentally commits him to, which is that it is not. The commitment of the model is clear towards the end, where Locke says that the idea is what we would describe as a ‘plane’, a two-dimensional structure, which can be compared to a painting, and what it presents is ‘truly’ a variety of colours. But he tries to escape this problem, a task that is a measure of Locke’s own commitment to respecting the truth, by suggesting just before this quotation, that ‘the Ideas we receive by sensation, are often in grown People alter’d by the Judgement, without our taking notice of it’. In effect, in making this suggestion Locke is grafting onto his basic model a modification (or addition) that it cannot incorporate. For, how can an idea be modified by judgement? Indeed, what modification along spatial lines is possible for the idea? Locke’s real commitment comes out when he tells us what ‘truly’ the idea we receive is like, namely a ‘variety of colour’. For Locke the real significance of Molyneux’s 24  I do not mean to suggest that Berkeley himself had a solution to this problem which was better than Locke’s. The general conclusion should in fact be that the basic model in terms of which they were thinking of the problem is fatally flawed and should be abandoned. 25  Talk of transparency in the theory of experience is tricky. Some mean by it that the experience is itself, as one might say, invisible. Whereas others mean the experience simply opens up the complete reality of the object. It is the second sort of transparency that needs eliminating. 26  Mohan Matthen has correctly reminded me that Frank Jackson is an exception to this description. His theory of sense-data located them in public space. I  can here only voice the suspicion that this characterization does not cohere with the other supposed properties of sense-data, nor with our understanding of public space.    27  Locke (1975), Bk 2, ch 9, s 8.

Sense-Data   133 famous question, to which he immediately turns, is that there is no depth in basic visual experience, and it is only after experience and learning, that someone can ‘distinguish’ on the basis of sight between a sphere and a cube. The upshot of E. J. Gibson’s famous Visual Cliff experiment is that it suggests that visual perception of depth does not depend on learning, contrary to one commitment of Locke’s theory.28 The moral of this discussion, illustrated by the very interesting case of Locke, is that the standard sense-datum model, in which the visually apprehended entity is a two-dimensional picture-like plane, cannot accommodate the rich and obvious three-dimensional character of visual experience (and not simply of adult visual experience). This is serious, because ultimately any model of perception has to be judged by its ability to explain the evident role that perception has for us, which is to inform us of our environment. It is a serious failing that the sense-datum model cannot satisfactorily do this for a central aspect of vision. We can, I  think, by reflecting on the consequences of this problem reveal two other serious drawbacks to the sense-datum model. The sense-datum theorists face the further question; if visual experience is two dimensional, is any human mode of experience three dimensional? If it is said that none is the one problem that arises is how we are led to think of our environment as spatially three dimensional. If no experiences indicate that why should we think that way? The second problem is that it is very hard to deny that tactile experience and our awareness of our own bodies is three dimensional. Indeed, those who viewed vision as, strictly, two dimensional usually regarded tactile experience as the source for us of awareness of three-dimensional space. But that element in their view brings with it a deep puzzle. If the quality of experience within an act/object model is explained by the real character of the ‘object’ how can we conceive of the object in such three-dimensional experience? It is not genuinely in space or spatial, being a sense-datum, but it cannot be conceived of as plane-like, since then no three-dimensional layout can be presented. It is a manifestly mysterious thing—a thing so mysterious that we can only say that there is no coherent model for this sort of case.29 With that problem in mind—the problem of no coherent model for the tactile/bodily case—we can consider another case, say that of olfaction. In this case the sense-datum theorist has to postulate an inner mental entity that ‘presents’ olfactory features to the subject. That specification fixes a role for the postulated object, but it does not enable us to envisage its nature. How does it do this? What kind of thing is it? The truth seems to be that we have no way of understanding an inner mental item which presents to the subject the qualities within olfactory experience other than by simply thinking of it as an ‘inner smell’. But it is clear that there is something deeply unsatisfactory about such a conception. The problem I want to highlight is not to do with the idea of an ‘inner smell’ which depends for its existence on the awareness of it, something quite unlike normal smells and, arguably, a genuine difficulty, but rather with making sense of the possibility of an item which is outside real

28  For

a description and very interesting discussion of the visual cliff experiment, see Gibson (1986: 157–159), and also Gibson and Walk (1960: 67–71). 29  The difficulty in this case for the sense-datum model perhaps lies behind a persistent tendency, when thinking about the ‘location’ of sensations, such as pain, for philosophers to treat their ‘location’ as something not felt or experienced, unlike the ‘painfulness’, but rather, as it were, added solely by the spatial reaction of the subject, in, for example, rubbing a certain part of the body in response to the pain. In truth, the pain is experienced as located.

134   Paul Snowdon space, outside all normal causal relations, and without the real nature, whatever it is, of real smells, but which has the property of being, as it were, ‘smelly’. I suggest that we should wonder whether this is a model that makes sense. It involves ascribing a property when it is completely detached from the circumstances and groundings and dispositions which sustain our understanding of its presence normally. It has to be conceded that since there are no established principles about what really makes sense, it cannot be demonstrated that this hypothesis lacks sense. The issue that remains is what sort of object is it that presents to the subject the qualities of smell (but which is not a real smell)? It seems to me that no answer to this question is forthcoming. Why did a similar problem not occur to the sense-datum theorists when they were thinking about the visual case? It is as hard, really, to understand the presence of colour on an inner item quite detached from those conditions in the world which ground or are associated with colour, as it is to understand the presence of smells. What disguised this, I want to suggest, is that they possessed a real model for their theoretical model, which is the existence of pictures, which are two-dimensional surfaces (or planes) which give us visual experiences that can resemble those that vision normally gives us. The familiarity of this phenomenon generates the impression that we understand the way an internal picture, a sense-datum, can generate visual experience. In reality this overlooks three important things. The first thing overlooked is that if the existence of real pictures enables some sense to be made of an ‘inner picture’ model of visual cases there simply is nothing analogous to pictures in non-visual experience which might confer sense on the role of an ‘inner’ representation in those cases. There is, for example, nothing that stands to a real sound as a picture stands to a real scene.30 Second, as suggested above, there is no obvious way to credit ‘inner’ sense-data with the properties of colour which are what actual pictures have. And, third, as Wittgenstein pointed out, there is much in our experience of pictures that is not fixed by the picture itself. Thus, I can see it as a rabbit or as a duck. It is simply an illusion to think that visual experience can come down to a transparent apprehension of a coloured plane. What I have been suggesting is that as we think our way deeper into the model it stands revealed as unable to cope with the difficulties that emerge.

8 Conclusion We have known at least since Austin how to respond to the arguments in favour of sense-data, and we have gradually seen the difficulties in the conception, something that Austin explored less. We have, perhaps, also developed some understanding of the appeal

30 

Mohan Matthen has pointed out to me that this comparison between vision and hearing is much more complicated than the argument in the text acknowledges. The existence of pictures in our lives depends on the fact that the three-dimensional world around us actually contains two-dimensional surfaces, that these surfaces have causal properties that enable us to mark them in certain ways, and that our perceptual system responds to such marked objects in certain ways. In the world of sound there is nothing like the first contrast, nor do sounds have similar causal properties. But it is true that we can create sounds which seem to be of things they are not of. What needs more thought is whether this fact weakens the contrast.

Sense-Data   135 of the view. However, the main conclusion, which is not news, is that the sense-datum conception is unacceptable, and should be rejected. This is, though, in many ways a rather limited conclusion. Roughly, we can say that the sense-datum tradition in philosophy arose from combining two fundamental ideas. The first idea is that the experiential core of perception is the occurrence in subjects of states which can be described as sensations; the second idea is that any experience has to include an object of which the subject is aware and which presents the qualities inherent in the experience to the subject. The drift of the present discussion is that this second, highly appealing but disastrous model is wrong, but in itself that claim leaves the first idea untouched. How we should think of the nature of perceptual experience other than as not consisting in the transparent apprehension of a sense-datum remains open.31

References Austin, J. L. (1962). Sense and Sensibilia. Oxford: Oxford University Press. Ayer, A. J. (1940). Foundations of Empirical Knowledge. London: Macmillan. Ayer, A. J. (1956). Problems of Knowledge. London: Penguin. Baldwin, T. (1990). G. E. Moore. London: RKP. Berkeley, G. (1734). The Principles of Human Knowledge. In M. R. Ayers (ed.), George Berkeley Philosophical Works. London: Dent. Flew, A. (ed.) (1960). Logic and Language (First Series). Oxford: Blackwell. Gibson, E. J. and Walk, R. D. (1960). ‘The visual cliff’. Scientific American, 202. Gibson, J. J. (1986). The Ecological Approach to Visual Perception. Hillsdale, NJ: Lawrence Erlbaum Associates. Hume, D. (1964). A Treatise of Human Nature. London: Dent. Locke, J. (1975). Essay Concerning Human Understanding. Oxford: Clarendon Press. Millikan, R. (1991). ‘Perceptual content and Fregean myth’. Mind, 100(4), 439–459. Moore, G. E. (1903). ‘The refutation of idealism’. In G. E. Moore (ed.), Philosophical Studies (pp. 1–30). London: RKP. Paul, G. A. (1936). ‘Is there a problem about sense-data?’ Aristotelian Society Supplementary Proceedings. Pitcher, G. (1971). A Theory of Perception. Princeton: Princeton University Press. Robinson, H. (1994). Perception. London: RKP. Russell, B. (1912). Problems of Philosophy. London: Oxford University Press. Snowdon, P. F. (1992). ‘How to interpret "direct perception"’. In T. Crane (ed.), The Contents of Experience. Cambridge: Cambridge University Press. Snowdon, P. F. (2011). ‘Private experience and sense data’. In O. Kuusela and M. McGinn (eds), The Oxford Handbook of Wittgenstein. Oxford: Oxford University Press.

31  I wish to thank Mohan Matthen for the invitation to contribute to this volume and also for his encouragement and help with the chapter itself. I wish to thank Craig French, Mike Martin, Mark Kalderon, and Howard Robinson for discussions over the past few years which have influenced my thinking about sense-data.

Chapter 7

Phenom enol ogica l A pproaches Charles Siewert

1 Introduction Phenomenology (as a philosophical movement or tradition) originated in the late nineteenth century, partly in an effort to find philosophy’s place in a culture increasingly dominated by experimental science and technology—and in dialogue (sometimes in tension) with an emerging academic psychology. Beginning with Franz Brentano, phenomenology seeks an elucidation of just what the phenomena are that psychology purports to explain, via inquiry anchored in an understanding of mind available from the first person point of view. From this perspective experience or consciousness is seen as fundamentally ‘intentional’: it refers to or is directed at objects. Just how to describe this ‘intentionality’ and its forms becomes a basic theme. Beginning with Edmund Husserl, the intentionality of perception is investigated by asking: how can experience, itself in near constant flux, nonetheless be of stable objects, so that meaning and knowledge might be possible for us? The key to answering this question, he proposes, is to see perceptual consciousness as dynamic and prospective—a process wherein the needed constancies are achieved via the successful anticipation of further experience through movement and direction of attention. This conception of Husserl’s—with its emphasis on the experience of one’s own body—helped inspire Maurice Merleau-Ponty’s important mid-twentieth-century contribution to phenomenology. The following is a summary of approaches to perception (in Brentano, Husserl, and Merleau-Ponty) that are central to the phenomenological tradition, closing with a brief reference to recent work that interprets, stems from, or neighbours it.

2 Brentano Brentano’s philosophy has such continuity with what his student Husserl called ‘phenomenology’ that the term is fitting for both, though Brentano himself rarely used it, and

Phenomenological Approaches   137 generally preferred to call his approach ‘descriptive psychology’. But this label could be misleading. Psychological description in his sense does not (as one might think) consist in saying what happens at a particular time in an individual’s mind. Rather Brentano purports to describe mental phenomena by identifying their fundamental kinds—to tell us what distinguishes them, and how they are necessarily related to one another. And he conducts ‘psychology’ not by performing experiments, but largely through philosophical dialectic reliant on first-person reflection—necessary, he thought, for clarity about the domain of experimental research. In Brentano’s view descriptive psychology or phenomenology is in this way foundational for explanatory or ‘genetic’ psychology, and crucial to the development of logic, ethics, and aesthetics. It must, he thought, draw on a first person understanding of the phenomena to be taxonomized, because this gives us our basic grasp of what we are talking about when we talk about, for example, consciousness, perception, or judgement (Brentano 1972: 29, 128). He attempts to justify his account of mental kinds by illustrating them in ways we are invited to confirm with reference to our own first person experience, and by continually seeking out puzzles and objections, responding to these with detailed argument. But what is the general notion of perception that Brentano proposes? He was convinced by modern philosophy and science that the actual denizens of space and time do not, in fact, bear the qualities (such as colour or smell) that sensibly appear to us. But his irrealism was also shaped by Aristotle’s doctrine that in perception the sense organ receives the ‘form’ of a sensible thing (e.g. the form of a colour) without its ‘matter’. In adapting ancient and scholastic conceptions, Brentano was led to the single most important aspect of his approach to perception—a revival of the notion of intentionality or (as he would put it) ‘intentional inexistence’ (1972: 88). For Brentano, red (for instance) exists ‘in mind’, as an accusative of ‘mental reference’, even though no individual, mental or otherwise, is in fact red. Thus he thinks, more generally, what is perceived in the case of ‘outer’ (e.g. visual) perception is not an individual private to someone’s mind that unfailingly is just the way it appears, like the ‘sense-data’ of the empiricist tradition. On Brentano’s view, the colours that are presented to us in vision exist ‘in our minds’, but this does not mean that there are coloured things to be found there: when red appears to you, the way it exists in your mind is nothing like the way it is supposed to exist in a tomato. (It should be noted, however, that the interpretation of Brentano’s view on this key point is problematic, and some accounts (see Brandl 2005) would place him closer to sense-data theories than is done here.) The notion of existence ‘in the mind’ or ‘intentional in-existence’ gives rise to a number of logical and ontological quandaries variously addressed by philosophers Brentano directly influenced. Brentano himself eventually abandoned the idea that mental reference should be understood in terms of a distinctive ‘intentional’ mode of existence. But his neo-Scholastic turn had this lasting modern legacy: he implanted in phenomenology the notion that perceiving can be understood as a ‘directedness’ or ‘reference’ to what putatively exists beyond the mind, rather than as an immediate awareness of what actually exists inside it. To understand Brentano’s ‘intentionalist’ view of perception, one needs a grip on his distinction between judgement and ‘presentation’. Not only perception, but all mental phenomena, he held, are intentional in his sense, because they either consist in or include a presentation that refers to an object—an ‘appearance’ of it in the broadest sense (1972:  81,  198). This encompasses the appearing of something one sees, or visualizes in

138   Charles Siewert imagination, or even only entertains a thought about. Merely to have a presentation of an object involves no commitment to its existence. To make this commitment, to judge there is a blue sphere, say, one must, in addition, affirm or accept the object so apparent—a blue sphere (and this is at least part of what distinguishes perceiving from imagining). For Brentano all perception is a form of judgement, in which something presented is affirmed. When a blue sphere is visually apparent to you, and you accept what is apparent, you perceive a blue sphere. And for Brentano, this very perceiving also presents itself to you, and you accept (and thus perceive) that as well. Thus he maintains that in addition to ‘outer’ perception of physical phenomena (like colour and shape) there is ‘inner’ perception of mental phenomena (such as the appearance of colour and shape). Brentano holds that, as a matter of fact (though not of necessity) all of our outer perceptions implicitly contain inner perceptions of themselves. And on his account, for a mental act to be internally perceived is just what it is for it to be conscious (1972: 100–29, 275–277). In response to the worry that he over-intellectualizes perception by making it a form of judgement, Brentano argues that the mere acceptance of an object presented is an effortless, cognitively primitive feat; it does not require an act of ‘synthesis’ whereby one subsumes an object, together with others, under a concept, in virtue of their similarity (1972: 141–142). In this sense judgement (hence perception) can be ‘non-conceptual’. This point holds for both inner and outer perception. The two, however, do differ in (methodologically) significant respects, according to Brentano. Whereas we can, through outer perception, make observations, we cannot, in inner perception, strictly speaking, concurrently ‘observe’ our own minds at all. This is because observing something involves increasing attention to it so as to discover how it already is, and any attempt to thus attend to one’s own current mental phenomena will (Brentano claims) alter what one wants to reveal (1972:  29–30). (This does not mean, for Brentano, that one cannot ‘notice’ one’s own perceiving and thinking as it occurs.) But even though inner perception cannot, like outer perception, constitute observation, it has the following advantage over it. In outer perception there generally is no real object that is just as it is presented, while in inner perception appearance and reality inevitably coincide (1972: 3, 10, 19–20). So, our understanding of the terms by which we describe our minds (unlike our understanding of those by which we describe external things) is grounded in a kind of constant implicit self-perception wherein things invariably appear (and are accepted) exactly as they are in reality. However, this infallible inner perception does not guarantee the correctness of whatever sincere first-person judgements we happen to express about what kinds of minds we have. While inner perception guarantees descriptive psychology a real subject matter, it cannot ensure this will be correctly categorized.

3 Husserl Brentano was certainly not the only major influence on Husserl’s first mature philosophical work, the Logical Investigations. But he was a singularly important one, insofar as the phenomenological approach heralded there, its aims, ‘intentionality’ as a philosophical theme, and its application to perception, all carry over ideas from Brentano—albeit substantially transformed through criticism. Although Husserl’s views on perception

Phenomenological Approaches   139 developed importantly after his Investigations, some grasp of this work is necessary to understand the basics of his approach. For Husserl phenomenology remains ‘descriptive’ in something like Brentano’s sense—it relies on critical first person reflection for understanding the categories needed for studying the mind. But Husserl thought Brentano had not fully recognized that we must sharply distinguish this enterprise from empirical psychology by explicitly rejecting all ‘psychologism’. As Husserl understood it, psychologism in its most basic form holds that principles of logical inference ultimately concern (or are justified by reference to) inductively discoverable processes in actual psychological subjects. Such an attempt to subordinate logic to psychology he saw as an intellectual disaster, for it leads to a relativism about truth that would undermine the rational presuppositions of all theoretical inquiry, and circularly assumes, in its search for the laws of mental processes, the very norms of reason it purports to legitimize. The defining task of logic, as Husserl saw it, is to investigate the presuppositions of theoretical knowledge—including those relating to meaning and perception (2001a: Prolegomena, §§1–16). Thus ‘logic’ in his sense extends well beyond the formal study of valid inference and includes (phenomenological) philosophy. To completely avoid psychologistic error, it must, Husserl thought, in all its subdivisions remain as steadfastly a priori as geometry, and hold its justification aloof from empirical claims (2001a: Prolegomena, 75–76, 149–150, 153–154, 165–166, 168–170). Husserl thus approaches perception via an a priori investigation of the possibility of knowledge. Like Brentano, he makes clarifying the ways in which perception and other mental phenomena ‘refer to objects’ central. Unlike his teacher, he bases his conception of the intentionality of perception on the idea that the objects of perceptual appearance are sensory constants presented through changes in experience. For Husserl perceptual experience is an extended temporal process with a special sort of unity constitutive of its intentionality—the understanding of which is essential to making sense of the possibility of knowledge. Husserl early on illustrates his conception of sensory constancy with reference to colour, shape, and sound (2001a: V, §§2, 14). The surface appears to you uniform, unchanging in colour, even as you experience that appearance differently depending on changes in viewing conditions. The box appears to remain the same cubical shape as you experience this appearance differently with changes in perspective. Your experience as you hear the violin’s adagio or the twittering of birds can also undergo change with attention, though the sounds heard do not thereby appear to change. This is the kind of constancy amid experiential flux that makes sensory appearance refer to an object—an object that goes beyond (‘transcends’) what is strictly speaking a part of (something ‘immanent to’) the experience. It must be emphasized that, in making perceptual constancy crucial to sensory intentionality, Husserl remains within the sphere accessible to first person reflection. He does not conceive of visual constancy as a uniformity of what is seen through change in correlative retinal stimulation. He is interested in object constancy amid experi­ ential flux, our awareness of which does not depend on our knowing anything about (e.g.) our retinas and their condition. Before seeing how Husserl developed this account further, we must consider how to align it with his general view of intentionality, the goal of which is to elucidate the intentionality of experience—where an ‘experience’ is for him a component of someone’s ‘stream of consciousness’, which he takes to include episodes of conceptual thought and volition as well as sense experience and imagery (2001a: V, §1). He starts from paradigms

140   Charles Siewert of ‘intentional mental acts’ Brentano would recognize, including perception, but also judgement, doubt, love, imagination, etc., and the Brentanian observation that in each case we may look to the accusative of the corresponding verb to identify what the act is ‘directed toward’—its object of reference: in judgement something is judged (about), in loved something loved, in imagination something imagined, etc. (2001a: V, §10). The fundamental points for Husserl then are these. First, we must distinguish between the object to which the act refers, and the object as it is referred to—that is, the manner in which the act is directed towards it (2001a: V, §17). Husserl illustrates this with an example in which the object to which two thoughts refer—the German Kaiser—is the same, though he is differently thought of: alternately as the son of Emperor Frederick III, and as the grandson of Queen Victoria. He then goes on to distinguish two important general ways in which the manner of reference may be the same or differ—one (just illustrated) involves a difference in the ‘matter’ or ‘interpretive sense’ of the act, a difference in ‘as what’ the object is referred to. The other involves a sameness or difference in ‘act quality’. (2001a: V, §§20– 21). For example, one may judge that the Kaiser is the grandson of Queen Victoria—and one may also doubt or wonder whether he is. Here we see the matter/sense of the mental acts remains the same, though they differ in quality. Likewise, quality may remain the same while matter varies. We see here too that the matter of an act can correspond to a whole proposition. (Husserl would say that the object to which the act refers is typically not a proposition, but the state of affairs that makes it true.) Finally, every intentional experience must have both quality and matter, and in virtue of this has intentionality or mental reference. However, it is not necessary that there exist an object to which such an act refers. It may be true that you are thinking of the god Jupiter, and what your experience refers to is Jupiter, but this does not entail that there is someone—the god Jupiter—of whom you are thinking (2001a: V, §11). This basic picture is elaborated and revised in elusive ways post-Investigations, when (in Ideas I (1982)) Husserl replaces his ‘matter/quality’ terminology with talk of an act’s ‘noema’ and its components. But leaving these complications aside, we can see how Husserl’s quality/matter schema raises questions about the relationship between thought and judgement on the one hand, and sense experience on the other. On his view, much as what is thought about is thought of as something, what is perceptually apparent also appears to one as something—the appearance involves an ‘interpretation’; it has an ‘interpretive sense’. But are we in either case to regard this as a ‘conceptualization’ of the object? Is the content of perception also ‘conceptual’? And just as we say someone judges that the paper is white, and distinguish the matter/sense/content of this judgement from the state of affairs judged, may we also say someone sees that the paper is white, attributing to one’s visual experience the very same content and object as that of the judgement? Husserl’s Sixth Logical Investigation bears on such questions, but the discussion is tentative and its interpretation uncertain. For present purposes we may limit ourselves to the following. Husserl discusses perception’s role in understanding the reference of demonstrative expressions such as ‘this’ and ‘that’ (and so its role in forming the thoughts they express)— and he holds that the way that we experience the object picked out by ‘this’ so as to understand the reference cannot be expressed in terms of general concepts applied to the object; intentional experience here involves what he calls a ‘non-attributive’ sense (2001a:  I, §§24–27, VI, §5) Further, there is indeed, for Husserl, an experience of seeing that the paper is white, as distinct both from one of judging that the paper is white, and of merely seeing

Phenomenological Approaches   141 the white paper. He uses this ‘seeing that’ locution not to invoke a ‘factive’ sense of ‘see’, but to indicate that the experience is ‘categorially’ structured, and ‘predicative’—which is not guaranteed, for Husserl, by an object’s merely appearing ‘as’ something in a ‘straightforward’ perception. Seeing that—a ‘categorial’ perception—essentially involves (is ‘founded on’) such ‘straightforward’ perception of an object—for example seeing the white paper. This latter, basic object identification is made possible, again, through the sort of constancy phenomenon discussed earlier, distinctive of sensory appearance. This sensory appearance constitutes one form of ‘intuition’ of an object, where ‘intuitive’ intentional experiences have the distinctive role of ‘fulfilling’ other intentional experience, in the sense in which the visual appearance of white paper ‘fulfils’ the judgement that there is some white paper by (to some extent) confirming or warranting it. Husserl recognizes that to get from merely seeing the white paper to seeing that the paper is white (so as to confirm the corresponding judgement)—that is, to move from straightforward to ‘categorial’ perception—one cannot simply pile up object perceptions—as if (absurdly) seeing that the paper is white consisted in seeing three items corresponding to: ‘the paper’, ‘is’, and ‘white.’ Husserl proposes to understand the epistemically crucial link between mere object perception and categorial perception via a kind of sensory attention in which an individual aspect of the object is ‘cast into relief’—you may, he says, be struck by the ‘peculiar colouring’ or ‘noble form’ of an object seen, in a way that does not necessarily involve applying a ‘general presentation’ of the specific type of colour or form involved. Now, however, not just seeing the white paper, but in this special way attending to the paper—seeing the white in the paper—makes it possible for us to acquire concepts from experience and—once those concepts are possessed—it enables one also to see that something is the case, that is, to have a form of categorial perception (2001a: II, §21, VI, §§40–43, 45–48). Subsequent to the Investigations, Husserl enriches his conception of the type of unity in experience over time that makes object perception possible, and allows us to confirm or disconfirm (‘fulfil’ or ‘frustrate’) prior experience through later experience. His idea that all perception involves an ‘indeterminate’ ‘horizon’ whereby future experience is ‘anticipated’ is crucial here (1982: §§24, 35, 41, 113; 2001b: §§1–3). Husserl’s notion of horizon includes a recognition that there is a ‘field’ of visual experience with a ‘fringe’, ‘margin’, or ‘periphery’ where what appears, appears less determinately in its features—for example, shape, size, location—than does what one is focusing on, what one is looking at. But the area of what is less determinately apparent is not confined to some region at the limits of what is experienced—a ‘fringe’. For example, as one looks at a series of words in a text as one is reading, the horizon of one’s experience would include the area immediately surrounding whatever bit of the text one is looking at, as well as the area within it—for the individual letters and their parts are not as determinately apparent as they would be if one focused on each letter individually, as typically one does not. Further, the visual horizon ordinarily includes not only the indeterminately but still visually apparent surfaces and areas before one, but also non-apparent sides and parts of what appears. For on Husserl’s view, part of what makes your perspectivally varying, temporally extended visual experience refer to an object at least partially constant in its spatial features is your successful ongoing ‘anticipation’ of the appearance of its as-yet-hidden, unapparent aspects. Specifically what shape, texture, etc. you visually anticipate on the far side of the object you are looking at is left fairly open—quite indeterminate relative to the appearance of the sides so far facing you. On the other hand, you do not merely anticipate ‘some surface contour or

142   Charles Siewert other’. Some future appearances would reveal the earlier experience to be illusory—by running contrary to what was anticipated—one would, we might say, ‘experience (visual) disillusionment’. This links to the idea that perceptual experience involves an ‘interpretive sense’ (a part of what Husserl came to call the ‘noema’). The sense of your visual experience—what you experience the thing seen as—will ‘predelineate’ the range of how it can appear from additional perspectives while these appearances still remain in ‘harmony’ with those that have gone before. In texts such as Thing and Space (1997) and Ideas II (1989) Husserl emphasizes the uniqueness of the experience of one’s own body and connects this to his notions of perceptual horizons and anticipation. He draws a distinction between the Körper—your body as an object among others, site of various physico-chemical processes—and the Leib—your body as you yourself experience it in normal active life. The latter sort of bodily self-experience is involved in the sort of the anticipation essential to sensory intentionality. For how one anticipates the hidden or less determinately apparent aspects of an object will appear is somehow contingent on one’s movement with respect to it—and one experiences the fulfilment (or frustration) of such anticipations through the experience of one’s own body and its movement. For Husserl then, what is experienced as in space is experienced as having hidden or relatively more determinately experiencable aspects; spatial experience is thus, in this sense, essentially partial, perspectival. He then takes this, in turn, to justify his conception of proper phenomenological method, since it shows that no fulfilment of past spatial experience through satisfied anticipations of future experience is ever complete—ever, in his terms, ‘adequate’. Future experience can always offer past experience something more in the way of confirmation, and the prospect of disconfirmation of past appearances is never entirely ruled out. Husserl seems to infer from this that it is possible to philosophize about experience while suspending commitment to the existence of particular objects in the natural world that it reveals—and by means of this ‘phenomenological reduction’ achieve the sort of epistemic independence from assertions about them he thought his a priori investigation needed (1982: §§42–50). This understanding of the essence of spatial experience and its methodological significance joins with a view of self-awareness that reworks themes from Brentano’s account of inner perception. For multiple reasons Husserl rejects Brentano’s presentation/judgement analysis of perception generally, as well as the idea that our perceptual appearings themselves appear to us in a univocal sense of ‘appear’ and are continually objects of reflexive judgement (2001a: V, ch. 3). Thus he rejects Brentano’s notions of inner perception and consciousness. However, Husserl does maintain analogues of Brentano’s contrast between inner and outer perception, and his notion that all consciousness involves inner perception. For Husserl holds that while it is conceivable that there are no spatial objects one has actually experienced though one has an intact stream of consciousness—even then, one retains a primitive kind of consciousness of one’s own experience that is present in all experience. And Husserl says that when one is, in this way, conscious of experience, one cannot conceivably lack actual experience that is just as one is conscious of it being. A key difference between Brentano and Husserl here lies in the fact that for Husserl this primitive, ubiquitous consciousness of one’s own experience does not render it a continual object of appearance or of judgement—this is a ‘non-objectivating’ consciousness of one’s own experience. Nonetheless, this basic ‘self-givenness’ of experience, in which it—unlike

Phenomenological Approaches   143 its spatial objects—are ‘adequately’ (i.e. incorrigibly) evident, plays a role in grounding the conception of consciousness that his phenomenology aims to articulate, similar to that played by Brentanian self-presentation (1982: §§33, 34, 42, 46, 49, 138). The views just sketched might seem to oppose what in contemporary terms would be styled an ‘externalist’ doctrine about perceptual experience and its content. That is, it might seem that, for Husserl, no finite spatial experience, understood phenomenologically, ever guarantees that any actual spatial object has been perceived. Thus no ‘transcendent’ concrete particular to which a given perceptual experience may refer and by which it is fulfilled could ever be an essential constituent of such experience itself, or of its sense or noema. However, this interpretation is contested. Some (e.g. A.D. Smith 2002 and Zahavi 2003) see Husserl as committed to a ‘relationalist’ conception of perceptual experience, on which objects in space are indeed part of the content of perceptual experience, and are not left behind by methodological reduction, but retained to be considered merely under a certain ‘reduced’ aspect—namely, ‘as perceived’.

4 Merleau-Ponty Merleau-Ponty saw his main work, Phenomenology of Perception, as developing the insights of Husserl, and many of his central concepts are clearly Husserl-inspired. Merleau-Ponty’s approach is avowedly ‘descriptive’ in the sense that descends through Husserl from Brentano: phenomenology proposes to describe perception from ‘the perspective of consciousness’, rather than try to explain it from ‘the perspective of science’ (Merleau-Ponty 2012: xxi–xxii). And for Merleau-Ponty, as for Husserl, this is an effort to characterize the nature of perception as it is experienced by a perceiver—partly as a corrective to traditional theories that allegedly neglect or distort this perspective. As with Husserl, this is motivated partly by a desire to make intelligible the constancy-amid-flux sensory consciousness ordinarily exhibits—for again, perceptual object constancy is viewed as a basic form of intentionality, underlying an objective conception of the world. How is it possible for a perspectivally limited, ever-fluctuating experience to make stable objects apparent to us, constant in, for example colour, size, and shape? How can vision, for example, ‘be brought into being from somewhere, without being locked within its perspective’—so that objective thought, which common sense and science both take for granted, becomes possible? (2012: 69–74). Husserl-derived notions of ‘horizon’, of the ‘indeterminacy’ of experience, and of ‘anticipation’ all contribute to Merleau-Ponty’s answer. However, in certain respects Merleau-Ponty seems to depart significantly from Husserl’s approach. Merleau-Ponty’s text (unlike Husserl’s) is replete with references to experimental and clinical studies—particularly ones having to do with psychological deficits and pathologies—and these feature prominently in his argument. He does not see himself as bound by a strict a priorist methodology, and regards the distinction between the a priori and a posteriori as in some sense a relative matter. He holds that Husserl’s methodological reduction ‘cannot be completed’, and purports to motivate a phenomenological attitude towards perception, in which we attend to perception as we experience it, not by means of some global suspension of commitment to the reality of perceived things, but by recognition of the divergence between the character of objective sensory stimuli, proximal

144   Charles Siewert and distal, and the world as it perceptually appears to us—a divergence he thinks modern psychology helps make evident (2012: xxiv–xxviii, 7–10, 47, 51–54, 60–62). This perspective informs Merleau-Ponty’s Phenomenology from its opening pages, in which he attacks the idea of the ‘sensation as a unit of experience’—that is, of primitive non-intentional elements in experience, subject to processes of association or interpretation through judgement. Here he draws on the early Gestalt psychologists (who themselves had been influenced by Brentano’s school and by Husserl), and on the phenomenologist Aron Gurwitsch, whose lectures introduced Merleau-Ponty to Gestalt Psychology. Merleau-Ponty maintains that even simple perceptual experiences involve a distinction between ‘figure’ and ‘ground’ that goes beyond putative ‘meaningless’ sensory elements— ‘sensations’—and he argues that there is no compelling reason to posit such components of experience as subjective correlates of the perceived objects’ qualities (e.g. colours), or of proximal stimuli (e.g. retinal ‘images’)—as did those psychologists who held the ‘constancy hypothesis’ criticized by the Gestaltists. In objecting to sensations in this sense, Merleau-Ponty also in effect rejects Husserl’s idea of a primitive uninterpreted, non-intentional sensory ‘stuff’ of experience (‘sensory’ or ‘hyletic’ data). But he motivates this opposition in part by appeal to the Husserlian idea that experience is pervaded by a kind of indeterminacy incompatible with supposing its character is constituted out of a set of definite sensory qualities (2012: 6–7, 10–11). For instance, two lines, both apparent, may appear to you neither equal nor unequal in length; a person’s eyes may commonly look somehow coloured to you, even when (without a closer look) there is no specific colour they then appear to you; a many-sided crystal may well appear to you regular in its shape—although there is no specific number of sides it appears to you to have. Merleau-Ponty regards this indeterminacy of appearance as a ‘positive phenomenon’. By this he seems to mean that appearances that are similarly indeterminate with respect to specifically what is apparent (with respect, e.g., to apparent shape, size, colour) may nevertheless really differ in ways accessible to reflection. This idea figures importantly in his view of attention. He objects to the assumption that the direction of attention in perception involves merely bringing to consciousness what was already determinately in the mind—as one might shine a light on what was already there in the attic. What this misses, he thinks, is the aspect of attention exhibited constantly by the movement of our gaze, through which we learn about what is before us by enriching our experience of it: reflection reveals that what is at first only dimly prefigured in experience moves from indeterminacy to determinacy, so as to emerge more clearly for us, while what was more determinately apparent dissolves into the background (2012: 31–34). The ‘positive indeterminacy’ of experience, though ubiquitously evident in shifts of sensory attention, is nonetheless prone to neglect, since perception promotes its own oblivion by plunging our thought into the things we perceive, which makes us liable to read the determinacy of these things back into their manner of appearance. All this prepares us to understand better the notion of a visual (or more broadly a phenomenal) ‘field’. For we now see that there can be for us an indefinitely bounded region of space variously apparent in ways that cannot be cashed out in terms of a definite set of objects identified and attributed a set of properties. This connects with Merleau-Ponty’s appropriation of the Husserlian notion of ‘horizon’, and shapes his interpretation of the guiding ‘transcendental’ question he gets from Husserl, heir to Kant’s legacy, of how consciousness of objects is possible for us. While Merleau-Ponty, steeped in the Kantianism

Phenomenological Approaches   145 of his French teachers, certainly recognizes this heritage, he is determined to avoid what he sees as the ‘intellectualist’ pitfalls of their approach. This requires getting a proper phenomenological understanding of our actual experience, such as emerges from the critique of ‘traditional prejudices’, and using this to frame the challenge. When we do so, and take proper account of the positive indeterminacy of experience, we see that perspective should not be construed—in, for example, the visual case—merely in terms of what parts of the surfaces of objects are exposed to view, given one’s location. For it is far from true that even everything to be found in the facing surfaces is apparent to one. Much that is right before one’s eyes is, in a sense, ‘hidden’ by being not yet as determinately apparent as it can be. And this kind of ‘hidden-ness’ (not just the way things are hidden by being occluded) also contributes to the perspectival limitation in which perception escapes being ‘locked up’ (2012: 69–74). Just when Merleau-Ponty has posed the problem of how this escape is possible—to put it somewhat paradoxically, how there can be more to what one experiences than one experiences—his thought takes a curious turn. He does not address this central question directly. Rather he proposes we first concentrate at length on what is special about the perception of one’s own body—conjecturing that this will furnish the key to understanding our experience of everything else (2012: 74). What is special about the way I experience my body? Partly it is this: I experience a body as my own insofar as it is the body I experience whose movements seem to determine my indefinitely varying perspective on all other things, while affording me a uniquely limited capacity to vary my perspective on it (2012: 92–99). But this still leaves open questions about just how I experience this body’s movement. We might suppose that, even allowing for the special character just mentioned, my mind otherwise represents my own movements much as it represents the position and movements of other objects. The main difference is just that, in the case of my body, the position and movements represented figure in the execution of my intentions uniquely and fundamentally:  my body’s movements are those my mind chooses as basic means to the ends it sets. This is precisely the picture Merleau-Ponty defines his view against. On his account, my ordinary experienced bodily movement in the service of everyday tasks is not in this way merely the effect of some such separate internal planning, nor is it just this plus a cause of inputs to mental processes. Rather, my experienced movement is itself non-derivatively a way of understanding things; it is a way of being conscious of them, a form of intentionality, no less than the thoughts in which I may engage when reasoning—though this ‘motor intentionality’, as he calls it, is distinct in kind from the operations of the intellect. So, it’s not that I am only ‘directed at’ things through representations in my mind, which on their basis formulate commands to a certain body to attain goals it also represents. Rather, I am directed at things through the experienced (‘lived’) movements themselves—looking at things, and touching them; it is literally true then that my body thereby understands things perceived. In this sense I am one with my body: in experiencing my own bodily movement as I am engaged in looking at, touching, reaching, grasping, etc., I am conscious of myself ‘qua subject’—that is, as one who actively understands (2012: 248). His case for this position is elliptical, indirect, and still far from adequately analysed. But it seems to turn on the following considerations. First, there is an appeal to our ordinary experience of movements in executing tasks. From a phenomenological point of view, when I reach to touch my knee, I don’t need to think of how to move, and I am aware, in

146   Charles Siewert the way I am feeling myself reach, of my success (or failure) in executing my intention. When the phone rings and I answer, I ordinarily experience my effortless adjustment of posture, and reach for the phone in a way appropriate to my situation with no awareness of a selection of these movements from others possible as means to a given end. Nevertheless, I am able to smoothly adapt my movements to varying circumstances to secure the same end—all such movements equally experienced as (e.g.) ‘reaching for the phone’—as varying manifestations of a unified skill or bodily ‘habit’. Generally, I may say I experience an indefinite range of my own movements as in this and similar ways functionally equivalent. Thus I have a ‘body schema’: a systematic but open-ended capacity for engaging in patterns of movement, experienced as functionally equivalent, such as my task and situation require (2012: 100–105, 142, 149–151). But one might still think such movements are generally to be regarded as responses to commands issuing from the choices of some inner planning faculty—even if we do not experience them as such. Merleau-Ponty argues this would be a mistake. For there are several phenomena he thinks this would leave us no satisfactory way of understanding. For example, he asks, how can creatures as primitive as insects adapt their behaviour to serve their ends without deliberation (as when a beetle substitutes the action of another limb for that of one that has been severed)? Why do our habits sometimes persist when our avowed beliefs should make the futility of our alleged ‘choice’ of movement obvious (as when an amputee tries to stand on his phantom leg)? Why do severe deficits in subjects’ ability to perform bodily ‘movements to order’ nevertheless leave largely intact their capacity to exhibit similar motor activity as their everyday tasks demand it? (2012: 80–85, 105–113). Suppose we agree with Merleau-Ponty that to respond properly to such questions we must give up thinking of skilled movement as always the product of planning and commands. How should we think of it instead? His alternative is rooted in the phenomenological claim that the practical demands of your tasks are part of what you ordinarily perceive in your situation, as what you are trying to do makes certain things perceptually salient for you. For instance, as you are about to use the scissors, you see where they are to be grasped, and then you see where the material is to be cut. Generally, much as you are conscious of what is required for the completion of a pattern—such as a melody you begin to hear—you see what is to be done with what lies before you, given your goals, and you are (without deliberation, conscious or unconscious) motivated by such experience to do what is called for (to complete this ‘melody’). Moreover, given your projects, you see opportunities for action—for example, something appears to you as reachable, a space appears as a way through. (Here Merleau-Ponty’s account joins with later Gibsonian talk of perceived ‘affordances’ 2012: 108–109, 113–115). And, as you acquire more skills, your capacity to spontaneously recognize and respond to the potential offered in your situation becomes less constrained by circumstances. You acquire a liberty lacking altogether in non-human animals locked into more stereotyped responses to their environment, a sort of spontaneity degraded in human subjects whose brain damage sharply diminishes what opportunities they can perceive. Such pathological cases cast into relief our normal, culturally shaped and loosely constrained perception of the practical significance of what we encounter, which partly constitutes what it is for us not just (like other animals) to have an environment, but—as Merleau-Ponty puts it (alluding to Heidegger)—to be in the world (2012: 89–91, 131–141). On this basis Merleau-Ponty argues that it makes sense to regard movement itself as a form of understanding. For we see that movement is highly flexible or adaptive in pursuit of

Phenomenological Approaches   147 one’s goals, and experienced in a way sensitive to norms (of success or failure). And though it reflects and is guided by one’s plans and intentions, it does not simply derive its teleologically adaptive, norm-sensitive status from a causal relation to a separate goal-oriented mental activity, such as might be found in some planning subsystem. This suffices to make movement itself an exercise of ‘understanding’ in a non-trivial sense (2012: 143–148). We will resist this, if we cling to a theoretical tradition for which what is understood always includes some general idea or concept that one can understand and employ in thought even when not applying it to perceived instances. But we should recognize that what is ‘understood’ through sensorimotor activity is not a concept or rule whose formulation we might apprehend independently of its concrete application, but belongs rather to the category of ‘style’. In this sense ‘style’ is involved in understanding a work of art. We recognize that what is expressed in an artwork strongly resists paraphrase or translation into other media or languages, since it is so closely bound up with a specific sensible manner of expression. Accordingly, one cannot grasp the specific style belonging to the work without perceiving this manner of expression in a concrete instance. Similarly, we can understand the ‘style’ of our movements through which things are perceptually accessible to us, and the ‘style’ of appearance they present to us, only in performing such movements ourselves and encountering what appears; no formulation comprehensible in abstraction from such sensorimotor engagement will provide the same understanding. In this sense, the experienced unity of one’s own body in action is like the unity perceived in a work of art (2012: 149–155). In Part Two of Phenomenology of Perception, Merleau-Ponty proposes to put this conception to work illuminating a range of basic perceptual phenomena:  sensory integration; perceived orientation, depth and motion; and perceptual constancies. We can see how sensory integration is achieved within a modality—as when we resolve our double vision to see a single thing—if we think of this as the exercise of a motor understanding of how to focus and coordinate our eyes (2012: 239–242). And synaesthesia and what are now called ‘cross modal’ phenomena are most intelligible if we understand the boundaries of the sensory modalities in terms of the motor skills they involve, for this can account for how the senses interpenetrate and mutually condition one another in experience as they do (2012: 237–239, 242–244). Perception of orientated space—specifically, of ‘up and down’—also becomes, Merleau-Ponty maintains, more intelligible from the perspective of sensorimotor understanding. Working from George Stratton’s late nineteenth-century experiments, Merleau-Ponty observes that a subject wearing lenses that invert the usual pattern of retinal stimulation says (after some initial confusion), that things ‘appear upside down’. But gradually, after bodily interaction with their surroundings, he maintains that things begin to appear to him oriented more or less as before (2012: 254–265). It is legitimate to accept (as we should) the accuracy of these reports, Merleau-Ponty argues, provided that the perception of up/down orientation is constitutively dependent on the perceiver’s motor skills for dealing with what is thus oriented. Finally, consider the phenomenology of perceptual constancy. The perspectival experience of a size or shape, for instance, is not an experience of a determinate measureable size or shape, and the object does not appear to shrink as I move away, or to morph as I tour it. Thus, while I am given perspectival variation in the experience, I am not given data from which the true objective constant size or shape of a thing could be inferred—as per ‘intellectualist’ accounts of perception. Nonetheless, my perspectivally variant experience of size and shape somehow bears

148   Charles Siewert on my experience of an invariant size and shape. We can understand this, according to Merleau-Ponty, if we see it as essential to experiencing a given constant size or shape that we exercise and are set to exercise a capacity for movements (in looking at, in touching) that appropriately vary systematically with these perspectival changes in experience, so as to generate appearances of constancy. Size and shape constancy is not an inference from data, but an achievement of motor understanding (2012: 312–331). We can now see how all this yields Merleau-Ponty’s answer to the question of how experience can escape being ‘locked within its perspective’, and his take on Husserl’s notion of the sort of ‘anticipation’ of experience whose fulfilment makes sensory intentionality (and thus an objective conception and knowledge of the world) possible. One experiences a stable thing by anticipating the style of its future appearances in the style of one’s movements. This movement (of, e.g., looking and touching) is not merely derivatively prospective—it is not guided by a prediction, as by a separable representation of ‘what will happen if . . .’. Rather the movement itself constitutes the anticipation of what will appear, as when one shapes one’s grip in reaching for something ‘in anticipation’. And by successfully anticipating experience so as to sustain the appearance of a complex style of constancy (in shape, colour, position, etc.), experience is confirmed as the perception of things in the world, rather than illusion or hallucination (2012: 310–311, 349–360). Merleau-Ponty agrees with Husserl that no such fulfilment is ever complete; no experience affords us absolute certainty there is an object of which it is a correct experience, and precludes all possibility of any future reason to doubt this. However (and here perhaps he parts with Husserl) this does not mean that we can remain generally certain of the character of our own experience, while judgements about ‘the external world’ are either doubted or suspended en masse. For in recognizing the possibility of visual error in a particular case, phenomenologically I am left with a merely disjunctive characterization of my experience: either this is a case of genuine (‘factive’) seeing (there is actually (e.g.) an ashtray that I see)—and consequently my experience is essentially relational, not ontologically independent of the thing seen—or else this is a case where my experience is merely as if I am seeing a thing (I ‘seem to see it’). But I wouldn’t understand the second disjunct at all, if I did not think such experience similar to some case in which the first sort of disjunct obtains, where I took myself to genuinely see something, and the experience to be object-involving. (Merleau-Ponty’s views here might be compared to more recent ones in the neighbourhood—see Heather Logue’s entry on disjunctivism.) This, Merleau-Ponty thinks, shows that I cannot rationally, even in philosophical reflection, globally withdraw commitment to the reality of things perceived, and retreat to some certainty regarding my experience: to question whether there really is something I see is equally to put into question what sort of experience I am having, and the reality of a world transcending my experience of it is not something I can ultimately intelligibly doubt (2012: 308–311, 359–360, 393–396).

5  Related contemporary work It remains to indicate briefly some writings where one may find the phenomenological authors discussed above situated with respect to more recent philosophy, and see how the

Phenomenological Approaches   149 tradition to which they belong inspires new work. General treatments of topics in phenomenology, many relevant to philosophy of perception, and incorporating reference to recent debates, can be seen in Luft and Overgaard (2011). A diverse selection of essays representing contemporary phenomenology (several bearing on the themes discussed here) are collected in Zahavi (2012). Helpful detailed overviews of Brentano’s and Husserl’s views of perception sensitive to contemporary concerns are found in Mulligan (1995, 2004). Hopp (2011) interprets and develops Husserl’s Investigations-era views on perception to engage with current debates—particularly those stemming from the ‘conceptualist’ view of John McDowell and opposed accounts of ‘non-conceptual content’. Yoshimi (2011) develops a framework for showing how ‘the dynamics of neural activity, as described using a connectionist formalism, relate to the dynamics of consciousness, as described by Husserl’. A. D. Smith (2002, 2008) defends a theory of perception influenced by Husserl as well as an externalist reading of his position. Opposing treatments of the question regarding Husserl’s internalism or externalism are found in the recent general accounts of Husserl offered in D. W. Smith (2009) and Zahavi (2003). Controversies over the alleged ‘intellectualism’ of McDowell’s understanding of perception and action, raised by Hubert Dreyfus from his Husserl-averse, and Heideggerand Merleau-Ponty-inspired viewpoint, are variously discussed in a collection of papers (Schear 2013) in which interpretation and extension of the phenomenological tradition often figures importantly. Dreyfus (2004) explains how he takes his view of Merleau-Ponty to bear on contemporary cognitive science. Kelly (2004), Wrathall (2004), and Carman (2008) propose and defend interpretations of Merleau-Ponty influenced by Dreyfus’ perspective. Romdehn-Romluc (2007) and Siewert (2005, 2013), partly responding to Dreyfus, offer their takes on crucial aspects of Merleau-Ponty’s account. Gallagher (2005) works out his own conception of ‘body schema’, against the backdrop of his reading of phenomenology. Husserl’s and Merleau-Ponty’s writings generally provide an important background to recent work in ‘embodied cognition’. Thompson (2007) proposes one such ambitious, explicitly phenomenological ‘embodied’ view of perception, building on Husserl and Merleau-Ponty and developed in the context of the philosophy of biology and dynamic systems approaches in neuroscience. Noë’s (2004, 2012) sensorimotor view of perception and of the ‘problem of presence’, though less directly engaged with Merleau-Ponty’s account, significantly resembles it in certain respects, and raises similar issues in its challenge to orthodoxy.

References Brandl, J. (2005). ‘The Immanence Theory of Intentionality.’ In D. W. Smith and A. Thomasson (eds), Phenomenology and the Philosophy of Mind (pp. 167–182). Oxford: Oxford University Press. Brentano, F. (1972). Psychology from an Empirical Standpoint, trans. T. Rancurello, D. Terrell, and L. McAlister. London: Routledge. Carman, T. (2008). Merleau-Ponty. London: Routledge. Dreyfus, H. (2004). ‘Merleau-Ponty and Recent Cognitive Science’. In T. Carman and M. Hansen (eds), The Cambridge Companion to Merleau-Ponty (pp. 129–150). Cambridge: Cambridge University Press.

150   Charles Siewert Gallagher, S. (2005). How the Body Shapes the Mind. Oxford: Oxford University Press. Hopp, W. (2011). Perception and Knowledge:  A  Phenomenological Account. Cambridge: Cambridge University Press. Husserl, E. (1982). Ideas Pertaining to a Pure Phenomenology and to a Phenomenological Philosophy: First Book, trans F. Kersten. Dordrecht and Boston MA: Kluwer. Husserl, E. (1989). Ideas Pertaining to a Pure Phenomenology and to a Phenomenological Philosophy: Second Book, trans. R. Rojcewicz and André Schwer. Dordrecht and Boston MA: Kluwer. Husserl, E. (1997). Thing and Space: Lectures from 1907, trans. and ed. Richard Rojcewicz. Dordrecht and Boston, MA: Kluwer Academic Publishers. Husserl, E. (2001a). Logical Investigations, trans. J. Findlay. London: Routledge. Husserl, E. (2001b). Analyses Concerning Active and Passive Synthesis, trans. A. J. Steinbock. Dordrecht and Boston MA: Kluwer. Kelly, S. (2004). ‘Seeing Things in Merleau-Ponty’. In T. Carman and M. Hansen (eds), The Cambridge Companion to Merleau-Ponty (pp. 74–110). Cambridge:  Cambridge University Press. Luft, S. and Overgaard, S. (eds) (2011). The Routledge Companion to Phenomenology. London: Routledge. Merleau-Ponty, M. (2012). Phenomenology of Perception, trans. Donald A. Landes. London: Routledge. Mulligan, K. (1995). ‘Perception’. In B. Smith and D. W. Smith (eds), The Cambridge Companion to Husserl (pp. 168–238). Cambridge: Cambridge University Press. Mulligan, K. (2004). ‘Brentano on the Mind’. In D. Jacquette (ed.), The Cambridge Companion to Brentano (pp. 66–97). Cambridge: Cambridge University Press. Noë, A. (2004). Action in Perception. Cambridge, MA: MIT Press. Noë, A. (2012). Varieties of Presence. Cambridge, MA: Harvard University Press. Romdehn-Romluc, K. (2007). ‘Merleau-Ponty and the Power to Reckon with the Possible’. In T. Baldwin (ed.), Reading Merleau-Ponty (pp. 44–58). London: Routledge. Schear, J. (ed.) (2013). Mind, Reason, and Being-in-the-World: the McDowell/Dreyfus Debate. Abingdon: Routledge Press. Siewert, C. (2005). ‘Attention and Sensorimotor Intentionality’. In D. W. Smith and A.  Thomasson (eds), Phenomenology and the Philosophy of Mind (pp. 270–294). Oxford: Oxford University Press. Siewert, C. (2013). ‘Intellectualism, Experience and Motor Understanding’. In J. Schear (ed.), Mind, Reason, and Being-in-the-World: the McDowell/Dreyfu Debate (pp. 194–226). Abingdon: Routledge Press. Smith, A. D. (2002). The Problem of Perception. Cambridge MA: Harvard University Press. Smith, A. D. (2008). ‘Husserl and Externalism’. Synthese, 160, 313–333. Smith, D. W. (2009). Husserl. London: Routledge. Thompson, E. (2007). Mind in Life. Cambridge, MA: Harvard University Press. Wrathall, M. (2004). ‘Motives, Reasons and Causes’. In T. Carman and M. Hansen (eds), The Cambridge Companion to Merleau-Ponty (pp. 111–128). Cambridge: Cambridge University Press. Yoshimi. J. (2011). ‘Phenomenology and Connectionism’. Frontiers in Psychology, 2, 1–12.. Zahavi, D. (2003). Husserl’s Phenomenology. Stanford, CA: Stanford University Press. Zahavi, D. (ed.) (2012). The Oxford Handbook of Contemporary Phenomenology. Oxford: Oxford University Press.

Pa rt  I I

C ON T E M P OR A RY PH I L O S OPH IC A L A PPROAC H E S

Chapter 8

Perceptua l R epr esen tation/ Perceptua l Con ten t Bence Nanay

There are two major questions about perceptual representations: (1) Do they exist? (2) What are they?

Are there perceptual representations? Do perceptual representations exist? Twenty years ago, the vast majority of philosophers of perception would have agreed that they do, but this is no longer so. In fact, this issue seems to be one of the most widely discussed questions about perception these days (see Brogaard 2014 for the current state of the debate). I will give (a) some reasons to think perceptual representations do exist, (b) some reasons to think that they do not, and (c) some potential ways of resolving this debate. An important clarification and disclaimer before we begin: (1) and (2) are about perception in general: not just about conscious perceptual experiences but all perception, conscious and unconscious. Both debates have sometimes been hijacked by those primarily concerned about consciousness, but this is a mistake unless one is happy to deny that there are unconscious perceptual processes (see also Prinz, Chapter 19 of this volume). Those who are interested in the peculiarities of conscious perception can read Siewert, Chapter 7 and Peacocke, Chapter 9 of this volume. This chapter is about perception in general.

Representationalism Many of our mental states are representations: my belief that it is raining outside represents a putative state of affairs: that it is raining outside. If I am afraid of a tiger, this fear is also directed at, or is about, something: a tiger. In other words, many mental states refer to something, they are about something: they have content. But then it is tempting to assume that perceptual states are also representations: they also have content: if I see a cat, it would

154   Bence Nanay be natural to say that my perceptual state is about this cat. The cat (or some of the cat’s properties) is part of the content of my perceptual state.1 A further reason for being representationalist (see also Pautz 2010): it allows us to give simple explanations for illusions and hallucinations, as well as for perceptual justification. If we think of perceptual states as representations, then veridical perception amounts to having a correct perceptual representation, whereas illusion and hallucination amount to perceptual misrepresentations (not everyone thinks this is an advantage; see Brewer 2006 and see Logue, Chapter 11 of this volume for analysis). And as perceptual states are at least sometimes capable of justifying beliefs, thinking of them as representations allows us to explain perceptual justification as a relation between two different representations: a perceptual and a non-perceptual one (see also Siegel and Silins, Chapter 41 of this volume). Thinking of perceptual states as representations is also a default assumption of (mainstream) perceptual psychology and vision science (see Burge 2005 and Nanay 2014 for summaries). But some philosophers (and some psychologists) are not convinced and they conceive of perception in a non-representational manner.

Anti-representationalism Anti-representationalism is the view that there are no perceptual representations. As it is a merely negative view, the question arises: what happens when we perceive, according to the anti-representationalist? There are a number of different suggestions, which fall into two broad categories: enactivism and relationalism. According to relationalism, perceptual states are, in part, constituted by the actual perceived objects. Perception is a genuine relation between the perceiver and the perceived object—and not between the agent and some abstract entity called ‘perceptual content’ (Travis 2004, Brewer 2006, Campbell 2002, Martin 2004, 2006, but see also criticism by Byrne and Logue 2008, and Burge 2005, as well as Crane 2006 and Logue, Chapter 11 of this volume). One reason why relationalism may seem appealing is that it captures the particularity of perception, the intuitively plausible assumption that the object of perception is always a particular token object, better than representationalism (see Soteriou 2000 for a summary). Suppose that I am looking at a pillow. What happens if someone, unbeknownst to me, replaces this pillow with another, indistinguishable, pillow? Most representationalists will say that my perceptual state is still the same, as this replacement does not make a difference to the content of my perceptual state. (Note that not all versions of representationalism are committed to this claim: those, for example, that conceive of content as Russellian, gappy, or ‘singular when filled’ [see, e.g., Tye 2007, Schellenberg 2010] are not.) But I am looking at two entirely different token objects before and after the swap. The relationalist thus insists that I have two completely different perceptual states. Like relationalists, enactivists also deny that there are perceptual representations, but they give a different (but not incompatible, see Noë 2004) positive account of

1  Most of my examples are about the visual-sense modality, but all the discussed views apply to all the sense modalities.

Perceptual Representation/Perceptual Content    155 perception (Brooks 1991, Ramsey 2007). According to one version of enactivism, perception is an active and dynamic process between the agent and the environment and this dynamic interaction doesn’t have to be (or maybe even couldn’t be) mediated by static entities like representations (Chemero 2009, Port and Van Gelden 1995). Another version of enactivism emphasizes that when we see a scene, the whole scene in all its details is not coded in our perceptual system. Only small portions of it are: the ones we are attending to. The details of the rest of the scene are not coded at all, but they are available to us all along—we have immediate perceptual access to them without representing them (O’Regan 1992, Noë 2004, esp. pp. 22–24). One may wonder whether these enactivist arguments give us reason to abandon the idea of perceptual representations per se or maybe only to conclude that they are not static or not detailed. In short, some of the enactivist arguments may give us good reason to prefer certain kinds of perceptual representations over others within the representationalist framework. But that is clearly not the aim of most enactivists, who want to reject the whole idea of perceptual representations.2

Ways of resolving this debate The debate about perceptual representation is a subtle one and both sides should be taken seriously. I offer four possible ways of resolving this debate: by (i) capturing some anti-representationalist intuitions within the representationalist framework; by (ii) disputing anti-representationalism on empirical grounds; by (iii) exploring the possibility that the two camps are talking about different phenomena; and by (iv) finding a framework where the two views can co-exist as different explanations in different explanatory projects.

Capturing anti-representationalist intuitions within the representationalist framework One way of resolving the representationalism versus anti-representationalism debate would be to account for the most important anti-representationalist considerations within a representationalist theory. The enactivist considerations against static and detailed, snapshot-like representations may be easier to accommodate within the representationalist framework (by conceiving of perceptual representations as dynamic and dependent on attention, see Clark 1997, Nanay 2010a) than the relationalist ones. As we have seen, a crucial relationalist argument comes from the particularity of perception: we always perceive token objects and the perception of different token objects constitute very different perceptual states. Representationalism, the argument goes, cannot account for this.

2  A

consequence of both versions of anti-representationalism is that perceptual illusion cannot be accounted for as misrepresentation. If I see an object as P but it is in fact Q, this cannot be explained in terms of perceptually misrepresenting the properties of this object. Different anti-representationalists give different alternative explanations for perceptual illusions. I will not say much about this—the question is discussed at length in Logue, Chapter 11 of this volume (see also Travis 2004, Brewer 2006).

156   Bence Nanay But is this argument conclusive? It has been argued that if we interpret perceptual content as ‘Russellian’, ‘gappy’, ‘Russellian gappy’, ‘Fregean gappy’, ‘singular’, ‘object-involving’, or ‘singular-when-filled’ (see, e.g., Soteriou 2000, Martin 2002, Loar 2003, Tye 2007, Schellenberg 2010, and see Chalmers 2004, 2006, Siegel 2006b, Bach 2007 for discussion), then we can account for the particularity of perception within the representationalist framework. The general idea is that perceptual content is different from the content of beliefs in that it depends constitutively on the perceived token object. This dependence can take various forms (see below), but the general idea is that this allows for a difference in our perceptual content when we are looking at the two pillows in the example I used above.3 According to a somewhat different suggestion, we could use the old idea that perception attributes tropes (property-instances that are logically incapable of being instantiated by two different entities at the same time) and not universals (Mulligan 1999, Mulligan et al. 1984, Campbell 1990) to argue for the particularity of perception within a representationalist framework (Nanay 2012b).

Disputing anti-representationalism on empirical grounds We can also bring in empirical considerations to decide this debate. There seem to be at least two well-documented empirical phenomena that are difficult to account for in an anti-representationalist manner: dorsal vision and the multimodal character of perception (see Nanay 2014). The first one is dorsal vision. Humans (and other mammals) have two visual subsystems that use different regions of our central nervous system, the ventral and dorsal streams. To put it very simply, the ventral stream is responsible for identification and recognition, whereas the function of the dorsal stream is the visual control of our motor actions. In normal circumstances, these two systems co-function, but if one of them is removed or malfunctioning, the other can still function relatively well (see Milner and Goodale 1995, Goodale and Milner 2004, Jacob and Jeannerod 2003 for overviews, see also Brogaard forthcoming, as well as Jacob, Chapter 12 of this volume). In healthy humans the way the dorsal and the ventral stream works can come apart in some circumstances, as in the case of the three-dimensional Ebbinghaus illusion. The twodimensional Ebbinghaus illusion is a simple optical illusion. A circle that is surrounded by smaller circles looks larger than a circle of the same size that is surrounded by larger circles. The three-dimensional Ebbinghaus illusion reproduces this illusion in space: a poker chip surrounded by smaller poker chips appears to be larger than a poker chip of the same diameter surrounded by larger ones. The surprising finding is that although our judgement and experience of the comparative size of these two chips is incorrect as we judge the first chip to be larger than the second one, if we are asked to pick up one of the chips, our grip-size is barely influenced by the illusion (Aglioti et al. 1995, cf. Gillam 1998, and Franz et al. 2003, see also Daprati and Gentilucci 1997 and Bruno 2001). The usual way of explaining this 3 Another way of accounting for the particularity of perception within the representationalist framework is to make a distinction between the demonstrative meaning (a la Kaplan 1989) and the content of a perceptual state, where the latter is different, but the former is the same when we are looking at the two pillows.

Perceptual Representation/Perceptual Content    157 finding is that our dorsal stream represents more or less correctly, but the ventral stream misrepresents. This is the representationalist way of describing the 3D Ebbinghaus case: we have two perceptual representations, a dorsal and a ventral one, and they represent the poker chip as having different size properties. But what can the anti-representationalist say? If perception is a relation between the perceiver and the properties of the perceived token object, then we have one perceptual relation here: the one between the perceiver and the perceived token poker chip. But then which property of the perceived object constitutes the other one of the two relata of this relation? The property we experience the chip as having or the one that our grip-size seems to be tracking? These two perceptual episodes are both relations to the very same token object: the same poker chip, and the properties of this same poker chip. And two different perceptual episodes cannot be constituted by the very same perceptual relation. If, on the other hand, as the enactivist says, ‘the world is our external memory’, then what serves as our external memory here, the property we experience the chip as having or the one that our grip-size seems to be tracking? It is difficult to see what would even be meant by having two different ‘worlds as our external memory’. The second empirical phenomenon that may cast doubt on the anti-representationalist framework is multimodal perception—the fact that our sense modalities interact in a variety of ways (see Spence and Driver 2004 for a summary as well as O’Callaghan 2008b, 2012 and Matthen, Chapter 30 of this volume, for philosophical overviews). Information in one sense modality can influence the information processing in another sense modality at a very early stage of perceptual processing (often in the primary visual cortex in the case of vision, for example, see Watkins et al. 2006). A simple example of this is ventriloquism, where vision influences our audition: we experience the voices as coming from the dummy and not from the ventriloquist (see Bertelson 1999). But there are more surprising examples: if there is a flash in your visual scene and you hear two beeps while the flash lasts, you experience it as two flashes (Shams et al. 2000). What is the most important for us from this literature is that the multimodality of perception presupposes that information from two different sense modalities is unified in a shared framework (see, e.g., Vroomen et al. 2001, Bertelson and de Gelder 2004). Noise coming from above and from the left and visual information from the upper-left corner of my visual field are interpreted by the perceptual system as belonging to (or bound to) the same sensory individual (whatever that may be—see below). This is easy for the representationalist to analyze: vision attributes a property to a part of the perceived scene and audition attributes a different property to the same perceived scene. The two different sense modalities represent the same scene as having different properties. To put it very simply, multimodal perception seems to require matching two representations, a visual with the auditory one. If we cannot talk about perceptual representation, how can we talk about what is being matched? The auditory-sense modality gives us a soundscape and vision gives us a visual scene, and our perceptual system puts the two together. It is difficult to explain this without any appeal to representations. The enactivist arsenal seems insufficient:  enactivists can appeal to the active exploration of the multimodal environment, but this is unlikely to help here: we are actively exploring the world that is given to us in both sense modalities—but this in itself requires multimodal integration. In short, the active exploration of the environment presupposes multimodal

158   Bence Nanay integration, which, in turn, seems to presuppose representations. They can also insist that the active exploration of the environment happens separately in each sense modality—but this is in conflict with the findings about multimodal integration very early in perceptual processing (as early as the primary visual cortex, see Watkins et al. 2006). The relationalist version of anti-representationalism also seems powerless, as the relation between the perceiver and the token perceived object that constitutes perception seems to be the outcome of this process of unifying multimodal information: our experience of the perceived token object (thus, presumably, the perceptual relation) is brought about by this unification process. The argument from multimodality seems to show that the phenomena anti-representationalists emphasize, be they the active and dynamic exploration of the environment or the relation to a token object, presuppose the coordination of information in the different sense modalities, but this can only be accounted for in representational terms.

Different explanada? The most promising strategy for the anti-representationalist to counter these empirical considerations is probably to insist that the claim that there are no perceptual representations is to be understood as a claim about perceptual experiences: it is perceptual experiences that are not representations; unconscious perceptual states may well be. In fact, at least some of the relationalist accounts are explicitly about perceptual experiences and not about perceptual states. Enactivists would be less happy with this proposal as they are often explicit about not limiting their attention to conscious or even personal-level phenomena (see esp. Ballard 1996, Noë 2004, 28–32). The suggestion then would be:  representationalism for unconscious (or maybe subpersonal-level) perception and anti-representationalism for conscious (or maybe personal- level) perception (I leave aside the differences between these two distinctions as well as the general worries about the personal/subpersonal divide (see esp. Bermúdez 2000). In fact, John McDowell could be interpreted as endorsing a version of this proposal: he argued that while a representationalist picture is the correct one for the sub-personal level, we should accept J. J. Gibson’s claims with regards to the personal level, which would make his view (at least in this respect) a version of enactivism (McDowell 1994). One important problem with this view is that the differential treatment of conscious and unconscious perception is difficult to square with the general aim of both the representationalist and the relationalist camp to give a general account of perception—that is, not just conscious perception, but perception per se.

Different explanatory projects? Finally, one could argue that we need both representationalism and antirepresentationalism, as they will be able to help us in different explanatory projects about perception (Nanay forthcoming). We can think of the representationalism versus antirepresentationalism debate as a debate about how to individuate perceptual states. As we have seen in the pillow example above, representationalism (or at least some versions thereof) lumps together the two perceptual episodes, whereas relationalism thinks of them as two very different perceptual states. Hence, the real question is whether these

Perceptual Representation/Perceptual Content    159 two perceptual states belong not just to the same type but whether they belong to ‘the same fundamental kind’ (Martin 2004, 39 and 43). The representational view says they do; the relational view says they don’t. Belonging to a ‘fundamental kind’ is supposed to ‘tell what essentially the event or episode is’ (Martin 2006, 361). It is easy to spot the essentialist assumptions in this way of characterizing the representationalism versus anti-representationalism debate. And the hope is that if we discard this essentialist assumption, we may be able to reconcile the two views. Why should we always individuate perceptual states in the same way? It seems that the individuation of biological traits in general is dependent on the explanatory project at hand; why would perceptual states constitute an exception? There are at least three ways of individuating biological traits: the functional (in terms of what they are for), the morphological (in terms of their structural properties), and the homological (in terms of their history). But depending on the explanatory project, biologists use different ways of individuating trait-types. Paleontologists do not consider the forelegs of an ancient amphibian to be wings. But embryologists do consider the morphologically very similar trait of the embryos of birds to be wings. Biologists and philosophers of biology then gave up on trying to find one unified theory of trait-type individuation: in different explanatory contexts, we should use different criteria for individuating biological traits (Nanay 2010b). The suggestion is that philosophers of perception would be well advised to make the same move. Our perceptual system is an evolved mechanism, just like birds’ wings. Thus, if we have good reasons to doubt that there is one and only one way of individuating wings, we also have a prima facie reason to doubt that there is one and only one way of individuating perceptual states. If the individuation of other biological traits depends on the explanatory project, we should expect that so does the individuation of perceptual states (see also Matthen 1998). In the case of some explanatory projects, we should individuate perceptual states according to representationalist criteria. If, for example, a vision scientist is doing research on the shape-recognition mechanisms of the human perceptual system, this may be the natural way to proceed. But in the case of some other explanatory projects, the relationalist way of individuating perceptual states is more appropriate: if a psychologist or philosopher is, for example, enquiring into the differences and similarities between vision and visual imagery, then thinking of perceptual states in a relationalist manner may be more helpful.

1 What are perceptual representations? Let us suppose that there are perceptual representations. The question now is: what are they? There are two very different approaches to characterizing perceptual representations (these are not two kinds of theories, but rather two kinds of general approaches). The first one is to start out with non-perceptual representations, typically beliefs or other propositional attitudes, and see how what we know about representations of this kind can be modified in order to apply to the perceptual case. Some think that there is no need for any modification: perceptual content is exactly the same as belief content. But most philosophers who think of perceptual content in this way allow for some differences—while

160   Bence Nanay nonetheless maintaining that we should use propositional content as a model for understanding perceptual content. Many of these proposed modifications aim to address the problem of the particularity of perception that I mentioned above. The general idea is that unlike the content of beliefs, perceptual content somehow depends constitutively on the token perceived object. These ‘Russellian’, ‘gappy’, ‘singular’, ‘object-involving’, or ‘singular-when-filled’ conceptions of perceptual content, however, are nonetheless conceptions of propositional content—as David Chalmers says, these accounts are thinking about perceptual content as a ‘structured complex’ (Chalmers 2006, 54—Thompson 2009 describes them even more aptly as ‘structured propositions’). The second approach to characterizing perceptual representations is to resist the temptation to start out with belief content and instead use a more basic way of thinking about content in general that can subsume both belief content and perceptual content. We have no reason to believe that all mental representations are linguistically or propositionally structured (see Crane 2009, but see also Siegel 2010a and 2010b). Some (but not all) mental states have content. Some of these (but not all of them) have conceptual content (see also Wright, Chapter 10 of this volume). And some of these (but not all of them) have propositional content. But perceptual states don’t. What would then be a general enough way of thinking about mental representations in a manner that is not necessarily propositional? A reasonable suggestion is to think of them as attributing properties to entities. And if we think of mental representations in general as attributing properties to entities, then we should think of perceptual representations as perceptually attributing properties to the perceived scene. Clarifications: (a) What are these properties? (b) What is the ‘perceived scene’? (c) What makes the attribution perceptual?

Perceptually attributed properties What are these properties that are perceptually attributed when we perceive? We have seen one way of understanding this question: are these properties tropes or universals? I  address two more ways in which the nature of the perceptually attributed properties needs to be specified: (i) What is the range of properties that are perceptually attributed? (ii) Are they determinates or determinables (or maybe super-determinates)?

Which properties are perceptually attributed? Beliefs can represent their objects as having any property. Perceptual states, in contrast, represent their objects as having a limited set of properties. Some plausible candidates include having a certain shape, size, colour, and spatial location. The list may be extended but it will not encompass all properties. The property of having been made in 2008 in Malaysia is unlikely to be represented perceptually—it is a property that is likely to be attributed by a non-perceptual state. The question is then about which properties are represented in perception and which ones are not. A couple of quick examples: it has been argued that we perceive objects as

Perceptual Representation/Perceptual Content    161 trees and tables (Siegel 2006a), as being causally efficacious (Siegel 2005, 2009), as edible, climbable, or Q-able in general (Nanay 2011a, 2012a), as having action-properties (Nanay 2013), as agents (Scholl and Tremoullet 2000), as having some kind of normative character or value (Kelly 2010, Matthen 2010), as having dispositional properties (Nanay 2011b), as having moral value (Kriegel 2007), and as affording certain actions (for very different versions of this claim, see Gibson 1966, 1979, Bach 1978, esp. 368, Jeannerod 1994, esp. section 5, Jeannerod 1997, Jacob and Jeannerod 2003, esp. 202–204, Humphreys and Riddoch 2001, Riddoch et al. 1998, esp. 678). Depending on our view on what range of properties we attribute perceptually, we end up with a very different view of perceptual content and, as a result, of perception in general.

The determinacy of perceptually attributed properties Another important question about perceptually attributed properties concerns their degree of determinacy (Johnston 1921, Funkhouser 2006). Being red is determinate of being coloured, but determinable of being scarlet. The determinable-determinate relation is a relative one: the same property, for example, of being red, can be the determinate of the determinable being coloured, but the determinable of the determinate being scarlet. Properties with no further determinates, if there are any, are known as super-determinates. Are the perceptually attributed properties super-determinates? It has been argued that quite often they are not (Dennett 1996). Some of the properties we perceptually attribute to the perceived scene are determinates or even super-determinates. But some others are determinable properties. Our peripheral vision is only capable of attributing extremely determinable properties. But even some of the properties we perceptually attribute to the objects that are in our fovea can be determinable. The perceptually attributed properties differ in their determinacy and, as we shall see below, part of what this difference in determinacy depends on is a difference in our perceptual attention.

Sensory individuals If we have clarified what properties are attributed in perception, we need to ask what our perceptual system attributes these properties to. In other words, what are the individuals that we perceptually represent as having these properties? Following Cohen 2004, I call these individuals ‘sensory individuals’. I’ll address two questions about sensory individuals: what they are and how they show up in perceptual content. One widespread view about sensory individuals is that they are ordinary objects like apples and chairs (Matthen 2005, Pylyshyn 2007, Cohen 2004, Matthen 2004, 2010). Another, much less widespread, one is that they are regions in space-time (Clark 2000, 2004). The ordinary-object view is seen as the more promising one, both on conceptual (Cohen 2004, Matthen 2012, Siegel 2002) and on empirical (Blaser et al. 2000) grounds (see also Casati, Chapter 20 of this volume). But, to make things even more complicated, it is not clear that sensory individuals of different sense modalities are the same. It has been argued that while the sensory individuals of vision are ordinary objects, in the auditory-sense modality they are sounds

162   Bence Nanay (O’Callaghan 2008a, Nudds 2001, 2010). This suggestion, in turn, raises various questions about what sounds are (Kulvicki 2008, O’Callaghan 2007, Pasnau 1999, Nudds and O’Callaghan 2009, Casati and Dokic 1994). Similar suggestions have been made about olfaction, where the sensory individuals are supposed to be odours (Lycan 2000, Batty 2010, 2011). See Nudds, Chapter 15 and Smith, Chapter 17 of this volume on these sense modalities. Another important question about sensory individuals is about how they show up in perceptual content. The classic representationalist view is that they are also represented by our perceptual states: both the attributed properties and the sensory individuals that these properties are attributed to are part of our perceptual content. But, partly under pressure to account for the particularity of perception, it has been suggested that the sensory individual does not need to be represented: only the properties are and there is a ‘gap’ in the perceptual content where actual objects stand in for sensory individuals (Tye 2007, Schellenberg 2010). Although, as we have seen above, most of these proposals consider perceptual content to be propositional, this is not a necessary feature of this general strategy. If we, as I suggest, think of perceptual content as the perceptual attribution of properties, this leaves open the possibility that the entity these properties are attributed to is not part of the perceptual content, but ‘fills the gap’ that is in the perceptual content. This would be a move equivalent to the one made by the advocates of the ‘Russellian’, ‘gappy’, ‘singular’, or ‘singular if filled’ accounts of perceptual content and it would address the problem of the particularity of perception in a similar manner.

Perceptual content What makes this attribution of properties perceptual? The sentence ‘The cat I am looking at is wet’ also attributes properties to the perceived object, but it nonetheless does not do so perceptually. Without intending to come up with a necessary and sufficient condition for perception, it needs to be pointed out how perceptual content differs from the content of this sentence. There is no easy way to draw this distinction. One important potential difference is that while the entity that the properties are attributed to is propositionally identified in the sentence, it is identified spatially in the perceptual case (see Peacocke 1989, 1992). Perceptual content, in short, is not propositionally but spatially organized (on this classic difference see, e.g. Kosslyn et al. 2006). And this leads to another difference between the content of this sentence and perceptual content: the different role that attention plays. It has been argued that perceptual attention is a necessary feature of perceptual content (Nanay 2010a). More precisely, attention makes the attended property more determinate (see also Yeshurun and Carasco 1998 for empirical evidence and Findlay and Gilchrist 2003 for a summary). If I am attending to the colour of my office telephone, I attribute very determinate (arguably super-determinate) properties to it. If, as it is more often the case, I am not attending to the colour of my office telephone, I attribute only determinable properties to it (of, say, being light-coloured or maybe just being coloured). In short, attention makes the perceived property more determinate. If this is indeed so, that would constitute a genuine and unique feature of perceptual content. The concept of attention plays a more and more important role in philosophy of perception (see Prinz 2010, and

Perceptual Representation/Perceptual Content    163 Chapter 19 of this volume). One important question is whether and how it characterizes perceptual content.

References Aglioti, S., DeSouza, J. F. X., and Goodale, M. A. (1995). ‘Size-Contrast Illusions Deceive the Eye but not the Hand’, Current Biology, 5, 679–685. Bach, Kent (1978). ‘A Representational Theory of Action', Philosophical Studies, 34: 361–379. Bach, Kent (2007). ‘Searle against the World: How Can Experiences Find their Objects?'. In S. L. Tsohatzidis (ed.), John Searle’s Philosophy of Language: Force, Meaning, and Thought (pp. 64–78). Cambridge: Cambridge University Press. Ballard, D. H. (1996). ‘On the Function of Visual Representation'. In Kathleen Akins (ed.), Perception (pp. 111–131), ed. Kathleen Akins. New York: Oxford University Press. Batty, C. (2010). ‘Scents and Sensibilia’. American Philosophical Quarterly, 47, 103–118. Batty, C. (2011). ‘Smelling Lessons’. Philosophical Studies, 153, 161–174. Bermúdez, José Luis (2000). ‘Personal and Subpersonal: A Difference Without a Distinction’. Philosophical Explorations, 3(1), 63–82. Bertelson, P. (1999). ‘Ventriloquism: A Case of Cross-Modal Perceptual Grouping'. In G. Aschersleben, T. Bachmann, and J. Müsseler (eds), Cognitive Contributions to the Perception of Spatial and Temporal Events (pp. 347–362). Amsterdam: Elsevier. Bertelson, P. and de Gelder, B. (2004). ‘The Psychology of Multimodal Perception’. In C. Spence and J. Driver (eds), Crossmodal Space and Crossmodal Attention (pp. 141–177). Oxford: Oxford University Press. Blaser, E., Pylyshyn, Z. W., and Holcombe, A. O. (2000). ‘Tracking an Object through Feature Space, Nature'. 408, 196–199. Brewer, Bill (2006). ‘Perception and Content’. European Journal of Philosophy, 14, 165–181. Brogaard, B. (2011). ‘Are there Unconscious Perceptual Processes?’. Consciousness and Cognition, 20, 449–463. Brogaard, B. (forthcoming). ‘Conscious Vision for Action versus Unconscious Vision for Action?’. Journal of Philosophy. Brogaard, B. (2014). Does Perception Have Content? New York: Oxford University Press. Brooks, R. A. (1991). ‘Intelligence without Representation’. Artificial Intelligence, 47, 139–159. Bruno, Nicola (2001). ‘When Does Action Resist Visual Illusions?’. Trends in Cognitive Sciences, 5, 385–388. Burge, Tyler (2005). ‘Disjunctivism and Perceptual Psychology’. Philosophical Topics, 33, 1–78. Byrne, Alex and Logue, Heather (2008). ‘Either/Or’. In Adrian Haddock and Fiona MacPherson (eds), Disjunctivism: Perception, Action, Knowledge (pp. 57–94). Oxford: Oxford University Press. Campbell, John (2002). Reference and Consciousness. Oxford: Oxford University Press. Campbell, Keith (1990). Abstract Particulars. Oxford: Blackwell. Casati, R. and Dokic, J. (1994). La Philosopie du Son. Paris: Chambon. Chalmers, D. J. (2004). ‘The Representational Character of Experience’. In B. Leiter (ed.), The Future for Philosophy (pp. 153–181). Oxford: Oxford University Press. Chalmers, D. J. (2006). ‘Perception and the Fall from Eden’. In T. Gendler and J. Hawthorne (eds), Perceptual Experience (pp. 49–125). New York: Oxford University Press.

164   Bence Nanay Chemero A. (2009). Radical Embodied Cognitive Science. Cambridge, MA: MIT Press. Clark, Andy (1997). Being There. Cambridge, MA: MIT Press. Clark, Austen (2000). A Theory of Sentience. Oxford: Clarendon Press. Clark, Austen (2004). ‘Sensing, Objects, and Awareness: Reply to Commentators’. Philosophical Psychology, 17, 563–589. Cohen, Jonathan (2004). ‘Objects, Places, and Perception’. Philosophical Psychology, 17, 471–495. Crane, Tim (2006). ‘Is there a Perceptual Relation?’. In T. Gendler and J. Hawthorne (eds), Perceptual Experience (pp. 126–146). Oxford: Oxford University Press. Crane, Tim (2009). ‘Is Perception a Propositional Attitude?’. Philosophical Quarterly, 59, 452–469. Daprati, E. and Gentilucci, M. (1997). ‘Grasping an Illusion’. Neuropsychologia, 35, 1,577–1,582. Dennett, D. C. (1996). ‘Seeing is Believing: Or is it?’. In K. Akins (ed.), Perception (pp. 158–172). Oxford: Oxford University Press. Findlay, John M. and Gilchrist, Iain D. (2003). Active Vision: The Psychology of Looking and Seeing. Oxford: Oxford University Press. Franz, V. H., Bülthoff, H. H., and Fahle, M. (2003). ‘Grasp Effects of the Ebbinghaus Illusion: Obstacle Avoidance is Not the Explanation’. Experiental Brain Research, 149, 470–477. Funkhouser, E. (2006). ‘The Determinable-Determinate Relation’. Nous, 40, 548–569. Gibson, James J. (1979). An Ecological Approach to Visual Perception. Boston, MA: Houghton Mifflin. Gibson, James J. (1966). The Senses Considered as Perceptual Systems. Boston, MA: Houghton Mifflin. Gillam, Barbara (1998). ‘Illusions at Century’s End'. In Julian Hochberg (ed.), Perception and Cognition at Century’s End (pp. 95–136). San Diego, CA: Academic Press. Goodale, M. A. and Milner, A. D. (2004). Sights Unseen. Oxford: Oxford University Press. Humphreys, Glyn W. and Riddoch, M. Jane (2001). ‘Detection by Action: Neuropsychological Evidence for Action-Defined Templates in Search'. Nature Neuroscience, 4, 84–88. Jacob, Pierre and Jeannerod, Marc (2003). Ways of Seeing: The Scope and Limits of Visual Cognition. Oxford: Oxford University Press. Jeannerod, M. (1997). The Cognitive Neuroscience of Action. Oxford: Blackwell. Jeannerod, M., Decety, J., and Michel, F. (1994). ‘Impairment of Grasping Movements Following a Bilateral Posterior Parietal Lesion’. Neuropsychologia, 32, 369–380. Johnston, W. E. (1921). Logic: Part I. Cambridge: Cambridge University Press. Kaplan, David (1977/1989). ‘Demonstratives'. In Almog, Perry, and Wettstein (eds), Themes from Kaplan (pp. 481–504). Oxford: Oxford University Press. Kelly, Sean (2010). ‘The Normative Nature of Perceptual Experience'. In Bence Nanay (ed.), Perceiving the World (pp. 146–159). New York: Oxford University Press. Kosslyn, Stephen M., Thompson, William L., and Ganis, Giorgio (2006). The Case for Mental Imagery. Oxford: Oxford University Press. Kriegel, Uriah (2007). ‘The phenomenologically manifest'. Phenomenology and the Cognitive Sciences, 6, 115–136. Kulvicki, J. (2008). ‘The Nature of Noise’. Philosophers’ Imprint, 8, 1–16. Loar, B. (2003). ‘Transparent Experience and the Availability of Qualia'. In Q. Smith and A. Jokic (eds), New Philosophical Perspectives (pp. 77–96). New York: Oxford University Press.

Perceptual Representation/Perceptual Content    165 Lycan, W. (2000). ‘The Slighting of Smell'. In N. Bhushan and S. Rosenfeld (eds), Of Minds and Molecules: New Philosophical Perspectives on Chemistry (pp. 273–289). Oxford: Oxford University Press. Martin, M. G. F. (2002). ‘Particular Thoughts and Singular Thought’. Royal Institute of Philosophy Supplement, 51, 173–214. Martin, M. G. F. (2004). ‘The Limits of Self-Awareness’. Philosophical Studies, 120, 37–89. Martin, M. G. F. (2006). 'On Being Alienated'. In T. Gendler and J. Hawthorne (eds), Perceptual Experience (pp. 354–410). Oxford: Oxford University Press. Martin, M. G. F. (forthcoming). Uncovering Appearances. Oxford: Oxford University Press. Matthen, Mohan (1998). ‘Biological Universals and the Nature of Fear’. Journal of Philosophy, 95, 105–132. Matthen, Mohan (2004). ‘Features, Places and Things’. Philosophical Psychology, 17, 497–519. Matthen, Mohan (2005). Seeing, Doing, and Knowing:  A  Philosophical Theory of SensePerception. Oxford: Clarendon Press. Matthen, Mohan (2010). ‘On the Diversity of Auditory Objects’. Review of Philosophy and Psychology, 1, 63–89. Matthen, Mohan (2012). ‘Visual Demonstratives'. In Athanasios Raftopoulos and Peter Machamer (eds), Perception, Realism, and the Problem of Reference (pp. 43–67). Athanasios Raftopoulos and Peter Machamer. Cambridge: Cambridge University Press. McDowell, J. (1994). ‘The Content of Perceptual Experience’. Philosophical Quarterly, 44, 190–205. Milner, A. D. and Goodale, M. A. (1995). The Visual Brain in Action. Oxford: Oxford University Press. Mulligan, Kevin (1999). 'Perception, Particulars and Predicates'. In D. Fisette (ed.), Con­ sciousness and Intentionality: Models and Modalities of Attribution (pp. 163–194). Dordrecht: Kluwer. Mulligan, Kevin, Smith, Barry, and Simons, Peter (1984). ‘Truth Makers’. Philosophy and Phenomenological Research, 44, 278–321. Nanay, Bence (2010a). ‘Attention and Perceptual Content’. Analysis, 70, 263–270. Nanay, Bence (2010b). ‘A Modal Theory of Function’. Journal of Philosophy, 107, 412–431. Nanay, Bence (2011a). ‘Do we See Apples as Edible?’ Pacific Philosophical Quarterly, 92, 305–322. Nanay, Bence (2011b). ‘Do we Sense Modalities with our Sense Modalities?’ Ratio, 24, 299–310. Nanay, Bence (2012a). ‘Action-Oriented Perception’. European Journal of Philosophy, 20, 430–446. Nanay, Bence (2012b). ‘Perceiving Tropes’. Erkenntnis, 77, 1–14. Nanay, Bence (2013). Between Perception and Action. Oxford: Oxford University Press. Nanay, Bence (forthcoming). ‘The Representationalism versus Relationalism Debate: Explanatory Contextualism about Perception’. European Journal of Philosophy. Nanay, Bence (2014). ‘Empirical Problems with Anti-Representationalism’. In B. Brogaard (ed.), Does Perception Have Content? New York: Oxford University Press. Noë, Alva (2004). Action in Perception. Cambridge, MA: MIT Press. Nudds, M. (2001). ‘Experiencing the Production of Sounds’. European Journal of Philosophy, 9, 210–229. Nudds, M. (2010). ‘What Are Auditory Objects?’ Review of Philosophy and Psychology, 1, 105–122. O’Callaghan, C. (2007). Sounds. Oxford: Oxford University Press.

166   Bence Nanay O’Callaghan, C. (2008a). ‘ObjectPerception: Vision and Audition’. Philosophy Compass, 3(4): 803–829. O’Callaghan, C. (2008b). ‘Seeing What you Hear: Crossmodal Illusions and Perception’. Philosophical Issues, 18, 316–338. O’Callaghan, C. (2012). ‘Perception and Multimodality'. In E. Margolis, R. Samuels, and S. Stich (eds), The Oxford Handbook of Philosophy and Cognitive Science (pp. 92–117). Oxford: Oxford University Press. O’Regan, K. (1992). ‘Solving the “Real” Mysteries of Visual Perception: The World as an Outside Memory’. Canadian Journal of Psychology, 46, 461–488. Pasnau, R. (1999). ‘What is sound?’. Philosophical Quarterly, 49, 309–324. Pautz, Adam (2010). ‘An Argument for the Intentional View of Visual Experience'. In Bence Nanay (ed.), Perceiving the World (pp. 254–309). New York: Oxford University Press. Peacocke, C. (1989). ‘Perceptual Content'. In J. Almong, J. Perry, and H. Wettstein (eds), Themes from Kaplan (pp. 297–329). Oxford: Oxford University Press. Peacocke, C. (1992). A Study of Concepts. Cambridge, MA: MIT Press. Port, R. and van Gelder, T. J. (eds) (1995). Mind as Motion: Explorations in the Dynamics of Cognition. Cambridge, MA: MIT Press. Prinz, Jesse (2010). ‘How Do Perceptual States Become Conscious?’ In Bence Nanay (ed.), Perceiving the World. New Essays on Perception (pp. 310–332). New York: Oxford University Press. Pylyshyn, Zenon W. (2007). Things and Places:  How the Mind Connects with the World. Cambridge, MA: MIT Press. Ramsey, W. M. (2007). Representation Reconsidered. Cambridge: Cambridge University Press. Riddoch, M. Jane, Edwards, Martin G., and Humphreys, Glyn W. (1998). ‘Visual Affordances Direct Action: Neuropsychological Evidence from Manual Interference'. Cognitive Neuropsychology, 15, 645–693. Schellenberg, Susanna (2010). ‘Particularity and Phenomenology of Perceptual Experience’. Philosophical Studies, 149, 19–48. Scholl, B. J. and Tremoulet, P. D. (2000). ‘Perceptual Causality and Animacy’, Trends in Cognitive Sciences, 4: 299–309. Shams, L., Kamitani, Y., and Shimojo, S. (2000). ‘What You See Is What You Hear’. Nature, 408, 788. Siegel, Susanna (2002). ‘Review of Austen Clark'. A Theory of Sentience. Philosophical Review, 111, 135–138. Siegel, Susanna (2005). ‘The Phenomenology of Efficacy’. Philosophical Topics, 33, 65–84. Siegel, Susanna (2006a). ‘Which Properties are Represented in Perception?’ in T. Gendler and J. Hawthorne (eds), Perceptual Experience (pp. 481–503). Oxford: Oxford University Press. Siegel, Susanna (2006b). ‘Subject and Object in the Contents of Visual Experience’, Philosophical Review, 115: 355–388. Siegel, Susanna (2009). ‘The Visual Experience of Causation’. Philosophical Quarterly, 59, 519–540. Siegel, Susanna (2010a). ‘Do Visual Experiences Have Contents?. In Bence Nanay (ed.), Perceiving the World (pp. 333–368). Oxford: Oxford University Press. Siegel, Susanna (2010b). The Contents of Visual Experience. New York: Oxford University Press. Soteriou, Matthew (2000). ‘The Particularlity of Visual Perception’. European Journal of Philosophy, 8, 173–189.

Perceptual Representation/Perceptual Content    167 Spence, C. and Driver, J. (eds) (2004). Crossmodal Space and Crossmodal Attention. Oxford: Oxford University Press. Thompson, Brad (2009). ‘Senses for Senses’. Australasian Journal of Philosophy, 87, 99–117. Travis, Charles (2004). ‘The Silence of the Senses’. Mind, 113, 57–94. Tye, Michael (2007). ‘Intentionalism and the Problem of No Common Content'. Philosophical Perspectives, 21, 495–541. Vroomen, J., Bertelson, P., and de Gelder, B. (2001). ‘Auditory-Visual Spatial Interactions: Automatic versus Intentional Components'. In B. de Gelder, E. de Haan, and C. Heywood (eds), Out of Mind (pp. 140–150). Oxford: Oxford University Press. Watkins, S., Shams, L., Tanaka, S., Haynes, J. D., and Rees, G. (2006). ‘Sound Alters Activity in Human V1 in Association with Illusory Visual Perception’. NeuroImage, 31, 1,247–1,256. Yeshurun, Y. and Carrasco, M. (1998). ‘Attention Improves or Impairs Visual Performance by Enhancing Spatial Resolutio’. Nature, 396, 72–75.

Chapter 9

Perception a n d the First  Person Christopher Peacocke

Perception and the first person stand in a relation that is both close and puzzling. Here are six questions on the subject: (1) You characteristically perceive objects and events as standing in various relations to you. Your perceptions have a first person content; their correctness conditions concern you. What does this involve, given that this feature can be present even when you perceive no part of yourself? We can call this ‘The puzzle of perceiving in relation to yourself’. (2) You need to keep track of objects in your environment if you are to learn in part from perception that an object that is now thus-and-so is the same as the one that was such-and-such in the past. You do not, it seems, need in any way to keep track of yourself to have such knowledge. How is this possible? (‘The no-tracking puzzle’.) (3) You do perceive your own body from the inside, as when you experience pressure on the palm of your hand, experience your left arm as extended, or feel the inside of your mouth as hot. But you do not merely experience a body from the inside as having these properties: you also experience these body parts as your own. What is it to perceive something as yours? (‘The puzzle of perceived ownership’.) (4) There seems to be something in Hume’s point that he can never catch himself in introspection. Even when Hume is perceiving his body, either from the inside, or as he might perceive another’s body in vision, the thought ‘this body is mine’ is potentially informative. It is informative in the case in which he needs to consider the possibility that his experiences are caused by the states of the perceptual organs and proprioceptive apparatus of someone else’s body. So experiences as of one’s own body being a certain way may mislead. Moreoever, there does not seem to be such a thing as simply and merely perceiving oneself, as opposed to perceiving some body or bodily part that is experienced as one’s own. How can all this be so? If it is so, why is it so, and how do we reconcile the fact with our answers to the earlier questions? (‘The puzzle of perceiving oneself’.)

Perception and the First Person    169

(5) If our perceptual states are veridical, we both have a spatial location and are embodied. But it seems that we can conceive of first person sequences of conscious states that do not require or involve embodiment at all. Is there a tension here, and if so, how is it to be resolved? Is embodiment as given in perceptual experience, both proprioceptive and by other senses, fundamental to being a subject, or not? (‘The puzzle of embodiment’.) (6) Ordinary experiences with a first person content entitle us to form first person beliefs, containing the first person concept. In a wide range of cases, such ordinary experiences lead to knowledge of the form I am F, that is, knowledge of a first person conceptualized content. Yet it is not at all clear that the entitling experience has a conceptualized content at all. What is the right conception of the nexus of relations between perception, the first person concept, its reference, and first person knowledge? (‘The puzzle of first person content, concepts, and entitlement’). I take these questions, which vary in character from the merely puzzling to the near paradoxical, in turn. Adequate answers to them must, as elsewhere in philosophy, integrate metaphysics with the theory of intentional content. In the present case, the metaphysics in question is the metaphysics of the subject of experience, the self. The intentional contents in question are the first personal, so-called de se contents. What is distinctive of de se content in a mental state or event is that the correctness condition for the state or event concerns the very subject who enjoys that state or event, and it concerns that very subject in a non-derivative way. There are complex contents such as the subject of this experience that necessarily and a priori concern the subject of the experience, but they do so derivatively, by way of the subject satisfying a complex descriptive and demonstrative property, that of being the subject of the experience in question. By contrast, when you have a perception with the content That window is straight ahead of me, the perception does not have a content to the effect that the subject of such-and-such experience is thus-and-so. Its content is just that you are thus-and-so. It is a task of the philosophy of mind to integrate the metaphysics of the self with de se intentional content so understood.

1  Perceiving in relation to yourself It has long been recognized that spatial content and de se content are, in a wide range of experiences, intimately related. Many would agree that what J.  J. Gibson said about information applies to spatial perceptual content: ‘Information about the self accompanies information about the environment, and the two are inseparable . . . One perceives the environment and coperceives oneself’ (1986: 126). This applies both to experience of a stationary array, and to motion. One may experience oneself as moving in relation to the environment, or experience things as moving around one. Experiences with these de se contents may involve perception of one’s own body parts, either in proprioception or through seeing one’s limbs, torso, and nose. But they can also occur without any such perception of one’s own body at all. Spatial experiences represent the world around oneself as being a certain way. It is natural to capture that way by specifying it as a spatial type: the way the world around the

170   Christopher Peacocke perceiver, as given in relation to the perceiver’s body, must be filled in if the experience is to be veridical. This is sometimes called scenario content (Peacocke, 1992), and it can be elaborated along several different lines. Common to such elaborations will be the notion of an origin (the point of view from which the world is perceived, in purely visual perception), axes (derived from body type), and some account of what the ‘filling in’ is. It may be specified what properties and relations hold between the regions in the spatial type. Those who think that perceptual content is dependent upon the identity of particular objects that the perception is about can insert objects into a notion of scenario content should they so wish. The apparatus can serve many comers. Consider the spatial perceptual content (1) That object is in that direction from this place

where this place picks out the origin of the scenario content in the perception, a way of thinking of the place made available by the perception itself (unlike the way of thinking whatever place it is at which I’m located, which is available in thought even if one is not perceiving at all); and consider by contrast the de se perceptual content (2) That object is in that direction from me.

What is the relation between these two? They cannot be identical, for they have distinct correctness conditions. As a result of the insertion of some radio device into your optic nerves, in such a way that the nerves receive input from some other person’s retinas, you may temporarily be perceiving the scene around someone else, in a wholly distinct environment from your own (Dennett, 1978). In such a case, it can be that (1) is true but (2) is false. ‘I’m not really in this place’, you may truly think if you find yourself in such circumstances. Purely spatial correctness conditions are one thing; de se correctness conditions concerning the subject enjoying the experience are a different thing. Different—but it seems that the two are related. It is plausible that for a spatial or material perceptual content F(me) to be true is for F to hold of my body. It is also plausible that my body is the one from which I  perceive in normal circumstances, circumstances in which the scenario-origin this place refers to the place which is in fact the location of my body. Call the conjunction of these two plausible claims ‘the normality thesis’. The normality thesis is neutral as between two radically different competing explanations of why it is true. One proposal is that the normality thesis is explained by the fact that having a point of view on a spatial world from a body located in that world is constitutive of being a conscious subject (Strawson, 1966; Evans, 1982; Campbell, 1994). A  rival proposal does not accept that view of subjecthood, but does hold that the normality thesis is explained by what it is for a conscious subject to have a body it represents as its own (Peacocke, 2008). Some examples suggest that it is too strong to hold that any perceptual states with spatial content must also have a de se content. There could be an organism that perceptually represents events and objects as having properties and standing in spatial relations to the place that is the origin in its scenario contents, an organism that does not have any states with de se contents at all (neither conceptual nor nonconceptual). The organism could have a cognitive map of its environment, keep track of a ‘here’ on that map, and engage in such actions as changing its colour or the electric charge it generates, in response to threats or

Perception and the First Person    171 opportunities. The creature would not be capable of bodily movements; it may live in a fluid. This creature has a perceptual apparatus and control centre that is in fact in the spatial world; but because it does not represent itself at all, a fortiori it does not represent itself as having a spatial location. Shoemaker (1984) has argued that for any conscious subject at all, there must be an account of what it is for it to be embodied. If that is true, we have to add that for an organism of the sort just considered, any shape, size, and material kind of embodiment is consistent with the contents of its representational states, provided the embodiment allows for its perceptions and its limited range of action-types. If the example is a genuine possibility, then not all perceiving, embodied subjects have to self-represent (Peacocke, 2014).

2  Absence of self-tracking Suppose that yesterday you perceived yourself to be in a sunny street. If you remember being there, you can today know that you were in a sunny street. You can know this without reliance on any identity of yourself with something given in a non-first-personal way. Contrast your knowledge of ‘This pen [as given demonstratively in perception now] is the one I bought in the sunny street’. To know this, you need either to have kept track of the pen (it has been in your pocket since the purchase); or to know some identifying marks of that pen, which you know both the purchased pen, and the one you now perceive, to possess. Nothing analogous holds in the first person case. You can know you were in a sunny street without keeping track of yourself, and without relying on any identifying marks of yourself. What explains the difference? First person content in a mental state or event refers, de jure, to the subject who enjoys that state or event. Necessarily and a priori, if one and the same subject both held I am F in the past and now accepts I was F, then what he thereby accepts now will be true if what he held earlier was true. There is no need to rely on a risky identity: no risky identity is involved. By contrast, any transition by a subject to a content of the form ‘This [perceptually given] object is F’ from an earlier acceptance of ‘That [perceptually given] object is F’ needs further information if it is to be a rational transition. The further information required is that it is the same object that is given in the two perceptual presentations. The point of difference in this respect between perceptual demonstratives and the first person shows up in what would be adequate subpersonal mechanisms for registering, and as bases for knowledge, in the two kinds of case. In perceptual tracking of an object, we need to acknowledge not only perceptual object files, labelled by the egocentric locations of objects. We also need something that functions to keep track of when successive files are of the same object. This is the function for which Pylyshyn proposes his ‘FINSTS’, subpersonal pointers which underlie the perception of identity of an object over time (Pylyshyn, 2007). By contrast, we do not need a subpersonal analogue of FINSTS for de se contents. A subject can have a subpersonal self-file, which contains representations of properties he perceives himself to possess. As time passes, what was a present tense predicate in this file merely needs to be temporally updated in the appropriate way to a past tense predication of the same notion. If the earlier representation ‘is F’ in the subject’s self-file is correct, then so will the later representation ‘was F’ in the same file also be correct.

172   Christopher Peacocke These points are completely independent of the metaphysical nature of subjects of consciousness. They apply whether subjects are essentially embodied and perceptible both from the inside and from the outside, or are not essentially embodied, or are essentially such that embodiment makes sense for them. The point turns only on the nature of the reference rule for the de se, whatever the metaphysics of its referent may be. A concern sometimes expressed about this treatment is that in a world in which there is frequent fission and fusion of conscious subjects, then one really would need to keep track of oneself in some additional way if the transition from {I was F, I was G} to I was both F and G is to be soundly made. Now, if in a world of fission and fusion I was F is allowed to be true if one of the subject’s ancestors was F, and I was both F and G requires some ancestor to have been both F and G in the past, then indeed that transition fails. But on that understanding, the transition is not an application of the valid rule of conjunction-introduction within complex predicates. It is rather an instance of the clearly fallacious form {Something standing in R to me was F, Something standing in R to me was G} / Something standing in R to me was F and G. In a world of repeated fission and fusion, memories of experiences may mislead a subject on whether she really has sufficiently strong premisses needed for the application of the conjunction-introduction rule within complex predicates. Given that this explanation of the difference in respect of the need for a certain kind of tracking between the first person and the perceptual cases holds entirely independently of the nature of subjects, the explanation is consistent with the thesis that subjects are things that can be perceived by themselves and others. A mechanism that gives genuine awareness and knowledge of identity over time, of an entity that can in fact be perceived, does not itself have to be a perceptual mechanism. Temporal updating of a subject’s file on itself is precisely such a non-perceptual mechanism. On this view, then, Kant seems to make a mistake when, in his treatment of the Third Paralogism in the First Critique, he moves from the true point that certain kinds of apparent awareness of oneself do not involve an intuition of oneself (through which one is given ‘as object’) to the conclusion that such non-perceptual awareness cannot ‘signify the identity of the person’ (point (3) in B408, Kant (1998)). It does signify the identity of the person, but not by way of any kind of identification or tracking that is involved in purely perceptual-demonstrative cases.

3  Experienced ownership For a body to be yours is for it to be the one from which you perceive, the one some of whose movements are your actions, and the one in which you experience bodily sensations as located. For a body part to be yours is for it to be part of the body so identified. Given these conditions on ownership, the nature of ownership involves a subject who perceives, acts, and senses. These conditions on ownership specify what is required for the correctness of the content of any experience in which a body or a body part is experienced as your own. Most of us experience a particular body and certain body parts as our own, and normally these experiences are veridical. But in less common cases, there are also striking and theoretically revealing illusions of ownership. The phantom limb phenomenon experienced by some of the injured, by amputees, and by some of those born without a particular limb, are well known. Almost equally well known today is the rubber hand illusion, in

Perception and the First Person    173 which tactile stimulation of a subject’s unseen hand, when matched by seen touching of a rubber hand, can produce the illusion that the rubber hand is the subject’s own (Botvinick and Cohen, 1998). A more radical illusion can be produced to the effect that the rear of a head, seen by a subject, is that subject’s own head (Lenggenhager et al., 2007). In the condition of apotemnophilia, a person may experience a healthy, undamaged, functioning limb, such as his arm or lower leg, as not belonging to him, as intrusive, and insist that it be amputated (Ramachandran, 2011). The subject suffering from apotemnophilia nonetheless experiences sensations in the limb in question, and may employ it in such actions as walking. It is widely agreed that the explanation of these illusions must involve a mental representation of the body, called the body schema. The body schema can represent there being a body part when there is not (phantom limb). It may fail to represent as part of one’s body something that really is so (apotemnophilia). The body schema is involved in a persisting representational state that concerns what kind of body the subject possesses. It is to be distinguished from what is sometimes called the body image, which represents the particular spatial properties and internal relations of the subject’s body parts at any one time (Gallagher, 2005). The body schema influences the conditions and character of these illusions (Costantini and Haggard, 2007). These illusions should constrain our constitutive account of the phenomenology of ownership. In a paper on the sense of ownership, Martin makes an important and convincing case that bodily sensations have a representational content concerning the subject’s body (1995). But he also further argues that ‘we should think of apparent ownership not as being a quality additional to the other qualities of experience but as somehow already inherent within them’ (1995: 278). The proposal is that ‘when one feels a sensation, one thereby feels as if something is occurring within one’s body’ (1995: 267). The subject suffering from apotemnophilia is a counterexample to this: that subject feels a sensation in what is in fact his lower arm (say), but experiences that arm as not his own. It follows that, no doubt surprisingly, that we must distinguish sharply between experiences that represent a body part indexically, from the inside, and experiences that represent that body part as one’s own. It also follows from the nature of these illusions that we cannot characterize a sense of ownership reductively in terms of the subject’s body schema, if that schema is characterized only in indexical terms—not even if the schema is required functionally to have a connection with action (see de Vignemont, 2007). The subject with apotemnophilia with respect to his lower leg may still use that leg in the action of walking. (Using something in action, even a basic action, is not the same as experiencing it as being one’s own.) If, by contrast, it is supposed to be part of the representational content of the body schema that it also labels various body parts as one’s own, such a body schema could then contribute to the explanation of these various pathologies. But it would do so then by taking for granted the notion of ownership by a subject, rather than by offering some kind of reductive explanation of the notion. None of these phenomena, nor their explanations, establish that you do not perceive your own body. The contrary is argued by Metzinger: ‘At this point into our investigations into consciousness, it seems obvious that we are never in direct contact with our physical bodies but rather with a particular kind of representational content. . . What you experience is not reality but virtual reality, a possibility. Strictly speaking, and on the level of conscious experience alone, you live your life in a virtual body and not in a real one’ (2009: 113–14). Metzinger’s argument for this conclusion is that ordinary

174   Christopher Peacocke perception uses the same kind of representational systems as virtual reality systems that can be attached to a perceiver’s head. This position is open to two objections. First, to say that you are in ‘direct contact’ only with a certain kind of representational content is to confuse the level of intentional content with the level of reference. A perceptual state can be of an object, including one’s own body, consistently with the perceptual state being a result of computations involving representational contents. (Arguably, it must so result if the state is to be genuinely perceptual rather than merely sensational: see Burge 2010: ch. 9.) If Metzinger’s arguments on this issue were sound, they would equally establish that one does not perceive any physical objects at all. Second, and more generally, the states of consciousness involved in enjoying a virtual reality system have the representational content they do because they stand in certain similarity relations to ordinary perceptual states that do for the most part correctly represent objects, events, and the subject’s own real body in ordinary cases. Genuine perception cannot be elucidated without circularity in terms of its relations to something whose nature is parasitic on genuine perception itself.

4  Perceiving yourself In one of philosophy’s famous passages, Hume wrote, ‘when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe anything but the perception’ (Hume, 2000: Book 1, Part 4, Section 6, p. 165). Hume was surely well aware that he could perceive his own body and his body parts. Evidently he did not take this obvious fact as a counterexample to his intended thesis. Many have been similarly tempted by Hume’s claim even if they have found it hard to say exactly what is right in it. The claim has an affinity to a thought of the young Wittgenstein, when in the Notebooks he wrote ‘I objectively confront every object. But not the I.’ (1979, entry for 11 August 1916, p. 80e). We can learn about perception and its relation to the first person by identifying what is right in Hume’s intended claim. What Hume rightly found is that there is a sense in which he could not attend to himself. Whenever a subject attends to something, the subject attends to it as given in a certain way. When hiking, you may attend to a mountain as given in a certain distance and direction from you. That is to be distinguished from attending to the same mountain, which happens also, unobviously, to be the same one as the one presented in a different direction, some of its parts being obscured by an intervening hill. We can then formulate Hume’s claim thus: there is no such thing as attending to something as given in a purely first personal way. Attending to something given as one’s body, or as one’s hand, is no counterexample to this formulation. In such cases, one’s body and one’s hand are given in perception in perceptual-demonstrative ways that are not purely first personal. There is, for example, a perceptual component in your seeing what is in fact your hand which is common both to your experience of your hand, and the experience of the hand by someone suffering from apotemnophilia with respect to that hand. The latter sees and feels it, but not as his own. Attending to oneself seems to be possible only when there is an experience of something not given purely as oneself.

Perception and the First Person    175 If Hume’s claim, so understood, is true, what is the explanation of its truth? The explanation lies jointly in the nature of attention and the nature of de se content. Attention must always be to something apparently given in perception or sensation (or, perhaps, in memory or imagination). But de se content is arguably individuated, like any other element of intentional content, by its fundamental reference rule, which in the case of the first person is this: as a de jure matter, in any mental state or event in whose content the first person occurs, it refers to the subject who enjoys that state. This rule does not require that the subject of the state with first person content also be presented in any other way, in perception or by any other conscious state or event. There are mental states and events with first person content in which the subject is not presented in any other way. As we noted, you can see something as coming towards you, or as at a certain distance from you, even if you are not perceiving or sensing your body at the time at all. You experience your hand as your own, you experience a sensation as your own, but neither of these requires that you be given in some further way a non-first-personal way in these conscious events. Since anything to which you can attend must be given in a perceptual or sensational way (or in imagination or memory), it follows that there is no such thing as attending to something given purely in a first personal way, and not in any other. That was precisely Hume’s claim. Since the claim seems to follow from the nature of attention and the nature of de se content, the claim is not a merely contingent matter. I do not say that these points were clearly in Hume’s own mind. My position is rather that even those who think that Hume’s conclusion about the nonexistence of a subject distinct from its experiences was a nonsequitur nonetheless often feel that there is something right about his starting point. I offer this account in terms of attention and its relation to de se content as a way of stating what is right in his starting point. So construed, Hume’s insight concerns de se intentional content. No conclusions can be drawn from what is right in Hume’s claim about the reference of the de se component, the subject or owner of conscious experiences. The argument just given for Hume’s claim is consistent with the thesis that persons, Hume included, are essentially embodied. The argument is equally consistent with Shoemaker’s thesis that for any given subject, there must be an account of what it is for the subject to be embodied. The argument does not involve any commitment to Hume’s further view that each of his ‘perceptions’ is an independent entity which requires nothing else for its existence. The argument outlined here for Hume’s claim is equally consistent with the view that all mental events must have subjects, subjects whose existence cannot be reduced to subject-free entities. Nor is there any support in the argument for Hume’s view for the younger Wittgenstein’s conclusion that subjects of consciousness are not in the world. From the fact that veridical conscious states do not and could not present their subject as an entity in the world, it does not follow that their subject is not in the world.

5  Objective perception as constitutive of the subject? Is perceiving an objective world from a spatial standpoint a necessary part of either what it is to be a subject, or (what is not quite the same) what it is to be capable of mental states with

176   Christopher Peacocke first person contents? An affirmative answer to either question results in a Kantian thesis. Both theses are endorsed by Strawson (1966). More than one kind of argument has been offered for such Kantian theses. The argument in Strawson (1966) is built from the following elements. A subject enjoys unity of consciousness; this requires the possibility of self-ascription by the subject of the experiences enjoyed by the subject; experiences involve the recognition of entities as falling under kinds; this recognitional component requires a seems/is distinction, whose basis is present in the experiences themselves; and this in turn requires ‘the distinction between the subjective order and arrangement of a series of such experiences on the one hand and the objective order and arrangement of the items of which they are experiences on the other’ (Strawson 1966: 101). The argument is meant to show that there could not be a subject with a series of conscious experiences consisting only of states with no content about the objective world—with merely such objects as ‘red, round patches, brown oblongs, flashes, whistles’ (Strawson 1966: 99), all of which Strawson takes to be subjective. The links and underlying principles of Strawson’s argument are not entirely clear, and this ambitious argument remains a target of identification and discussion. It is clear that the argument would need to meet the following objections. Prima facie, ownership of an experience is more fundamental than self-ascription of that experience. Ownership explains proper self-ascriptions. That would mean that the early stages of the argument would need revision. Identity of subject over time may also be founded in identity of the subpersonal apparatus that integrates information and yields multiple and complex states of consciousness at a given time in a given subject. Such an identity of integrating apparatus can underlie a sequence of experiences that lack objective representational content. Even when experience is as of objects and events on a path through a spatio-temporal world, the unity of such a consciousness is underlain by identity of integrating apparatus. This suggests that we can make sense of a notion of a subject of consciousness under which a subject may or may not have perceptions of, or even as of, an objective world. Ordinary subjects need not have any conception of an integrating apparatus. That identity of subject consists in identity of integrating apparatus is a constitutive, metaphysical thesis. The ordinary subject simply enjoys or suffers states with de se content, such as the content that he recently experienced an acrid smell. The thesis about integrating apparatus concerns the nature of the entity that is the reference of the de se component in the content of a given mental state. The thesis is not meant to be something immediately obvious from the nature of de se intentional content. Under the metaphysical thesis, a subject can be under an illusion that he was recently thus-and-so. Even if someone else was recently thus-and-so, an apparent memory of that event may be transmitted to a subject whose identity involves a different integrating apparatus. So seeming identity is not sufficient for genuine identity (a requirement on which Kant would also insist). But there is also no obstacle to genuine awareness of identity over time, in good cases. To say that identity of subject is not to be explained in terms of perception of an objective world is not to imply that there are not major insights in the work of those who have endorsed these Kantian theses. The theses are also implied by the treatment in Evans (1982). Evans’s book contains accounts of why various bodily and spatial self-ascriptions, made on the basis of proprioception and outer senses respectively, can be knowledge, knowledge

Perception and the First Person    177 that does not rely on any substantive belief I am identical with m, for some singular concept m other than the first person. The accounts in Evans of self-ascriptive knowledge can be retained, consistently with rejection of the Kantian theses. The accounts can be seen as elaborations of the epistemology and metaphysics of bodily and spatial predications in the first person, when the subject does in fact enjoy perception of an objective world and enjoy embodiment within it. That would be consistent with admitting the possibility (denied by Evans 1982: 250–1) that there can be a subject whose conscious states are realized in the states of a brain permanently in a vat, a subject who cannot locate himself in the objective world, but who still succeeds in referring to a subject—himself—when he thinks ‘I wonder if this apparent world is real’ (or even ‘Cogito ergo sum’). This subject in fact has an integrating apparatus whose operations explain his complex experiences at a time and over time. The condition for an entity to be the reference of the de se component of the intentional content of his experiences is met, viz. the condition that it be the subject of those experiences. It is met by the subject itself, a subject realized in a real integrating apparatus. We can distinguish between this subject having correct and having incorrect apparent memories of his earlier experiences. All this is consistent with a philosophical account of what it is for his experiences to have the representational content needing to be cast in terms of their environmental causes and effects when the subject’s integrating apparatus is properly connected to the world, rather than being sustained in the vat.

6  De se content, first person concept, entitlement, and knowledge An animal without language can see something as moving away from it, can hear something as coming towards it. These perceptions have a de se content, and it is very implausible that their occurrence in any way presupposes the possession of concepts in any strict use of that term. Conceptual content is content of the sort that a thinker can accept or reject for reasons. The exact nature of the connection between concepts and reasons is a matter of some disagreement. Some thinkers would write the connection immediately into the individuation of each particular concept. Under that approach, a concept is individuated by what gives reasons for making certain judgements whose content contains the concept, or is individuated by what certain judgements involving the concept in turn give reasons for judging (Brandom, 1994). Concepts with the same reason-involving powers are identical, as an immediate consequence of this approach. Other approaches to conceptual content would regard the connection between concepts and reasons for making certain judgements as derivative. Many truth-conditional approaches to the individuation of content and concepts would regard the connection between a concept and reasons for judging contents containing the concept as explicable from the concept’s contribution to the truth-conditions of contents in which it occurs (Peacocke, 2008). Whatever the source of the connection between reasons and concepts, it is highly plausible that it exists. But the de se perceptual states, and other de se states of some animals, such as intention, memory, and action awareness, seem to lie below the level of anything essentially involved with, or individuated by, relations to reasons. Yet we nevertheless use the first person concept, as

178   Christopher Peacocke expressed by ‘I’ and ‘me’ in English, both in describing and in expressing these perceptual states with nonconceptual de se content. ‘It looks as if the cyclist is moving away from me’ is the entirely natural expression of the de se content of a visual experience we can enjoy. ‘It looks as if the ball is being thrown far away from him’ is an entirely natural description of the dog’s visual experience. That in itself is a puzzle, but it also leads to at least three other questions. What more generally is the relation between the first person concept and nonconceptual de se content? Can experiences with nonconceptual de se content entitle a thinker to make judgements with conceptual content? Can those experiences in appropriate circumstances lead not just to rational judgement, but to knowledge? I will outline a position on these issues, but readers should be alerted that I am not a neutral party in current discussions on these issues. (A very different approach, one which treats at least all human perceptual content as conceptual, is given in McDowell (1994).) Suppose a thinker makes a first person judgement I am F, and suppose too he also enjoys various perceptual experiences with nonconceptual de se contents. A  creature without concepts could also have experiences with such nonconceptual de se contents. Then the object our thinker is judging to be F is identical with the object his de se perceptual states represent to be thus-and-so when they have the nonconceptual content that he is thus-and-so. This identity is not an a posteriori truth. Rather, the identity follows from the very nature of the first person concept and the nature of de se nonconceptual content. The first person concept is individuated by the condition that in any judgement involving it, it refers to the subject who is doing the judging. The reference of the de se component of the intentional content of his experience is the subject enjoying the experience. That is the rule of reference that individuates the nonconceptual de se notion. But we have already said the case is one in which the judger is enjoying the experience. It follows that in such a case, the reference of the thinker’s use of the first person concept is identical with the object represented as thus-and-so in his de se perceptual experiences of being thus-and-so. So the reference of the first person concept, as used by the thinker, is identical with the reference of the nonconceptual de se in such a case. This identity of reference is a necessary condition for a stronger claim, the claim that nonconceptual de se contents of perceptual experience defeasibly entitle the thinker, in the absence of good reasons for doubt, to judge corresponding first person conceptual contents. A perceptual experience with the nonconceptual content that a tree is in a certain direction (picked out in the scenario content) from oneself can entitle a thinker to judge a corresponding conceptual content that tree is in that direction from me. This is structurally parallel to the way in which a perceptual experience in which something perceived nonconceptually as a four-sided equilateral figure, and as symmetrical about the bisectors of its opposite angles, can entitle a thinker to judge the conceptual content that’s regular diamond-shaped (Peacocke, 1992). In both this shape case, and in the de se examples, if the nonconceptual content is correct, then so too is the content of the conceptualized content to whose judgement it provides an entitlement. This conditional holds in virtue of the nature of the contents in question. It is because the conditional holds in virtue of the nature of the contents involved that the entitlement exists. The identity of the reference of the thinker’s first person concept, as employed by him, with the reference of the de se component of his perceptual states, is also a necessary condition for the conditional to hold. This treatment of the relations between the nonconceptual de se contents of perceptual experience and conceptualized first person judgements is available both to those who hold

Perception and the First Person    179 that embodiment is fundamental to subjecthood, and to those who hold that it is not so fundamental. The latter can hold that a conscious subject may not need a bodily realization, but when the subject does, then these entitlement relations just identified are derivative from what it is for the subject to have a particular embodiment. The treatment above also contributes to an explanation of why we so naturally employ the first person concept in describing the de se perceptual states of creatures that do not possess concepts at all. Since our own de se nonconceptual perceptual states entitle us to make first person judgements about ourselves and our relations to our environment, it is natural to identify the perceptual representational states of a nonconceptual creature by the contents those states would entitle us to judge. We engage in such identification not only in the case of the first person concept, but also with many spatial, temporal, and other concepts that have constitutive entitlement relations with the nonconceptual content of perception. The point applies as much to the linguistic expression of our own perceptual states as it does to the description of those of others. Perceptual experiences with de se contents can lead not merely to correspondingly entitled judgements, but also to knowledge. A necessary condition for knowledge is one of the several requirements that have been called ‘safety’, viz., that the method by which the belief is attained leads to truth in other circumstances that could easily have obtained (Peacocke, 1986; Sosa, 1999). The de se contents of perceptual experience exhibit the phenomenon of constancy. You perceive the door as being in the same direction from you, even if your eyes move in their sockets, or your head moves, and the result is a different pattern of local (in this case retinal) stimulation. Constancy implies that in a range of circumstances that can easily obtain, you will have an experience with the same representational content if the relevant objective features of the world remain the same. This in turn means that if you make a judgement which a corresponding perceptual experience with a nonconceptual content entitles you to make, the resulting belief will be safe with respect at least to the range of circumstances under which constancy holds. First person beliefs appropriately based on de se nonconceptual contents of perception can thereby meet this necessary condition for knowledge. Though the self and the de se have many distinctive features, some so briefly outlined in this chapter, these most recent considerations show that they do share with the other contents of perception the general nature of many of their entitlement relations.

References Botvinick, M. and Cohen, J. (1998). 'Rubber hands "feel" touch that eyes see'. Nature, 391, 756. Brandom, R. (1994). Making It Explicit: Reasoning, Representing, and Discursive Commitment. Cambridge MA: Harvard University Press. Burge, T. (2010). Origins of Objectivity. Oxford: Oxford University Press. Campbell, J. (1994). Past, Space, and Self. Cambridge MA: MIT Press. Costantini, M. and Haggard, P. (2007). 'The Rubber Hand Illusion: sensitivity and reference frame for body ownership'. Consciousness and Cognition 16(2), 229–240. Dennett, D. (1978). 'Where am I?' In Brainstorms. Montgomery VT: Bradford Books. Evans, G. (1982). The Varieties of Reference. Oxford: Oxford University Press. Gallagher, S. (2005). How the Body Shapes the Mind. Oxford: Oxford University Press. Gibson, J. J. (1986). The Ecological Approach to Visual Perception. Hillsdale NJ: Erlbaum.

180   Christopher Peacocke Hume, D. (2000). A Treatise of Human Nature, ed. D. Norton and M. Norton. Oxford: Oxford University Press. Kant, I. (1998). Critique of Pure Reason, trans. A. Wood and P. Guyer. Cambridge: Cambridge University Press. Lenggenhager, B., Tadi, T., Metzinger, T., and Blanke, O. (2007). 'Video Ergo Sum: Manipulating bodily self-consciousness'. Science, 317, 1096–1099. McDowell, J. (1994). Mind and World. Cambridge MA: Harvard University Press. Martin, M. (1995). 'Bodily awareness: A sense of ownership'. In J. Bermúdez, A. Marcel, and N. Eilan (eds), The Body and the Self (pp. 267–289). Cambridge MA: MIT Press. Metzinger, T. (2009). The Ego Tunnel:  The Science of the Mind and the Myth of the Self. New York: Basic Books. Peacocke, C. (1986). Thoughts: An Essay on Content. Oxford: Blackwell. Peacocke, C. (1992). A Study of Concepts. Cambridge MA: MIT Press. Peacocke, C. (2008). Truly Understood. Oxford: Oxford University Press. Peacocke, C. (2014). The Mirror of the World: Subjects, Consciousness, and Self-Consciousness. Oxford: Oxford University Press. Pylyshyn, Z. (2007). Things and Places: How the Mind Connects with the World. Cambridge MA: MIT Press. Ramachandran, V. (2011). The Tell-Tale Brain: A Neuroscientist’s Quest for What Makes Us Human. New York: Norton. Shoemaker, S. (1984). 'Embodiment and behavior'. In Identity, Cause, and Mind. Cambridge: Cambridge University Press. Sosa, E. (1999). 'How to defeat opposition to Moore'. Philosophical Perspectives, 13, 141–153. Strawson, P. (1966). The Bounds of Sense. London: Methuen. de Vignemont, F. (2007). 'Habeus Corpus: The sense of ownership of one’s own body'. Mind & Language, 22(4), 427–449. Wittgenstein, L. (1979). Notebooks 1914–1916, ed. G.H. von Wright and G. E. M. Anscombe. Oxford: Blackwell.

Chapter 10

Nonconceptua l Con ten t

1

Wayne Wright

1 Introduction The main debate about whether perceptual experience has nonconceptual content begins with agreement that experience represents the world and that an experience’s content is the way it represents things as being. Assuming this much, the debate centres on the question:  Is the range of content-bearing perceptual experiences a creature can enjoy independent of its conceptual resources? Conceptualists answer negatively, nonconceptualists affirmatively. Bill Brewer (1999, 203) provides an example of conceptualism, claiming that ‘[perceptual] experiences . . . have representational contents which are characterizable only in terms of concepts which the subject himself must possess.’ John McDowell (1994, 10; original emphases) proposes that ‘when we enjoy experience conceptual capacities are drawn on in receptivity, not exercised on some supposedly prior deliverances of receptivity’; receptivity is our capacity to be affected by and form representations of objects (Kant A19/ B33). McDowell’s remark indicates that conceptualism does not take concepts merely to impose a top-down constraint on the range of permissible experiential contents. They are intimately involved in the production of that content. In contrast, nonconceptualists hold that creatures can have experiences with contents that are not limited by their arsenal of concepts. Michael Tye (2006, 507) characterizes nonconceptualism in terms of the specification of correctness conditions. Tye’s idea is that while concepts would have to be exercised in providing a (theory-relative) canonical statement of a given content’s correctness conditions, having an experience with that content does not require possessing or deploying any of those concepts. Consider the fine-grained nature of the properties encountered in experience, which many nonconceptualists emphasize. Gareth Evans (1982, 229) asked, ‘Do we really understand the proposal that we have as many colour concepts as there are shades of colour that we can sensibly discriminate’? Let us assume momentarily that re-identification by means of stored representations 1  I thank Mohan Matthen for much useful feedback on a draft of this chapter. I am also grateful for discussions of these issues with Michael Tye, Gerald Vision, and the late David Welker.

182   Wayne Wright is a criterion of concept possession. Subjects simultaneously viewing two uniformly coloured surfaces of similar shades of red (say, Munsell chips 2.5R 6/12 and 5R 5/14) can discriminate them from one another in terms of colour despite not possessing a stored icon for the specific shade of either sample, being ignorant of the Munsell conceptual system or any other colour order system, and so forth. If such performance depends on differences in how the surfaces’ fine-grained colours are represented, experience has nonconceptual representational content. Endorsing nonconceptualism does not automatically commit one to claiming that a creature could have perceptual experiences with nonconceptual contents without possessing any concepts whatsoever or that perceptual experience cannot also have conceptual content. Although the dispute between conceptualists and nonconceptualists looks easy to get a handle on, there are several complications. The debate turns on notions about which there is ample controversy: the nature of concepts and their possession conditions, the grounds for attributing states with representational content, and what counts as a perceptual experience. Another problem is that conceptualists and nonconceptualists often are motivated by different concerns. Adina Roskies (2008, 634) notes that conceptualists such as Brewer and McDowell are chiefly wrangling with epistemological considerations. They charge that perceptual experiences could not justify beliefs about the world if their contents were not fully conceptual. Nonconceptualists tend to stress either features of the relationship between concepts and experience besides justification (see Peacocke 1992, 2001; Roskies 2008, 2010) or a range of empirical findings and introspective observations that clash with the conceptualist’s thesis (see Evans 1982; Kelly 2001a; Peacocke 1992 and 1998; Raftopoulos 2009; Tye 2006). The varied nature of the goals and motives in play raises the possibility that researchers are sometimes talking past one another or misjudging the resources available to their opponents. There is also the appearance that central terms of the debate are unclear in a way that obscures the positions available. Richard Heck (2000) points out that there are two different ways of being nonconceptual (each with a corresponding way of being conceptual) and it is not always clear which is on the table (see also Crowther 2006; Speaks 2005). Content nonconceptualism is a matter of a state’s representational content not being constituted by concepts. State nonconceptualism has it that being in a given representational state is independent of whether one possesses concepts that reflect the state’s content. Perhaps there is one kind of content, but two kinds of content-bearing state. One kind of state (exemplified by belief) has a content-relative requirement of concept possession while the other (exemplified by experience) does not. Although reasons to pare down the slate of choices might subsequently emerge, we initially have to recognize all four possible pairings of state and content views as options, rather than just simple conceptualism and nonconceptualism. This chapter examines some of the arguments made on both sides of the nonconceptual content debate and the complications just introduced. The primary goal is to shed light on the motivations for and challenges facing both conceptualism and nonconceptualism. I also aim to show that each side has to grant significant concessions to the other. I suspect that this result diminishes the significance of the debate, but the more ecumenically minded might interpret this as a situation in which the truth falls somewhere between opposing views.

Nonconceptual Content   183

2 State and content views Brewer’s and McDowell’s aforementioned remarks reveal that conceptualism as typically understood encompasses both state and content conceptualism. According to this ‘pure’ conceptualism, experiential content is constituted not just by concepts, but by concepts the experiencing creature possesses and which are deployed. This fits with a common approach to attributions of representational content to a range of states like belief and desire that we can group together as ‘thoughts’: thought contents are constituted by concepts and content attributions must capture how things are from the point of view of the subject. The ‘point of view’ requirement would be violated if a thinker were attributed a thought with a content featuring a concept she either did not possess or possessed but did not employ. For example, it would be wrong to use concepts from modern genetics to characterize an eighteenth-century farmer’s beliefs about annual crop variation, and MOTHER 2 ought not figure in the specification of Oedipus’s thoughts about Iocasta prior to his encounter with the herdsman. If perceptual experience has the same sort of conceptual content as our thoughts about the world, we can literally believe what we see, see what we want, and so forth. In such a circumstance, it seems unproblematic to hold that perceptual experiences are capable of both justifying beliefs and feeding their contents into our decision-making and action-planning processes. Matters with nonconceptualism are more complicated. Some nonconceptualist statements suggest a ‘pure’ (i.e. state and content) nonconceptualism. Gareth Evans (1982, 227) claimed that ‘[the] process of conceptualization or judgement takes the subject from his being in one kind of informational state (with a content of a certain kind, namely, nonconceptual content) to his being in another kind of cognitive state (with a content of a different kind, namely, conceptual content)’. Different accounts of a nonconceptual form of content have been offered; viz. Russellian propositions (Tye 2006), sets of possible worlds (Stalnaker 1998), and specifications of how the space around the perceiver is filled out in terms of surfaces and their properties (this is the scenario content of Peacocke 1992). However, arguments for nonconceptualism often neglect what constitutes the content of perceptual experience. Instead, they target what is required to have a content-bearing experience and are relevant only to state nonconceptualism. Recall the argument from fine-grained detail. Alex Byrne (2005, 235–236) notes that a conclusion about what constitutes experiential content does not directly follow from the claim that having an X-representing experience carries no demand that the perceiver is able to conceive of instances of X qua instances of X. This applies mutatis mutandis to other prominent arguments for nonconceptualism (Speaks 2005, 366). These points might be taken as exposing confusion or ineffectiveness in nonconceptualists’ opposition to conceptualism. However, Josefa Toribio (2008) argues that the distinction between state and content nonconceptualism is untenable for those who hold that content attributions must reflect the way the world seems to the subject. Toribio (2008, 360) contends that content-talk earns its keep through its explanatory usefulness, such explana­ tory usefulness requires that content attributions capture how things seem to be from the 2 

I adopt the practice of entirely capitalizing words used to refer to concepts.

184   Wayne Wright perspective of the creature in question, and the range of ways things can seem to a creature is constrained by that creature’s cognitive abilities. This package of ideas appears essential to the relevance of how the world is represented in experience to explanations of intentional behaviour, the formation of perceptual beliefs, and discriminatory abilities. Toribio concludes that this perspective on content attribution makes the pairing of state nonconceptualism and content conceptualism incoherent, as it has the consequence that a creature could be attributed conceptual capacities (in order to fill out the content specification) that it does not possess. Thus should there be a convincing case for state nonconceptualism, there is a path to content (and ‘pure’) nonconceptualism. While the thesis that content attributions must reflect the subject’s point of view has dissenters, conceptualists such as Brewer and McDowell embrace it. Hence the most interesting challenge to conceptualism would begin with agreement on that thesis and move to developing a case for there being a way of representing the world in experience that is not determined by the subject’s conceptual capacities but that can interact with such capacities in the requisite ways. Many nonconceptualists’ efforts fit this mould. This is certainly true of nonconceptualists who build their case on appeals to the empirical literature that are supposed to establish either that there is a species of perceptual output that is genuinely representational and encapsulated with respect to information from epistemic/semantic centres (Bermúdez 1995; Raftopoulos 2009) or that there is not the right sort of match between the conceptual capacities humans possess and the concepts necessary to characterize experiential content in a way that captures how things seem to the subject (Dokic and Pacherie 2001; Tye 2006).

3 Why be a conceptualist? Since nonconceptualism is often positioned as reacting against conceptualism, it is routinely introduced in terms of what it is not (Vision 1997, 244; Bermúdez and Cahen 2011, section 2). So, it will be helpful to get a sense of conceptualism’s appeal. McDowell (1994) serves as a useful point of focus. His formulation of conceptualism turns on the axiom that perceptual belief is justified by perceptual experience. Without an ‘external rational constraint’ (p. 25) on the beliefs we form about our surroundings, we are left with an unsatisfying view of our epistemic circumstances. What is sought is an account of our perceptual contact with the world that makes it a source of justification while standing outside the realm of thought. Unfortunately, the two positions commonly taken up regarding the epistemic relationship between experience and belief put us in bad straits. McDowell locates the failures of these different views in the same source: in the course of making experience distinct from thought, both place experience outside the conceptual realm. On the one hand, we could acknowledge only causal relations between extra-conceptual experiences and beliefs while taking justification to come from some concept-involving source other than experience. Donald Davidson’s coherentism is representative of this sort of thinking. This abandonment of ‘external friction’ (McDowell 1994, 11) faces worries about how thought can get any bearing on empirical reality, as on this approach we ‘cannot get outside our beliefs’ (p. 16). Thus the world’s impacts on our senses place no rational constraints on our thoughts about the state of the world. This view also offers an implausible

Nonconceptual Content   185 picture of belief formation. Intuitively, beliefs are formed for reasons. However, on this account it is unavoidable that many of a subject’s beliefs are causally foisted on her, as though (for example) she had taken a pill that produces in her the belief that her spouse’s shirt is blue (Heck 2000, 51). These problems are significant enough to make the alternative tempting. This other approach has it that experience—understood as unstructured or unprocessed ‘bare presences’ (McDowell 1994, 19)—can justify belief despite being extra-conceptual. This extension of the ‘space of reasons’ beyond the ‘space of concepts’ is the Myth of the Given that Wilfrid Sellars (1956) is supposed to have demolished. The Myth is alluring because it promises the external grounding of belief that is lacking in Davidson’s coherentism, but it cannot deliver on that promise. We can make sense of an experience being a subject’s reason for believing something about the state of the world, conceptualists say, only if there are conceptual relations between the experience and the belief (Brewer 1999, 149–152; McDowell 1994, 7–9). McDowell regards Evans’ (1982) nonconceptualism as a post-1956 lapse back into the Myth. McDowell (1994, 46) presents his conceptualism as a way out of the problems facing the Myth of the Given and Davidsonian coherentism. The core of his proposal is that perceptual experience is able to justify belief because the same conceptual capacities are operative in both, despite experience and belief being distinct. For McDowell, experience draws on our conceptual capacities to impose the sort of order on the deliverances from our senses required for rational relations between experience and thought. McDowell’s rejection of the two traditional options and the motivation for his own view largely turn on his handling of a famous quote from Kant: ‘Thoughts without content are empty, intuitions without concepts are blind’ (A51/B75). For Kant, intuitions are the outputs of the sensibility, the mind’s faculty for being affected by the world, while thoughts are products of our faculty of understanding. According to McDowell’s Kant, representational content requires the joint contribution of concepts and intuitions. Thoughts unconnected to intuitions are a mere shuffling around of concepts, making them incapable of representing anything (McDowell 1994, 3–4). As for intuitions not brought under concepts, their blindness is a failure to present to the subject something which is intelligible to her as a feature of an objective world (McDowell 1994, 54). They lack representational significance and cannot justify beliefs about the world. McDowell claims that while concepts are actively deployed in reflective thought, they operate passively at the level at which external objects impinge on us. We can choose what we think, but not how things are conceptually represented in our experiences (McDowell 1994, 11). Kant’s account of experience is supposed to offer ‘precisely the picture’ McDowell recommends (1994, 41), but McDowell breaks with Kant on matters of critical importance. McDowell’s interpretation of Kant’s dictum about concepts and intuitions leads him to state that ‘[we] should understand what Kant calls “intuition”—experiential intake—not as a bare getting of an extra-conceptual Given, but as a kind of occurrence that already has conceptual content’ (1994, 9). Kant takes intuitions and concepts as cooperative with respect to achieving empirical knowledge, but he also portrays them as fundamentally distinct, as they have different relations to the objects that affect our senses. Intuitions have ‘immediate relations’ to objects (A19/B33, A320/B377) whereas concepts are ‘never immediately related to an object’ (A68/B92–93). This difference is irreconcilable with the idea that intuitions include a conceptual element.

186   Wayne Wright The idea here is not to advance a Kantian refutation of conceptualism, but to point out that central features of Kant’s actual views do not square with what is supposed to be the most persuasive case for conceptualism. Thus it is unclear what Kantian basis there is for conceptualism. According to McDowell, his conceptualism alone offers a means of grounding justification for belief about the world in perceptual experience. However, Robert Hanna (2005, 262–265) argues that Kant held that extra-conceptual intuition has a structure that endows it with non-inferential ‘evidential force’ and that intuition’s immediate relation to objects enables it to serve as the basis for fixing demonstrative reference. Consequently, the list of options McDowell considers—Davidsonian coherentism and the Myth of the Given—looks profoundly incomplete from the Kantian perspective. Gerald Vision (1998) argues that empirical research also reveals McDowell has underestimated the range of options. The evidence at hand demonstrates that our perceptual faculties do not hand over to our cognitive centres an unstructured Given that is disconnected from the world. It is also compelling to think that at least some of the structured outputs of perceptual processes do not result from contributions of concepts that the perceiver is able to deploy in thought; i.e. at least some experiential content is cognitively encapsulated and not subject to top-down influences from stored semantic/epistemic resources. It will emerge later that this does not decisively refute conceptualism. For now, it suffices to note that the central defect of the Myth of the Given—its commitment to a bizarre picture on which a slurry of experiential intake could somehow provide reasons for beliefs about distinct objects, properties, and events in the world—does not obviously attach to an account of nonconceptual content developed around structured outputs of cognitively encapsulated perceptual processes. A story is required about how these perceptual contents might be connected with beliefs in the required ways, but there are no prima facie grounds for thinking such a story is impossible (Heck 2000, 511–520; Peacocke 1992, 74–80). Additionally, perhaps McDowell’s conceptualism does little more than push a bump under a rug from one spot to another. McDowell’s solution to the epistemic challenge at hand is to put the same conceptual capacities to work in both thought and experience. However, more needs to be said about how conceptual capacities are recruited to do the work in experience that McDowell assigns them. This concern is not about the psychological or neural plausibility of McDowell’s proposal. Rather it targets how we can get a grip on the application conditions of concepts at the level of experience. While talk of ‘reasons for’ might be reserved only for states like belief and judgement, something similar should apply when it comes to the deployment of concepts in experience. Otherwise, it seems as though conceptual experiential content is produced in willy-nilly fashion and McDowell’s account looks no better off than those he rejects. Certainly, if conceptual experiential contents are supposed to justify empirical beliefs, providing reasons for a perceiver to believe one thing or another, the relevant concepts must have some reason-conducing basis for figuring in those experiential contents. Let us call this basis the ‘grounds for’ the application of a concept in the content of perceptual experience. Consider a visual illusion like that induced by viewing the Müller-Lyer figure. Whatever concepts constitute the content of such an experience, conceptualism requires that the two lines are represented as having different lengths by means of those concepts. On what grounds are those concepts, rather than others, passively drawn into the content of that visual experience? Since the actual state of the world is that the lines are of the same length, it looks as though the answer cannot involve an appeal to how the world is (cf. McDowell

Nonconceptual Content   187 1994, 39 and 143). In fact, reflection on cases of veridical experience should suffice to reveal that an appeal to the state of the world will not immediately quell the current concern. Despite misgivings, I will grant McDowell that the state of the world can always be conceptualized. Even if the world does not stand outside the boundaries of what can be conceived, we would still require an account of how the world impresses on our senses in a way that allows it to serve as the grounds for the application of the concepts that figure in the content of experience. Relevant here are McDowell’s (1982/1988) epistemological disjunctivism and themes from the work of J. J. Gibson (1979) that find a place in McDowell’s thinking. McDowell, like Gibson, takes our perception of the world to be direct and emphasizes that perceiving creatures (and not brains) inhabit an environment. Drawing on Daniel Dennett’s (1969) distinction between sub-personal and personal levels, McDowell holds that the computational operations performed in the visual system are no more than syntactic transformations carried out by physical processes. This sub-personal activity begins with the retinal stimulus and never makes contact with the environment itself. Consequently, the outputs of those processes cannot tell us anything that would bear on the justification of empirical beliefs. The world itself is what informs us of how things are (McDowell 1994/2002, 450). McDowell states that an information-processing framework such as David Marr’s (1982) is appropriate for studying a syntactic mechanism like the visual system. McDowell has no objection to talking of nonconceptual content for that purpose, but he regards such content attributions as merely ‘as if’ (1994, 55, and 1994/2002, 452; see Bermúdez 1995 on nonconceptual content and sub-personal computational states). The processes and contents that figure in theories pitched at this level are claimed to be only causally relevant to the ‘real’ (i.e. genuinely semantic or intentional) content that figures in perception and thought (McDowell 1994/2002, 452). They play no role in constituting the contents of experiences of and thoughts about the world, as by their very nature they are blind to the world. Gibson’s ecological approach, with its focus on the perceiving creature coming into unmediated contact with its environment, is apt for the study of vision, understood as a personal-level achievement of finding out how things are in the world. For McDowell, since vision puts us in direct contact with our environment, there is no problem with the world itself serving as the grounds for the concepts that figure in the content of experience. Of course, the way the world appears to be in experience can be mistaken and we might be unable to distinguish deceptive and accurate experience on the basis of how things appear. Undetectable misperception has fuelled many of the theories of perception McDowell sets himself against. McDowell (1994/2002, 450–451) explains misperception causally, in terms of things ‘going well’ with the sub-personal processes that begin at the retina. If those processes do not unfold appropriately, we have mere appearance rather than direct perception of the state of the environment. Since the epistemic differences between perception and misperception get a purely causal explanation, there is no room for a reason-conducing intermediate link between perception and the world (see also McDowell 1982/1988, 218 n.15). Thus the above worry dissolves. Empirical thought is rationally constrained by facts about the world due to experience being conceptual and putting us directly in touch with our surroundings. Appeals to epistemological disjunctivism and direct perception will not defuse the problem at hand. Heck (2000, 497–498) argues that the central thesis of epistemological disjunctivism—that from the standpoint of justification there are two kinds of experiential

188   Wayne Wright state, one veridical and the other nonveridical—cannot be extended to the representational content of experience. The content of an experiential state cannot depend on whether or not it is veridical, as the veridicality or nonveridicality of the experience depends on whether the world is as it is represented in the experience. The same reasoning also blocks disjunctivism about what fixes or grounds experiential content. Even if McDowell is correct that veridical and nonveridical experience are distinct states, there has to be a common content-fixing factor between them. That factor cannot be the state of the world itself, as the world is other than how it is represented when we misperceive it (see also Tye 2006, 523). In that case, it is still unclear why an experience would have one conceptual content rather than another. This is a serious problem for McDowell, as the advertised chief advantage of his conceptualism is that it secures reason-based relations between experience and belief.

4 Motivations for nonconceptualism Jeff Speaks (2005, 362–363) identifies seven kinds of arguments that have been offered for nonconceptualism and places them into two categories: ‘arguments from features of perception’ and ‘arguments from general theses about the conceptual’ (see also Bermúdez and Cahen 2011, section 4.1). In this section I focus on one argument from each of the categories Speaks identifies: the arguments from fine-grained detail and concept acquisition. The argument from fine-grained detail has already been introduced. Perceivers are able to perform discriminations, similarity judgements, and categorizations involving determinate features of their experiences that go well beyond their conceptual capacities. Granting that subject performance in these tasks depends on the representation of the determinate qualities in question, the representational content of experience is not constrained by the subject’s conceptual capacities. A related line of reasoning concerns the perceptual faculties of human infants and (some) nonhuman animals. It is compelling to think that these creatures have experiences much like our own in some respects, which should be reflected in continuities between (some of) the contents attributed to their experiences and to adult human experiences. However, infants and nonhuman animals, if they possess concepts at all (see Bermúdez 2003), do not have conceptual resources nearly as rich as those possessed by adult humans. If one is at all tempted by the fineness of grain argument to think that perceptual contents can outrun the conceptual resources of adult humans, the cases of infants and nonhuman animals offer further reason to suppose that a notion of nonconceptual content is needed. Leading conceptualists deny that animals and infants possess concepts and consequently hold that such creatures do not have experiences with genuine representational content (Brewer 1999, 177–179; McDowell 1994, 114– 123, 182–183). Conceptualists have countered the argument from fine-grain by appealing to demonstrative concepts (Brewer 1999, 170–174; McDowell 1994, 56–60). Our capacity for demonstrative thought and general concepts that we antecedently possess are supposed to allow us to pick out fine-grained features for which we lack concepts as such. McDowell (1994, 56–57) offers the following regarding colour experience:

Nonconceptual Content   189 In the throes of an experience of the kind that putatively transcends one’s conceptual powers—an experience that ex hypothesi affords a suitable sample—one can give linguistic expression to a concept that is exactly as fine-grained as the experience, by uttering a phrase like ‘that shade’, in which the demonstrative exploits the presence of the sample.

McDowell contends that these resources are always available and that they are applicable to all features of experience. Thus constructions such as ‘that figure’, ‘that scent’, and ‘that texture’ should suffice for a conceptual representation of the detail present in experience. Nonconceptualists have responded to the appeal to demonstrative concepts in a variety of ways (see Dokic and Pacherie 2001; Heck 2000; Kelly 2001b; Peacocke 2001; Roskies 2010; Tye 2006). One worry is that McDowell’s way of putting things clashes with the claim that conceptual capacities are passively deployed in experience. What McDowell describes suggests the spontaneous engagement of conceptual resources in reflective judgement about what one is currently experiencing (cf. also Brewer 1999, 172 and 227 n.7). The invocation of linguistic expression and utterance, as well as the suggestion that the relevant conceptual resources are directed at an experience, is hard to reconcile with the idea that conceptual capacities are passively at work in experience. This leads into a common reaction to the appeal to demonstrative concepts. It is natural to think that exposure to certain kinds of experiences is central to a causal explanation of the possession of demonstrative capacities. Heck (2000, 493) stresses that one reason Evans was interested in nonconceptual content is that he saw it as essential to an account of demonstrative reference. Conceptualists look to be assuming that demonstratives can successfully point to their targets, without much consideration of what makes that possible. The idea shared by nonconceptualists who pursue this line is that a perceptual demonstrative concept gets a fix on its referent by means of a subject isolating that item in experience and displaying an appropriate sensitivity to information about that item gathered through experience (Heck 2000, 493; Levine 2010, 191; Roskies 2010, 119–122). The challenge to the appeal to demonstrative concepts is that on pain of circularity one cannot account for the fine-grained details represented in experience by appealing to demonstrative concepts for those details while also claiming that possession of demonstrative concepts for fine-grained details depends on those details being present in experiential content. If experiential content is nonconceptual, the circularity can be avoided. Brewer (2005) replies to the charge of circularity by rejecting the understandings of demonstrative concepts and experience it turns on. He takes the relation between experience and demonstrative concepts to be constitutive, not causal. Brewer claims that ‘experience of a colour sample, R, just is a matter of entertaining a content in which the demonstrative “thatR shade” figures as a constituent’ (Brewer 2005, 222). He goes on to offer an account of content fixation for demonstrative concepts that draws on ideas similar to those from McDowell discussed before. Instead of relying on the relevant fine-grained feature itself being isolated in experience by attention, Brewer contends that a demonstrative expression has the content it does because the subject is appropriately sensitive to the feature itself—out in the world—in a way that ‘in large part depends upon [the perceiver’s] normal neurophysiological perceptual processing’ (ibid). This obviates the need for nonconceptual content. Brewer recognizes that his account has to deal with misperception. Heck (2000, 495–499) and Tye (2006, 523)  develop their misperception-based arguments with the

190   Wayne Wright demonstrative concepts gambit in mind, but the preceding section shows that their points apply equally well to general concerns about what fixes the conceptual content of experience. In responding to Heck’s objection from misperception, Brewer (2005, 223) fills in the details of how demonstrative content is fixed by appealing to Evans’ views. He proposes that demonstrative reference requires the subject’s ability to keep track of an item and suitably modify her attitudes toward it through changes over time due to its own movement, the perceiver’s movement, alterations in ambient conditions, and so forth. There is veridical experience when this tracking succeeds. When it fails, we have misperception, which will be causally explained in terms of limitations or malfunction of the perceptual system. This reply misses the most important point of the misperception objection. McDowell and Brewer can, in some sense, give an account of what is supposed to make perceptual error possible. For both, it’s attributable to purely causal processes. However, that does not address, at least consistently with the conceptualist’s other commitments, why an instance of misperception has the particular content it does. As before, direct perception may help in dealing with certain issues that suggest a need for a notion of nonconceptual content, but it brings its own challenges for the conceptualist. Nonconceptualists’ arguments based on concept acquisition also bear on the conceptualists’ appeal to demonstrative concepts. Christopher Peacocke (2001) argues that conceptualists are unable to account for the learning of new observational concepts, such as the shape concept PYRAMID. Peacocke reasons that in the course of acquiring this concept, the subject must have experiences with contents that, for someone who already has PYRAMID, provide an appropriate basis for applying that concept. Suppose the representational contents of those experiences include PYRAMID. That would imply, in keeping with the discussion of content attribution in section 2, that the subject in question already had PYRAMID. In that case, learning does not occur. Unless one wants to abandon the idea that observational concepts are learned, it looks like the way to go is to ‘acknowledge that there is such a thing as having an experience of something as being pyramid shaped that does not involve already having the concept of being pyramid shaped’ (Peacocke 2001, 252). Hence, nonconceptualism should be endorsed. To deal with concept acquisition, Brewer (2005) again invokes demonstrative concepts. Brewer grants Peacocke the claim just quoted, but offers a different conclusion: ‘What such an experience will have is a conceptual content involving the demonstrative concept, “that (shape)”, referring to the pyramid shape of the object in question’ (p. 224). The demonstrative expression’s content is fixed by means of the tracking relations introduced before. Over a sufficient run of learning opportunities, the demonstrative contents of those experiences become linked with a new observational concept, PYRAMID. Obviously, this response depends on the appeal to demonstrative concepts tackled above. Roskies (2010) has further argued that the demonstrative concepts implicated in this response require that experience has a nonconceptual content. As the earlier talk of ‘keeping track’ indicates, attention is crucial to the intentional selection of the target of demonstration. At the core of Roskies’ argument is that such demonstration involves ‘delimiting . . . the referent of the demonstrative by focusing attention’ (2010, 127). This delimiting can be plausibly explained only by taking experience to already be structured in terms of properties, boundaries, locations, and so forth. Otherwise, we are left with a ‘magic coloring book’ account of demonstrative concept formation: that someone could successfully pick out the intended object of demonstration without access to such properties is on a par with the

Nonconceptual Content   191 suggestion that a child managed to ‘stay within the lines’ by colouring as she wished on a blank page and, once she was done, lines magically appeared on the page in a manner that fit what the child produced (ibid). The structuring of experiential content that Roskies and other nonconceptualists have in mind is further examined next.

5 Perceptual structure and concepts In this concluding section, I introduce additional considerations and offer an appraisal of where the conceptualist/nonconceptualist debate stands. Instead of taking a side in the debate, I aim to show that neither view is fully satisfactory. Nonconceptualists might be heartened by empirical evidence (introduced presently) that supports the claim that there is a way of experiencing the world that is both genuinely representational and not determined by the conceptual capacities we bring to bear in thought. On the other hand, the same empirical evidence also strongly suggests that our most familiar way of experiencing the world is dependent on concept-involving cognitive resources. Moreover, there is room to argue that our perceptual systems, which generate the pre-cognitive experiential states mentioned above, have their own conceptual vocabulary and that the contents of those pre-cognitive experiential states are also conceptual. Although this point seems to favour conceptualism, it is unlikely to be welcomed by conceptualists such as Brewer and McDowell. Recall that they insist that the conceptual capacities which shape conceptual content are the same ones we spontaneously engage in thought. In short, the situation is much more complicated, and the significance of the debate is much more uncertain, than is usually appreciated. The ensuing discussion of empirical findings focuses on vision and follows much of Athanassios Raftopoulos’s (2009) synthesis of a diverse body of research, as he assembles the extant empirical evidence in a credible way. Also, the view he develops serves as a useful stepping-off point for the points I wish to advance. While an oversimplification in several respects, it suffices for now to say that the picture which emerges from this research is that as one moves through the stages of processing that begin with light striking the retina and culminate with full-blown visual experience, information about the retinal stimulus is progressively discarded in the service of generating structures that are ultimately interpretable in terms of three-dimensional objects and their properties. This is achieved by means of specialized neurons that take ‘measurements’ of certain parameters (e.g. edges, direction of motion, faces) based on the input they receive and output only a verdict about their parameter of interest (Cavanagh 2011, 1539; see also Matthen 2005, 44–54). Since these measurements provide only ‘hints at what might be out there’ (Cavanagh ibid), inference (or interpretation) is required to form from them the visual percept of a distal world. The relevant operations begin with pre-attentive activity confined to the canonical visual system (see Lamme 2003). Initially, there is bottom-up processing, known as the feedforward sweep (FFS). The FFS is quick, parallel, and independent of feedback from higher visual areas or sources beyond the visual system. It extracts features using series of filters (cells with specialized receptive fields) into which is fed information about patterns of light intensity at the retina. Nothing at this point has cognitive significance.

192   Wayne Wright After the FFS, top-down and horizontal interactions arise through recurrent processing (RP). RP integrates disparate pockets of information and enables more complex, highly structured information to be extracted. The first stage of RP takes place within the visual system (hence its designation as local; LRP) and yields representations of shapes and spatial relations, individuation of objects or proto-objects (e.g. figure-ground segmentation), and the binding of some different features to the same object (‘the binding problem’). These object segmentation processes are dominated by spatiotemporal information and produce object files for discrete objects, to which information about the object’s properties can subsequently be added. (See Rensink 2000 on proto-objects and Kahneman et al. 1992 on object files.) Object files allow an object to be treated as the same across changes in its perceived qualities (e.g. colour, shape, size), location, and relative position. The representations at the LRP stage are highly volatile, as they are not encoded ‘in any kind of memory other than the visual sensory memory’ (Raftopoulos 2009, 114). They are subject to overwriting as the changing pattern of retinal stimulation suggests new parsings into distinct objects. Beyond LRP, the ‘attentional bottleneck’ becomes relevant. Object-based attention selects some of the objects delivered by LRP for further, cognitively informed processing. Focusing on tasks in which the subject voluntarily searches for a target, this is driven by top-down effects from working memory that allow pre-attentive objects to be registered as relevant or irrelevant. For relevant objects, the associated structures from the FFS and LRP receive enhanced activity and are subjected to further processing involving global RP (GRP). Irrelevant objects are suppressed and overwritten. GRP allows the object to be entered into working memory and connections to be established with epistemic/semantic centres. This both (a) makes the object available for report and use in further cognitive processes, and (b) gives it a coherence and stability that was lacking when only LRP was present. GRP thus facilitates object recognition/classification and representation of 3D object shape, as objects can be compared to representations included in the perceiver’s stored knowledge. Crucially, instead of including the fine-grained detail of pre-attentive content, GRP-involving states have abstract contents; e.g. encoding object colour in terms of categories rather than determinate shades. These states also represent properties beyond those extracted at prior stages; e.g. function. The transition from operations involving only LRP to those in which GRP figures can be thought of along the lines of moving from Marr’s (1982) 2-½D sketch to 3D model or from Zenon Pylyshyn’s (2003, 2007) ‘early vision’ to ‘late vision’ (see Raftopoulos 2009, 51). Following Victor Lamme (2003) and Ned Block (2007), Raftopoulos takes RP to be the neural marker of awareness and uses the two different kinds of RP to distinguish between two different kinds of awareness. Employing Block’s phenomenal/access distinction, Raftopoulos aligns LRP with the former and GRP with the latter. The objects of phenomenal awareness are fleeting and unavailable for report. These representations also are nonconceptual, as they arise independently of resources employed in higher cognitive functions. Raftopoulos (2009, 134) contends, understandably, that this phenomenal awareness is not our familiar mode of experience. Phenomenal awareness is the sort of awareness that subjects in partial-report tasks (Sperling 1960) are supposed to be talking about when they claim to see all the stimuli in very brief displays. Our ordinary experience is due to late vision’s stable representations. Because late vision requires contributions from concept-involving higher cognitive resources, its content is conceptual (Raftopoulos

Nonconceptual Content   193 2009, 148). The content of late vision is conceptual not because it is merely the nonconceptual content of early vision now brought under concepts; i.e. the conceptual content of late vision is not just a conceptualized reiteration of what is nonconceptually represented in early vision. Rather, the conceptual contents of late vision ‘reflect but do not record’ the nonconceptual contents of early vision (ibid, 164); Heck (2000, 514–515) offers similar remarks. Thus not only are early and late vision different kinds of states, but their contents are fundamentally different. The interpretation of the empirical literature just sketched and the view Raftopoulos develops based on it appear to bolster nonconceptualism. However, setting aside a number of other issues worth exploring,3 the friendliness of this story to nonconceptualism can surely be questioned. Two points merit attention at this juncture. First, it is a major concession to the conceptualist to admit that our everyday experience is conceptual. The contents of early vision are inaccessible for report or any other voluntary cognitive task. We cannot form beliefs about the objects of early vision, because any attempt to isolate them brings in attention and concepts, resulting in late vision. As Raftopoulos points out, GRP radically transforms pre-attentive content along a number of dimensions. Beyond the differences between early and late vision when it comes to the stability of their representations, early vision deals with distinct objects qua distinct objects (i.e. in terms of individuated objects having generic surface shapes and without concern for their 3D shape, token identity, or kind membership), while our beliefs based on experience tend to be about tokens of things like mountains, chickens, and hammers considered as such. Whatever evidential relation there is between phenomenal experience and empirical belief has to be indirect and not dependent on how perceivers cognitively grasp the former’s content, as perceivers can do no such thing (see also Lyons 2010). Late vision does seem apt to serve as the immediate evidential basis for empirical beliefs. Since late vision is conceptual, we have arrived at a position much like Brewer’s and McDowell’s conceptualism. The other point is that one might object that demonstrating that (some) experiential content is independent of the conceptual resources deployed in thought is not sufficient for establishing that no conceptual resources whatsoever determine that content (see Laurence and Margolis 2012; Matthen 2005). As a start, consider what Raftopoulos says in fleshing out the evidential relationship between early and late vision, which is relevant to avoiding the charge that early vision content is just another form of the Given. Raftopoulos (2009, 195) claims that ‘the structure of nonconceptual content renders possible the evidential relation between perceptual states with nonconceptual content and perceptual judgments made on the basis of those states’. Our visual system by its very nature parses input from the world into objects and (certain of) their properties, and such structuring (presumably non-coincidentally) turns out to be well suited for exploitation by our higher cognitive faculties. This point is made in varying ways by Heck (2000, 522), Rainer 3  One issue is the debate about whether LRP alone forms the neural basis of phenomenal consciousness. This is brought out in several commentaries on the ‘mesh’ argument of Block (2007) and by Phillips (2011). For now, I’ll note that whether (a) LRP is insufficient for awareness but provides the phenomenal aspect of awareness once GRP is established, or (b) GRP alone is the neural basis of phenomenal consciousness, the contents of early vision are likely still to be relevant to a nonconceptualist thesis. (a) is basically a variation on the ‘LRP alone’ account. In the case of (b), early vision states could be construed as subpersonal, pre-cognitive visual states with contents upon which the contents of experience are systematically dependent.

194   Wayne Wright Mausfeld (2003, 387–388), and Vision (1998, 413). Suppose object recognition is a matter of template matching or matching to an internal description formed by decomposing objects into simpler generic components. In either case, the structured early vision content that feeds into recognition is highly relevant to the application conditions for the concepts that figure in late vision. Since (a) the stored representations of objects consist (at least in part) of the templates or descriptions to be matched to early vision content, and (b) early vision content is structured in terms of objects (or object parts) and their features, this relevance seems semantic or epistemic, not merely causal. How does experiential content gets its structure? A persuasive answer is that the visual system imposes that structure through its own categories. The above discussion of visual processing naturally lends itself to being understood in terms of classification, from the talk of neurons with receptive fields selective for particular features (the classificatory nature of which is emphasized by Matthen 2005), to the segmentation of figure from ground, to the creation of object files to which information about object properties can be added. This is not to say that the categories of the visual system are all hard-wired or permanently fixed, that they can be recruited for use in thought, or that they are arbitrary with respect to the nature of the mind-independent world. The idea only is that the visual system employs a set of proprietary classifications in building representations that are suitably structured to form the basis of useful inferences about the distal scene. Should these classifications be counted as conceptual? Evans (1982, 100–105) argued that what distinguishes thought as conceptual and sensation as nonconceptual is that thought has compositional structure while sensation does not. Matthen (2005, 77–85), however, contends that perceivers can conceptually ‘grasp’ features present in sensation (basically, Pylyshyn’s early vision), where such grasp is understood in terms of stimulus generalization and stimulus discrimination. Matthen’s point is that if we are to make sense of (for example) the disposition of a bird that has been trained to peck at blue squares to also peck at a blue disc, sensational content must be understood as consisting of separable and recombinable elements. In that case, an appeal to compositional structure will not support a conceptual/nonconceptual distinction between the contents of thought and sensation. Matthen’s response to arguments based on compositional structure does not address other nonconceptualist reasons for rejecting that the visual system’s classifications are conceptual. For example, Tye (2006) contends that nonconceptual content is structured. However, he does not count the classificatory activity of the visual system as genuinely conceptual on the grounds that perceivers might be unable either to recognize a previously encountered fine-grained perceptual quality when they experience it again or employ a representation of that fine-grained quality (as such) in thought (Tye 2000, 75; 2006, 506–507). Pylyshyn’s work on object tracking informs the account of the empirical literature presented herein and he is adamant that early vision is nonconceptual because it does not rely on top-down contributions from cognitive centres (Pylyshyn 2003, 214–215). Heck (2000, 487–489) points out that much of what Evans had to say in connection with the argument from compositional structure deals with the perceiver’s cognitive resources. Note also that McDowell (1994, 11) states that the capacities ‘in play in experience . . . would not be recognized as conceptual capacities at all unless they could also be exercised in active thinking’. One reply to Matthen, therefore, is that if concepts are restricted to the cognitive realm and the preceding account of early vision is on the mark, sensation is

Nonconceptual Content   195 nonconceptual despite having compositional structure. Matthen, however, is unlikely to simply grant that sort of narrow understanding of concepts. At this point, it is tempting to cast about for an account of concepts that would decide matters. Such an endeavour could prove unfruitful for any number of reasons (Laurence and Margolis 2012). Picking up on Vision’s (1998, 424) remark that ‘[it] is . . . difficult to motivate [the conceptual/nonconceptual] distinction if . . . we think of what we experience as already featured’, I suggest that any effort along these lines will add little to the discussion. The empirical research discussed in this section shows that the concerns which stimulate so much of the interest in the conceptual/nonconceptual distinction can be addressed (and perhaps are approaching resolution) independently of sorting out where, if at all, to draw the line between them. Where one places the conceptual/ nonconceptual border is likely to affect the terms in which answers are stated to questions about, inter alia, the epistemic and semantic relationships between perception and belief, continuities between human and animal perception, and the theory-ladenness of perception. Nothing about the substance of those answers, though, would change. One researcher might have a perfectly legitimate reason to use a notion of concepts that prioritizes classification and shows little or no concern for a cognitive/noncognitive divide. Another researcher, driven to understand the nature and extent of influence of our cognitive faculties, may very well limit talk of concepts to the cognitive domain. It is hopeless to try to argue for one of these (or any number of others) as the single correct understanding of concepts. It is also unmotivated. Whichever understanding one opts for, the classifications of early vision remain importantly distinct from the concepts employed in thought, as early vision content is not determined by top-down contributions from cognitive centres, perceivers are not able directly to access cognitively early vision contents, and GRP’s involvement in late vision radically transforms early vision content. It also continues to be true that early vision content is structured in a way that underwrites semantic/epistemic connections with full-blown experience and thought. It is likely that many (admittedly, not all) parties to the nonconceptual content debate are much more interested in these results—fleshing them out, piecing them together, contesting them, and so forth—than they are in the question of how to mark a principled distinction between the conceptual and the nonconceptual. Thus the downbeat assessment offered here applies only to the significance of the nonconceptual/conceptual distinction, not to the significance of the issues that lead many researchers to engage in the nonconceptual content debate.

References Bermúdez, J. L. (1995). ‘Nonconceptual Content: From Perceptual Experience to Subpersonal Computational States’. Mind and Language, 10, 333–369. Bermúdez, J. L. (2003). Thinking Without Words. Oxford: Oxford University Press. Bermúdez, J. L. and Cahen, A. (2011). ‘Nonconceptual Mental Content’. Stanford Encyclopedia of Philosophy. Block, N. (2007). 'Consciousness, Accessibility, and the Mesh between Psychology and Neuroscience'. Behavioral and Brain Sciences, 30, 481–548. Brewer, B. (1999). Perception and Reason. Oxford: Oxford University Press.

196   Wayne Wright Brewer, B. (2005). 'Perceptual Experience Has Conceptual Content'. In E. Sosa and M. Steup (eds), Contemporary Debates in Epistemology (pp. 217–230). Oxford: Blackwell. Byrne, A. (2005). 'Perception and Conceptual Content'. In E. Sosa and M. Steup (eds), Contemporary Debates in Epistemology (pp. 230–250). Oxford: Blackwell. Cavanagh, P. (2011). 'Visual Cognition'. Vision Research, 51, 1538–1551. Crowther, T. (2006). 'Two Conceptions of Conceptualism and Nonconceptualism'. Erkenntnis, 65, 245–276. Dennett, D. (1969). Content and Consciousness. London: Routledge. Dokic, J. and Pacherie, E. (2001). 'Shades and Concepts'. Analysis, 61, 193–202. Evans, G. (1982). The Varieties of Reference. Oxford: Oxford University Press. Gibson, J. J. (1979). The Ecological Approach to Visual Perception. New York: Psychology Press. Hanna, R. (2005). 'Kant and Nonconceptual Content'. European Journal of Philosophy, 13, 247–290. Heck, R. (2000). 'Nonconceptual Content and the Space of Reasons'. Philosophical Review, 109, 483–523. Kahneman, D., Treisman, A., and Gibbs, B. (1992). 'The Reviewing of Object Files: ObjectSpecific Integration of Information'. Cognitive Psychology, 24, 175–219. Kant, I. (1998). Critique of Pure Reason, eds. P. Guyer and A. Wood. Cambridge: Cambridge University Press. Kelly, S. (2001a). 'The Non-Conceptual Content of Perceptual Experience: Situation Dependence and Fineness of Grain'. Philosophy and Phenomenological Research, 62, 601–608. Kelly, S. (2001b). 'Demonstrative Concepts and experience'. Philosophical Review, 110, 397–420. Lamme, V. (2003). 'Why Visual Attention and Awareness are Different'. Trends in Cognitive Sciences, 7, 12–18. Laurence, S. and Margolis, E. (2012). 'The Scope of the Conceptual'. In E. Margolis, R. Samuel, and S. Stich (eds), The Oxford Handbook of Philosophy of Cognitive Science (pp. 291–317). Oxford: Oxford University Press. Levine, J. (2010). 'Demonstrative Thought'. Mind and Language, 25, 169–195. Lyons, J. (2010). 'Cognition and Perception: How Do Psychology and Neural Science Inform Philosophy?' Notre Dame Philosophical Reviews. Downloaded 21 February 2011. . Marr, D. (1982). Vision. New York: W. H. Freeman and Company. Matthen, M. (2005). Seeing, Doing, and Knowing. Oxford: Oxford University Press. Mausfeld, R. (2003). ' “Colour” As Part of the Format of Different Perceptual Primitives: The Dual Coding of Colour'. In R. Mausfeld and D. Heyer (eds), Colour Perception: Mind and the Physical World (pp. 381–430). Oxford: Oxford University Press. McDowell, J. (1982/1988). ‘Criteria, Defeasibility, and Knowledge'. In J. Dancy (ed.), Perceptual Knowledge (pp. 209–219). Oxford: Oxford University Press. McDowell, J. (1994). Mind and World. Cambridge, MA: Harvard University Press. McDowell, J. (1994/2002). 'The Content of Perceptual Experience'. In A. Noë and E. Thompson (eds), Vision and Mind: Selected Readings in the Philosophy of Perception (pp. 443–458). Cambridge, MA: MIT Press. Peacocke, C. (1992). A Study of Concepts. Cambridge, MA: MIT Press. Peacocke, C. (1998). 'Nonconceptual Content defended'. Philosophy and Phenomenological Research, 58, 381–388.

Nonconceptual Content   197 Peacocke, C. (2001). 'Does Perception Have a Nonconceptual Content?' Journal of Philosophy, 98, 239–264. Pylyshyn, Z. (2003). Seeing and Visualizing:  It’s Not What You Think. Cambridge, MA: MIT Press. Pylyshyn, Z. (2007). Things and Places: How the Mind Connects with the World. Cambridge, MA: MIT Press. Raftopoulos, A. (2009). Cognition and Perception. Cambridge, MA: MIT Press. Rensink, R. (2000). 'The Dynamic Representation of Scenes'. Visual Cognition, 7, 17–42. Roskies, A. (2008). 'A New Argument for Nonconceptual Content'. Philosophy and Phenomenological Research, 76, 633–659. Roskies, A. (2010). ' “That” Response Doesn’t Work: Against a Demonstrative Defense of Nonconceptualism'. Noûs, 44, 112–134. Sellars, W. (1956). 'Empiricism and the Philosophy of Mind'. In H. Feigl and M. Scriven (eds), Minnesota Studies in the Philosophy of Science, vol. 1. Minneapolis, MN: University of Minnesota Press. Speaks, J. (2005). 'Is There a Problem about Nonconceptual Content?' Philosophical Review, 114, 359–398. Sperling, G. (1960). 'The Information Available in Brief Visual Presentations'. Psychological Monographs: General and Applied, 74,1–29. Stalnaker, R. (1998). 'What might Nonconceptual Content be?' In E. Villanueva (ed.), Philosophical Issues, 9 (pp. 339–352). Atascadero, CA: Ridgeview Press. Toribio, J. (2008). 'State versus Content: The Unfair Trial of Perceptual Nonconceptualism'. Erkenntnis, 69, 351–361. Tye, M. (2000). Consciousness, Color, and Content. Cambridge, MA: MIT Press. Tye, M. (2006). 'Nonconceptual Content: Richness and Fineness of Grain'. In T. Gendler and J. Hawthorne (eds), Perceptual Experience (pp. 504–530). Oxford: Oxford University Press. Vision, G. (1997). Problems of Vision. Oxford: Oxford University Press. Vision, G. (1998). 'Perceptual Content'. Philosophy, 73, 395–427.

Chapter 11

Disj u ncti v ism Heather Logue

1

Take an ordinary perceptual experience in which I see a yellow, crescent-shaped banana, and it is as it looks to me to be—what philosophers call a veridical experience. Plausibly, it is possible (at least in principle) for a scientist to stimulate my brain so as to produce a subjectively indistinguishable experience, i.e. one that I couldn’t tell apart from the veridical experience by introspection alone. (I could tell such an experience apart from the veridical one by testimony if the scientist told me what she was up to. But if I restrict myself to introspection—the mode of access one has to one’s own mental states—I couldn’t notice any difference.) The scientist could generate such an experience in the total absence of yellow, crescent-shaped bananas, and it would nevertheless seem to me that there’s a yellow, crescent-shaped thing before me. Philosophers call this sort of experience a hallucination, which is one kind of non-veridical experience. Although these experiences differ in their causal antecedents, it’s natural to suppose that they are fundamentally the same kind of experience—that they are at bottom the same type of mental state. (One might suggest: after all, the subject can’t tell them apart, and what more could there be to a mental state than what the subject can discern through introspection?) Indeed, for much of the history of philosophy of perception, no alternative view was on anyone’s radar. Up until fairly recently, philosophers assumed that a veridical experience and a subjectively indistinguishable hallucination are fundamentally the same. However, in recent years some have felt compelled to reject this tempting claim. Although the veridical experience and the hallucination described above are both experiences as of a yellow, crescent-shaped thing, they think we have good reason to say that they are radically unalike. A common way of expressing this idea is to say that perceptual experience is supposed to be in some sense disjunctive: either an experience is of one kind (including veridical experiences), or of another radically different kind (including at least some non-veridical experiences). Hence, this broad type of view has come to be known as ‘disjunctivism’. The claim that veridical experiences are radically different from at least some non-veridical experiences can be fleshed out in a variety of ways, and the project of doing so raises two questions: 1 

Thanks to Mohan Matthen and Alex Byrne for helpful comments.

Disjunctivism   199 A. In what way are the two classes of experiences unalike? (By ‘radically unalike’, presumably the disjunctivist doesn’t mean totally unalike—e.g. the veridical experience and the hallucination are alike in that they are both perceptual experiences as of a yellow, crescent-shaped thing. So she must mean that they are dissimilar in certain crucial respects; but which ones?) B. Why on earth would someone endorse such a claim? (Given that non-veridical experiences can seem exactly like veridical ones, it might seem pretty implausible that they are radically unalike.)

As it turns out, the answer to (A) depends upon the answer to (B). In this chapter, I will discuss four answers to (B), and discuss how they affect the answer to (A). I will discuss a version of disjunctivism motivated by a desire to defend Direct Realism (section 2): one motivated by a desire to defend the claim that the content of some perceptual experiences is object-dependent (section 3); one motivated by a desire to respond to a certain kind of argument for scepticism about the external world (section 4); and one motivated by a desire to defend Naïve Realism (section 5). First, though, we must unpack the terminology employed in stating the core disjunctivist claim (section 1).

1 Veridical and non-veridical experiences Before evaluating the claim that veridical experiences and non-veridical experiences are radically unalike, an elaboration of the distinction between veridical and non-veridical experiences is in order.2 Veridical experiences are those in which (i) the subject perceives things in her environment; (ii) her environment is as it appears to her to be; and (iii) for all properties F, if something the subject perceives appears to be F, this is because the subject perceives its being F. An example of a veridical experience is one in which I see a yellow banana, it looks yellow to me, and it looks yellow to me because I perceive its yellowness. (As we’ll see shortly, there are other reasons why a yellow thing might look yellow.) By contrast, non-veridical experiences are experiences in which at least one of these three conditions fails to obtain. Illusions are one of two broad categories of non-veridical experiences. In all cases of illusion, condition (i) is met—the subject perceives things in her environment. But (iii) isn’t—either something she perceives appears to be F but isn’t, or it appears to be F even though she doesn’t perceive its being F. An example of an illusion of the first sort is an experience in which I see a green banana that looks yellow to me as a result of unusual lighting conditions. An example of the second sort is an experience in which I see a yellow banana that looks yellow to me, but the lighting in the room is such that the banana would look green if it weren’t for the precise wavelength of light that happens to be coming 2 I

should note that some would object to the distinction between veridical and non-veridical experiences—namely, those who think that the distinction implies that perceptual experience has content, and that the claim implied is false (see, e.g., Travis 2004 and Brewer 2008). This debate is beyond the scope of this chapter; suffice it to say that I see no obstacle to translating the distinction I’m after into terms that don’t imply that experience has content.

200   Heather Logue through the window. Arguably, since there is a very nearby possible world in which the banana doesn’t look yellow to me, the connection between the yellowness of the banana and the banana’s looking yellow to me isn’t robust enough for me to count as perceiving the yellowness of the banana.3 Hallucinations are the other main category of non-veridical experiences. In all cases of hallucination, condition (iii) fails—there is some property F such that it appears to the subject that there is something F in her environment, but not as a result of the subject perceiving a thing’s being F. This is because what makes an experience hallucinatory is that some aspect of how things appear is generated without the appropriate stimulation of the relevant sensory organs (which is plausibly a necessary condition on perceiving a thing’s being F). For example, a visual hallucination has at least some aspects that aren’t the normal causal upshot of light hitting the subject’s retina. One could (at least in principle) tinker with my brain in a way that results in my hallucinating a pink patch on a wall. I would seem to see pink, but not because light of the relevant wavelength was hitting my retina—and hence not because I perceive the pinkness of something. In a case of total hallucination, condition (i) fails as well. A stock example of such an experience is one had by a ‘brain in a vat’, stimulated so that it has experiences that purport to be of the world around it, when in fact it doesn’t perceive anything in its environment at all. In the usual philosophical examples of hallucination condition (ii) fails as well, but this isn’t definitional of hallucination—it could be that the brain-in-a-vat’s environment happens to be exactly as it appears. In a case of partial hallucination, (i) is satisfied, but (iii) isn’t—e.g. an experience in which I perceive the room around me and the things in it, but hallucinate a pink patch on the wall.4 All forms of disjunctivism hold that hallucinations are radically different from veridical experiences. Some forms hold that illusions are too, while others deny this. Now that we’ve clarified the terminology that features in the basic disjunctivist claim, let us move on to the task of elaborating it.

2 The Direct Realist’s disjunctivism Let’s begin our path to the first version of disjunctivism by considering the following question: what does the subject of a total hallucination perceive? By definition, she doesn’t perceive anything in her environment. A  historically popular answer to this question was that she perceives mind-dependent, immaterial things (given that if she doesn’t perceive anything in her mind-independent, material environment, whatever she perceives must be mind-dependent and immaterial). Such things have been traditionally called 3  Another example of an illusion of this sort is the version of the ‘Ames Room’ illusion outlined in Johnston (2006: 272–273), in which the typical effects of the Ames Room are cancelled out by another illusion. In Susanna Siegel’s terminology (2010: 339–340), such illusions are weakly and strongly veridical but not superstrongly veridical, as the latter implies perception of the relevant objects and properties. By contrast, weak veridicality requires only ‘matching’ how things are in the environment, and strong veridicality requires matching and perception of the relevant objects (but not their properties). 4  The difference between an illusion in which only (iii) fails and a hallucination in which only (iii) fails has to do with the reason why (iii) fails. Very roughly, in the latter case the failure is due to goings-on in the subject’s brain, rather than in the subject’s environment.

Disjunctivism   201 sense-data.5 Moreover, since a total hallucination and a veridical experience can seem exactly alike, and can involve the same kinds of neural states, many have been led to the conclusion that the subject of a veridical experience must be aware of sense-data too. But then a question arises: how do the mind-independent, material things the subject of a veridical experience perceives fit into the picture?6 One answer is to chuck the mind-independent, material things out of the ontological picture altogether. That way lies Idealism—the claim that all that exists are our own ‘ideas’ (including our sense-data).7 A less radical answer is Indirect Realism—the view that when a subject perceives mind-independent, material things, she does so indirectly, in virtue of perceiving sense-data that they cause in her. For example, when I perceive a banana, I do so indirectly, by way of direct perception of something else (a sense-datum caused by the banana). Direct Realism, as the name suggests, rejects the claim that perception of mindindependent, material objects is indirect in this way. The Direct Realist holds that when I perceive a banana, there’s nothing I perceive more directly than the banana—I don’t have to perceive something other than the banana (such as a sense-datum) in order to perceive the banana itself. So there’s no room for sense-data in the Direct Realist’s account of veridical experience. But if we don’t perceive sense-data in having veridical experiences, what should we say about what we perceive when having total hallucinations? This is where our first form of disjunctivism comes in—disjunctivism about the objects of experience (see Thau 2004: 195). The basic idea is that the objects of experience (i.e. the things one perceives) in the course of veridical experience and an indistinguishable total hallucination are different: in the case of veridical experience, the subject perceives mind-independent, material things in her environment, but in the case of total hallucination, the subject doesn’t perceive such things. So veridical experiences and at least total hallucinations are radically unalike in that they have different objects. Note that this is compatible with the experiences having other features in common: e.g. their phenomenal character, or ‘what it is like’ for the subject to have the experience. Plausibly, what it is like for someone to have a veridical experience of a yellow, crescent-shaped banana could be the same as what it’s like for someone to have a total hallucination as of a yellow, crescent-shaped banana. Of course, the Direct Realist owes us an account of what one does perceive in the course of a total hallucination. One option is to claim that while the subject of a veridical experience perceives mind-independent, material entities, the subject of a total hallucination 5  When the term ‘sense datum’ was coined, it was intended to refer to whatever one is directly aware of in having an experience—be it a mind-dependent, immaterial entity or a mind-independent, material one. For example, G. E. Moore entertained the possibility that sense-data in this sense are the facing surfaces of mindindependent, material objects (Moore 1953). However, since most of the parties to the debate at the time the phrase was introduced came to the conclusion that sense-data are mind-dependent, immaterial objects (see, e.g., Russell 1912, Broad 1925, Price 1950, and Ayer 1956), the label eventually came to refer to such entities (see Huemer 2011 for this point, and Snowdon chapter 6, in this volume for a general discussion of sense-data). 6  One could run a similar line of thought concerning partial hallucinations or illusions in which the subject perceives things in her environment, but some of them appear to be a way they’re not—for example, an experience in which a green banana looks yellow to her. The subject doesn’t perceive a yellow banana, so we may ask: what does the subject perceive that accounts for the fact that her environment looks to contain a yellow thing? One historically popular answer: a yellow sense-datum. 7 Note that this also involves chucking out the distinction between veridical and non-veridical experiences—without mind-independent, material things out there for us to perceive, misperceive, or fail to perceive, we can’t make sense of the categories of illusion and hallucination.

202   Heather Logue perceives sense-data.8 However, this option is self-defeating. Plausibly, the subject of a veridical experience and the subject of a total hallucination could be in the same type of brain state. To see this, just hold fixed the neural goings-on in a case of veridical experience, and change the story about how those neural goings-on came to pass (instead of being generated by light reflected off a banana hitting the retina and so forth, let’s say that they’re generated by the tinkerings of a mad neuroscientist). Now, if such a brain state gives rise to perception of sense-data in the case of total hallucination, there’s no good reason to claim that it wouldn’t do so in the case of veridical experience. Hence, it appears that if we account for total hallucination in terms of perception of sense-data, we can’t achieve the Direct Realist aim of keeping sense-data out of our account of veridical experience.9 Fortunately, there are other options available. One is to say that the subject of a total hallucination perceives what Mark Johnston calls ‘sensible profiles’, i.e. complexes of properties and relations that are instantiated by things in the subject’s environment if her experience is veridical (2004: 134–135).10 On Johnston’s view, the subject of a veridical experience perceives a sensible profile and the (mind-independent, material) things that instantiate it. The subject of an illusion or a partial hallucination perceives a sensible profile that’s only partially instantiated by the things one perceives. Finally, the subject of a total hallucination perceives a sensible profile that’s not instantiated by anything one perceives.11 On Johnston’s view, veridical experiences, illusions, and partial hallucinations have objects that total hallucinations don’t (i.e. mind-independent, material particulars). But since all of these experiences have sensible profiles as objects, we don’t have complete dissimilarity across the disjuncts with respect to the objects of experience. Does this disqualify Johnston’s view from being a version of disjunctivism about the objects of experience? Arguably, no. If disjunctivism about x requires complete dissimilarity across the disjuncts with respect to x, then Johnston’s view isn’t a version of disjunctivism about the objects of experience. However, I see no reason to accept the antecedent. We should define disjunctivism about x as comprised of only the bare minimum set of claims required to preserve the view that motivates it. Direct Realism is the view that motivates disjunctivism about the objects of experience, and Johnston’s view illustrates a way in which a Direct Realist could accept that the experiences across the disjuncts have the same kinds of objects (just not all and only the same kinds of objects).12 8  This is the view labelled ‘Austinian disjunctivism’ in Byrne and Logue (2008), inspired by Austin (1962: 32). 9  This is in the vicinity of a line of thought endorsed by, e.g., Robinson (1994), Smith (2002), and Martin (2004). Robinson uses it to argue for the sense-datum theory, while Smith and Martin take the modus tollens route and conclude that one shouldn’t account for hallucination in terms of sense-data. 10  Although Johnston never uses the word ‘perceive’ to refer to a subject’s relation to sensible profiles, he does use the phrase ‘visually aware of’—which is presumably a determinate of the determinable perceiving relation. 11  On the face of it, Johnston’s account doesn’t have the resources to distinguish veridical experiences from illusions or partial hallucinations that happen to ‘match’ the subject’s environment. Moreover, it appears that Johnston holds that we can perceive abstracta: since the properties and relations that make up the perceived sensible profile may be uninstantiated in a hallucinating subject’s environment, sensible profiles cannot be complexes of property instances or tropes. I suspect this counterintuitive consequence of Johnston’s account of hallucination is what has kept most Direct Realists from endorsing it. 12  Although Johnston accepts disjunctivism about the objects of experience, he rejects a different view that goes by the name ‘disjunctivism’—namely, negative disjunctivism about the metaphysical structure of experience (which will be discussed in detail in section 5). His unqualified rejection of what he calls

Disjunctivism   203 Another option for the Direct Realist is to insist that the subject of a total hallucination perceives absolutely nothing. This might seem like an implausible suggestion on the face of it—after all, there’s something it’s like to have a total hallucination as of a yellow, crescent-shaped banana. How could this be if the subject of the experience doesn’t perceive anything at all? The reply is to deny that the only way of accounting for what it’s like to have a perceptual experience is in terms of what the subject perceives in the course of having it. One popular alternative is to account for experience in terms of the subject representing her environment as being a certain way (e.g. as containing a yellow, crescent-shaped thing). This is the core claim of Intentionalist theories of perceptual experience.13 The basic idea is that perceptual experience is structurally similar to belief, in that it is a certain kind of attitude to a proposition. Just as I can doxastically represent that there is a yellow, crescent-shaped thing before me, I can perceptually represent that there is a yellow, crescent-shaped thing before me. This allows the Intentionalist to account for total hallucination while denying that the subject perceives anything. Roughly speaking, according to Intentionalism, a total hallucination as of a yellow, crescent-shaped banana is a matter of the subject perceptually representing the proposition that there is a yellow, crescent-shaped thing before her—something she can do even if she doesn’t perceive such a thing. This view yields another version of disjunctivism about the objects of experience, as veridical experiences, illusions, and partial hallucinations have mindindependent, material things as objects, whereas total hallucinations have no objects whatsoever.14 Disjunctivism about the objects of experience is relatively uncontroversial—at least, it’s only as controversial as denials of Indirect Realism and Idealism. So these days, this form of disjunctivism has the status of orthodoxy.15 Let us now turn our attention to versions of disjunctivism that are currently more contentious.

3 An Intentionalist’s disjunctivism Another form of disjunctivism emerges from a division among Intentionalists. As I said in the last section, all Intentionalists hold that having a perceptual experience consists in the subject representing her environment as being a certain way (in a manner

‘disjunctivism’ (Johnston 2004: 122–127) reflects the fact that the label is more often used to refer to the latter view than the former. 13  There are other versions of this alternative besides the Intentionalist one—e.g. the accounts of total hallucination given by negative disjunctivists (see section 5). I’ve just picked one for the purposes of illustration. Intentionalist theories are defended by Peacocke (1983), Harman (1990), Dretske (1995), Block (1996), Tye (2000), and Byrne (2001), among others. The various versions of Intentionalism defended by these authors diverge from each other in many significant ways; but they all subscribe to the core claim identified in the main text. 14  I should note that there is another Direct Realist theory of perceptual experience—Naïve Realism, to be discussed in section 5. This view can be elaborated in terms of Johnston’s account, or in terms of the denial that a subject of a total hallucination perceives anything. For the sake of space, I won’t go into the details of a Naïve Realist disjunctivism about the objects of experience. 15  Recent expressions of dissent can be found in Jackson (1977), Robinson (1994), and Foster (2000).

204   Heather Logue distinctive of experiencing, as opposed to, say, believing).16 Another way of putting this core Intentionalist idea is to say that perceptual experience involves representing a proposition to the effect that one’s environment is thus-and-so. The proposition represented is called the content of the experience.17 Some Intentionalists hold that the content of a veridical experience is different from the contents at least some subjectively indistinguishable non-veridical experiences. Such a view is disjunctivism about the content of experience. Why might an Intentionalist endorse disjunctivism about the content of experience? One potential reason concerns the connection between perception and demonstrative thought.18 Perceiving the banana on my desk puts me in a position to have demonstrative thoughts about it, e.g. to think that this banana is ripe enough to eat. But since a total hallucination as of a yellow banana wouldn’t involve my perceiving any particular thing in my environment, it couldn’t put me in a position to have demonstrative thoughts about any such thing. Some Intentionalists think that in order to account for this difference between experiences which involve perceiving things in one’s environment and those that don’t, we should say that the contents of the former are object-dependent, i.e. that they are propositions whose truth depends on how things are with a particular object (e.g. the proposition that that thing is yellow). By contrast, object-independent propositions can be made true by different particular objects. The proposition that there is a yellow banana before me is true as long as there is some yellow banana or other before me—it doesn’t matter which one. These propositions are suited to be the contents of total hallucinations. A total hallucination as of a yellow banana involves the subject representing that there is a yellow banana before her, but not any particular one. The result is disjunctivism about the content of experience: veridical experiences, illusions, and partial hallucinations (all of which involve perceiving something in one’s environment) have object-dependent contents, whereas total hallucinations have object-independent contents.19 Note that this version of disjunctivism, like disjunctivism about the objects of experience, is compatible with there being plenty of similarities across the disjuncts. Indistinguishable experiences from different disjuncts are radically different in that they have different contents, but are supposed to be similar in respect of, for example, phenomenal character and broad metaphysical structure (they’re all propositional attitudes). Indeed, on some versions of disjunctivism about content, experiences involving perception have object-independent content in addition to object-dependent content, which means that all experiences have object-independent content.20 Of

16  For brevity’s sake, I’ll often leave out this qualification in what follows, and just talk of perceptual experience involving the subject representing her environment as being a certain way. 17  One might hold that experiences have content in a weaker sense; roughly, that there are propositions associated with them, but they aren’t perceptually represented by the subject (see Siegel’s Content View [2010], Schellenberg’s association thesis [2011], and my Mild Content View [Logue, 2014]). One who holds such a view could be a disjunctivist about the content of experience. However, since few people occupy this region of logical space, I’ll set this possibility aside. 18  See Brewer (1999). 19 For the view that perceptual experience involves representation of only object-independent propositions, see, e.g., McGinn (1982) and Davies (1992). For the view that perceptual experience involves representation of object-dependent propositions, see, e.g., Chalmers (2006) and Tye (2007). 20  See Byrne and Logue (2008) for such a view.

Disjunctivism   205 course, this wouldn’t count as a version of disjunctivism about content if that meant there must be no common content across the disjuncts whatsoever. But as I  said in the last section, disjunctivism about x should be only as strong a claim as is needed to preserve the motivation for it. And what’s important to the motivation for disjunctivism about content I  outlined is that only experiences involving perception have object-dependent content, not that there’s no other kind of content all experiences have in common. Is disjunctivism about content true? Obviously, it’s true only if experiences have content to begin with, and this debate is beyond the scope of this chapter.21 But suppose for the moment that it does. In that case, I see no good reason to reject disjunctivism about content, because I see no good reason to reject the claim that the contents of experiences involving perception are object-dependent. One might resist this claim on the grounds that it is possible for a total hallucination to be subjectively indistinguishable from a veridical experience—i.e. to be such that the subject cannot tell it apart from a veridical experience of a certain kind by introspection alone. For example, a brain-in-a-vat’s hallucination as of a yellow banana may be subjectively indistinguishable from a veridical experience of one. Doesn’t this mean that the experiences have the same content? Well, only if we expect that introspection of our experiences to reveal the entirety of their metaphysical structures to us (e.g. whether or not the content of an experience is objectdependent). And I see no reason to think that introspection is this powerful. Moreover, there are a number of arguments against the claim that the content of experience is exclusively object-independent, which I don’t have the space to summarize here.22 But I think it’s pretty safe to say that if perceptual experience has content, then disjunctivism about content is true.

4 An anti-sceptic’s disjunctivism Let us work our way into the third form of disjunctivism by reflecting on a well-known argument for scepticism about the external world. The argument begins with the premise that I don’t know that I’m not a brain-in-a-vat (BIV). Why don’t I know this? Well, if I were a BIV, things could perceptually appear to be exactly as they do now (i.e. it could perceptually appear to me that there’s a yellow thing before me). So it seems that the perceptual evidence I have underdetermines whether I’m a normal embodied subject having a veridical experience of a yellow banana, or I’m a BIV being stimulated to have a subjectively indistinguishable hallucination—the evidence afforded by my experience provides just as much support for the first hypothesis as it does for the second. The second premise is that if I don’t know that I’m not a BIV, then I don’t know anything about the external world. Plausibly, in order to know things about the external world, I’ve got to know that I’m not ‘perceptually disconnected’ from it; that is, I’ve got to know that the experiences generating my beliefs about the world involve perceiving things in it, rather than resulting from someone (or something) tinkering with my brain to generate experiences that 21 

22 

But see, e.g., Travis (2004), Crane (2009), Siegel (2010), Schellenberg (2011), and Logue (2014 But see Tye (2007).

206   Heather Logue for all I know could be completely unreliable guides to what’s going on in the world.23 So from this premise, and the claim that I don’t know that I’m not a BIV (the first premise), it follows that I don’t know anything about the external world. One form of disjunctivism is supposed to undermine the first premise of this argument. Recall that the first premise was supported by appeal to the idea that I’d have the same perceptual evidence regardless of whether I’m having a veridical experience of a yellow banana or a total hallucination as of one. Disjunctivism about perceptual evidence (also known as epistemological disjunctivism) rejects this claim.24 The first key component of the view is that a subject of a veridical experience has more perceptual evidence concerning the goings-on in her environment than the subject of an indistinguishable illusion or hallucination. The latter kinds of experiences are epistemically defective—even if one hallucinates a yellow banana when there is a yellow banana before one, or one is the subject of an illusion where two illusion-generating features of a situation cancel each other out so that a yellow banana looks yellow, intuitively having these experiences wouldn’t put one in a position to know that there’s a yellow banana before one. Disjunctivism about perceptual evidence accounts for this defectiveness in terms of non-veridical experiences providing less evidence than veridical experiences do for claims about one’s environment. The second key component of this version of disjunctivism is that this special kind of perceptual evidence one gets when having a veridical experience is good enough to put one in a position to know things about one’s environment—which requires that it favours the proposition that there’s a yellow banana before me over the proposition that I’m a BIV being stimulated so as to have a hallucination of one in the total absence of bananas. Roughly, the idea is that a veridical experience provides me with evidence that enables me to know things about my environment (e.g. that there’s a yellow banana before me). This claim, in conjunction with the sceptic’s claim that if I don’t know that I’m not a BIV, then I don’t know anything about the external world, entails that I do know that I’m not a BIV after all.25 23  One could also support this premise by appeal to the principle that knowledge is closed under known entailment (i.e. if S knows that p, and S knows that p entails q, then S knows that q). If I know something about the external world, e.g. that I have hands, then I know that I’m not a BIV—since I know that my having hands entails that I’m not a (handless) BIV. Contraposing the conditional gets us the second premise. However, this closure principle won’t support the second premise of all analogous sceptical arguments. For example, if I don’t know that I’m not dreaming, then I don’t know anything about the external world either. But since my having hands doesn’t entail that I’m not dreaming, I don’t know that my having hands entails that I’m not dreaming. Hence, we can’t apply the closure principle to get us to this claim. The case for the second premise in the main text has wider applicability (cf. Stroud 1984: 29). 24 

The label ‘epistemological disjunctivism’ was coined in Snowdon (2005) and propagated in Byrne and Logue (2008). The view labelled was originated by John McDowell (see, e.g., his 1982 and 2008), and defended in Pritchard (2008) and Neta (2008). See Williamson (2000: ch. 8) for a broadly similar view. 25  Note the similarity of this line of thought to G. E. Moore’s response to the sceptic (Moore 1962)—in both cases, I can deny the sceptic’s conclusion (that I don’t know anything about the external world), and use the sceptic’s second premise in order to conclude that I know that I’m not a BIV. (This is why Pritchard 2008 calls epistemological disjunctivism ‘McDowellian Neo-Mooreanism’.) The difference between this view and Moore’s reply to the sceptic consists in the grounds given for rejecting the sceptic’s conclusion. Moore relies on his infamous proof, whereas the epistemological disjunctivist relies on the claim that the subject of a veridical experience has more and better perceptual evidence than a hallucinating or illuded counterpart. One might view epistemological disjunctivism as a way of defending the premises of Moore’s

Disjunctivism   207 The preceding is just a broad outline of epistemological disjunctivism. Two crucial issues have yet to be discussed: in particular, what exactly is the perceptual evidence the subject of a veridical experience has that the subject of an indistinguishable non-veridical experience lacks, and does it put the subject in a position to know things about her environment? For simplicity’s sake, let’s just stick to the answer given by Pritchard in his elaboration of McDowell’s view (analogous issues arise for other answers one could give). According to Pritchard, the relevant evidence is of the form: that one sees that such-and-such is the case (2008: 291).26 For example, when I have a veridical experience of a yellow banana on my desk, one item of perceptual evidence I have is that I see that there is a yellow banana before me. At this point, there are two broad routes an epistemological disjunctivist can take. The first is to provide an account of how one can know that one sees that p despite the sceptic’s argument to the contrary.27 The other is to claim that one can have the proposition that one sees that p as evidence even if one doesn’t know it, or isn’t even in a position to know it. However, this strategy raises the question of what makes this proposition part of one’s evidence, if not one’s knowing it. Surely one has to bear some cognitive relation to it for it to count as evidence one has, and merely believing it isn’t sufficient (believing that the earth is flat doesn’t make that proposition part of one’s evidence). Presumably, one has to at least be justified in believing it. In that case, the epistemological disjunctivist owes an account of how one can be justified in believing that one sees that p. So, is epistemological disjunctivism true? It is arguably a less revisionary anti-sceptical strategy than others on offer (e.g. reliabilism about knowledge, denying that knowledge is closed under known entailment, contextualism about knowledge attributions, and so forth). However, for the reasons just given, it’s true only if we can provide an acceptable account of either how one can know that one sees that p, or how one can be justified in believing that one sees that p—so further investigation is required.

5 The Naïve Realist’s disjunctivism Let us now turn to our fourth version of disjunctivism concerning perceptual experience. This version of disjunctivism aims to preserve a theory known as Naïve Realism. Naïve Realism holds that veridical experience fundamentally consists in the subject bearing the perceptual relation to things in her environment (and some of their properties). For example, according to the Naïve Realist, the veridical experience I’m currently having of the yellow, crescent-shaped banana on my desk fundamentally consists in my bearing the perceptual relation to the banana, as well as its yellowness and its crescent shape.28 (As for what the Naïve Realist says about non-veridical experience, we’ll turn to that question shortly.) proof (i.e. ‘here is a hand; here is another’). In any case, epistemological disjunctivism is intended to avoid the faults commonly attributed to Moore’s anti-sceptical strategy (e.g. the charge of question-begging). 26 

For other potential answers, see Logue (2011). proposals, see Johnston (2006:  287–288), McDowell (2008:  387), Millar (2008:  342), Kennedy (2011: 78–80), and Byrne (2012). 28  It may not be immediately obvious to readers familiar with Naïve Realism that this characterization captures the various formulations offered by its proponents. For discussion that aims to allay this suspicion, see Logue (2013). 27  For

208   Heather Logue The ‘fundamentally’ in the statement of Naïve Realism is important, as without it the claim on the table would simply be that veridical experience involves perceiving things in my (mind-independent, material) environment—which everyone but the idealist accepts. Naïve Realism is a much stronger claim. It is a claim about the metaphysical structure of veridical experience, i.e. about the ultimate psychological facts in virtue of which facts about experiences obtain. To say that an experience fundamentally consists in x is to say that x is the most basic psychological characterization of the experience, in the sense that all of its other psychological features (e.g. its phenomenal character, its epistemological role) are grounded in x. So according to the Naïve Realist, the ultimate psychological fact in virtue of which an experience has the phenomenal character it does, and gives rise to the beliefs and the behaviours it does, is that it consists in the subject bearing the perceptual relation to things in her environment.29 For example, my bearing the perceptual relation to the banana on my desk, and its yellowness and its crescent shape, is the most basic (personal-level) psychological explanation of why I believe that there’s a yellow, crescent-shaped banana on the table. (Of course, there are further neurological and information-processing facts by virtue of which I bear the perceptual relation to the banana and certain of its properties. But these are not the explanantia we’re after in a theory of the metaphysical structure of experience.) By contrast, strong versions of Intentionalism hold that all perceptual experiences, and hence veridical experiences, fundamentally consist in the subject representing her environment as being a certain way (e.g. as containing a yellow, crescent-shaped banana).30 Notice that both Intentionalism and Naïve Realism are compatible with Direct Realism as I described it earlier. For the idea that the subject of a veridical experience directly perceives things in her environment can be elaborated in two different ways: in terms of the experience fundamentally consisting in the subject (directly) perceiving such things, or in terms of the experience fundamentally consisting in the subject representing such things.31 Given that one wants to defend Direct Realism, why would one opt for the Naïve Realist version? This question has been given a variety of answers by proponents of Naïve Realism, and I don’t have space to do any of them justice here. One answer, from which the view presumably derives its name, is that it is the ‘naïve’ or ‘common’ conception of veridical 29  Note that this claim isn’t incompatible with a veridical experience and a hallucination having the same phenomenal character. For even if a veridical experience has its phenomenal character ultimately in virtue of the subject perceiving things in her environment, it could still be the case that a hallucination has the same phenomenal character ultimately by virtue of a different psychological fact. (More on this idea below.) 30  Some Intentionalists balk at explaining the phenomenal character of experience in terms of how the subject perceptually represents her environment as being, usually on the grounds that the representational content and phenomenal character can vary independently of each other. These Intentionalists typically explain the epistemological role of experience in terms of its representational content, while giving a separate account of what grounds its phenomenal character in terms of intrinsically non-representational ‘qualia’ (see, e.g., Block 1990 and 1996). 31 It’s important to keep in mind that the Intentionalist doesn’t hold that a subject perceives the representation in which her experience fundamentally consists—that claim wouldn’t be compatible with Direct Realism. The Intentionalist’s representation (unlike the Sense-Datum Theorist’s) is a state of the subject that enables perception of things in one’s environment without being perceived itself, much as the eye sees without being seen by its subject.

Disjunctivism   209 experience.32 Naïve Realists typically put little weight on this consideration, and they’re right not to do so—even if it is the common-sense view, it’s far from obvious why the deliverances of common sense should dictate our views about the metaphysics of veridical experience. And as Hume famously noted, the ‘slightest philosophy’ (1777/1993: 104) shakes our commitment to this particular naïve belief.33 The bit of philosophy Hume alludes to is, of course, reflection on non-veridical experiences, especially total hallucinations. For a moment’s thought reveals that Naïve Realism cannot be true of total hallucinations: these experiences by definition don’t involve perception of things in one’s environment, so they can’t fundamentally consist in perceiving things in one’s environment. Hence, Naïve Realism is committed to disjunctivism about the metaphysical structure of perceptual experience (metaphysical disjunctivism for short): veridical experience and at least total hallucination have radically different metaphysical structures. Veridical experience fundamentally consists in the subject perceiving things in her environment and certain of their properties, whereas total hallucination fundamentally consists in something else entirely. What about partial hallucinations and illusions? These involve the subject perceiving things in her environment, but misperceiving some of their properties.34 Even if they fundamentally consist in perceiving things in one’s environment, it’s not obvious that this fact could afford an exhaustive account of such experiences. This sort of account seems particularly inappropriate for partial hallucinations. For example, take a partial hallucination in which the subject perceives a green banana, which nevertheless looks yellow because a neuroscientist is fiddling with her brain. The facts in virtue of which the banana looks yellow have nothing to do with the way the banana is, so any attempt to account for the subject’s experience solely in terms of perception of the banana seems completely off-base. However, this isn’t obviously the case when it comes to illusions, which are generated by complicated interactions between properties of the things perceived, the circumstances in which they’re perceived, and the way the subject’s perceptual system normally functions in those circumstances (very roughly speaking). For example, take a garden-variety illusion in which a green banana looks yellow due to strange lighting conditions. We need to account for the fact that the banana looks yellow to the subject. Of course, we can’t account for this fact in terms of the subject perceiving the banana’s colour—it’s green, not yellow. But perhaps there’s another property the banana has (perhaps one closely related to colour properties) such that perceiving it would explain why it looks yellow to the subject. I don’t have the space to 32 

For discussion, see Fish (2009: ch. 1, section 3). For more compelling motivations for Naïve Realism, see Martin (2002), Campbell (2002: ch. 6), and (especially) Fish (2009: 75–79). It’s easy to get the false impression that Martin endorses the motivation described in the main text, as he claims that Naïve Realism is ‘ . . . the best articulation of how our experiences strike us as being to introspective reflection on them’ (2004: 42). If the introspective reflection is that of a philosophically naïve subject, then we have the motivation just outlined. In the footnote immediately following this claim, he refers the reader to his paper ‘The Transparency of Experience’ as the place where he develops it in detail. However, in this paper, he argues that introspection of perceptual experience alone doesn’t support Naïve Realism over Intentionalism (2002: 402). Rather, the motivation offered is a sophisticated philosophical argument utilizing premises about introspection of sensory imagination (not perceptual experience). So if we follow Martin in regarding his 2002 paper as the definitive statement of his motivation for Naïve Realism, he doesn’t endorse the one described in the main text after all. 34  Or, in the case of ‘veridical’ illusions and partial hallucinations, failing to perceive some property one of the things appears to have (see section 1). 33 

210   Heather Logue explore this possibility here; but suffice it to say that some fancy footwork is required in order make Naïve Realism work for illusions.35 In any case, the point to note for our purposes is that metaphysical disjunctivists divide into those who put illusions in the same disjunct as veridical experience (VI v H disjunctivists), and those who put them in the same disjunct as hallucinatory experiences (V v IH disjunctivists).36 (In what follows, we’ll set illusions and partial hallucinations aside for ease of exposition.) Of course, the Naïve Realist’s work is still far from over. It’s not enough to say that the metaphysical structure of hallucination is radically different from that of veridical experience. The Naïve Realist owes us an account of what exactly the metaphysical structure of hallucination is. Before turning to that issue, though, let us pause to reflect on what metaphysical disjunctivism is committed to. For arguably much of the resistance to this form of disjunctivism is the result of taking it to be a much stronger claim than it has to be in order to defend Naïve Realism. I suspect that one source of misunderstanding are characterizations of metaphysical disjunctivism as claiming that veridical experience and at least hallucination have no mental commonalities (e.g. Hinton 1973: 62; Martin 2004: 37; and Byrne and Logue 2009: ix).37 However, such characterizations are misleading. One thing a veridical experience of a yellow banana and a total hallucination as of one have in common is that they are perceptual experiences as of a yellow banana. Another thing they have in common (at least on the face of it) is their phenomenal character—what it’s like to have them is the same.38 Arguably, these are mental commonalities if anything is. So a more charitable formulation of metaphysical disjunctivism is the following: the ultimate psychological facts that ground a veridical experience are radically different from those that ground a subjectively indistinguishable hallucination. This claim allows for a wide range of mental commonalities across experiences that fall in different disjuncts—commonalities which can be employed in responding to critics of the view.39 Some Naïve Realists make a further claim that has raised eyebrows—namely, that their view requires not just disjunctivism about the metaphysical structure of experience, but also what we might call disjunctivism about phenomenology. The latter is the claim that what it is like to have a veridical experience is different from what it is like to have a subjectively indistinguishable hallucination. That is, even though the subject of a hallucination as of a yellow banana couldn’t tell her experience apart from a veridical one of a yellow banana upon the 35 

For fancy footwork along these lines, see Brewer (2008), Antony (2011), and Kalderon (2011). The ‘VI v H’ and ‘V v IH’ terminology was introduced in Byrne and Logue (2008: 69). Metaphysical disjunctivists tend to go for a V v IH version with little in the way of argument for it (see Martin 2006: 360 and Campbell 2002: 117), but for VI v H versions, see Snowdon (1979/80: 185) and Brewer (2008). 37  More precisely, the claim is usually that a veridical experience of (say) a yellow banana and a subjectively indistinguishable hallucination as of one have no reasonably specific commonalities, e.g. commonalities specific enough to not characterize an experience as of (say) a red tomato (see Byrne and Logue 2009: ix). The point I am about to make shows that even this qualified claim is too strong. 38  Some think that Naïve Realism entails that hallucinations are phenomenally different from veridical perceptions—I’ll discuss this claim shortly. 39  One quick example:  Tyler Burge objects to metaphysical disjunctivism on the grounds that it is incompatible with a principle presupposed by empirical study of perceptual experience—roughly, that there are commonalities across veridical experiences and illusions that have the same proximal cause which are relevant to explaining what the subject believes and does (Burge 2005). First, note that this is no objection at all to VI v H metaphysical disjunctivism. But more importantly, no V v IH disjunctivist in her right mind would deny there are mental commonalities between a veridical experience and an illusion with the same proximal cause—e.g. the property of being an experience as of a yellow banana, which is the sort of thing we appeal to all the time in explaining people’s beliefs and behaviours. 36 

Disjunctivism   211 most careful introspection, what it is like for her to have this hallucination is nevertheless different from what it would be like for her to have a veridical experience of the relevant kind. Indeed, some have gone so far as to deny that hallucinations have phenomenal character at all. According to William Fish (2009: 98), there’s nothing it’s like to have a total hallucination; rather, it’s just that hallucinators are prone to form the mistaken belief that they’re in states that have phenomenal character because these states tend to have the same behavioural and cognitive effects as states that do have phenomenal character (i.e. veridical experiences). Why would a Naïve Realist make such an eyebrow-raising claim? Disjunctivism about phenomenology follows if we identify phenomenal character with relational properties—e.g. if we identify what it’s like to experience yellowness with the property of seeing it (a property one couldn’t instantiate in the absence of a yellow thing).40 Given that the subject of a hallucination doesn’t see anything yellow, it follows that there’s nothing it’s like to be in that state. But the Naïve Realist need not account for phenomenal character in this way. Even though the Naïve Realist holds that a veridical experience has the psychological features it does in virtue of the subject bearing the perceptual relation to things in her environment, this doesn’t mean that all (or even any) of its psychological features are identical to the obtaining of this relation. In particular, when it comes to phenomenal character, the Naïve Realist could say that it is multiply realizable. Just as a functionalist about pain says that it can be realized by C-fibres firing or, say, a radically different state of an alien, the Naïve Realist could say that the phenomenal character associated with experience of yellowness can be realized by seeing an instance of it, or something else entirely (i.e. whatever’s going on in the case of total hallucination). Of course, this alternative isn’t entirely unproblematic; but it’s considerably more palatable than the claim that there’s nothing it’s like to have a total hallucination.41 Let us now turn to what the Naïve Realist really ought to say about hallucination. The options divide into two broad categories. First, we have positive (metaphysical) disjunctivism, which characterizes hallucination in terms that are independent of veridical experience. For example, a positive disjunctivist might say that hallucination fundamentally consists in perception of sense-data, perception of sensible profiles, or representing one’s environment as being a certain way—what these candidate accounts of hallucination have in common is that none of them makes reference to veridical experience. By contrast, a Naïve Realist might opt for negative (metaphysical) disjunctivism, which characterizes hallucination in terms of some relation to veridical experience. For example, one such account holds that hallucination fundamentally consists in the property of being subjectively indiscriminable from a veridical experience of a certain kind (e.g. a veridical experience of a yellow banana).42 One might find negative disjunctivism difficult to accept—the idea that there’s nothing to a total hallucination beyond being subjectively indiscriminable from a veridical experience 40 

Pace Johnston (2004). For further elaboration and defence of this alternative, see Logue (2013); for a (later but more quickly published) repudiation, see Logue (2012). 42  Negative accounts of hallucination along these lines are defended by Martin (2004, 2006) and Fish (2008, 2009). Their accounts differ with respect to what the relevant sort of subjective indiscriminability is. Positive disjunctivism is less popular, thanks to an argument of Martin’s that will be discussed below. But a version of it is endorsed in Johnston (2004) (although he wouldn’t call it that, since he takes ‘disjunctivism’ to pick out what I’m calling ‘negative disjunctivism’). The ‘positive’ and ‘negative’ terminology comes from Byrne and Logue (2008). 41 

212   Heather Logue of a certain kind strikes some as a rather unsatisfying account. To outline just one potential source of dissatisfaction: one might have hoped that whatever account of hallucination we give will specify the facts in virtue of which a hallucination is subjectively indistinguishable from a veridical experience of a yellow banana. A positive account would yield such an explanation: for example, if hallucination fundamentally consisted in representing one’s environment as being a certain way, we could then say that a hallucination as of a yellow banana is subjectively indistinguishable from a veridical experience of one in virtue of the fact that both kinds of experience fundamentally consist in representing that there’s a yellow thing before one. But if we say, as the negative disjunctivist does, that all there is to a total hallucination as of a yellow banana is being subjectively indiscriminable from a veridical experience of one, we’ve denied ourselves the resources to account for this fact. In spite of this worry, most metaphysical disjunctivists are negative disjunctivists—they have been persuaded by a powerful argument against positive disjunctivism given by M. G. F. Martin.43 The argument has two basic parts, the first of which we’ve already seen in section 2. Recall that the subject of a veridical experience and the subject of a total hallucination could be in the same type of brain state; and if such a brain state gives rise to a certain kind of psychological state in the case of total hallucination, there’s no good reason to claim that it wouldn’t do so in the case of veridical experience. Hence, whatever is going on in hallucination is going on in veridical experience too—if hallucination involves perception of sense-data, sensible profiles, or representing one’s environment as being a certain way, so does veridical experience.44 This fact in itself might not seem like a problem for the Naïve Realist—why couldn’t he say that veridical experience consists in the subject bearing the perceptual relation to things in her environment and something else? This is where the second stage of the argument comes in. It begins with the fact that a veridical experience of a yellow banana and a subjectively indiscriminable hallucinatory counterpart have doxastic, behavioural, and phenomenal commonalities. For example, they both tend to give rise to the belief that there’s a yellow banana before one, they both cause one to reach in a certain direction if one fancies a snack, and (pace Fish and Logue 2012) what it is like to have them is the same. Now, suppose for the sake of a reductio that some form of positive disjunctivism is true—say, that hallucinations fundamentally consist in the subject representing her environment as being a certain way. By the argument summarized in the last paragraph, veridical experience involves the subject representing her environment as being a certain way too. Given that the veridical experience and the hallucination have this representational commonality, it seems that it’s best suited to explain the doxastic, behavioural, and phenomenal features of the experiences. For example, if the hallucination gives rise to the belief that there’s a yellow banana before one in virtue of the fact that it consists in representing one’s environment as containing a yellow banana, presumably this is the case for veridical experience as well. The perceptual relation between the subject and things in her environment is effectively ‘screened off’ from explaining the veridical experience’s doxastic effects. So too with its behavioural effects and its phenomenal character. Naïve Realism cannot allow that the perceptual relation between subject and object is 43 See

Martin (2004) for the argument, and Brewer (2008:  173)  and Fish (2009:  84–85) for endorsements of it. 44  This stage of the argument is laid out in detail in Martin (2004: 52–58).

Disjunctivism   213 screened off in this manner, as it holds that a veridical experience has all of its psychological features ultimately in virtue of this perceptual relation.45 Hence, given that we’re interested in metaphysical disjunctivism for the purpose of preserving Naïve Realism, it appears that positive disjunctivism won’t do the trick—negative disjunctivism is our only option.46 Or is it? Suppose a positive disjunctivist says something like the following:  yes, a veridical experience of a yellow banana consists in (say) representing one’s environment as containing a yellow crescent-shaped banana. And yes, this representational fact explains the experience’s doxastic, behavioural, and phenomenal features. But this doesn’t screen off the obtaining of the perceptual relation from explaining these things too, because the subject is in the representational state in virtue of bearing the perceptual relation to the banana and certain of its properties. That is, while veridical experience consists in the subject representing her environment as being a certain way, it doesn’t fundamentally consist in this. The doxastic, behavioural, and phenomenal features of the experience are ultimately explained by the subject bearing the perceptual relation to the banana and certain of its properties. By contrast, the hallucination fundamentally consists in the subject representing her environment as being a certain way; there’s no further psychological fact in virtue of which she is in this representational state. Of course, this proposal raises a number of worries I don’t have the space to address here, for example: can a hallucination fundamentally consist in something while a veridical experience consists in the same sort of thing, but not fundamentally so? And what are the grounds for saying that the common property is instantiated in virtue of the perceptual relation obtaining in veridical experience?47 Nevertheless, since negative disjunctivism strikes many as an unsatisfactory account of hallucination, this positive disjunctivist proposal is worth pursuing.48 So is metaphysical disjunctivism true? If Naïve Realism is true, then yes. But Naïve Realism is true only if some form of metaphysical disjunctivism can provide an adequate account of hallucination. These issues are subjects of intense debate in contemporary philosophy of perception. In my view, the jury’s still out.

References Antony, L. (2011). ‘The Openness of Illusions’. Philosophical Issues, 21, 25–44. Austin, J. (1962). Sense and Sensibilia. Oxford: Oxford University Press.

45 

This stage of the argument is laid out in detail in Martin (2004: 58–63). course, on negative disjunctivism, both a veridical experience of a yellow banana and a hallucination as of one are subjectively indiscriminable from a veridical experience of a yellow banana. Martin argues that the indiscriminability property doesn’t screen off the obtaining of the perceptual relation because the explanatory power of the former depends on that of the latter (Martin 2004: 69–70). 47  For a fuller discussion of this positive disjunctivist proposal and objections to it, see Logue (2013). Another more radical positive disjunctivist proposal (one which involves denying that total hallucinations have phenomenal character) is elaborated and defended in Logue (2012). 48  For more nuanced objections to negative disjunctivism than the one presented earlier in this section, see Siegel (2004 and 2008), Johnston (2004: 124–127), and Sturgeon (2006: 208–210). 46  Of

214   Heather Logue Ayer, A. J. (1956). The Problem of Knowledge. Harmondsworth: Penguin. Block, N. (1990). ‘Inverted Earth’. Philosophical Perspectives, 4, 53–79. Block, N. (1996). ‘Mental Paint and Mental Latex’. Philosophical Issues, 7, 19–49. Brewer, B. (1999). Perception and Reason. Oxford: Oxford University Press. Brewer, B. (2008). 'How to Account for Illusion'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Broad, C. D. (1925). The Mind and its Place in Nature. London: Routledge and Kegan Paul. Burge, T. (2005). ‘Disjunctivism and Perceptual Psychology’. Philosophical Topics, 33, 1–78. Byrne, A. (2001). ‘Intentionalism Defended’. Philosophical Review, 110, 119–240. Byrne, A. (2012). 'Knowing what I See'. In D. Smithies and D. Stoljar (eds), Introspection and Consciousness. Oxford: Oxford University Press. Byrne, A. and Logue, H. (2008). 'Either/Or'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Byrne, A. and Logue, H. (2009). 'Introduction'. In A. Byrne and H. Logue (eds), Disjunctivism: Contemporary Readings. Cambridge, MA: MIT Press. Campbell, J. (2002). Reference and Consciousness. Oxford: Oxford University Press. Chalmers, D. (2006). 'Perception and the Fall from Eden'. In T. Gendler and J. Hawthorne (eds), Perceptual Experience . Oxford: Oxford University Press. Crane, T. (2009). 'Is Perception a Propositional Attitude?' Philosophical Quarterly, 59, 452–469. Davies, M. (1992). ‘Perceptual Content and Local Supervenience’. Proceedings of the Aristotelian Society, 92, 21–45. Dretske, F. (1995). Naturalizing the Mind. Cambridge, MA: MIT Press. Fish, W. (2008). 'Disjunctivism, Indistinguishability, and the Nature of Hallucination'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge . Oxford: Oxford University Press. Fish, W. (2009). Perception, Hallucination, and Illusion. Oxford: Oxford University Press. Foster, J. (2000). The Nature of Perception. Oxford: Oxford University Press. Harman, G. (1990). ‘The Intrinsic Quality of Experience’. Philosophical Perspectives, 4, 31–52. Hinton, J. M. (1973). Experiences:  An Inquiry into Some Ambiguities. Oxford:  Oxford University Press. Huemer, M. (2011). ’Sense-Data'. In E. Zalta (ed.), Stanford Encyclopedia of Philosophy. (accessed July 2011). Hume, D. (1777/1993). An Enquiry Concerning Human Understanding, (ed.) E. Steinberg, 2nd edn. Indianapolis, IN: Hackett Publishing Company. Jackson, F. (1977). Perception:  A  Representative Theory. Cambridge:  Cambridge University Press. Johnston, M. (2004). ‘The Obscure Object of Hallucination’. Philosophical Studies, 120, 113–183. Johnston, M. (2006). 'Better than Mere Knowledge? The Function of Sensory Awareness'. In T. Gendler and J. Hawthorne (eds), Perceptual Experience. Oxford: Oxford University Press. Kalderon, M. E. (2011). ‘Color Illusion’. Nous, 45, 751–775. Kennedy, M. (2011). ‘Naive Realism, Privileged Access, and Epistemic Safety’. Nous, 45, 77–102. Logue, H. (2011). ‘The Skeptic and the Naive Realist’. Philosophical Issues, 21, 268–288. Logue, H. (2012). 'What Should the Naïve Realist Say about Total Hallucinations?' Philosophical Perspectives, 26, 173–199. Logue, H. (2013). ‘Good News for the Disjunctivist about (one of) the Bad Cases’. Philosophy and Phenomenological Research, 86, 105–133.

Disjunctivism   215 Logue, H. (2014). 'Experiential content and Naive Realism: A Reconciliation'. In B. Brogaard (ed.), Does Perception Have Content? Oxford: Oxford University Press. Martin, M. G. F. (2002). ‘The Transparency of Experience'. Mind and Language, 17, 376–425. Martin, M. G. F. (2004). ‘The Limits of Self-Awareness’, Philosophical Studies, 120: 37–89. Martin, M. G. F. (2006). 'On Being Alienated'. In T. Gendler and J. Hawthorne, Perceptual Experience. Oxford: Oxford University Press. McDowell, J. (1982). ‘Criteria, Defeasibility, and Knowledge’. Proceedings of the British Academy, 68, 455–479. McDowell, J. (2008). 'The Disjunctive Conception of Experience as Material for a Transcendental Argument'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. McGinn, C. (1982). The Character of Mind. Oxford: Oxford University Press. Millar, A. (2008). 'Perceptual-Recognitional Abilities and Perceptual Knowledge'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Moore, G. E. (1953). Some Main Problems of Philosophy. London:  George, Allen, and Unwin. Moore, G. E. (1962). 'Proof of an External World'. Philosophical Papers. New York: Collier Books. Neta, R. (2008). 'In Defense of Disjunctivism'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Peacocke, C. (1983). Sense and Content. Oxford: Oxford University Press. Price, H. (1950). Perception, 2nd ed. London: Methuen. Pritchard, D. (2008). 'McDowellian Neo-Mooreanism'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Robinson, H. (1994). Perception. London: Routledge. Russell, B. (1912). Problems of Philosophy. Oxford: Oxford University Press. Schellenberg, S. (2011). ‘Perceptual Content Defended’. Nous. 45, 714–750. Siegel, S. (2004). ‘Indiscriminability and the Phenomenal’. Philosophical Studies, 120, 91–112. Siegel, S. (2008). 'The Epistemic Conception of Hallucination'. In A. Haddock and F. Macpherson (eds), Disjunctivism: Perception, Action, Knowledge. Oxford: Oxford University Press. Siegel, S. (2010). ‘Do Visual Experiences Have Contents?’ In B. Nanay (ed.), Perceiving the World. Oxford: Oxford University Press. Smith, A. D. (2002). The Problem of Perception. Cambridge, MA: Harvard University Press. Snowdon, P. (this volume). 'Sense-Data'. In M. Matthen (ed.), Oxford Handbook of the Philosophy of Perception. Oxford: Oxford University Press. Snowdon, P. F. (1979/80). ‘Perception, Vision, and Causation’. Proceedings of the Aristotelian Society, 81, 175–192. Snowdon, P. F. (2005). 'The Formulation of Disjunctivism: A Response to Fish'. Proceedings of the Aristotelian Society, 105, 129–141. Stroud, B. (1984). The Significance of Philosophical Skepticism. Oxford: Clarendon Press. Sturgeon, S. (2006). ‘Reflective Disjunctivism’. Proceedings of the Aristotelian Society, Supplement, 80, 185–216. Thau, M. (2004). ‘What is Disjunctivism?’. Philosophical Studies, 120, 193–253.

216   Heather Logue Travis, C. (2004). ‘The Silence of the Senses’. Mind, 113, 57–94. Tye, M. (2000). Consciousness, Color, and Content. Cambridge, MA: MIT Press. Tye, M. (2007). ‘Intentionalism and the Argument from no Common Content’. Philosophical Perspectives, 21, 589–613. Williamson, T. (2000). Knowledge and Its Limits. Oxford: Oxford University Press.

Chapter 12

Action-based Accou n ts of Perception Pierre Jacob

According to a prevalent view in twentieth-century analytic philosophy of action and perception, an agent’s ability to act on the world and her ability to perceive the world are two distinct abilities (cf. e.g. Davidson, 1980; Searle, 1983). For an agent to act is to change the world by executing bodily movements as a means to fulfil some intention or other. An agent’s intention is a psychological cause of her movements. It has, in Searle’s (1983) words, a world-to-mind direction of fit: to form an intention is to represent a possible (non-actual) state of affairs that the agent’s intended action would turn into a fact. To perceive the world is to register or record an actual state of affairs or a fact as it is, through one of the five fundamental sensory modalities: sight, hearing, touch, smell, or taste. There are two sides to perception, both of which reflect the mind-to-world direction of fit of perceptual experiences: an epistemic objective side and a phenomenological subjective side. On the objective side, perceptual experiences enable humans to form reliable beliefs about the way the world is. On the subjective side, perception in each sensory modality offers a distinctive phenomenological awareness of the world: there is something it is like to seeing a white leaf of paper that is different from what it is like to smelling it, tasting it, touching it, or hearing it being ripped. To a large extent, the dualism between action and perception seems to fit the rejection of the behaviourist approach to perception characteristic of the cognitive revolution of the 1950s and the subsequent rise of the computational paradigm in the scientific investigation of perception, advocated by David Marr (1982) and others. The computational paradigm in turn was in broad agreement with one of the dominant trends in twentieth-century analytic philosophy of perception, that is representationalism (also known as intentionalism), which stands in sharp contrast with disjunctivism. While advocates of disjunctivism endorse a version of direct realism and stress that in perception, an agent is directly related to mind-independent objects in the world, advocates of representationalism argue that perceptual experiences have content or conditions of satisfaction and depict the perceiver’s surroundings as being thus and so by representing some of the properties of perceivable objects. For example, visual experiences represent the sizes, shapes, spatial positions, colours, and textures of perceivable objects.1 1 For

a defence of disjunctivism, see Hinton (1973) and McDowell (1982). For a defence of representationalism, see Dretske (1995) and Tye (1995).

218   Pierre Jacob In recent years, the reciprocal interactions between action and perception have been the topic of intense investigations. As a result, many prominent cognitive scientists and philosophers of perception have engaged in the exploration of action-based approaches to perception. Not only does the success of an agent’s goal-directed action seem to depend on her ability to select and locate her target, but also an agent’s executed action has direct consequences on her own sensory experience. Action-based accounts of perception, however, do not content themselves with these causal interdependencies. They argue instead for stronger constitutive links between action and perception. There are two main motivations to action-based approaches to perception: one is their parsimonious assumption that, far from being two autonomous systems, each of which contributes to the function of the other, action and perception belong to a single overlapping functional system. The other one is the tendency to minimize the load of internal processing and the role of mental representations in perception. The goal of the present chapter is to assess the scope and limits of action-based approaches to perception, mostly in the visual modality. Many advocates of action-based approaches to perception link their rejection of the computational/representational approach to one or another version of the embodied cognition approach to perception, to which the first section of this chapter is devoted. The second section will examine the support that action-based approaches to perception can expect to derive from the so-called two-systems model of visual processing. The third section will be devoted to the problems faced by one of the recent most prominent action-based accounts of object-perception named enactivism. Finally, the last section will examine action-based accounts of social perception.

1  Embodied perception One of the earliest defences of the embodied perception research programme was Gibson’s (1979) ecological approach to visual perception, which contributed two related fundamental insights. One is that much object-perception consists in detecting possibilities for action, which Gibson called affordances. Different things afford different possibilities for action to different organisms: for example, the surface of a lake affords different possibilities of spatial navigation to insects, birds, and mammals. The second one is that much visual perception consists in an agent’s movements that enable her to extract and manipulate information lying in the optic array. It is also distinctive of embodied perception both to embrace an empiricist account of concepts and to reject the computational approach to perception.

Concept-empiricism Concept-empiricism, advocated by, for example, Barsalou (1999), Barsalou et al. (2003), and Prinz (2002, 2005), involves three basic ingredients. First, it is based on the rejection of the linguistic model of concepts as amodal symbols in some language of thought, whose meanings (or contents) stand to their non-phonetic forms (or vehicles) in the same arbitrary relation as the meanings of words of natural languages stand to their phonetic properties (cf. Barsalou et al., 2003). Secondly, on the empiricist view, concepts are (visual,

Action-Based Accounts of Perception    219 auditory, olfactory, tactile, or motor) images encoded in the various perceptual and motor systems. Finally and correlatively, conceptual processing is taken to be a re-enactment or simulation of basic perceptual and motor processing. For example, retrieving the concept of a dog would consist in re-enacting or simulating some perceptual representation or mental image of a dog (for further discussion, see Machery, 2006, 2007). While some philosophers (e.g. McDowell, 1994) have denied the distinction between representations with conceptual and nonconceptual content on the grounds that the content of perceptual experiences is fully conceptual, advocates of concept-empiricism also deny the same distinction, but for the opposite reason: they first assume that the representations of all perceivable objects have perceptual and/or sensorimotor, that is nonconceptual, content and they further assume that the contents of representations of non-perceivable (e.g. abstract, mathematical or theoretical) objects are derivable (or constructible) from the contents of the representations of perceivable objects. The empiricist denial of the conceptual/nonconceptual content distinction faces four basic challenges. The first one is that, as Descartes famously noticed, one can perceive (or imagine) triangular objects and one can also apply to them the concept of a triangle. But a chiliagon (i.e. a geometrical object with 1 000 sides) is a discursively defined concept that can only be represented and distinguished from a closed geometrical figure with 999 sides conceptually, not by the imagination. If this is right, then concept-empiricism seems forced to posit a dual account according to which the contents of some, not all, concepts can be grounded in perceptual and/or motor processes. The second one is the perceptual binding problem. One can see a poodle, an alsatian, a dalmatian, a bulldog, and so on. Seeing one of them is clearly a different experience from seeing another. But so is hearing, smelling, or touching one of them. The challenge for concept-empiricism is to account for cross-modal binding between the properties of one and the same individual dog represented in different sensory modalities without positing amodal vehicles with cross-modal, i.e. conceptual, content. The third challenge is the belief/experience distinction. Among the reasons why we need to draw a distinction between perceptual beliefs and perceptual experiences are perceptual illusions. For example, when one is presented with two segments of equal length, with arrows pointing respectively in and out (as in the Müller-Lyer illusion), the former unavoidably looks longer than the latter. One’s visual experience represents the two segments as unequal even if one believes that they are equal. This shows that the content of one’s visual experience is encapsulated from the content of one’s beliefs in Fodor’s (1983) terms: unlike a belief, a visual experience is not revisable in light of further evidence. Given that the content of one’s visual experience of the two segments as unequal persists in the presence of one’s belief that the two segments are equal, it follows that the function, content, and character of one’s visual experiences cannot be identified to the function, content, and character of one’s beliefs. The fourth challenge faced by concept-empiricism is the logical form challenge. Advocates of the view that conceptual vehicles are amodal symbols in some language of thought, like Fodor (1975), argue that whereas the content of a primitive concept (e.g. the concept of a dog) is not further definable, the content of a complex concept (e.g. the concept of a blue dog) systematically depends on the contents of its constituents. Symbols with conceptual content have a logical form, or in Fodor’s (2007) terms, a ‘canonical decomposition’: not every part of a complex symbol with conceptual content is one of its proper

220   Pierre Jacob constituents. Some of its constituents stand for individuals, others for properties, still others for logical operations. By contrast, visual percepts, visual mental images and pictures are representations with iconic or non-conceptual content. The iconicity of percepts, images, and pictures enables them to represent by virtue of the fact that their internal structure preserves some of the spatial relations (e.g. part–whole relations, overlap, and occlusion) holding among the constituents of the states of affairs that they depict. But iconic representations with non-conceptual contents lack a logical form and a canonical decomposition. The challenge for advocates of concept-empiricism is to show how representations without a canonical decomposition could generate representations with a canonical decomposition.

The rejection of the computational approach to perception Marr’s (1982) book on vision is a stepping-stone of the computational approach to visual perception. It is based on a tripartite distinction between three levels of analysis. The highest ‘computational’ level involves a specification of the task which the visual system has been designed to perform, that is, the construction of a three-dimensional representation of distal stimuli on the basis of retinal inputs.2 The lowest (hardware) level involves a description of how the computations are physically or biologically ‘implemented’ or ‘realized’ (by the neurochemical properties underlying photo-transduction in retinal cells). The intermediate ‘algorithmic’ level involves the particular operations used by the system in performing its computations. In his book on vision, Marr (1982) also proposed a model of the computational level itself, which involves three complementary stages, the first of which takes retinal stimulations as input and generates a so-called primal sketch of reflectance changes on the surface outside the viewer. Secondly, from the primal sketch as input, the visual system computes a 2.5-D sketch of the surface, which encodes information about depth and contours of the surface relative to the perceiver. Finally, given the 2.5-D sketch as input, the visual system computes a 3-D representation of objects, which captures their shapes and orientations. Following Gibson’s (1979) ecological approach, advocates of embodied perception reject two complementary aspects of the computational approach to perception. First, they reject the thesis of multiple realizability, which follows from Marr’s (1982) tripartite distinction between the computational, the algorithmic, and the implementation levels, that is, the thesis that one and the same computational state can be realized by several distinct underlying physical, chemical, or biological states.3 Thus, Shapiro (2004: 175), who embraces the embodied perception research programme, argues against the thesis of multiple realizability on the grounds that it entails two related theses which he calls respectively body neutrality and the separability thesis (i.e. the separability between the computer program that runs visual perception and the body that implements the program), both of which are consistent with the idea ‘that the mind is a program that can be characterized in abstraction 2  Noë (2004: 22) rejects the view that ‘vision is a matter of generating a detailed internal representation of the visual world on the basis of information available at the retina alone’ (cf. section 3). 3  For well-known defences of the thesis of multiple realizability, see Putnam (1967) and Fodor (1974). For a critique, see Kim (1993).

Action-Based Accounts of Perception    221 from the kind of body/brain that realizes it’. For example, Shapiro (2004: 187) stresses the significance for visual perception of the fact that the human body involves two eyes: an object (or distal stimulus) projects two distinct retinal images onto each eye and the brain makes use of disparity information from both eyes to compute the relative depth of the object. Secondly, as Shapiro (2007) puts it, ‘embodied cognition  . . .  departs from traditional cognitive science in its reluctance to conceive of cognition as computational and in its emphasis on the significance of an organism’s body in how and what the organism thinks and perceives’. In other words, embodied perception theorists reject the assumption that perceptual processes are computations that could be performed by a disembodied machine on abstract symbols in virtue of their syntactic properties alone, as if the individual’s full bodily anatomy did not matter to the process. Instead, they stress the role of the human body in perceptual processes because they accept the ecological Gibsonian emphasis on the role of an agent’s movements in extracting information from the optic array and the detection of affordances (i.e. possibilities of action) for visual perception, both of which depend on the agent’s bodily anatomy. There are, however, two possible interpretations of the claim made by embodied perception theorists: one is the uncontroversial claim that human perception causally depends on the anatomical structure of the human body. The other is the more controversial claim that the character and content of human perceptual experiences are constitutively determined by the human anatomy (for a critical evaluation of the stronger constitutive claim, see Aizawa, 2007; Block, 2005). The distinction between the weaker and the stronger version of the dependency of perceptual processes on human anatomy is important for evaluating the tension between the embodied perception framework and the traditional action/perception dualism.

2  The two-visual systems model of human vision In the past forty years or so, a number of surprising dissociations between visual perception and visually guided actions have been at the basis of a novel approach to human vision: the two-visual systems model, first advocated by Milner and Goodale (1995). First of all, this model is based on the insight that the visual guidance of actions of prehension and the perceptual experience of objects make inconsistent demands on the visual processing of information about objects. Secondly, this model maps the functional distinction between visually guided actions and visual perception onto the anatomical segregation between the so-called ‘dorsal’ stream and the so-called ‘ventral’ stream of the human visual system. Finally, it assumes that activity in the so-called ‘ventral’ stream plays a distinctive role in visual awareness of the world. Humans have dexterous hands that enable them to grasp targets in their peripersonal space with either precision grip or full prehension. For the purpose of reaching a target of prehension, an agent must represent its spatial position in an egocentric coordinate system centred on her body. For the purpose of grasping it, the agent must represent its size, shape,

222   Pierre Jacob and orientation, not its colour. Arguably, a visuomotor representation of a target of prehension has, like Millikan’s (1996) pushmi-pullyu representations, a dual direction of fit: it describes some relevant features of the target in a format appropriate for the guidance of action. By contrast, the visual experience of objects serves two complementary functions: selection and recognition (or identification). Selecting an object consists in both segregating a complex visual array into several separable objects and in attributing to each item its own set of appropriate visual attributes (this is the so-called ‘binding’ problem). Usually, the colour and texture of an object will be highly relevant to its perceptual selection from a set of neighbouring objects. Segregation and binding require that the relative spatial locations of different objects in a visual array be coded by the perceptual system. Since perceptual recognition of an object must be achieved from many different spatial perspectives on many different times of the day in different seasons, it requires encoding visual information about an object’s enduring properties.

An anatomical bifurcation in the primate visual system Ungerleider and Mishkin (1982) were the first to report evidence for an anatomical bifurcation between two streams within the primate visual cortex itself: the ventral stream that projects the primary visual areas onto the inferotemporal cortex and the dorsal stream that projects the primary visual cortex onto the parietal lobe.4 They examined the selective effects of lesions in the brains of macaque monkeys on two kinds of behavioural tasks: a landmark task and an object-discrimination task. In the former task, the monkey had to discriminate between two covered wells—one empty and one containing a reward—according to whether they were located far away or near a landmark. In the latter task, the monkey had to discriminate two objects of different shapes, colours, and textures. Ungerleider and Mishkin found that a lesion in the inferotemporal cortex severely impaired the animal in the object-discrimination task, but not in the landmark task. Conversely, they found that a lesion in the posterior parietal cortex severely affected the animal’s performance in the landmark task, but not in the object-discrimination task. On the basis of these experiments, Ungerleider and Mishkin (1982) concluded that the ventral stream (which they called the ‘object-channel’) and the dorsal stream (which they called the ‘space-channel’) were each specialized in perceiving different aspects of the visual world. Indeed, their landmark task tested the animal’s ability to perceive spatial relations, not to act on a target.

Neuropsychological dissociations Further work based on the neuropsychological examination of brain-lesioned human patients gave rise to what is now known as the ‘two-visual systems model’ of human

4 For evidence that different neural networks underlie different visual capacities respectively in amphibians and in small rodents, without a visual cortex, cf. Ingle (1973) and Schneider (1969).

Action-Based Accounts of Perception    223 vision, the first step of which was the striking discovery of the phenomenon called ‘blindsight’. Weiskrantz et al. (1974) reported that patients who had lost conscious visual perception following a lesion in their primary visual cortex were still able to produce accurate visuomotor responses to visual stimuli presented in the part of their visual field impaired by the lesion, in forced choice conditions.5 The second major step was the discovery in the 1990s of a double dissociation between the visual capacities of patients with two kinds of visual impairments: visual form apperceptive agnosia and optic ataxia. On the one hand, Milner et al. (1991) and Goodale and Milner (1992) reported that examination of patient D.F. with apperceptive visual agnosia following bilateral damage to her ventral stream had become unable to recognize the sizes and shapes of three-dimensional objects (and drawings) visually presented to her, but she was still able to grasp these three-dimensional objects with precision grip. For example, her maximum grip aperture (i.e. her finger–thumb precision grip) turned out to be correlated with the physical sizes of targets in tasks of grasping. However, when asked to mime the width of a target in tasks of perceptual judgements, the distance between her thumb and index finger turned out to be at chance. Furthermore, while she was able to insert a card within a slot at different orientations, she was unable to match the different orientations of the slot by appropriately rotating her wrist in tasks of perceptual judgement. Finally, when asked to point to a peripheral target, her accuracy was like that of the controls. However, when a delay was interposed between the presentation of the stimulus and the signal to respond her performances decreased. On the other hand, Jeannerod et al. (1994) reported that patient A.T. with optic ataxia following bilateral damage to her dorsal stream had become unable to reach and grasp with accuracy objects whose shapes and sizes she was able to visually recognize. In visuomotor tasks, A.T. was able to reach for the target, but her grasp was systematically incorrect. However, when asked to match the size of objects with the distance between her thumb and index finger, she gave accurate estimates in positive correlation with the sizes of the objects.6 In contrast to patient D.F., when asked to point to a target, patient A.T.’s performances improved when a delay was interposed between the presentation of the stimulus and the signal to respond.

Psychophysical dissociations in healthy participants In addition to neuropsychological dissociations, numerous experiments have provided evidence of dissociations between perceptual judgements and visuomotor responses by healthy human adults. For example, Goodale et al. (1986) report that participants were able

5 

Rossetti (1998) describes a case of so-called ‘numbsense’ in which a patient exhibited a complete loss of all somatosensory processing on the left half of his whole body. When blindfolded and required to guess verbally the locus of tactile stimuli delivered to his forearm and hand, he performed at chance level. Nevertheless he showed a significant ability to point his finger at the accurate location of stimuli delivered to his arm. 6  For discussion of the scope and limits of the double dissociation between visual form agnosia and optic ataxia, see Pisella et al. (2006) and Rossetti et al. (2010), and for a reply, see Milner and Goodale (2010).

224   Pierre Jacob to accurately point their index finger to visual targets that changed position during a concurrent saccadic eye-movement, while they showed no conscious awareness of the motion of the target. Whereas activity in the dorsal stream enabled participants to unconsciously track the motion of the target and point, the conscious image of the target depends on slower computations performed by the ventral stream. This is consistent with the results of experiments by Pisella et al. (2000), in which healthy participants were instructed to perform a pointing task at a target that could change location at the onset of participants’ movements. In response to target perturbation, the instruction was to either correct or stop the ongoing movement (stop condition). Pisella et  al. (2000) report that participants in the stop condition irrepressibly produced a significant percentage of very fast non-intentional unwilled corrective movements, which they attributed to the ‘automatic pilot’. Furthermore, Rossetti and Pisella (2002) also report that, unlike the change of a target’s location, the change of the target’s colour did not elicit very fast, unwilled, corrective hand movements. Króliczak et al. (2006) report the following dissociation prompted by seeing the hollow mask illusion, in which a concave hollow face is perceived as being convex. Participants were presented with one of three distinct displays: they could see a convex mask that looked convex, a hollow mask that looked convex or a hollow mask that looked concave. On the forehead and cheek of each display, a small magnetic dot was attached. If asked to deliberately point to the small dot attached to the hollow mask, participants directed their finger movements to the illusory location of the target. However, if asked to quickly flick the target off the face (as if it were a small insect), they directed their finger movements to the actual or veridical location of the target, despite the presence of a strong hollow-face perceptual illusion. Many experiments have investigated dissociations between perceptual judgements and visuomotor responses to displays consisting of size-contrast visual illusions.7 For example, Ganel et al. (2008) report an experiment based on the Ponzo illusion in which participants saw two targets that were unequal in length, but due to the presence of the illusory background constituted by two converging lines, the shorter target (at the converging end) looked longer than the other one (at the diverging end). Participants were requested to either grasp one of the targets or use the distance between their index finger and thumb to estimate its length. Despite the fact that participants believed that the shorter object was the longer one, Ganel et al. (2008) report that, when requested to grasp it, their grip aperture in flight reflected the real not the illusory size of the target objects. But when participants were asked to estimate the size of the target objects rather than pick them up, their manual estimates reflected the apparent not the real size of the targets. In other words, on the same trials in which participants erroneously decided that one object was the longer (or shorter) of the two, the anticipatory opening between their fingers reflected the real direction and magnitude of size differences between the two objects.8

7  The investigation of the Ebbinghaus illusion has given rise to much controversy (cf. Franz et al., 2000, and replies by Goodale, 2011, and Milner and Goodale, 2010). 8  Further dissociations between perceptual overestimation of the slants of hills and the accuracy of the visuomotor guidance of locomotion have been reported by Proffitt et al. (1995).

Action-Based Accounts of Perception    225 The evidence (succinctly summarized in this section) for the two-visual systems model raises two complementary challenges for action-based approaches to visual perception: to what extent is action necessary and sufficient for visual perception? There is room for controversy and further investigation. Some scientists and philosophers (e.g. Jacob and Jeannerod, 2003; Block, 2005; Clark, 2010; Jacob and Vignemont, 2010; Milner and Goodale, 2010) have argued that the dissociations between visually-guided actions and conscious visual perception show that the former are neither necessary nor sufficient for the latter: on their interpretation, the residual visuomotor capacities of visual agnosic patients show that the ability to accurately reach and grasp an object is not sufficient for consciously perceiving its size and shape. The visuomotor impairment of optic ataxic patients shows that the ability to accurately reach and grasp an object is not necessary for consciously perceiving its size and shape. Conversely, other scientists and philosophers (e.g. O’Regan and Noë, 2001; Hurley, 2008; Noë, 2010) have responded that the above dissociations fail to demonstrate that while activity in the ventral stream supports conscious visual perception, activity in the dorsal stream underlies the automatic unconscious control of visually-guided actions. Instead, they have argued that all they show is that conscious visual perception can at best be dissociated from visual processing involved in the setting of low-level parameters for reaching and grasping. Furthermore, they have argued that since visual agnosic patients fail to recognize the function and significance of visually presented objects, they cannot act on them in ways appropriate to their use or function. Thus, they argue that so far, the evidence fails to show that the visual guidance of actions is independent from conscious visual perception.

3  The enactive approach to object-perception Whereas the embodied perception framework rejects the computational approach to perception, advocates of the so-called ‘enactive’ framework see an agent’s action as an alternative to classical representationalist approaches to perception. On the enactive conception (advocated by e.g. O’Regan and Noë, 2001; Noë, 2004), perception is intrinsically active and perceptual experiences are ways of acting. The content of an agent’s perceptual experience is determined by her practical or implicit knowledge of sensorimotor contingencies, that is the sensory consequences of her own movements. Noë (2004) has argued that enactivism solves the puzzle of perceptual presence: in perceiving an object whose back surface is occluded from my view (e.g. the back of a tomato in front of me), I am perceptually aware of the occluded part that does not reflect photons on my retina. On the enactive account, the reason I am perceptually aware of the occluded part is that I tacitly know that were I to pick up the tomato and turn it over, I would see the back of the tomato.9 The enactive account of perception gives rise to two important questions. 9 For an entirely different account of the feeling of the perceptual presence of graspable objects (as opposed to images) based on visual processing in the dorsal stream, cf. Matthen (2005, 2010).

226   Pierre Jacob

Can enactivism be a constitutive account of perceptual experience? The first question is:  to what extent is enactivism a constitutive account of the content of perceptual experience? There are two related reasons for caution. Consider a skilled driver’s visual experience of her red Porsche. On the one hand, her driver’s skill might underlie the content of her visual experience of her car as drivable. But she might also see her car as non-drivable (if e.g. the engine has been disassembled or after a bad accident), or on sale, or as a member of her collection of cars, and so on. It is not clear how her implicit knowledge of the sensory consequences of her skilled ability to drive it grounds the content of her visual experience of her car in these cases. On the other hand, she could only see her car as drivable if she had already identified it, that is, sorted it out from the background and from distracting cars in a visual scene. So the question arises: how could tacit knowledge of the sensory consequences of her driving actions onto her car enable her visual system to bind the colour, shape, texture of the body, and wheels of the car together. Unless she was antecedently able to sort it out from neighbouring distractors and from the background, how could she plan to act on it? For example, O’Regan (2010, ch. 9) has argued that the phenomenology of seeing redness is like the feel of driving a Porsche. But it remains unclear how one’s Porsche-driving skills, exercised while sitting at the wheel, could capture what it is like to see the redness of the body of the car while looking at it from the outside.

Enactivism and behaviourism The second question is whether enactivism is not a new version of psychological behaviourism, that is, the view that only observable inputs (i.e. stimuli that impinge on an organism’s body) and observable output (i.e. an organism’s behavioural responses) can be part of a scientific psychological explanation. To a large extent, the cognitive revolution that gave rise to the cognitive sciences was based on the rejection of behaviourism and the rehabilitation of mental representations in psychological explanation (see Chomsky, 1959). Arguably, the enactivist account can dissociate itself from behaviourism since its main thesis is not  that an agent’s perceptual experience arises from the lawful dependencies between her bodily movements and her sensory stimulations, but from the agent’s implicit sensorimotor knowledge of these lawful dependencies. Still the question arises to what extent the concept of action used by enactivists really differs from the behaviourist conception of a response to a stimulus. On behalf of action-based approaches to perception, Hurley (1998, 2001, 2008) has criticized ‘the classical sandwich conception of the mind . . . [that] regards perception as input from world to mind, action as output from mind to world, and cognition as sandwiched between’. The sandwich model of cognition makes two crucial assumptions: the first is the linearity assumption, according to which information flows from the outside world in, through sensory systems to perception, cognition, the motor system and then out again into the world. The second is the instrumentality assumption, according to which action and perception stand as a means to each other. While the ecological approach to perception rejects the

Action-Based Accounts of Perception    227 linearity assumption, behaviourism rejects the instrumentality assumption since it makes action constitutive, rather than a mere enabling condition, of perception. But as Hurley points out, behaviourism casts action as output, that is, as a mere response or reaction to a stimulus. One thing that psychological behaviourism missed is that an agent’s bodily movements cause re-afferent sensory changes in her own environment and the agent must be able to distinguish endogenously caused from externally caused sensory changes in her environment. Helmholtz was the first to raise the puzzle of how to explain the stability of the visual world during eye and head movements: the brain must be able to discriminate the visual signals on the retina respectively produced by externally moving objects and by the agent’s own eye and head movements. In answer to this puzzle, it has been hypothesized that when the motor system sends a motor instruction to contract the eye-muscles, it also produces a so-called ‘efference copy’ (or ‘corollary discharge’) of the motor instruction, which is the signature of the agent’s own agency. Furthermore, according to so-called ‘internal forward models of action’, from the efference copy of the motor command as input, the motor system is able to derive a prediction of the sensory consequences of the agent’s movements.10 This sensory prediction can further be compared with the actual sensory consequences (or re-afferences) of the agent’s movements and be used either for filtering incoming sensory information or for online correction of a failed action. Thus, the theory of internal forward models of action predicts that the more a sensory change is predictable by an agent, the more its phenomenological experience will be attenuated and conversely the less predictable a sensory change, the more its phenomenological experience will be highlighted (see Wolpert et al., 1998; Jeannerod, 2006). This prediction is supported by experiments by Blakemore et al. (2000) showing that healthy human adults are unable to tickle themselves because the sensory consequences of their own self-directed movements are too predictable. On the one hand, the problem for behaviourism is that a stimulus–response framework lacks the resources for distinguishing endogenously caused from exogenously caused sensory changes. On the other hand, it is not entirely clear whether the view that the experience of self-produced (as opposed to exogenously caused) sensory changes should be attenuated is compatible with the enactivist idea that the content and phenomenal character of an agent’s perceptual experience of an object arise from her tacit knowledge of the sensory consequences of her own actions onto the object.

An externalist account of perceptual experience Arguably, one important source of evidence for the enactive account of perception derives from the experimental discovery of so-called change blindness, that is, the surprising phenomenon that observers can fail for a surprisingly long time to notice large changes to visual scenes. To borrow an ordinary example from Dretske (2007), suppose that Sarah looks for a few seconds at a group of seven visible people gathered around a table, without

10  So-called ‘inverse models of action’ take the agent’s goal or expected sensory change as input and compute the best motor command suitable for achieving this goal.

228   Pierre Jacob attending to any in particular. Suppose that while she looks away, Sam joins the group. When Sarah looks back, there are now eight visible people gathered around the table, not seven. She fails to notice the difference made by Sam’s novel presence at the table: if asked whether she sees a difference between what she saw before and after she looked away, her answer is negative. If so, then she is said to be blind to the change created by adding one member to a group of seven individuals. In scientific experiments on change blindness conducted by O’Regan (1992) and others, participants are shown displays of natural scenes and asked to detect cyclically repeated changes, such as a large object shifting, changing colour, or appearing and disappearing. Under normal circumstances a change of this type creates a transient signal in the visual system: it is detected by low-level visual mechanisms and exogenously attracts attention to the location of the change, which is, therefore, immediately perceived. However, in change blindness experiments, the transient is prevented from playing its attention-grabbing role by different methods. In some cases, a global flicker is superimposed over the whole visual field at the moment of the change. In other cases, the change coincides with an eye saccade, an eye blink, or a film cut in a film sequence. Still in other cases, extraneous transients are distributed over the picture, somewhat like mud-splashes on a car windscreen. In all cases, participants’ attention is attracted away from the location of the change (see e.g. Simons and Levin, 1997, for review).11 On the enactivist interpretation, these findings are evidence for a failure to represent the details of visual stimuli. We do not see as much as we think we do: visual perception delivers impoverished and gappy representations of distal stimuli. As Dehaene et al. (2006) have put it, experiments on change blindness show that our over-confidence in the phenomenological richness of visual experience derives from the cognitive illusion that we see more than we do. On Noë’s (2004: 50) interpretation, change blindness shows that visual awareness of details is virtual awareness (i.e. awareness of the availability of details): there is no need to build up a detailed internal model of the visible world on one’s own internal memory drive. It is enough to know where in the world to go and what action to perform to retrieve the accessible details if needed. Advocates of enactivism endorse a version of what has been variously called ‘the extended mind thesis’, ‘vehicle externalism’, or ‘active externalism’, that is, the view that an individual’s mind extends beyond the limits of her brain and body and includes features of her environment. Clark and Chalmers (1998) have argued that the vehicles of an individual’s beliefs and other propositional attitudes should not be restricted to states of her brain on the grounds that the use of tools located outside an individual’s brain enhances her ability to solve problems. Advocates of enactivism (e.g. Noë, 2004, 2009; Wilson, 2010) similarly argue that the vehicles of an individual’s perceptual experiences are not restricted to the boundaries of her brain on the grounds that visual perception consists in sensorimotor skills that enable a perceiver to retrieve the details which lie in the outside world and are not fully represented in her brain.12 Clearly, the application of the extended mind thesis to perceptual experience relies on the enactivist premiss that the change blindness experiments are evidence of a

11 

A related phenomenon is inattentional blindness (see Simons and Chabris, 1999). Clark (2008) resists extending the extended mind thesis to visual experiences. For a survey of the links between embodied cognition and extended mind approaches, cf. Rowlands (2010). 12 

Action-Based Accounts of Perception    229 representational failure to see large changes to visual scenes. But this interpretation is questionable (see Dretske, 2004, 2007; Block, 2007) for two reasons. First, what people fail to notice in change blindness experiments is not the change itself (which is carefully concealed by the experimenters), but the difference between two scenes produced by a concealed change. Failure to see the change (an event) caused failure to notice the difference. In Dretske’s example, Sarah could not see Sam join the group (the change) since she was looking away. Thus, what she failed to notice was the difference in number. Secondly, from the fact that people fail to notice a difference between two stimuli, it does not follow that they failed to see something that was either present in the first stimulus and absent from the second stimulus or vice versa. It is one thing to see a pair of stimuli; it is another to make the appropriate comparison that enables an observer to tell the difference between them (cf. Simons and Rensink, 2005). For example, from the fact that Sarah failed to notice the difference between the groups of people before and after she looked away, it does not follow that she failed to see Sam the second time she looked at the group of people. Whether enactivism offers an alternative to the action/perception dualism depends in part on whether the failure to notice a difference between two stimuli counts as a perceptual or a cognitive failure.

4  Action-based accounts of social perception Humans do not perceive only objects that they can reach, grasp, and manipulate, but also gases, clouds, flames, smoke, rivers, liquids, holes, events, and especially actions, some of which are performed by other humans—as noticed long ago by the philosopher John Austin (1962). Broadly speaking, by ‘social perception’ cognitive scientists refer to the mechanisms involved in the perception of other people. To perceive other people is to perceive their bodies and actions. To perceive the bodies of other people is inter alia to perceive their faces. The perception of invariant aspects of a face helps us to recognize the identity of an individual. The perception of variable facial expressions helps in the understanding of an individual’s emotional state. To perceive others’ actions is inter alia to perceive their voice, their posture, and their gait, which, like all instances of biological motion, is governed by biomechanical constraints. Much research in cognitive neuroscience has been devoted to the mechanisms leading to the understanding of others’ psychological states (e.g. goals, emotions, intentions, desires, or beliefs) from the perception of others’ bodies, faces, and actions (for an overview, see Allison et al., 2000; Jacob and Jeannerod, 2003). Arguably, what makes social perception different from the perception of inanimate objects is that in social perception, while we observe the actions performed by others and perceive cues of others’ goals and emotions, we also have the capacity to execute similar actions, form similar goals, and experience similar emotions. Thus the question arises to what extent the mechanisms at work in social perception, which enable humans to understand the psychological states of others from the perception of their bodily actions and facial expressions, are processes of mental simulation or covert imitation. In fact, the discovery of mirror neurons has been interpreted as vindicating the assumption that

230   Pierre Jacob understanding others’ goals, intentions, and emotions depends on mentally rehearsing their bodily actions and/or their facial expressions.

Action-mirroring In the early 1990s a group of neuroscientists led by Giacomo Rizzolatti discovered by single-cell recording a class of sensorimotor neurons located in the ventral premotor cortex of macaque monkeys that fire both when an animal executes some particular action directed to a physical target and when the animal observes the same action being performed by another agent. These cells were called mirror neurons because their activity in an observer’s brain is taken to ‘mirror’ (simulate or resonate with) their activity in the agent’s brain, without giving rise to action execution. In accordance with the motor theory of speech perception (Liberman and Mattingly, 1985) and the theory of event coding (Hommel et  al., 2001), these findings have been widely interpreted as showing that the execution and the perception of actions share common representational resources in primates’ brain. Subsequent work based on brain imaging and transcranial magnetic stimulation confirmed the existence of a mirror system in humans. For example, brain-imaging studies conducted by Buccino et al. (2004) have revealed greater activations of motor and premotor areas when human observers see without hearing a video-clip displaying a human being produce silent speech (which the observers could covertly imitate) than when they see a video-clip displaying a dog bark (which the observers could not covertly imitate). In another brain-imaging study by Calvo-Merino et al. (2005), capoeira and ballet dancers saw short films displaying dance steps by either capoeira or classical dancers. They found enhanced activations in the mirror-neuron system of dancers observing movements belonging to their respective dancing motor repertoire. Mirror neuron activity in an observer’s brain has been interpreted as generating a neural similarity between the agent and the observer who comes to entertain and share the motor representation that guides the agent’s own action. This process of action-mirroring has been taken to enable the observer to understand an agent’s goal and even an agent’s intention by means of the so-called direct-matching model of action-understanding (cf. Rizzolatti et al., 2001; Rizzolatti and Craighero, 2004). According to this three-step model of action-understanding, the perception of the agent’s act first causes the observer to automatically map (or match) the agent’s act onto her own motor repertoire, that is to mentally rehearse or covertly imitate the agent’s act. Secondly, the mental rehearsal of the agent’s act is taken to enable the observer to share the agent’s goal. Finally, by sharing the agent’s goal, the observer is expected to understand it and to ascribe it to the agent. This model has led Fogassi et al. (2005: 662) to conclude that mirror neuron activity not only ‘codes the observed motor act but also allows the observer to understand the agent’s intentions’. Following the seminal ideas of Lipps (1900), a similar tripartite model has been extended from the perception of goal-directed actions and the understanding of an agent’s goal to the perception of expressive actions and the understanding of an agent’s emotions (cf. Gallese, 2001; Goldman, 2006; Rizzolatti and Sinigaglia, 2008). On the basis of the direct-matching model of action-understanding, Rizzolatti et al. (2001) and Rizzolatti and Craighero (2004) have drawn a contrast between two ways an action

Action-Based Accounts of Perception    231 might be understood: either through a purely perceptual analysis of the agent’s bodily movements or by mapping the agent’s perceived movements onto the observer’s motor repertoire. If and when an observer (e.g. a primate) cannot map a perceived action (e.g. a bird’s flight) onto his own motor repertoire, then, according to Rizzolatti et  al. (2001), the observer’s understanding of the perceived action cannot be grounded in ‘motor resonance’. As a result, there is something about the perceived action that the observer fails to understand: the action can only be categorized on the basis of its visual, not its motor, properties.

The scope and limits of mirroring-based accounts of social perception Assuming that mirror neuron activity results in an observer’s sharing an agent’s goal or intention, the direct-matching model of action-understanding raises at least the two further questions whether sharing an agent’s goal or intention is both necessary and sufficient for understanding it and ascribing it to the agent. The reason why sharing an agent’s goal might not be sufficient is that to share an agent’s goal is to have a goal. To have a goal is to be in a psychological state with a world-to-mind direction of fit that can be fulfilled or unfulfilled by the output of the agent’s action. But to ascribe a goal to an agent is to believe that the agent has a goal, that is, to be in a psychological state with a mind-to-world direction of fit that can be true or false, whether or not the agent performs her planned action. If so, then there is a gap between sharing a goal and ascribing a goal. Mere reflection suggests that mirroring might not be necessary for understanding an agent’s goal. For example, I may understand the goal of an agent who picks up a vanilla ice cream rather than a chocolate ice cream even though I myself would rather pick up a chocolate ice cream. Furthermore, some experimental evidence suggests that mirroring might not be necessary for ascribing a goal or intention to the agent. Much of this evidence comes from experiments in developmental psychology based on the violation-ofexpectation paradigm. This paradigm, which rests on the assumption corroborated by magic tricks that individuals look longer at an unexpected than an expected event, is applicable to preverbal human infants. Typical experiments involve two phases: in the course of habituation or familiarization trials, infants are induced to form an expectation by seeing an agent repeatedly execute one and the same action. In the pair of test trials, they see a novel action that is either consistent or inconsistent with their expectation. By measuring infants’ looking times respectively in the consistent and inconsistent test trials, psychologists get evidence bearing on the nature and content of an observer’s expectations about an agent’s goal-direction action. Unlike mirroring, expectations have the mind-to-world direction of fit, appropriate for ascribing a goal to the agent. In the familiarization trials of one experiment reported by Southgate et al. (2008), an experimental group of 6- to 8-month-olds saw a video showing a human hand perform a two-step goal-directed action during which the hand removed a box lying in its path before it retrieved a target that was located behind the box. A control group of infants of the same age saw a human hand inefficiently remove a box that did not lie in its path before retrieving a target. In the test trials, all infants either saw a human hand remove a box that was lying in its path before retrieving a target or they saw a human hand perform a biologically impossible but more efficient action whereby it retrieved the target by snaking

232   Pierre Jacob around the obstacles. Only infants in the experimental group (not infants in the control group) looked reliably longer at the biologically possible but less efficient hand-action than at the more efficient but biologically impossible hand-action. While it does not seem very likely that infants could mirror the biologically impossible snaking hand-movements, this experiment further suggests that goal-ascription by preverbal human infants is guided by the efficiency of the means selected by an agent for achieving a particular goal-state, in the presence of situational constraints (cf. Gergely and Csibra, 2003). At this stage, the contribution made by mirroring processes to social perception is very much an open question. Some scientists and philosophers (e.g. Gallese and Goldman, 1998; Goldman, 2006) assume that mirroring an agent’s action plays a causal role in the process whereby an agent’s goal or emotion is being ascribed to the agent. Others have argued for an alternative interpretation according to which the causal arrow might run in the reverse direction: mirroring an agent’s action might be the effect, not the cause, of the observer’s prior understanding of the agent’s goal or intention, which itself would be based on the perception of contextual cues such as whether a graspable target is edible or not (cf. Csibra, 2007; Jacob, 2008).

5  Concluding remarks Action-based accounts have yielded many new experimental findings and intriguing philosophical ideas about perception. Much of their appeal derives from their commitment to minimalist assumptions in the study of perception. This minimalism has two sides: first, it is based on the parsimonious assumption that the mechanisms underlying action also underlie perception. Secondly, the professed goal of action-based accounts is to minimize (if not to eliminate) the contribution of internal processing and mental representations to perception. One of the central challenges (if not the central challenge) for the two-fold minimalist commitment of action-based accounts of perception is that there is more to action than the execution of bodily movements. As philosophers of action have stressed for a long time, an agent’s bodily movements count as an action only if they are appropriately caused by the agent’s intentions. For example, an agent can execute one and the same hand gesture to frighten a fly or waive bye-bye to a departing host. Only by representing her intention can one action be distinguished from the other. Furthermore, there is much empirical evidence showing that an agent’s motor system is activated in at least two situations in which he or she fails to perform any overt action. In such situations, the agent’s motor system is activated off-line (see Jeannerod, 2006). On the one hand, some areas of an observer’s motor and premotor systems (e.g. mirror neurons) are active when he or she perceives an action performed by another agent (cf. section 4). On the other hand, parts of an agent’s motor system are active in tasks of motor imagery whereby the agent plans and/or imagines an action, which, for some reason or another, he or she fails to execute. In fact, we mentally represent and even plan many actions that we never carry out. The question is whether mental representations, which action-based accounts of perception mean to kick out, might not be surreptitiously coming in by the backdoor through the scientific study of motor cognition.13 13 

I am grateful to Mohan Matthen for his extended comments.

Action-Based Accounts of Perception    233

References Aizawa, K. (2007). ‘Understanding the embodiment of perception’. The Journal of Philosophy, 54(1), 6–25. Allison, T., Puce, A, and McCarthy, G. (2000). ‘Social perception from visual cues: role of the STS region’. Trends in Cognitive Sciences, 4(7), 267–78. Austin, J. L. (1962). Sense and Sensibilia, Oxford: Oxford University Press. Barsalou, L. W. (1999). ‘Perceptual symbol systems’. Behavioral and Brain Sciences, 22, 577–660. Barsalou, L. W., Simmons, W. K., Barbey, A. K., and Wilson, C. D. (2003). ‘Grounding conceptual knowledge in modality-specific systems’. Trends in Cognitive Sciences, 7(2), 84–91. Blakemore, S.-J., Wolpert, D., and Frith, C. D. (2000). ‘Why can’t you tickle yourself?’ NeuroReport, 11, R11–R16. Block, N (2005). ‘Review of Alva Noë’s Action in Perception’. The Journal of Philosophy, 52, 259–72. Block, N. (2007). ‘Consciousness, accessibility, and the mesh between psychology and neuroscience’. Behavioral and Brain Sciences, 30, 481–548. Buccino, G., Lui, F., Canessa, N., Patteri, I., Lagravinese, G., Benuzzi, F., Porro, C. A., and Rizzolatti, G. (2004). ‘Neural circuits involved in the recognition of actions performed by non-conspecifics: an fMRI study’. Journal of Cognitive Neuroscience, 16, 114–126. Calvo-Merino, B., Glaser, D. E., Grezes, J., Passingham, R. E., and Haggard, P. (2005). ‘Action observation and acquired motor skills: an fMRI study with expert dancers’. Cerebral Cortex, 15, 1243–49. Chomsky, N. (1959). ‘A Review of B. F. Skinner’s Verbal Behavior Language’. 35, 1, 26–58. Clark, A. (2008). Supersizing the Mind, Embodiment, Action, and Cognitive Extension. Oxford: Oxford University Press. Clark, A. (2010). ‘Perception, action and experience: unravelling the golden brain’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Clark, A. and Chalmers, D. (1998). ‘The extended mind’. Analysis, 58(1), 7–19. Csibra, G. (2007). ‘Action mirroring and action understanding’. In P. Haggard, Y. Rossetti, and M. Kawato (eds), Sensorimotor Foundations of Higher Cognition, Attention and Performance XXII. Oxford: Oxford University Press. Davidson, D. (1980). Essays on Actions and Events. Oxford: Oxford University Press. Dehaene, S., Changeux, J.-P., Naccache, L., Sackur, J., and Sergent, C. (2006). ‘Conscious, preconscious, and subliminal processing: A testable taxonomy’. Trends in Cognitive Sciences, 10(5), 204–11. Dretske, F. (1995). Naturalizing the Mind. Cambridge, MA: MIT Press. Dretske, F. (2007). ‘What change blindness teaches about consciousness’. Philosophical Perspectives, 1, 215–20. Fodor, J. A. (1974). ‘Special Sciences’. Synthese, 28, 97–115. Fodor, J. A. (1975). The Language of Thought. New York: Crowell. Fodor, J. A. (1983). The Modularity of Mind. Cambridge, MA: MIT Press. Fodor, J. A. (2007). ‘The revenge of the given’. In B. P. McLaughlin and J. D. Cohen (eds), Contemporary Debates in Philosophy of Mind. Oxford: Oxford University Press. Fogassi, L., Ferrari, P. F., Gesierich, B., Rozzi, S., Chersi, F., and Rizzolatti, G. (2005). ‘Parietal lobe: from action organisation to intention understanding’. Science, 308, 662–67.

234   Pierre Jacob Franz, V. H., Gegenfurtner, K. R., Bulthoff, H. H., and Fahle, M. (2000). ‘Grasping visual illusions: No evidence for a dissociation between perception and action’. Psychological Science, 11, 20–25. Gallese, V. (2001). ‘The "Shared Manifold" hypothesis, from mirror neurons to empathy’. Journal of Consciousness Studies, 8, 5–7, 33–50. Gallese, V. and Goldman, A. I. (1998). ‘Mirror neurons and the simulation theory of mindreading’. Trends in Cognitive Sciences, 2, 493–501. Ganel, T., Tanzer, M., and Goodale, M. A. (2008). ‘A double dissociation between action and perception in the context of visual illusions: Opposite effects of real and illusory size’. Psychological Science, 19, 221–225. Gergely, G. and Csibra, G. (2003). ‘Teleological reasoning about actions: the naïve theory of rational actions’. Trends in Cognitive Sciences, 7, 287–292. Gibson, J. J. (1979). The Ecological Approach to Visual Perception. Boston: Houghton-Mifflin. Goldman, A. (2006). Simulating Minds. Oxford: Oxford University Press. Goodale, M. (2011). ‘Transforming vision into action’. Vision Research, 51(13), 1567–1587. Goodale, M. A. and Milner, A. D. (1992). ‘Separate visual pathways for perception and action’. Trends in Neuroscience, 15, 20–25. Hinton, J. M. (1973). Experiences. Oxford: Clarendon Press. Hommel, B., Müsseler, J., Aschersleben, G., and Prinz, W. (2001). ‘The theory of event coding (TEC): a framework for perception and action planning’. Behavioral and Brain Sciences, 24, 849–937. Hurley, S. (1998). Consciousness in Action. Cambridge, MA: Harvard University Press. Hurley, S. (2001). ‘Perception and action: alternative views’. Synthese, 129, 3–40. Hurley, S. (2008). ‘The shared circuits model: how control, mirroring and simulation can enable imitation and mindreading’. Behavioral and Brain Sciences, 31, 1–58. Ingle, D. J. (1973). ‘Two visual systems in the frog’. Science, 181, 1053–1055. Jacob, P. (2008). ‘What do mirror neurons contribute to human social cognition?’ Mind and Language, 23(2), 190–223. Jacob, P. and Jeannerod, M. (2003). Ways of Seeing, the Scope and Limits of Visual Cognition. Oxford: Oxford University Press. Jacob, P. and de Vignemont, F. (2010). ‘Spatial coordinates and phenomenology in the two visual systems model’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Jeannerod, M. (2006). Motor Cognition. Oxford: Oxford University Press. Jeannerod, M., Decety, J., and Michel, F. (1994). ‘Impairment of grasping movements following a bilateral posterior parietal lesion’. Neuropsychologia, 32, 369–380. Kim, J. (1993). Supervenience and the Mind. Cambridge: Cambridge University Press. Króliczak, G., Heard, P., Goodale, M. A., and Gregory, R. L. (2006). ‘Dissociation of perception and action unmasked by the hollow-face illusion’. Brain Research, 1080, 9–16. Liberman, A. M. and Mattingly, I. G. (1985). ‘The motor theory of speech perception revised’. Cognition, 21, 1–36. Lipps, T. (1900). ‘Asthetische Einfuhlung’. Zeitschrift fur Psychologie und Physiologie der Sinnesorgane, 22, 415–450. McDowell, J. (1982). ‘Criteria, defeasibility and knowledge’. Proceedings of the British Academy, 68. McDowell, J. (1994). Mind and the World. Cambridge, MA: Harvard University Press. Machery, E. (2006). ‘Two dogmas of neo-empiricism’. Philosophy Compass, 1(4), 398–412.

Action-Based Accounts of Perception    235 Machery, E. (2007). ‘Concept empiricism: A methodological critique’. Cognition, 104, 19–46. Marr, D. (1982). Vision. San Francisco: Freeman. Matthen, M. (2005). Seeing, Doing, and Knowing: A Philosophical Theory of Sense Perception. Oxford: Oxford University Press. Matthen, M. (2010). ‘Two visual systems and the feeling of presence’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Millikan, R. G. (1996). ‘Pushmi-pullyu representations’. In J. Tomberlin (ed.), Philosophical Perspectives, vol. IX. Atascadero CA: Ridgeview Publishing. Milner, A. D. and Goodale, M. A. (1995). The Visual Brain in Action. Oxford:  Oxford University Press. Milner, A. D. and Goodale, M. A. (2010). ‘Cortical visual systems for perception and action’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Milner, A. D., Perrett, D. I., Johnston, R. S., Benson, P. J., Jordan, T. R., Heeley, D. W., Bettucci, D., Mortara, F., Mutani, R., Terazzi, E. and Davidson, D. L. W. (1991). ‘Perception and action in "visual form agnosia" ’. Brain, 114, 405–428. Noë, A. (2004). Action in Perception. Cambridge, MA: MIT Press. Noë, A. (2009). Out of our Heads. New York: Hill and Wang. Noë, A. (2010). ‘Vision without representation’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. O’Regan, J. K. (1992). ‘Solving the "real" mysteries of visual perception: the world as an outside memory’. Canadian Journal of Psychology, 46(3), 461–488. O’Regan, J. K. (2010). Why Red Doesn’t Sound Like a Bell, Understanding the Feel of Consciousness. Oxford: Oxford University Press. O’Regan, J. K. and Noë, A. (2001). ‘A sensorimotor account of vision and visual consciousness’. Behavioral and Brain Sciences, 24, 939–1031. Pisella, L., Gréa, H., Tilikete, C. A. Vighetto, A. M. Desmurget, G., Rode, G., Boisson, D., and Rossetti, Y. (2000). ‘An "automatic pilot" for the hand in human posterior parietal cortex: toward reinterpreting optic ataxia’. Nature Neuroscience, 3(7), 729–736. Pisella, L., Binkofski, F., Lasek, K., Toni, I., and Rossetti, Y. (2006). ‘No double-dissociation between optic ataxia and visual agnosia: multiple sub-streams for multiple visuo-manual integrations’. Neuropsychologia, 44, 2734–2748. Prinz, J. (2002). Furnishing the Mind:  Concepts and their Perceptual Basis. Cambridge, MA: MIT Press. Prinz, J. (2005). ‘The return of concept empiricism’. In H. Cohen and C. Leferbvre (eds), Categorization and Cognitive Science. Oxford: Elsevier. Proffitt, D. R., Bhalla, M., Gossweiler, R., and Midgett, J. (1995). ‘Perceiving geographical slant’. Psychonomic Bulletin & Review, 2, 409–428. Putnam, H. (1967). ‘The nature of mental states’. In H. Putnam (1975), Mind, Language and Reality, Philosophical Papers, vol. 2. Cambridge: Cambridge University Press. Rizzolatti, G. and Craighero, L. (2004). ‘The mirror-neuron system’. Annual Review of Neuroscience, 27, 169–192. Rizzolatti, G., Fogassi, L., and Gallese, V. (2001). ‘Neurophysiological mechanisms underlying the understanding and imitation of action’. Nature Review of Neuroscience, 2, 661–670. Rizzolatti, G. and Sinigaglia, C. (2008). Mirrors in the Brain: How Our Minds Share Actions and Emotions. Oxford: Oxford University Press.

236   Pierre Jacob Rossetti, Y. (1998). ‘Implicit short-Lived motor representations of space in brain damaged and healthy subjects’. Consciousness and Cognition, 7, 520–558. Rossetti, Y. and Pisella, L. (2002). ‘Several "vision for action" systems: a guide to dissociating and integrating dorsal and ventral functions (tutorial)’. In W. Prinz and B. Hommel (eds), Common Mechanisms in Perception and Action. Oxford: Oxford University Press. Rossetti, Y., Ota, H., Blangero, A., Vighetto, and Pisella, L. (2010). ‘Why does the perceptionaction functional dichotomy not match the ventral-dorsal streams anatomical segregation: optic ataxia and the function of the dorsal stream’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Rowlands, M. (2010). The New Science of the Mind, from Extended Mind to Embodied Phenomenology. Cambridge, MA: MIT Press. Schneider, G. E. (1969). ‘Two visual systems’. Science, 163, 895–902. Searle, J. (1983). Intentionality: An Essay in the Philosophy of Mind. Cambridge: Cambridge University Press. Shapiro, L. (2004). The Mind Incarnate. Cambridge, MA: MIT Press. Shapiro, L. (2007). ‘The embodied cognition research programme’. Philosophy Compass, 2(2), 338–346. Simons, D. J. and Chabris, C. F. (1999). ‘Gorillas in our midst: sustained inattentional blindness for dynamic events’. Perception, 28(9), 1059–1074. Simons, D. J. and Levin, D. T. (1997). ‘Change blindness’. Trends in Cognitive Sciences, 1, 261–267. Simons, D. J. and Rensink, R. A. (2005). ‘Change blindness: past, present, and future’. Trends in Cognitive Sciences, 9(1), 16–20. Southgate, V., Johnson, M. H., and Csibra, G. (2008). ‘Infants attribute goals to even biologically impossible actions’. Cognition, 107, 1059–1069. Tye, M. (1995). Ten Problems of Consciousness. Cambridge, MA: MIT Press. Ungerleider, L. and Mishkin, M. (1982). ‘Two cortical visual systems’. In D. J. Ingle, M. A. Goodale, and R. J. W. Mansfield (eds), Analysis of Visual Behavior (pp. 549–586). Cambridge, MA: MIT Press. Weiskrantz, L., Warrington, E. R., Sanders, M. D., and Marshall, J. (1974). ‘Visual capacity in the hemianopic field following a restricted occipital ablation’. Brain, 97, 709–728. Wilson, R. (2010). ‘Extended vision’. In N. Gangopadhyay, M. Madary, and F. Spicer (eds), Perception, Action and Consciousness. Oxford: Oxford University Press. Wolpert, D. M., Miall, R. C., and Kawato, M. (1998). ‘Internal models in the cerebellum’. Trends in Cognitive Sciences, 2(9), 338–347.

Chapter 13

Perceptua l R eports Berit Brogaard

1 Perceptual verbs and their etymology Perceptual reports are utterances of sentences that contain a perceptual verb. Perceptual verbs include, among others, ‘look’, ‘sound’, ‘feel’, ‘taste’, ‘smell’, ‘see’, ‘hear’, and ‘perceive’. Consider:  (1)

(a) My chair looks red but it’s really white. (b) His voice sounded deep and earnest. (c) Vegemite tastes like spreadable beer. (d) Last night my house smelled like a Mexican restaurant. (e) The entrance is so white that it feels as if you’re walking into a huge iPod. (f) This fabric feels like velvet. (g) John saw Mary cry. (h) The witness heard a noise and found the victim on the ground.

Perceptual reports such as these purport to describe how objects in the world are perceived by subjects. It is natural to suppose that at least in many cases, these reports reflect aspects of the phenomenal character and representational content of a subject’s perceptual experiences. Whether perceptual reports actually reflect these things is a substantial question and one with which I will be partially concerned in this entry. Perceptual reports containing the verbs ‘look’, ‘seem’, ‘appear’, ‘taste’, ‘smell’, and ‘sound’ are likely to occur either with an implicit or explicit relativization to a perceiver. Syntactically, this can occur with a ‘to-X’ clause or other local constituents that make the relevant perceiver and perceiving conditions explicit, as in ‘Vegemite tastes like spreadable beer to me [in normal taste conditions]’ or ‘Vegemite tastes like spreadable beer to Americans the first time they taste it’. Perceptual verbs have an interesting etymology that has some bearing on their semantics in modern English. Starting with visual ‘appear’ verbs, ‘seem’ originates from the Old English ‘beseon’, which is a contraction of ‘be’ and ‘seon’ (literally: ‘to see’) (The Oxford

238   Berit Brogaard Dictionary of English Etymology and A Guide to Old English, p. 325). ‘Beseon’ was used in most of the grammatical constructions for which ‘look’ is used in modern English. Consider the following examples:  ‘Hwa don Willelm of Normandige beseon gelic’? What-does-William-of-Normandy-be-see-like? (What does William the Conqueror look like?) ‘Angelcynn beseon micel lytlian nu.’ England-be-see-very-different-now. (England looks so different now.)

‘Beseon’ functions as a subject-raising verb. ‘England looks so different now’ is a raising construction because ‘England’ is the surface-grammatical subject of ‘look’ but the semantic subject of ‘to be different now’. Verbs that take this position in a raising construction are called ‘(subject)-raising verbs’. ‘England be see so different now’ is the raised form of ‘It is seen that England is very different now’. ‘Look’ comes from the Old English verb ‘locian’, which means ‘to see, to gaze’. ‘Locian’, in turn, comes from from the West Germanic ‘lokjan’. ‘Locian’ in the sense of ‘having a certain appearance’ entered Old English around 1400, at which point it began to occur in the positions in which ‘beseon’ had previously occurred. As ‘look’ originated from ‘locian’ and ‘locian’ occurs in the same positions as the older ‘beseon’, it is very plausible to think that ‘look’ and ‘seem’ function in the same way. ‘Appear’ entered Old English from Old French ‘aparoir’ around the same time and acquired a meaning in Old English that is similar to ‘locian’ in the ‘appear’ sense. It is around the same time or later that ‘sound’, ‘taste’, ‘smell’, and ‘feel’ acquire the ‘appear’ meaning. ‘Taste’ entered Old English around 1300. It stems from the Old French ‘taster’ (‘to taste’), which originally meant ‘to touch, to handle’. Around 1550 it replaced the Old English ‘smack’. ‘Sound’ stems from the Latin ‘sonare’ and entered Old English in late 1300. It began to be used in the ‘appear’ sense some time in 1400. ‘Feel’ stems from the Old English ‘felan’ and slowly acquired its multiple senses between 1300 and 1829. ‘Smell’ was not found in Old English and is of unknown origin. The etymology of ‘appear’ words strongly suggests that ‘seem’, ‘appear’, and ‘look’ function in the same way. As ‘taste’, ‘sound’, and ‘feel’ took on the ‘appear’ sense by replacing the visual verbs in equivalent sentences, it is plausible that ‘appear’ words have a unified semantic theory. I return to this theory below.

2 Epistemic, comparative, and phenomenal uses of appearance verbs The first philosopher to offer a systematic account of visual ‘appear’ words was Roderick Chisholm (1957: ch. 4). Chisholm identified three uses of ‘look’: The epistemic, the

Perceptual Reports   239 comparative, and the non-comparative (non-epistemic) use. Frank Jackson (1977) calls the latter use the phenomenal use of ‘look’. Chisholm’s distinction plays a crucial role in Frank Jackson’s argument for the sense-datum theory of perception. According to Jackson, the hypothesis that there are accurate phenomenal ‘looks’ reports partially indicates that we do not perceive the world directly but perceive it via a veil of appearances. I will argue that this conclusion lends support, not to the sense-datum theory, but to the hypothesis that visual perception has representational content.

Epistemic uses If I hear on the radio that Bank of America has put the financial crisis behind it, I may say ‘It looks like I won’t need to find a new bank’. This use of ‘look’ is different from the ‘look’ that occurs in ‘It looks like the road is wet (but it’s not)’, said on the basis of how the road looks. In the former case, if I am presented with a defeater, it will no longer look to me as if I won’t need to find a new bank. For example, if the radio host later announces that Bank of America is going bankrupt, then it will no longer look to me as if I won’t need to find a new bank. In the latter case, a defeater is not going to change how things look. If I am told that the city has painted the roads to make them look wet as part of their drive-safe campaign, it will still look to me as if the roads are wet. Chisholm called the use of ‘look’ that is subject to defeat ‘the epistemic use’. Epistemic uses are less closely tied to perception than the other uses are. When ‘look’ is used epistemically, the description sentence containing it purports to describe a cognitive state concerning what is subjectively probable conditional on (total, total inner, total relevant, total relevant presented so far . . .) evidence. Furthermore, when ‘look’ is used epistemically, the cognitive state ceases to exist in the presence of a defeater (if the agent is rational). I will say of epistemic reports that they are evidence bearing for the speaker. When epistemic ‘looks’ reports are not evidence bearing, they are relativized to a third party. Suppose, for example, after stating the usual antidote and Fink problems, I say ‘It looks, prima facie, like one cannot analyze dispositions in terms of conditionals’. I then give a new more elaborate theory in which the proposal is in fact to analyze dispositions in terms of conditionals. Here, the ‘looks’ report is not evidence bearing for the speaker because it makes implicit reference to the evidence of a person who is not acquainted with the new theory. Like ‘look’, ‘seem’, ‘appear’, and ‘sound’ all have epistemic uses. Consider:  (2) (a) It seems that some companies do this on purpose. (b) This modelling school appears to be a scam. (c) That sounds like a personal problem for me. When so used ‘seem’, ‘appear’, and ‘sound’ reports also purport to describe a cognitive state concerning what is subjectively probable conditional on (total, total inner, total relevant, total relevant presented so far . . .) evidence. For example, in the epistemic sense, ‘This modelling school appears to be a scam’ can be interpreted as meaning ‘This modelling school probably is a scam’.

240   Berit Brogaard ‘Taste’ and ‘smell’ do not have any widespread epistemic uses. They are normally used epistemically only in idiomatic phrases and non-literal speech, as in:  (3) (a) [That attitude] smells like teen spirit (Nirvana). (b) This tastes like victory. 3(b) can but need not have an epistemic reading. In some contexts it signals an emotional response to something that might not actually be victory. For instance, you could say it after you came a close second to Usain Bolt.

Comparative uses Comparative perceptual reports tell us that two experiences have certain properties in common but they need not tell us what the properties are. For example, if I notice that Rose is visually similar to her sister, I can say ‘Rose looks like her sister’. ‘Look’, 'seem’, ‘appear’, ‘sound’, ‘taste’, and ‘smell’ all have non-epistemic comparative uses: (4) (a) The cliff looked like a dried-out body. (b) The cliff seemed like a dried-out body. (c) They appeared like the perfect couple in public. (d) The 95 Tiger 885 I just purchased sounds like a diesel truck. (e) The cookies smell like marzipan. (f) Homemade wine tastes like yeast. At least some comparative reports are epistemic reports. For example, suppose I say about war 1: ‘this looks like war 2’. That’s comparative but plausibly epistemic. As comparative reports have a distinctly comparative structure, it is natural to think that they are structurally related to more familiar comparative sentences. Consider:  (5) (a) John is taller than every girl. (b) John is taller than every girl is. (c) Ellen is as rich as her father. (d) It is warmer today than it might be tomorrow. (e) George is richer than his father was and his son will be. (f) John dances like Tom. (g) Mary eats like a bird. As Richard Larson (1988) argues, 5(a) can be dealt with by positing that (i) the quantified noun phrase (e.g. ‘every girl’ or ‘one of the girls’) moves to a wide-scope position, and (ii) the comparative expression ‘taller than’ combines with two type e expressions (i.e. variables or referring terms). On this view, 5(a) is of the form ‘[Every girl, x] tallerthan (John, x)’. However, ‘than’-clauses are syntactically akin to relative clauses such as ‘that every girl likes’ as it occurs in ‘John is a guy that every girl likes’. Quantified noun phrases cannot scope out of relative clauses. As ‘than’-clauses are syntactically akin to relative clauses, it is

Perceptual Reports   241 extremely implausible to think that quantified noun phrases (e.g. ‘every girl’) can move to a wide-scope position. Irene Heim (2006) argues that even if quantified noun phrases could scope out of ‘than’clauses, modal expressions, adverbs of quantification (e.g. ‘Mary typically eats breakfast’), and floating quantifiers (e.g. ‘the girls all went outside’) cannot possibly do that. So, Larson’s suggestion does not carry over to 5(b) to 5(c). Heim offers a new account of comparatives according to which comparatives ascribe relations between what she calls ‘degrees’ (i.e. abstract entities like heights, weights, ways, etc.). To account for quantifier scopes, Heim suggests that there are semantically vacuous ‘wh’-items in the sentence structure. 5(b) can be read as: ‘John is taller than every girl is wh’. To a first approximation, ‘every girl is wh’ is to be read as: ‘every girl x: x is this tall’. This item scopes out of the comparative clause, and the ‘wh’-item raises to a wide-scope position, yielding: [wh1[every girl is t1]]2 [John is taller than t2]

Likewise, 5(f), which is superficially similar to ‘looks’ reports, can be read as: ‘John dances like Tom does wh’, where ‘Tom does wh’ is to be read, roughly, as: ‘Tom dances this way’. This item scopes out of the comparative clause, yielding: [wh1[Tom dances t1]]2 [John dances t2]

We can assign the following truth-condition to 5(f): for some way w such that w is a way that Tom dances, John dances that way too. As comparative ‘looks’-reports are superficially similar to the comparatives in 5(f) and 5(g), it is very plausible that they have the same underlying structure (Brogaard 2010, 2012b, 2014). On this hypothesis, ‘X looks like Y’ contains the implicit wh-clause ‘wh1[Y looks t1]’. This item scopes out of the comparative clause, yielding:  [wh1[Y looks t1]]2 [X looks t2]

For example, ‘Rose looks like her sister’ is to be read as containing the implicit clause wh-clause:  ‘wh1[Rose’s sister looks t1]’. This item scopes out of the comparative clause, yielding:  [wh1[Rose’s sister looks t1]]2[Rose looks t2]

The comparative analysis of comparative ‘looks’ reports offers the full answer to the question of how to analyze comparative ‘looks’ reports linguistically, but it does not address the question of how to assign truth-conditions (see Byrne 2009; Martin 2010; Travis 2004, 2013). The reason is that the analysis makes unreduced appeal to a notion of ‘look x’. This notion needs further analysis in non-comparative terms.

Perceptual uses Non-comparative (non-epistemic) ‘looks’ reports purport to describe the properties of experience directly (rather than comparatively) (Glüer 2009; Byrne 2009; Brogaard 2012b).

242   Berit Brogaard For example, if I look at my red chair and say ‘the chair looks red’, what I said is plausibly a non-comparative report. ‘Look’, ‘seem’, ‘appear’, ‘sound’, ‘taste’, and ‘smell’ all have nonepistemic non-comparative uses. Consider: (6) (a) Her skin looked as smooth as silk. (b) Her skin seemed smooth as silk. (c) Her skin appeared smooth as silk. (d) The music sounded bracingly fresh and quite moving. (e) The strawberries taste sour. (f) The flowers smell sweet. Non-epistemic ‘looks’ reports fail to be evidence bearing. Even if I am told that the lines in the Müller-Lyer optical illusion have the same length, it will still look to me as if they have different lengths. Some apparently non-comparative ‘looks’ reports are implicitly comparative. For example, ‘John looks drunk’ is plausibly a contraction of ‘John looks like someone who is drunk’. Likewise, ‘John’s voice sounded earnest’ plausibly is a contraction of ‘John’s voice sounded like the voice of someone who is earnest’. There are, however, three reasons to think not all non-comparative reports are implicitly comparative. First, comparative ‘looks’ reports plausibly just are existentially quantified noncomparative ‘looks’ reports at the level of logical form. Second, it is evident that we cannot successfully reduce all non-comparative ‘looks’ reports to comparative reports. ‘That chair looks purely qualitatively red’ and ‘That chair looks the way a purely qualitatively red object would look’ plausibly have the same truth-conditions. Hence, the comparative report presupposes a non-comparative use of ‘looks’. Third, as Chisholm (1957:  51)  argues, if ‘look red’ is given a comparative reading, ‘red things look red’ is an analytic truth. It says ‘things that are red look the way things that are red look’, which is trivially true. If, on the other hand, ‘look red’ is given a non-comparative reading, then ‘red things look red’ is a synthetic truth. Even before she started studying neuroscience and physics, Frank Jackson’s Mary knew that red things look the way red things look. But she didn’t know that red things looked non-comparatively red.

3 Adverbial and raising accounts of ‘looks’ It remains to give a semantic analysis of the non-comparative ‘looks x’. The most important theoretical options for analyzing the semantics of non-comparative ‘looks x’ are treating ‘appear’ words as adverbs or treating them as subject-raising verbs. Let us consider the adverbial treatment first. It is consistent with a comparative linguistic analysis of comparative ‘looks’ reports that the truth-condition for ‘X dances like Y’ involves ‘X dances P-ly’. For example, ‘Amy dances like Eli’ is true if Amy and Eli both dance wildly with their eyes closed. When an

Perceptual Reports   243 adverb occurs in a final position it describes the manner of the activity picked out by the verb. Consider:  (7) (a) John spilled the beans clumsily. (b) John dances clumsily. 7(a) means ‘John spilled the beans in a clumsy manner’, and 7(b) means ‘John dances in a clumsy manner’. Adverbs that describe the manner of the activity picked out by the verb are also known as ‘manner adverbials’. 7(a) can be assigned the following truth-conditions using Davidsonian event semantics:  ‘e[spill(e, John, beans) & clumsily(e)]’. In English: There is an event e such that e is a spilling event that has John as an agent and the beans as a patient, and e was done clumsily. 7(b) can be assigned the following truth-condition: ‘e[dance(e, John) & clumsily(e)]’. In English: There is an event e such that e is a dance event that has John as an agent, and e was done clumsily. It is theoretically possible that the truth-condition for ‘X looks like Y’ likewise involves ‘X looks x-ly’, where ‘x-ly’ is a manner adverbial. ‘The tomato looks red to me’ would be assigned the truth-condition:  ‘e[look(e, tomato, me) & redly(e)]’. Or:  there is a looking event with the tomato and I as participants (agent and patient respectively), and the event takes place in a redly manner. This would be consistent with an adverbial theory of perception, according to which perceiving is an object acting upon a perceiver in a certain manner. I believe there are several reasons to resist an adverbial interpretation of ‘look x’. I offer some reasons below. In what follows I will briefly outline what I believe is the correct interpretation of ‘look’. A lot of what I am saying here carries over to ‘feel’, ‘taste’, ‘smell’, and ‘sound’. On my preferred account, when ‘look’ takes an adjective it functions semantically in the same way as the (subject)-raising verb (e.g. ‘seem’, ‘strike (me)’, ‘turn out’, ‘prove’) in the following sentences:  (8) (a) Tom was found missing. (b) Susan was proven guilty. (c) A laptop was reported stolen. (d) Patrick was assumed dead [after disappearing in South America in the 1970s]. (e) Some 67% of the students’ writing was deemed outstanding or good. The sentences in (8) are pleonastic paraphrases of ‘Tom was found to be missing’, ‘Susan was proven to be guilty’, ‘A laptop was reported to be stolen’, ‘Patrick was assumed to be dead’, and ‘Some 67% of the students’ writing was deemed to be outstanding or good’. They are thus structurally similar to sentences with raising verbs and infinitive predicates such as ‘John is expected to arrive on time’, ‘Mary is believed to have stolen two library books’, ‘The summer promises to be great’, ‘Tom was seen eating a sandwich’. One reason for thinking that ‘looks’ should be given the same semantics is that the etymology of ‘appear’ words strongly suggests that ‘look’ functions in the same way as ‘seem’. As ‘seem’ uncontroversially functions as a raising verb, so does ‘look’. The weakness of this argument, that etymology indicates a unified semantics for ‘appear’ words, is that even if there is strong evidence that the Old English ‘locian’ and

244   Berit Brogaard ‘besean’ function in the same way, ‘look’ and ‘seem’ could later have come to function differently. But it is more likely that changes and idiosyncrasies over the years explain why ‘look’ sometimes behaves differently from ‘seem’ and ‘appear’. Transformational grammar has taught us that sentences with raising verbs do not have the surface form that they appear to have. On the face of it, ‘John looked to be happy’ seems to have the same surface grammar as ‘John wanted to be happy’. However, this is not so. One of the big advances of transformational grammar was that it offered a way to distinguish between the different underlying forms of sentences like ‘John wants to be happy’ and ‘John looks to be happy’ (Partee 1975). The ‘want’ sentence has the underlying form ‘John wants [John to be happy]' and the ‘look’ sentence has the underlying form ‘[e looks[John to be happy]]’. ‘John looks to be happy’ is generated by applying the transformation rule Subject-to-Subject-Raising. When this rule is applied, ‘John’ is raised to become the surface-grammatical subject of ‘looks’. The subjects of raising verbs like ‘seem’, ‘proven’, and ‘look’ thus have no semantic relation to these experiential or epistemic verbs. Rather, the subjects are associated with the infinitive predicate or the verb of the embedded clause. For example, in ‘The apple looked to be red’ the subject ‘the apple’ is associated with ‘to be red’, and in ‘John seemed to prefer red wine’ the subject ‘John’ is associated with the verb ‘prefers’. In their unraised logical form, raising verbs often take an expletive, or dummy, subject, as in ‘It was proven that she was guilty’, ‘It seemed as if she was turning red’, or ‘It looks like she is done’ (Postal 1974; Chomsky 1981, 1986). Most verbs that function as raising verbs can also function as transitive verbs, as in ‘John looked (shy, shyly) at Mary’, ‘Tom (eagerly) expected the car crash’, and ‘Alice (enthusiastically) tasted the soup’. When they function as transitive verbs, they describe acts or actions of the referent of the semantic subject. When they function as intransitive raising verbs, they describe a passive experiential or epistemic state of an implicitly or explicitly mentioned perceiver. For example, ‘Lisa seemed angry to Paul’ describes a passive experiential or epistemic state of Paul, and ‘The tomato looks red to me’ describes a passive experiential or epistemic state of the speaker. If ‘appear’ words are raising verbs, then there are at least two reasons to think the adjectival treatment of ‘look’ is wrong. First, raising verbs are always followed by adjectives or infinitive clauses rather than adverbs. The ‘to be’ of infinitive clauses always takes an adjectival complement, not an adverbial one, as is apparent in ‘John was proven guilty’ and ‘Susan turned out to be a liar’. Hence, while complements of raising verbs can be modified by adverbs, as in ‘extremely beautiful’, they cannot themselves be adverbs or ‘to be’ plus adverbial clauses. Second, unlike adverbial modifiers, the adjectival complements of raising verbs and the corresponding infinitive clauses have the same meaning. The reason that they have the same meaning has to do with the underlying form of the sentences in which they occur. Raising verbs function as sentential operators. ‘John seemed worried’ has the underlying form ‘Seemed(John is worried)’. This underlying form is then transformed into the surface form ‘John seemed to be worried’. The latter can then undergo deletion of the predicate infinitive to become ‘John seemed worried’. The same goes for ‘looks’. ‘X looks red’ has the underlying form ‘Looks(X is red)’. This underlying form is transformed into the surface form ‘X looks to be red’, which through infinitive deletion becomes ‘X looks red’. The infinitive construction ‘X looks to be red’ is thus a pleonastic paraphrase of ‘X looks red’.

Perceptual Reports   245 In the case of ‘John dances clumsily’, on the other hand, there is no equivalent infinitive construction. For example, ‘John dances clumsily’ and ‘John dances to be clumsy’ have different truth-conditions.

4 Consequences for theories of perception How we use ‘appear’ words has some bearing on issues in the theories of perception. As Brogaard (2010) argues, from the hypothesis that ‘look’ is a raising verb, we can infer that some ‘looks’ reports reflect phenomenal properties of perception. From that we can infer that they reflect representational contents of perception and hence that perception has representational content. ‘S reflects property P’ and ‘S reflects content p’ can be defined as follows (Brogaard 2010):  Phenomenal Property Reflection A report that describes experience e reflects a phenomenal property P iff [necessarily, the report is true iff P is a phenomenal property of e] Content Reflection A report that describes experience e reflects a content p iff [necessarily, the report is true iff p is a content of e].

Phenomenal Property Reflection and Content Reflection are meant to be restricted to reports that are tokens of sentences that can have true tokens when uttered by us. As comparative ‘looks’ reports, if truly comparative, reduce to non-comparative reports, the question to be answered is that of whether some non-comparative ‘looks’ reports reflect phenomenal properties of perceptual experience. There are two components to this question: one is whether ‘looks’-reports mirror properties represented in perception. Another is whether these properties at least sometimes reflect distinctly phenomenal representation. As for the first question, we have already seen that ‘looks’, used as an intransitive verb, functions as a sentential operator at the level of logical form. ‘X looks red’ has the underlying structure ‘Looks(X is red)’. In the transformation of the underlying structure, ‘X’ raises to become a constituent of the higher clause ‘X looks to be red’. This then undergoes infinitive deletion to yield ‘X looks red’. ‘X looks red’ thus has the same underlying structure as ‘A laptop was reported stolen’ and ‘Patrick was assumed dead’. In all of these cases the underlying structure contains a subject-predicate subordinate clause with a predicate that expresses a property attributed to the referent of the semantic subject term. For example, ‘a laptop was reported stolen’ says that it was reported that a laptop was stolen. The subordinate clause thus attributes being stolen to some laptop. Likewise, the subordinate clause in ‘X looks red’ attributes being red to X. The subordinate clauses of ‘looks’ reports thus attribute properties expressed by the predicate term to the referent of the subject term of the subordinate clause. The sentential operator indicates how the properties got attributed. Being stolen was attributed to a laptop in an act of reporting. Being red is attributed to X in a perceptual act. It follows that the subordinate clauses of non-epistemic (or ‘perceptual) ‘looks’ reports mirror properties represented in perception.

246   Berit Brogaard The second question to be answered was whether at least some ‘looks’ reports reflect distinctly phenomenal properties. Here is an argument that they do. Let ‘X looks [ADJ] to O at t’ be a non-comparative ‘looks’ reports. Let the domain consist of properties that correspond to ‘[ADJ]’. Now, for some property P, if ‘X looks [ADJ] to O at t’ does not reflect P, then either the report is necessarily false, or it is not necessary that it is true iff P is a phenomenal property of O’s experience. As for the first horn of the dilemma: ‘X looks [ADJ] to O at t’ cannot plausibly be necessarily false for all values of ‘X’, ‘[ADJ]’, ‘O’, and ‘t’. If I look at a ripe tomato in good lighting conditions and say ‘That looks red to me now’, that obviously is true. As for the second horn of the dilemma: According to Jackson, ‘X looks red’ is true when X has an experience that is red. However, this is not the best way to interpret ‘X looks red’. As we have already established, ‘look’ expresses a perceiver’s experiential attitude relative to a represented property. When used non-epistemically, ‘look’ is a marker of experiential modality as opposed to epistemic modality. A non-epistemic ‘looks’ report states that the world as experienced is the way indicated by the subordinate clause. By making a ‘looks’ reports one thus seeks to eliminate the set of possible situations in which the subordinate clause is false. When used epistemically, ‘look’ is a marker of epistemic modality. An epistemic ‘looks’ report states that the world likely is the way indicated by the subordinate clause. Both experiential modality and epistemic modality relativize truth to individuals (perceivers or believers) by relating their current experiential state or their current state of belief to the content of their utterances. One difference between raising verbs (both epistemic and nonepistemic) and epistemic modals, such as ‘may’, ‘might’, ‘should’, and ‘must’, is that raising verbs often indicate the source of the perceiver’s experiential attitude or the believer’s belief. ‘The tomato looked red’ indicates that the perceiver was looking at the tomato. ‘The table felt hard’ indicates that the perceiver was feeling the table. ‘Tom was seen eating a sandwich’ indicates that the perceiver saw Tom. ‘John is expected to arrive on time’ indicates that a thinker was expecting something. Now, we need to show that:  For some ‘looks’ reports of the form ‘X looks [ADJ] to O’, the report is true iff a property corresponding to the adjectival phrase of the subordinate clause is a phenomenal property of O’s experience.

The right-to-left direction is obvious. Where P corresponds to ‘[ADJ]’, it is necessarily the case that if P is a phenomenal property of O’s experience, then ‘X looks [ADJ] to O’ is true. The left-to-right direction is less obvious. To see that it holds, consider a special case of blindsight. Blindsight is a kind of residual vision that some people with lesions to the primary visual cortex have. Blindsighters can make above-chance predictions about the attributes of visual stimuli presented to them in their blind field, without any distinctly visual awareness. In ordinary cases of blindsight, the stimulus does not seem or look any way to the blindsighter. Blindsighters feel that they are simply guessing. But consider the case of Ned Block’s super-blindsighter. A super-blindsighter has acquired the ability to guess correctly when to make a guess about a stimulus in her blind field. If someone were to ask a super-blindsighter ‘What colour does the stimulus in your blind field seem to be?’

Perceptual Reports   247 or ‘How does the stimulus look to you?’, she may just reply with ‘It seems red to me’ or ‘It looks red to me’. Consider another case, that of achromatopsia. When a person with achromatopsia looks at a red object, he has a phenomenally black experience of the object. Hence, he cannot tell on the basis of his perceptual experience whether the object is red or black. But suppose he is given a device that presents a black dot on a screen when it detects that an object is red. By means of this device an achromatopsic can discriminate between red and black objects. If shown a red object and asked ‘What colour does the stimulus seem to be?’ Or ‘How does the stimulus look to you?’, he may just reply with ‘It seems to be red to me’ or ‘It looks red to me’. These cases seem exceedingly plausible. However, as argued by Brogaard (2010), the occurrence of ‘look’ in these cases is epistemic. When a super-blindsighter detects the colour of a visual stimulus presented to her in her blind field, she has no distinctly visual awareness of the colour of the stimulus. So, when she reports on the colour of a stimulus presented to her in her blind field, she cannot make use of any visual phenomenology associated with the colour information. Rather, she must infer from her inclination to guess that the stimulus is red, that it is red. Were she to be presented with a defeater, she would no longer have the inclination to state that the stimulus looks read. So, when she says that the stimulus looks red, her report is evidence bearing and hence epistemic. Likewise, when a person with achromatopsia detects the colour of a visual stimulus by looking at a computer screen, he has no distinctly visual awareness of the colour of the stimulus. So, when he reports on the colour of the stimulus, he cannot make use of any visual phenomenology directly associated with the colour information. Rather, he must infer from the black dot on the screen that the stimulus must be red. Were he to be presented with a defeater, he would no longer have the inclination to state that the object looks red. So, when he says that the stimulus looks red, his report is evidence-bearing and hence epistemic. Generalizing:  (1) All and only epistemic ‘looks’ reports reflecting the speaker’s internal evidence state are evidence bearing. (2) When we use a ‘looks’ report to report on a visual stimulus without basing the report in any way on phenomenal properties of an experience of the stimulus, the report is always evidence bearing. (3) So, when we use a ‘looks’ report to report on a visual stimulus without basing the report in any way on phenomenal properties of an experience of the stimulus, the report is epistemic. A ‘looks’ report that reports on a visual stimulus can be true only if it is based on the visual phenomenology of an experience of the stimulus or is based on other information available about the stimulus. It follows that when we use a non-epistemic ‘looks’ report to report on a visual stimulus, the report is true just in case it is based on the phenomenal properties of an experience of the stimulus. So, for non-epistemic reports of the form ‘X looks [ADJ] to O’, it is necessary that if the report is true, then there is an experience with property P, where P corresponds to ‘[ADJ]’. Hence, for some ‘looks’ reports of the form ‘X looks [ADJ] to O’, the report is true iff a property corresponding to the adjectival phrase of the

248   Berit Brogaard subordinate clause is a phenomenal property of O’s experience. Hence, at least some ‘looks’ reports reflect distinctly phenomenal properties. Brogaard (2010) further argues that if ‘looks’ reports reflect phenomenal properties, they do not reflect non-phenomenal properties. Suppose I have a rough and imprecise experience of John, because I am not wearing my glasses. My experience then has the representational phenomenal property of representing a certain content in a rough and imprecise way (see Chalmers 2004). It also has the non-representational property of being rough and imprecise. But I cannot accurately report the roughness and imprecision of my experience using:  (9) John looks rough and imprecise. ‘My experience represents John in a rough and imprecise way’ and ‘My experience is rough and imprecise’ do not entail ‘my experience represents John as being rough and imprecise’. My rough and imprecise experience does not give rise to an appearance that attributes roughness and imprecision to John. Imprecision is similar to consciousness in this respect. A conscious visual experience of an apple does not represent the apple as conscious. The correct thing to say here is that not all of the phenomenal properties of perceptual experience can be accurately reported using a phenomenal ‘looks’ report. The argument from the claim that some ‘looks’ reports reflect representational phenomenal properties of perception to the claim that perception has content is straightforward (Brogaard 2010). The argument rests on the following principle:  Looks-Representation Bridge Principle (LRB) If X phenomenally looks to be P to O at t, then O’s experience at t has the representational phenomenal property of representing something as P.

LRB links phenomenal looks for a person at a time to a phenomenal property of that person’s experience at that time. Here is an argument for LRB. Suppose LRB is false. Then X phenomenally looks to be P to O at t, but O’s experience at t does not have the property of representing something as P. Then either P corresponds to a non-representational phenomenal property of O’s experience at t, or it does not correspond to any phenomenal property of O’s experience at t. P cannot correspond to a non-representational phenomenal property of O’s experience at t, for, as I argued earlier, things cannot phenomenally look to have a property that corresponds to a purely non-representational phenomenal property. So, P does not correspond to any phenomenal property of O’s experience at t. So, P does not contribute to what it is like for O to have the experience he has at t. But it is conceptually impossible for X to look to be P to O at t, despite the fact that P does not contribute in any way to what it is like for O to have the experience she has at t. So, LRB is true. By the LRB principle and the hypothesis that things cannot phenomenally look to have non-representational phenomenal properties, it follows that the properties which things can phenomenally look to have to observer O correspond to representational phenomenal properties of O’s experience. So, if a sentence of the form ‘X looks like Y to O’ is true, then there is a P such that the property of representing something as P is a representational phenomenal property of O’s experience, and P is how X and Y look to O. But a report that describes experience e reflects the representational phenomenal property of representing

Perceptual Reports   249 something as P iff [necessarily, the report is true iff representing something as P is a phenomenal property of e]. So, comparative phenomenal ‘looks’ reports reflect representational phenomenal properties of the perceptual experience they describe. What about non-comparative phenomenal ‘looks’ reports? Non-comparative phenomenal ‘looks’ reports typically have the form ‘X looks [ADJ] to O at t’. Sentences which have this surface form and which are not used epistemically are either implicitly comparative or non-comparative. If they are implicitly comparative, then, as we have just seen, they reflect representational phenomenal properties of the perceptual experience they describe. If they are non-comparative, and they are true, then it follows that X phenomenally looks [ADJ] to O at t. But by the LRB principle and the hypothesis that things cannot phenomenally look to have non-representational phenomenal properties, it follows that the property of representing something as [ADJ] is a representational phenomenal property of O’s experience at t. So, if ‘X looks [ADJ] to O at t’ is true, then O has an experience at t with the phenomenal property of representing something as [ADJ]. But a report that describes experience e, and is a token of a sentence S that can have true tokens, reflects the phenomenal property of representing something as P iff [necessarily, the report is true iff the property of representing something as P is a phenomenal property of e]. So, non-comparative phenomenal ‘looks’ reports reflect representational phenomenal properties of the perceptual experience they describe. Both comparative and non-comparative phenomenal reports reflect representational phenomenal properties of the experiences they describe. As Brogaard (2010) argues, there is a simple argument from the premise that phenomenal ‘looks’ reports reflect phenomenal properties of the experiences they describe to the conclusion that phenomenal ‘looks’ reports reflect contents of the experiences they describe. The argument runs as follows:  Look-Content Argument



(1) Phenomenal ‘looks’ reports reflect representational phenomenal properties of the perceptual experience they describe. (2) Any representational property of perceptual experience is the property of having a certain perceptual content. (3) Hence, phenomenal ‘looks’ reports reflect a content of the perceptual experience they describe.

We have already established that (1) is true. Here is an argument for premise (2). It is a priori that if an experience has the property of representing p, then the experience represents p. But if an experience has representational content, and it represents p, then p is a content of the experience. So, if an experience has the representational property of representing p, then p is a content of the experience. The thesis that perception has content rules out a number of theories of perception according to which perception does not have content. These include some versions of naive realism, disjunctivist versions of naive realism, sense-datum theories, and raw-feels theories. A standard objection to my arguments from perceptual reports to the metaphysics of perception is that even if the arguments are sound, the conclusion only settles that

250   Berit Brogaard perceptual experience has representational phenomenal properties and representational content in a weak sense of content. In the weak sense of content, disjunctivists, adverbialists, raw-feels theorists, and so on, may agree that perception has content. A stronger claim would be that part of what it is for an act to be a perceptual experience is for it to have phenomenal properties and/or content. Experiences can be said to have strong content in this sense (see Siegel 2009, 2010 for this distinction; see also Pautz 2009). This is not the place to address this issue at great length. But a few words about this distinction are in order. An argument can be made from ‘looks’ reports to the conclusion that some ‘looks’ reports reflect wide object-involving content. For example, ‘He looks like Dave’ reflects a wide content that contains Dave as a constituent (see Brogaard 2010). Most thinkers who deny that experience has content in the strong sense would disagree that experiences have this kind of wide object-involving content. It is thus possible to use arguments similar to those presented here to argue for the strong-content thesis. Another standard objection to arguments from language to metaphysics is that we cannot assume that the words of ordinary language are those that theories of perception are concerned with. It may be said, for example, that the ordinary language words ‘look’ and ‘see’ express concepts that are distinct from the concepts employed by philosophers of perception (cf. Brogaard 2012a). I grant that this is a genuine possibility. Philosophers of perception certainly use the word ‘experience’ differently from most people (Byrne 2009). In ordinary language, ‘experience’ has a variety of meanings none of which is exactly the one philosophers of perception have in mind. As a verb, it means ‘undergo’ (cf. ‘experience a great adventure’). As a noun, it can mean an event participated in (cf. ‘the trip was a fantastic experience’), knowledge that derives from participating in a given event or series of events (‘a lesson taught by experience’) or perceptual exposure to (cf. ‘my first experience of NP’). However, there is no similar difference between our ordinary and philosophical uses of ‘see’ and ‘look’. In fact, all of the examples philosophers normally use when addressing issues concerning events of seeing and looking come from ordinary language. So, I highly doubt that there are concepts of seeing and looking that are distinct from those of ordinary language. A third objection is this: The look-content argument only works if ordinary perceptual reports are true. If, however, their truth-conditions involve a false theory of perception they may be false. I grant that there is ordinary language discourse that is treated as true but is in fact false. A good example is ‘The sun rises’. This statement is strictly false. But the latter statement is about an object, viz. the sun, whereas perceptual reports involving ‘appear’ words are about how things appear to a particular perceiver. It is unlikely that all our expressions of how things appear to us are false. A fourth objection is this: The correct semantics for ‘looks’-sentences needs to be sensitive not just to armchair linguistic evidence, but also to philosophical reasoning about perception. For example, when science tells us that water is H2O, that tells us something about the semantics of ‘water’; if philosophy or science were to tell us, for example, that sense-datum theory or naive realism is true, that would tell us something about the semantics of ‘looks’. So, we can’t conclusively argue from semantics to metaphysics unless we have already done the metaphysics. By way of reply, it is doubtful that science can determine how things look to us. How things look to me seems to be something only I can determine. So, while science can help

Perceptual Reports   251 us discover the content of ‘water’, it cannot help us discover the content of perceptual reports. I think the same sort of point applies to the thought that science might discover that sense-datum theory or naïve realism is true. Because theories of content are intimately tied to how things look to us, as we have seen, science cannot confirm or falsify them. Of course, to the extent that linguistics is a science, science can indeed help us settle which theory of content is correct, but this is just the approach taken here.

5 Intensional uses and intentional content David Bourget (2010) has argued that the intensional nature of perceptual verbs causes trouble for Hinton’s argument (1967) for a disjunctive account of perception. Hinton argues that (10) should be analyzed in terms of (11):  (10) I am experiencing a flash of light. (11) Either (A) I see a flash of light, or (B) I have an illusion of a flash of light. On Hinton’s disjunctive account of perception, when I experience something I either stand in direct perceptual relation to an entity (in this case, a flash of light) or I have an illusion (or hallucination of that entity. So, if (11) is the correct analysis of (10), then that seems to provide evidence for a disjunctive analysis of perception. However, as Bourget points out, ‘see’ appears to have uses that introduce intensional contexts. Suppose the heartbroken Lois Lane takes a strong hallucinatory drug and then utters the following (these are modifications of Bourget’s examples):  (12) (a) Wow, I see Superman on my left. That’s a really strong drug. (b) I see Superman spinning in front of me, even though I know he isn’t even here. (c) I see Superman all over the place. Maybe I should stop taking the drug. The sentences in (12) seem intuitively true. But if they are true, then the result of substituting ‘Clark Kent’ for ‘Superman’ is false. So, ‘see’ introduces an intensional context, at least sometimes. If ‘see’ is used in this way in (10), then the hypothesis that (10) is to be analyzed as (11) does not lend evidence to a disjunctive analysis of perception. The occurrence of ‘see’ could be interpreted in the same way as the occurrence of ‘see’ in ‘Someone is poking my brain. I see stars everywhere’. Here is a further reason to think ‘see’ can have intensional uses (see Brogaard 2013). When we see an event, we needn’t see all of it. For example, ‘John saw the car accident’ does not imply ‘John saw every part of the car accident’. We see (or witness) complex events, and other high-level properties, in part by visually detecting other properties that typically are associated with the event in question. For example, ‘John witnessed the murder’ may be true if John heard a gunshot and saw a man fall to the ground and then ran away. Likewise, John can see a crying event by virtue of seeing various properties that typically are associated with crying, for instance, a shivering body, a handkerchief, runny mascara, and so on.

252   Berit Brogaard Hence, even if all crying events essentially involve shedding tears, it can be true that John saw someone cry even if he didn’t see them shed any tears. So, ‘John saw Mary cry’ and ‘John saw Mary shed tears’ need not be equivalent, even if we assume that crying events essentially involve shedding tears. The opacity of seeing reports of this type adds further support to the argument that ‘see’ has intensional uses.

References Bourget, D. (2010). ‘Intensional and Phenomenal Uses of Perceptual Verbs’, Chapter in ANU Dissertation. Brogaard, B. (2010). ‘Do “looks” Reports Reflect the Contents of Perception’, manuscript, University of Missouri, St. Louis. Brogaard, B. (2012a). Transient Truths: An Essay in the Metaphysics of Propositions. New York: Oxford University Press. Brogaard, B. (2012b). ‘What do We Say When We Say How or What We Feel?’ Philosophers’ Imprint, 12 (11), June 2012. Brogaard, B. (2013). ‘Seeing as a Non-Experiental Mental State: The Case from Synesthesia and Visual Imagery’. In R. Brown (ed.), Consciousness Inside and Out: Phenomenology, Neuroscience, and the Nature of Experience. Neuroscience Series, Synthese Library. Brogaard, B. (2014). ‘It’s Not What It Seems. A Semantic Account of "Seems" and Seemings’. In H. Cappelen and S. Shapiro (eds), Contextualism and Relativism, special issue of Inquiry. Byrne, A. (2009). ‘Experience and Content’. Philosophical Quarterly, 59, 429–451. Chalmers, D. (2004). ‘The Representational Character of Experience’. In B. Leiter (ed.), The Future for Philosophy (pp. 153–181). Oxford: Oxford University Press. Chisholm, R. M. (1957). Perceiving: A Philosophical Study. Ithaca, NY: Cornell University Press. Chomsky, N. (1981). Lectures on Government and Binding. Dordrecht: Foris. Chomsky, N. (1986). Knowledge of Language. New York: Praeger. Glüer, K. (2009). ‘In Defence of a Doxastic Account of Experience’. Mind and Language, 24, 297–327. Heim, I. (2006). ‘Remarks on Comparative Clauses as Generalized Quantifiers’, Manuscript, MIT. Hinton, J. M. (1967). ‘Visual Experiences’. Mind, 76, 217–227. Jackson, F. (1977). Perception: A Representative Theory. Cambridge: Cambridge University Press. Larson, R. (1988). ‘Scope and Comparatives’. Linguistics & and Philosophy, 11, 1–26 Martin, M. (2010). ‘What’s in a Look?’ In B. Nanay (ed.), Perceiving the World (pp. 160–226) Oxford: Oxford University Press. Matthen, M. (2010). ‘Colour Experience: A Semantic Theory’. In Jonathan Cohen and Mohan Matthen (eds), Colour Ontology and Colour Science (pp. 67–90). Cambridge, MA: MIT Press. Maund, B. J. (1986). ‘The Phenomenal and Other Uses of “Looks”’. Australasian Journal of Philosophy, 64, 170–180. Mitchell, B. and Robinson, F. C. (2001). A Guide to Old English, sixth edition. Oxford: Blackwell. Partee, B. (1975). ‘Deletion and Variable Binding’. In E. Klima (ed.), Formal Semantics of Natural Language (pp. 16–34). Cambridge: Cambridge University Press. Pautz, A. (2009). ‘What are the Contents of Experiences’. The Philosophical Quarterly 59, 483–507.

Perceptual Reports   253 Postal, P. (1974). On Raising. Cambridge, MA: MIT Press. Siegel, S. (2009). ‘Do Visual Experiences Have Contents?’ In B. Nanay (ed.), Perceiving the World (pp. 333–368). New York: Oxford University Press. Siegel, S. (2010). The Contents of Visual Experience. New York: Oxford University Press. Travis, C. (2004). ‘The Silence of the Senses’. Mind 113, 57–94. Travis, C. (2013). ‘The Preserve of Thinkers’. In Berit Brogaard (ed.), Does Perception Have Content? New York: Oxford University Press.

Pa rt  I I I

T H E  SE NSE S

Chapter 14

V ision David R. Hilbert

1  Vision in the philosophy of perception Discussions of vision dominate the philosophy of perception. Although the other senses are mentioned from time to time, the standard budget of philosophical examples that are used to explore issues in perception almost all involve seeing. From seeing sticks partially immersed in water to looking at pillars reflected in mirrors with a steady diet of ellipticallooking coins in between, discussion of most of the central issues in philosophy of perception is focused on visual examples. The philosophical obsession with vision has had two untoward effects. First, and most obvious, generalizations drawn from vision are inappropriately applied to the other senses (for discussion of this problem in the case of sound see, O’Callaghan, 2007, 2008). Second, and less commonly recognized, vision itself, with its own peculiarities and distinctive features has a tendency to fade from view and what we are left with is a generic sense, suitable for serving as the model for perception in general. Vision is, as philosophers intermittently recognize, quirky in the way characteristic of evolved capacities more generally. It combines great sophistication with surprising limitations and sometimes accomplishes its basic task of acquiring environmental information from ambient light in ways that are extremely counterintuitive.

2  Basics of vision Vision can be discussed from many different points of view: from philosophical reflections on the nature of the relation between mind and world involved in seeing to the quantum interactions that underlie the physics of reflection and the physiology of photon detection with the psychology of visual processing somewhere in between. For the purpose of philosophy of perception, many of these details can usually be safely ignored but there is a substrate of basic vision science that constrains the possibilities at higher levels in ways that are sometimes philosophically important. I will divide this material into two sections. First, a discussion of the optical process that includes the interaction of light with objects

258   David R. Hilbert in the environment and culminates in the formation of an image on the retina. Second, a discussion of some of the biological processes that begin with the absorption of photons by pigment molecules within the photoreceptors in the retina. Although this material will be familiar to many readers, not all of it will be familiar to all readers and there may be some surprises even for those who think they know this material. (A slightly dated but very useful overview of vision science is Palmer, 1999).

Visual optics As most of us were repeatedly taught, starting in grade school, the process of vision typically begins with a source of light that illuminates the objects in a scene.1 The light is reflected from the surfaces of objects and some of it enters the eye where the cornea and lens combine to focus the light and produce an image of the scene on the retina. This textbook scenario oversimplifies in numerous respects, most notably in ignoring the fact that we have two eyes with overlapping fields of view, but it captures two central truths about vision. First, it is light as modified by the surfaces and objects in the environment that enables vision. Differences between objects that don’t affect light (or aren’t correlated with differences that affect light) are not visible.2 Thus, it is the variable effects of different parts of the scene on the light falling on them that enables us to see the objects present and their qualities. Second, a crucial part of the process that allows us to make use of the light reaching the eye to see the objects in our surroundings is the formation of an image within the eye. Image formation is important because the formation of the retinal image separates the light coming from the different parts of the scene and thus enables spatial vision and with it the ability to visually attribute properties to different locations within the scene.

Light sources The light sources that initiate the process of vision can be described in terms of two sets of characteristics: spatial and spectral. First, light sources can be divided into those that are of significant spatial extent, like the sky on an overcast day or a bank of fluorescent tubes behind a diffusing panel, and those that approximate point sources, like the sun or a street lamp. The first can provide much more uniform illumination across the scene while the second illuminates objects in a way that depends much more strongly on their position and orientation with respect to the light source and the other objects in the scene. The character of the light emitted by a light source can be described using the combination of the overall intensity of the light (its total power across the spectrum) with the spectral power distribution of the light (how the power is distributed across the wavelengths of the visible spectrum). Since the sensitivity of human vision to light of different wavelengths varies significantly across the spectrum, two light sources of equal intensity can be very different in their effectiveness at producing a visual response if they differ in spectral 1  I will ignore the special case of the perception of self-luminous objects as well as transparent and translucent objects. 2  I will set aside, for now, the possibility of input from the other senses to vision. The simplification will be useful in spite of the fact that acoustic inputs affect what we see (and visual inputs affect what we hear).

Vision   259 power distribution. For example, the principal cause of the high efficiency of the familiar yellow street lights is not that they are particularly efficient at turning electricity into light, but rather that they emit almost all of their light at wavelengths to which the human eye is very sensitive.

Objects When light falls on an object some proportion of the light at each wavelength is reflected, some proportion is absorbed within the object, and, for transparent and translucent objects, some proportion is transmitted. Reflection can be quite complicated but for many purposes it is useful to separate the reflected light into two components. First, a diffuse component, in which the intensity of the reflected light displays relatively little dependence on the angle between the eye, the object’s surface, and the light source. Second, a specular component in which the reflection is mirror-like and highly directional. Typically, the diffuse component is much more influenced by characteristics of the object, while the specularly reflected light approximates the light source. A number of the characteristics of an object affect the way in which it modifies the light it reflects, most notably its chemical composition and the roughness of its surface. Since many objects are heterogeneous in their composition the reflecting characteristics of an object are typically variable and the variation often is found at several different spatial scales giving rise to both visible patterns and visible texture.

Scenes The result of the interaction between light sources and objects in a scene is that a complex pattern of light varying in both spectral composition and intensity permeates the environment. Most scenes have multiple light sources. The sky and the sun dominate in many outdoor scenes but there can be significant amounts of illumination deriving from partially opaque objects like leaves and light reflected from one object in the scene often is part of the illumination for other objects in the scene. Multiple light sources, including inter-reflection, are common in indoor scenes as well. The structure of environmental light is the joint product of the characteristics of the light sources and the reflecting characteristics of the objects in the scene. Disentangling these two factors is one of the principal problems facing the visual system in using the structured light to acquire information about the environment.

Eyes In order for an organism to make use of light to find out about the environment it must have some method of sampling and characterizing light. For us, this task is accomplished by the eye. Although essentially every theory of vision since antiquity recognizes the central role that light plays in vision, the exact nature of that role and its relation to the anatomy and physiology of the eye emerged surprisingly late. The most detailed and successful theories of vision in antiquity involved the emission of visual rays from the eye, rather than

260   David R. Hilbert the reception of light by the eye. Rather than sampling environmental light that interacts with the sensitive parts of the eye, these theories essentially extended the eye’s sensitivity to the surface of the seen objects. In these theories, light plays an important enabling role but is not itself the carrier of information about the world around us. The first relatively successful intromissionist theory of vision is that of ibn al-Haytham in the eleventh century and it was not until Kepler in the sixteenth century that the image-forming nature of the optics of the eye was correctly described.3 Extramissionist theories provided a solution to one of the central problems in vision and that fact helps to explain their persistence in the face of the severe physical and philosophical problems that they confronted from the very beginning. Suppose we grant—anachronistically but no harm is done—that the retina is the sensitive part of the eye. Each point on the retina will receive light from every part of the scene that is not blocked by some opaque object. There is no way that measuring the characteristics of the light at the retina can reveal the spatial structure of the scene that generated it.4 The eye is spatially extended and the opaque parts of the eye and body will block light from many parts of the scene but nevertheless each point on the sensitive part of the eye will receive light from every unoccluded point in the field of view. If vision is to deliver information about the spatial distribution of properties in the world then some method is needed for sampling light that preserves the spatial structure from which it is reflected. Extramissionist theories of vision solved this problem by postulating visual rays originating in the eye and travelling in straight lines. This ensures each point in the scene is contacted by a single visual ray which allows the eye to be sensitive to the spatial structure of the scene. The price paid is the postulation of the existence of visual rays capable of extending to the most distant visible objects. The key contribution of ibn al-Haytham’s theory of vision was to put forward an intromissionist theory that allowed the eye to capture spatial structure by rejecting all of the rays reaching it except those perpendicular to the surface of the lens. Although the mechanism for this rejection was somewhat obscure, it allowed a point-to-point correspondence between locations in the scene and locations in the sensitive part of the eye (the lens for ibn al-Haytham) and thus provided a mechanism for spatial vision. Kepler’s contribution was to recognize that refraction at the cornea and lens had the effect of focusing all of the light originating in a single location in the scene on a specific point on the retina, producing the necessary point-to-point correspondence via a plausible mechanism. In its outlines, Kepler’s theory matches our current understanding of the optics of the eye. In its optics, the vertebrate eye is essentially similar to a camera (or perhaps a camera is essentially similar to an eye). It’s a bad camera in some respects, particularly in its inability to bring light from both ends of the spectrum into focus on the retina at the same time (the eye has a high degree of chromatic aberration). It’s like a modern digital camera in that the image that is formed by the optics is then sampled by an array of discrete receptors that then produce signals that make information about light intensity available for further processing. The point of image formation in both eyes and digital cameras is not to make 3 

For a relatively accessible treatment of this history, see Lindberg (1976). There are alternatives here. One is to imagine an eye with a very small pupil scanning the scene one small region at a time. There are other more complicated possibilities as well. Since human vision (and vertebrate vision more generally) does not implement these possibilities they will be ignored here. 4 

Vision   261 an image available for viewing but rather to allow measurement of the spatial structure of the light reflected off a scene. Image formation in both cases is the end of the optical part of vision,5 but only the beginning of another set of processes that involve detecting and transforming the information made available by the image.

3  Vision in the brain The retina and LGN The retina The retina is a complicated structure that contains neurons of several different kinds as well as a great deal of machinery that supports and interacts with the neurons. The retina contains two fundamentally different types of photoreceptors that contribute to vision known as rods and cones.6 The rods are very sensitive to light but are unable to signal differences in intensity at higher light levels. They primarily serve night vision although they do contribute to vision at the intermediate light levels found at twilight and in many indoor artificially lit areas. Rods are sufficiently sensitive, as is the neural processing in the retina, that under the right conditions, absorption of a single photon by a rod can produce a noticeable visual response. The cones don’t contribute to vision at low light levels but, in contrast to the rods, continue to provide a differential response as light intensity increases up to the point at which they are damaged. The cones are the primary input to vision at higher light levels. In the human eye, the cones are further subdivided into three types that are characterized by their differences in spectral sensitivity, how responsive they are to light of different wavelengths. One cone type, the S-cones, has its peak sensitivity at the short wavelength end of the spectrum and its response is essentially zero in the middle and long wavelengths. The other two cone types (M-cones and L-cones) have closely spaced peak sensitivities near the middle of the spectrum. By sampling the retinal image with three spectrally different photoreceptor types, the visual system acquires information about the spectral power distribution of the light falling on it and not just its intensity. This information is used, not only for colour vision, but also for various other aspects of vision. The distribution of photoreceptor types across the retina varies in systematic ways that affect how we see. The centre of the retina (the fovea) contains several specializations for

5 

The retina itself is optically active and since light must transit the retina (including the bulk of the photoreceptor itself) before being absorbed and initiating the physiological process of vision, image formation is not really the last step in which the optics are relevant. In addition, many nocturnal animals have eyes that contain a reflecting layer behind the retina so that light passes through it twice to increase the chance of absorption, adding another optical step to the process. 6  The names derive from the characteristic shape of the outer segments of the two types of photore­ ceptors, the part that contains the pigments that interact with light to initiate visual processing. The human retina, as is characteristic of mammals, has a very simple structure as compared to the retinae of many non-mammalian vertebrates. Other vertebrates have retinae with a wider variety of photoreceptor types and other specialized features that are lacking in mammals. I will be focusing exclusively on the human eye, which is a pretty standard eye for an old world primate.

262   David R. Hilbert high-resolution spatial vision. There are no rods in the fovea and the cones are more tightly packed than in the peripheral retina.7 Blood vessels and the cell bodies of retinal neurons through which the light would otherwise have to pass to reach the photoreceptors are shunted to the side. In the very centre of the fovea, there are no S-cones, exclusively L- and M-cones. The effect on vision is that we can resolve much finer spatial detail centrally than peripherally and, although it is rarely evident, we are all yellow-blue colour blind to small, centrally presented stimuli. S-cones are very much less common than L- and M-cones throughout the retina, which contributes to poor spatial resolution for short-wavelength stimuli. This also has the effect of mitigating the eye’s substantial chromatic aberration since, although a sharp image in the middle to long wavelengths will be blurred in the short wavelengths, the eye has such coarse resolution at the short wavelengths that the blur at those wavelengths is less visually significant. The process of vision is initiated by the absorption of photons by the photopigments within the photoreceptors. Although the relative sensitivity of the photoreceptors to light of different wavelengths is fixed, the absolute sensitivity of the photoreceptors dynamically adjusts to the light level. This adaptation allows the cones to provide usable signals at the very wide range of light intensities that we encounter as we move about the environment. One consequence of this is that the cone outputs provide relatively little information about the absolute intensity of the light stimulating them. The darkest areas of a scene lit by direct daylight are comparable in absolute intensity to the brightest areas of a scene viewed under typical reading light even after correcting for the change in pupil size. In what will shortly become a central theme, the cone responses provide more information about differences or changes in light intensity than they do about absolute intensity. Processing of visual information begins within the retina itself and the output neurons of the retina, the ganglion cells, which communicate with other parts of the brain, have very different response properties from the photoreceptors themselves. Ganglion cells receive inputs (indirectly) from multiple photoreceptors and typically have centre-surround receptive fields in which they are excited (inhibited) by light in the centre of the receptive field and inhibited (excited) by light in the periphery of the receptive field. The centre and periphery can also differ in their sensitivity to light of different wavelengths. One result of this is that ganglion cells are more sensitive to contrast than to absolute intensity. They respond poorly to uniform light and much more strongly when there is an appropriate contrast between the light falling into different parts of the receptive field. Because of adaptation at both the level of the photoreceptors and at the ganglion cell level (and the neurons connecting the two), ganglion cells respond better to changes in the light reaching their receptive fields than to unvarying light. Like the photoreceptor density, the size of the receptive fields of retinal ganglion cells varies systematically from centre to periphery. Receptive field sizes are very small in the fovea, with the centre response driven by a single photoreceptor in many cases, and increase towards the periphery. These features combine with the photoreceptor spacing to result in much higher spatial resolution in the centre of the visual field than towards the edge.

7  One consequence of the lack of rods in the central fovea is that night vision is very poor in central vision. To see an object in the dark it is best to look to one side of it.

Vision   263 This arrangement has consequences for how we see. Since the highest resolution area of the retina covers only about 1º of visual angle (a little smaller than a typical thumbnail viewed at arm’s length) and the entire fovea covers only a little over 5º of visual angle, the part of the scene for which we have high spatial resolution at any given time is quite small. To acquire high-resolution information about our environment, we move our eyes in a series of jumps (called saccades) and we move our head and body with larger motions. Rather than acquiring a high-resolution image all at once in the manner of a camera, we sample the structured light in bits and pieces. The sequence of saccades is not random and especially interesting parts of scene are typically sampled repeatedly. Vision, in this sense, involves active exploration of our environment, rather than passive reception. It also means that for human beings the direction of gaze is very informative about what is being attended to, a fact that plays an important role in social interactions. Retinal processing also begins a tendency towards specialization that continues through later stages of the visual system. The most important is the subdivision of retinal ganglion cells into two separate processing streams known as the parvocellular and magnocellular streams. Very roughly, the parvocellular (P) stream carries information about sustained, high spatial resolution aspects of the retinal image and it is also the principal carrier of chromatic information. The magnocellular (M) system is responsive to rapidly changing stimuli, has lower spatial resolution, and is relatively insensitive to chromatic information. These two pathways are driven by the M- and L-cone outputs and the S-cone signal is carried by a separate pathway that primarily contributes to chromatic processing. The axons from the ganglion cells collectively make up the optic nerve and most of them project to a mid-brain area in the thalamus. They exit the eye at a single point which, consequently, contains no photoreceptors. Each eye, thus, contains a blind spot, and there is a corresponding region of space about which no visual information is obtained. The blind spots are both located peripherally from the centre of vision so the blind spots from the two eyes do not capture information from the same region of space and the entire binocular field of view has coverage from at least one eye. It is thus not surprising that the blind spots are not noticeable with binocular vision. More surprisingly, even when looking at a scene with one eye closed it is not apparent that there is an area of the scene the light from which is not sampled by the eye. The blind spot is roughly comparable in size to the fovea so an object as large as a thumb nail at arms length fits comfortably within it. In a static display it is very difficult to detect the blind spot and it is only the surprising disappearance of objects as they move in and out of the blind spot that reveals its existence. Our lack of awareness of the existence of the blind spot is often explained by appeal to the visual system filling in the missing information on the basis of the characteristics of the surrounding scene although this interpretation is controversial.

Stereoscopic vision Human beings, like other primates, have two forward-facing eyes with substantial overlap in their field of view. The motion of the two eyes is coordinated so that they both fixate on a single object or point in space. Since the eyes have slightly different points of view, the position in the two retinal images of objects that differ in depth from the fixated object will differ slightly. The human visual system is exceptionally sensitive to these

264   David R. Hilbert slight differences, known as disparities, and uses disparity in performance of a number of visual tasks.8 Famously, disparity is a source of information about the distance (relative to the fixation point) of objects. Although the basic idea can be found in Ptolemy (and, once again, was clearly worked out by Kepler) it has had difficulty attracting consistent attention from philosophers. The two-dimensional nature of visual experience and its associated elliptical-appearing coins and the like has been a main stay of philosophical discussions of perception throughout the modern era. Setting aside the 150  years of psychophysical investigation, there is now abundant evidence from invasive studies in monkeys and non-invasive imaging in both monkeys and humans that disparity plays an important role in early vision. Not only depth, but also slant and aspects of shape and motion make use of disparity inputs as does control of eye movements. The overlapping fields of view that enable stereoscopic vision limit the total field of view for human beings to about 200º (with the two eyes overlapping for about the central 120º). Many other mammals, e.g. horses and rabbits, have much more panoramic visual systems and their field of view can be nearly a full 360º. As a consequence, human vision is much more active and the limited field of view, like the specialization of the central retina, leads to eye, head, and body movements being an integral part of the process of vision. Although the difference between the images in the two eyes provides important information about the scene, it also leads to a problem. The differences in the two images would seem to imply that we see two different scenes simultaneously. The correct description of what we see in cases of binocular vision is not, however, completely clear. For objects that are at depths similar to the fixation point it is clear that we fuse the information from the two images and experience a single object that reflects information from both eyes. For objects that differ significantly in depth from the fixation point fusion is not possible. It seems that in some circumstances we are aware of a doubleness in vision but in other circumstances the spatial information from one of the eyes is suppressed and what we see reflects the location of the object as seen by one of the eyes. If you point to a distant object with a finger and then alternately close one eye and then the other you will typically discover that the pointing is accurate with one of the eyes and not the other. Precise description of the phenomenology of stereoscopic vision is complicated and much more uncertain than philosophical discussions typically assume. It is also important to keep in mind that binocular stereopsis is just one of many processes that contribute to experienced depth and the relative importance of the numerous cues to depth relied on by the visual system varies with the scene and the task.

Cortical processes From the retina, the main pathway supporting vision proceeds to the primary visual cortex (V1) by way of the dorsal lateral geniculate nucleus of the thalamus (LGN). Although about 90 per cent of the fibres in the optic nerve follow this pathway, the optic nerve is so 8  The visual system is capable of making use of disparity differences smaller than the spacing between individual receptors. As in its basic resolution, the retina is not uniform in its sensitivity to disparity with the human visual system being much more sensitive to small horizontal displacements than to small vertical ones.

Vision   265 massive (about a million fibres) that the minority that follow other paths are comparable in number to the entire acoustic nerve. Although we will focus on the main pathway it’s important to keep in mind that there is significant flow of information along other pathways. Although we will also follow tradition in focusing on the flow of information from periphery to more central areas it’s also important to keep in mind that the back projection from cortex to the thalamus is comparable in size to the forward projection (Farah 2000 provides a useful overview of the neuroscience of vision).

Early vision Neurons in V1 respond in ways that show that they are tuned to moderately complicated features of the visual stimulus. Most cells are sensitive to stimulus orientation in the sense that they respond better to elongated stimuli at some orientations as opposed to others. There are also cells that respond to binocular disparity and other cells that respond to wavelength differences across their receptive field. These cells are arranged in systematic ways with, for example, preferred orientation changing systematically in some regions. Although the response properties of the cells found in early visual areas provide the basis of all of our visual abilities, their properties do not align in any simple way with what we see. Although we can see the orientation of the objects in a scene and this ability derives from the orientation information extracted by cells in early vision, those cells invariably are sensitive not only to orientation but also to other stimulus features like contrast or luminance. Although there are cells that respond to the wavelength differences that underlie colour vision they are also sensitive to the spatial structure of the stimulus. The lack of correlation between the features of objects we see and the properties of neurons in early vision goes the other way as well. Cells that respond to wavelength differences contribute to spatial vision as well as colour vision. Cells that respond to motion contribute to the perception of spatial structure as well as to motion itself.

Two pathways After V1 (and two other early visual areas) the flow of visual information splits into two anatomically separate but interacting streams. One, known as the ventral stream, proceeds along the bottom of the cortex and ultimately involves areas that are, among other things, involved in tasks like object recognition and face recognition. The other, known as the dorsal stream, proceeds upward towards the top of the cortex and contains a number of areas involved in various spatial tasks. The two pathways are anatomically distinct and there are differences between them in the types of stimulus features the neurons in the two pathways respond to, but the functional characterization of the two streams is still a matter of controversy. The early proposal that the two streams represent a functional separation between what (colour, face, object category) and where (spatial location) has largely fallen out of favour. An interesting and influential proposal that has dominated discussion more recently involves a separation between processing visual information for conscious perception and processing for motor control. According to this hypothesis, activity in the ventral stream gives rise to conscious perceptual experience and with that accessibility of visual information to planning and memory. The dorsal stream is used instead for guidance of bodily motion and the information present in the dorsal stream is not ordinarily

266   David R. Hilbert available for conscious perception. This hypothesis has given rise to an enormous literature with the early papers laying out the hypothesis having thousands of citations each. In spite of the sizeable body of research, it’s still a matter of controversy whether the idea that vision for action is separate from vision for perception is correct and the hypothesis itself is vague in important details.

Neuropsychology of vision The empirical study of vision until very recently has primarily relied on three sources of data: psychophysical studies of human beings, primarily college students in the developed world; anatomical and invasive physiological studies of non-human animals, especially the macaque; and neuropsychological studies of humans that have impaired vision as a result of damage to the brain, primarily the cortex. Since psychophysical research involves analysing human behaviour in response to systematic variation in stimuli, it provides useful data about how human beings perform visual tasks and can provide evidence about the mechanisms that underlie that performance. Since the mechanisms of vision are complicated and psychophysics provides data only on how visual inputs are related to behavioural output, there are many questions about visual processing that are difficult to address using psychophysical techniques. Some of these gaps can be supplemented using the results of invasive studies on monkeys. The macaque visual system is similar to the human one in many respects and the possibility of inserting electrodes to measure neural activity in an awake, behaving animal has produced most of the data relevant to the response properties of individual neurons in the cortex. These physiological measurements can be supplemented with anatomical data to provide much of what is known about the features of the various visual areas, their connectivity, and their function. Macaques are not, however, human and it can be difficult to relate the macaque data to the human data. Neuropsychological studies have provided important and fascinating additional information about the way in which visual information is processed in human beings that helps to relate human behaviour and anatomy. More recently, the advent of non-invasive functional imaging techniques (primarily fMRI) has led to a new source of constraints on hypotheses about human visual processing. Damage to the visual areas of the cortex can produce an enormously wide variety of effects ranging from complete blindness to surprisingly narrow impairment in specific visual abilities. The field is much too broad to adequately survey here so I will focus my discussion on briefly characterizing a handful of neuropsychological results either because they have drawn philosophical attention or because they highlight interesting features of the organization of visual processing. The methodology involved in drawing conclusions about visual processing on the basis of the behaviour of individuals with brain damage is itself an interesting subject which I will largely ignore. Damage to V1 can result in blindness in an area of the visual field with the size and location of the blind area (scotoma) depending on the size and location of the lesion. For example, complete (or nearly complete) destruction of V1 on the left side of the cortex will result in a right homonymous hemianopsia in which visual sensitivity is lacking to the right side of space for both eyes. Less extensive damage will result in a less extensive scotoma, and because the centre of the visual field is overrepresented in V1 it’s most common for the

Vision   267 scotoma to affect peripheral vision with central vision spared. This relation between damage to V1 and (nearly) complete loss of visual function to a region of space helps to confirm the hypothesis that the main pathway for visual information passes through V1. V1 and its role in vision is probably best known to philosophers via its role in the much discussed phenomenon of blindsight. In blindsight, there is the spared ability to engage in visually guided behaviour in response to stimuli presented within a scotoma. From the physiological point of view this is interesting (and perhaps surprising) since it shows that visual information that does not follow the principal pathway from retina to V1 via the LGN can guide voluntary behaviour. The sometimes radical conclusions about the relation between visual information and consciousness that some philosophers have drawn are less clearly fully supported by the characteristics of actual people with blindsight. (A useful recent review can be found in Cowey 2010.) From the point of view of understanding normal visual processing, cases that present a pattern of sparing of some visual abilities accompanied with deficits in others are often the most informative. These kinds of cases have given rise to proposals to the effect that specific visual tasks are associated with specific anatomical areas and accompanying the anatomical specificity is some degree of functional modularity. For example, in prosopagnosia there can be profound impairment in the ability to visually recognize faces in spite of relatively normal performance on many other visual tasks. Strikingly, severe impairment in face recognition can be accompanied by much more normal performance in visually recognizing other types of objects. Often associated with prosopagnosia is central achromatopsia, in which there can be a complete loss in the ability to see colour without a comparable impairment in other visual abilities. In both of these cases, the evidence from the specific combinations of spared and impaired abilities in patients has given support to hypotheses that there are anatomically localized brain areas dedicated to the processing of colour and to facial recognition. How strong this support is has been a matter of considerable controversy, as has been the correct functional characterization of the type of processing involved. One notable feature of the literature on the neuropsychology of vision is the prominent role that a single subject can play in the literature. A man referred to in the literature as MS is the source of much of what is known about central achromatopsia. Even more famously, a woman known as DF, who suffered cortical damage as a result of carbon monoxide poisoning, provided most of the early data offered in support of the proposal that the dorsal and ventral streams are specialized for action and perception respectively. As a result of her injury DF suffered from a disorder known as visual form agnosia. Visual form agnosics display an almost complete inability to visually perceive spatial features of scenes including the size, shape, and orientation of objects. Perception of other simple visual attributes like brightness and colour is relatively spared. In the case of DF, even though she is unable to report or otherwise indicate the spatial features of the objects she is viewing, her bodily movements appear to rely on the availability of information about those spatial features she is unable to report on. DF’s vision has been intensively studied and she is the subject of a fascinating popular book (Goodale and Milner 2005). A different impairment, known as optic ataxia, provides a fascinating and informative contrast. In optic ataxia, relatively spared ability to describe spatial features of objects is combined with severe impairments in visually guided behaviour. The possibility of these two contrasting impairments resulting from different anatomical patterns of cortical damage is thought to provide important support for the two visual systems hypothesis.

268   David R. Hilbert

Modularity of vision The evidence is overwhelming that there is a great deal of specialized processing involved in how we see. Different cortical areas are specialized for processing different types of information and even within a single anatomical region there can be subpopulations of neurons that have response properties that suggest that they are involved in specific tasks. Results from neuropsychology show that what might have been thought to be tightly coupled visual abilities are dissociable, with the use of wavelength information for form vision spared in spite of the complete loss of colour vision and colour vision persisting in spite of severe impairment in form vision. Motion and position can be decoupled in normal subjects where illusions like the waterfall illusion show that it is possible to perceive motion without change in position. The upshot is a picture of vision in which various visual attributes are processed independently of each other and contribute independently to our ability to perform various tasks. Our visual experience and the visual information driving action and cognition will be assembled from these diverse sources in a way that can vary with the specific task being performed. Consistency of the outputs of the specialized areas would largely be a consequence of their all deriving their inputs from a common source. Although different visual areas do engage in specialized and partially independent processing of visual information, it is equally important to keep in mind that there are significant interactions between the specialized areas. Form plays an important role in colour processing, shading is used for form vision, and there are even intermodal interactions effects with auditory stimuli affecting vision and vice versa. There is also no reason to expect that the kinds of processing and outputs of specialized areas will necessarily coincide with folk or philosophical conceptions of the primitive components of vision. Various types of contrast seem to play a central role in visual processing but contrast as a primitive is not usually found in folk lists of visual attributes and is not a basic component of those philosophical theories that have been most important historically. Even when the processing seems to be devoted to a familiar category like faces, the evidence for exactly what stimulus features an area responds to is typically complicated and difficult to interpret. Vision is clearly modular in some sense but in ways that defy easy assimilation into any simple conception of modularity.

4  Philosophical issues of vision Until quite recently there was relatively little contact between philosophical discussions of vision and even the most basic facts about the visual system and visual processing.9 Consequently, discussions of vision were primarily focused on it as an example used to 9  I am setting aside, for current purposes, the surprisingly fertile interaction between the empirical study of vision and philosophy that can be found in a number of historical figures. Some notable examples include the influence of ibn al-Haytham’s theory of vision on Roger Bacon and the central role of a serious engagement with early modern theories of depth perception in the development of Berkeley’s philosophy. Descartes, like Berkeley, was a contributor both to the empirical study of vision and also to its philosophical understanding.

Vision   269 illuminate very general questions in the philosophy of perception. Questions such as the nature of the immediate objects of perception or the distinction between immediate and mediate perception itself have been discussed in large part using examples drawn from vision. Much of the language and many of the metaphors used in discussions of perception more generally are drawn from vision: e.g. the transparency of perception, the objects of perception. In spite of the centrality of vision in discussions of perception generally, I will focus in what follows on philosophical questions that have a more substantive connection with the nature of vision itself.

The objects of vision Perception has been taken by many philosophers to fundamentally involve awareness of objects in the world around us. This assumption is particularly natural in the case of vision since one fundamental feature of visual processing is the parsing of scenes into object and background. It’s much less clear that this is an apt description of the chemical senses and even in the case of hearing and touch it requires the introduction of objects that can be very different from the ‘moderate-sized specimens of dry goods’ that are the usual focus of philosophical discussion.10 But in the case of vision, it very often seems natural to describe what we see as familiar objects like apples or tables or human beings. Given this assumption, we can then ask as to the nature of the connection between these objects and us when they are (among) the objects that we see. One popular and plausible answer here is that that the seen object is among the causes of our visual experience. Theories of this type are most often motivated by appeals to common sense rather than vision science and the arguments typically rely on a steady diet of examples involving mirrors, hallucinogenic drugs, and science fiction. It may be that it is possible to motivate in this way the claim that a causal relationship is necessary if we are to see an object but it is much less clear that it is possible to state a sufficient condition for seeing in these terms.11 The problems here are manifold. Since vision is not local in the sense that only light reflected from an object influences perception of that object, the way in which an object is perceived (and whether it is perceived at all) can, and usually does, depend on the features of other parts of the scene. The object and its properties are causally relevant but the cause of any given visual experience is the entire visible area of the scene (perhaps extended in time as well as space). Any attempt to state a sufficient condition for seeing in purely causal terms will, of necessity, run into difficulty since the relations of causal dependency are so complex in vision. Changing the features of a part of the scene remote from the putative object can often cause significant changes in how that object is perceived. Although we see scenes as containing objects at locations, the perception of those objects at those locations depends on the entirety of the visual stimulus, not just the part that originates in the object of interest. Although there are potential solutions to these difficulties, often involving appeal to either content or action, it 10  Although as Austin (from whom the phrase is taken) points out many of the things that we take ourselves to see do not fit this description either (Austin 1962: 8). 11  Grice (1961) is often cited here although he is clearly far from the first to make such a claim. Grice pretty clearly only intended the causal condition as necessary. Jackson (1977) defends the causal thesis as both necessary and sufficient. Also useful here is Tye (1982) and for recent discussion, see Campbell (2002); Arstila and Pihlainen (2009).

270   David R. Hilbert is important to avoid overly simple pictures of the typical causal pathway involved in the genesis of a visual experience (or a visually guided response).

Visual experience When I look at the banana in the bowl there are many things that may be true of me. My eye is sampling the structured light at a particular location and there is resulting activity in the retina and the visual areas of the brain. It also may be the case that I see the banana and I may see that there is something yellow before me. I may believe that there is a banana in the bowl and I may believe that Rachel did not eat the last banana. Although these kinds of truths are often philosophically significant, there is an addition to this list that is often at the centre of philosophical discussions of perception in general and vision in particular. That extra element is that when I look at the banana I am undergoing a visual experience. Philosophical claims concerning vision are often framed as claims about the properties of visual experiences. Visual experiences are typically taken in such discussions as occupying a distinctive place in the process that begins with light sources and objects in the world and often ends with knowledge and belief. Sensory experience in general and visual experience in particular is usually taken to be the first conscious stage of the perceptual process. The phenomenology of vision is also usually taken to be determined by the properties of visual experience. For this reason, most philosophical discussions of vision take there to be an important distinction to be made between visual experience and its properties and other types of sensory experience on the one hand and non-sensory features like believing and hoping on the other. Exactly how to draw this distinction in either conceptual or operational terms is a matter of some controversy and more than a little obscurity (see Schwartz 1994: 84–124). The working assumption of many philosophical discussions is that introspection supplies a crucial and reliable source of information about some of the properties of visual experience but this assumption is often left largely unexamined. Given that what seems introspectively obvious to one philosopher often seems incompatible with the introspective evidence to another this is surely an assumption worth more attention than it often gets.12 Equally often neglected is the possibility that the philosophical methods for singling out visual experience fail to pick anything out at all. Although this assumption is often carried over, though differently formulated, into psychology it finds little support in what is known of the neurobiology of vision. Although the behaviour of neurons early in the visual pathway often depends pretty much exclusively on purely visual inputs, the later stages of visual processing are much less isolated from inputs from non-visual areas of the brain.

The structure and content of visual experience Assuming that there is a well-defined kind of mental state answering to the description of visual experience, we can raise the question of exactly what properties it has. Here I will focus on a particular subset of the properties of visual experience. One of the oldest 12  And the fact that psychologists found it useful to largely abandon introspective methods in the study of perception in the early twentieth century may contain a moral.

Vision   271 debates concerning vision is whether there is a relatively short list of properties that constitute the basic properties of visual experience. In its simplest form this holds that our visual experience is fully characterized using colour and position. Once the colour of each position in the visual field has been characterized there is nothing more to be said about the specifically visual component of our experience. Any other properties that we become aware of as a consequence involve the operation of other more cognitive, non-sensory, processes. Although there are good empirical reasons to enrich the characterization beyond this simple mosaic view to include other attributes (e.g. depth, shadow, texture, edges), the other side of this debate has been the claim that our visual experience requires for its characterization other less basic properties. This view is most often and most naturally developed as an attempt to characterize the content of visual experience (or alternatively the features of the objects of visual experience). For example, one common claim is that content of visual experience is better characterized in terms of possibilities for successful action than in terms of the simple, non-dispositional properties just discussed. This line of argument is inspired by the attractiveness of thinking of perception as designed for guiding action and the idea that the content of perceptual experience should be closely tied to this function. A separate line of thought involves the claim that visual experience can involve relations like that of cause and effect or can include as part of its content membership in abstract kinds like fruit or person.13 Here the motivation is less clear but the effect of these kinds of claims is to attempt to shift the line dividing what we know on the basis of vision alone and what requires inference. The arguments for this kind of view often revolve around claims concerning subtle phenomenology and are subject to the kinds of worries concerning the reliability of introspection already mentioned.

Vision and action We see in order to act. As long as our conception of action is broad enough it seems hardly possible to deny this truism. Recently some philosophers have argued that this is not merely a platitude but an important source of constraints on the content of visual experience. On this approach, the content of a type of visual experience is (partly) determined by what it enables us to do. Rather than vision representing an apple as having some physical size it represents it as graspable by the hand but not by the thumb and forefinger. Rather than representing an object as spherical, vision represents it as something that can be rolled. If the kind of action relevant to the content of visual experience is restricted to actions involving bodily movements then there are some obvious prima-facie problems with this line of thought. It’s not completely clear exactly what kind of action some visual attributes can be connected to in this way. There is no specific kind of action enabled by seeing that the cover of the book is predominantly blue. Even if we restrict ourselves to the colours of natural objects similar difficulties are apparent. There doesn’t seem to be any general type of action enabled by perceiving something as

13 

A very useful discussion of these issues can be found in Siegel (2010).

272   David R. Hilbert brown, for example. It may indicate that the grass will burn, that the apple is inedible, or that the meat is cooked. Depending on one’s desires there will be a variety of different actions to be taken with respect to these objects. Although there are potential replies to these worries it still seems that the tie between perception and behaviour is too tight on this kind of theory. Why can’t vision inform us about attributes of objects which are only indirectly relevant to behaviour and whose significance for behaviour is variable rather than fixed? This version of the idea that vision is tied to action also sits uncomfortably with the empirical hypothesis that there are separate visual pathways for conscious perception and motor control mentioned above. Graspability would be a property represented in the dorsal stream and not in the ventral stream tied to conscious perception, memory, and planning. A broader conception of action which focuses on epistemic action rather than overt behaviour allows for development of a theory of visual content that avoids most of the problems just mentioned. Here the idea that the content of vision should be tied to what vision enables us to do includes things we do like coming to know, reasoning, and inference. There is something odd about the idea that there are visual contents that play no role in our epistemic lives. This formulation also avoids the unmotivated assumption that every perceptual content must somehow be directly relevant to behaviour. There is still a remaining question about how to justify the claim that the epistemic effects of a visual state (partly) determine its content as opposed to the content being independently determined and then determining the epistemic effects. However these debates are concluded the relation between what we find out about the world visually and action and epistemology are interesting questions that are matters of continuing controversy.14

References Arstila, V. and Pihlainen, K. (2009). 'The causal theory of perception revisited'. Erkenntnis, 70, 397–417. Austin, J. L. (1962). Sense and Sensibilia. Oxford: Oxford University Press. Campbell, S. (2002). 'Causal analyses of seeing'. Erkenntnis, 56, 169–180. Cowey, A. (2010). 'The blindsight saga'. Experimental Brain Research, 200, 3–24. Farah, M. J. (2000). The Cognitive Neuroscience of Vision. Oxford: Blackwell. Goodale, M. A. and Milner, A. D. (2005). Sight Unseen. Oxford: Oxford University Press. Grice, H. P. (1961). 'The causal theory of perception'. Proceedings of the Aristotelian Society, Supplementary Volumes, 35, 121–152. Jackson, F. (1977). Perception: A representative theory. Cambridge: Cambridge University Press. Lindberg, D. C. (1976). Theories of Vision from al-Kindi to Kepler. Chicago:  University of Chicago Press. Matthen, M. (2007). Seeing, Doing, and Knowing. Oxford: Oxford University Press. Noë, A. (2004). Action in Perception. Cambridge, MA: MIT Press. O’Callaghan, C. (2007). Sounds: A Philosophical Theory. Oxford: Oxford University Press.

14  For an extended treatment, see Noë (2004). Matthen (2007) develops the extended conception of action.

Vision   273 O’Callaghan, C. (2008). 'Object perception: Vision and audition'. Philosophy Compass, 3(4), 803–829. Palmer, S. E. (1999). Vision Science: Photons to phenomenology. Cambridge, MA: MIT Press. Schwartz, R. (1994). Vision: Variations on some Berkeleian themes. Oxford: Blackwell. Siegel, S. (2010). The Contents of Visual Experience. New York: Oxford University Press. Tye, M. (1982). 'A causal analysis of seeing'. Philosophy and Phenomenological Research, 42, 311–325.

Chapter 15

Au dition Matthew Nudds

1  The problem of auditory perception The things we hear are varied. As well as hearing sounds of various kinds—music, the sound of a dog barking, or the squeaking of a rusty hinge—we can hear the things that make these sounds—a violin; the dog and its barking (something it does); the door opening (an event). In addition, we can hear speech: someone speaking, the sounds they make, and what they say. Despite this variety, there is a unity to auditory perception: all auditory perception involves the perception of sounds, and whatever we hear that is not a sound we hear by hearing the sound it makes. An account of auditory perception must give some account of what it is to hear sounds and explain how we hear the things that make these sounds. At any moment you might hear a number of different sounds. You can focus your attention on any one of them.1 When you do so you attend to something—a sound—that has a characteristic appearance. For example, the bird song outside might appear high-pitched and quiet; the buzzing of the computer lower in pitch and louder.2 The properties of sounds that determine their appearance are the acoustic properties of sounds; they are the properties in virtue of which sounds appear the same or different to each other. It is usually supposed that sounds can appear the same or different along three dimensions, corresponding to three kinds of acoustic property—loudness, timbre,3 and pitch. In switching your attention between different sounds—between the bird song and the buzzing—you switch your attention between individual things that instantiate different acoustic properties. Sounds 1  You can attend to the sources of sounds as well as to the sounds they make, and I discuss this further in section 4. In this section my focus is on the character of the things you attend to when you attend to sounds—rather than to the sources of sounds. 2  We do not always experience sounds in this way. We sometimes experience many sounds at the same time, in such a way that we cannot distinguish individual sounds. Such examples don’t undermine the claim that auditory experience is fundamentally of individual sounds, any more than the fact that in vision we cannot always distinguish individuals—as, for example, we can’t distinguish the individual bricks when we look at a brick wall from a distance—undermines the claim that our visual experience is fundamentally of individuals things. 3  Timbre is a rather poorly defined property—it is sometimes said to be the dimension along which sounds that are of the same pitch and loudness can appear different. For example, notes of the same pitch

Audition   275 appear to be individual things in which acoustic properties inhere.4 They do not appear to be properties of material objects in the way that, say, colours appear to be properties of material objects; nor do they appear to be parts of material objects.5 Sounds take time. Some may be very brief; others may go on for hours or days. Individual sounds change over time—the same sound may appear low in pitch at one time and high in pitch at another time—and the identity of a sound is not fixed by how it is at any time, but depends on the way it unfolds over time. So sounds occupy time in a way similar to the way events and processes occupy time. Sounds—the things that we can pick out and attend to in our auditory experience—appear to be individuals that instantiate acoustic properties and which unfold over time in an event- or process-like way.6 Hume claimed that, in reflecting on our perceptual experience, we ‘always suppose the very images presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other’ (Hume 1751: 118). Hume was making a claim about how our perceptual experience introspectively seems to us. In reflecting on my visual experience of the cup on my desk, it is the cup and its properties (its shape and colour) that seem present in my experience. So reflection on our visual experience reveals it as seeming to present the mind-independent objects and properties that we take ourselves to see. It seems that my visual experience could not be as it actually is were the cup and its properties not present. The same is not true of auditory experience. In reflecting on my auditory experience of a barking dog, it is the sound of the barking and its acoustic properties that seem present in my experience, rather than the dog and its properties. It seems that my experience could not be as it actually is were the sound not present, but could be as it actually is were the dog that I take to be making the sound not making it. So reflection on our auditory experience reveals it as seeming to present sounds and the properties of sounds, rather than the mind-independent objects making those sounds that we take ourselves to hear.7 The problem of auditory perception is to explain, given the character of auditory experience, how we perceive the things that make the sounds we hear. Berkeley’s answer was that, strictly speaking, we don’t hear those things: ‘when I hear a coach driving along the streets, all I immediately perceive is the sound; but from my past experience that such and such a sound is connected with a coach, I am said to “hear the coach”. Still, it is obvious that in played at the same loudness on a clarinet and on a trumpet appear different; this difference is due to their having a different timbre. I use ‘timbre’ as a name for an aspect of the way sounds appear. It might be suggested that timbre can be identified with a property of a sound wave or a vibration, for example, some aspect of its spectral composition. Such an identification would result from the discovery that there is an underlying physical property in virtue of which sounds are the same or different in timbre. The claim that sounds have timbre is independent of any such further discoveries. 4 

For an extended defence of this claim, see O’Callaghan (2007: ch. 2). Of course to say that sounds do not appear to be properties of, or parts of, material objects doesn’t mean that they are not; just that they don’t appear to be. Similarly to say that the appearance of sounds is determined by acoustic properties doesn’t mean that they don’t also have non-acoustic properties. 6  This gives us a reason to reject Kulvicki’s ‘stable property’ view of sounds (2008) according to which sounds are dispositions of objects to vibrate in response to stimulation. 7  Heidegger says: ‘We never really first perceive a throng of sensations, e.g., tones and noises, in the appearance of things . . . rather we hear the storm whistling in the chimney, we hear the three-motored plane, we hear the Mercedes in immediate distinction from the Volkswagen. Much closer to us than all sensations are the things themselves. We hear the door shut in the house and never hear acoustical sensations or even mere sounds’ (Heidegger 1935: 151–152). He goes on to say that ‘in order to hear a bare sound we have to listen away from things, divert our ears from them, i.e. listen abstractly’ (152). We should 5 

276   Matthew Nudds truth and strictness nothing can be heard but the sound, and the coach in that example is not properly perceived by sense but only suggested from experience’ (Berkeley 1713/1996, First Dialogue). Was Berkeley right to claim this?

2  The epistemic account We can draw a distinction between perceiving a particular object or property, and perceiving a fact about that object. I can see the cat—a particular object—and I can see that the cat is black—a fact about the cat. To perceive a fact is to be in a position to know that fact on the basis of what is perceived. It is possible to perceive a fact about an object by perceiving some other object, as when I see that the battery in my phone is flat without seeing the battery, by seeing the flat battery indicator.8 Applied to auditory perception, we might say that hearing the sounds made by a dog barking puts me in a position to know facts about the dog. For example, I can recognize the sound as the kind of sound made by a dog barking, so can come to know that there is a dog barking, and so can be said to ‘hear the dog’, that is, hear that there is a dog, by hearing the sounds it makes. The dog itself is not an object of perception, so Berkeley is right that ‘in truth and strictness’ I don’t perceive the dog, I perceive that there is a dog. As a general account of hearing the sources of sounds this is inadequate. On occasions on which I can hear that the dog is barking, we can distinguish between those on which I can hear the dog and those on which I cannot hear the dog. Suppose I hear that the dog is barking in virtue of hearing the sound of the dog barking. In that case, I can hear the dog. Suppose I hear that the dog is barking in virtue of hearing the baby crying (and knowing that the baby cries only when the dog barks) without hearing any sound made by the dog. In that case I cannot hear the dog. In both cases hearing a sound puts me in a position to know that the dog is barking, but in the former case I hear that the dog is barking by hearing the dog’s barking. If that’s right, then hearing the sound of the dog’s barking puts me in a position to hear the dog in a way that doesn’t simply consist in being in a position to know some fact about the dog by hearing a sound.

3  The deferred demonstrative account We can refer in talk and thought to something that we cannot directly perceive by exploiting its relation to something that we can directly perceive. Pointing at a set of footprints,

understand Heidegger’s claim that we ‘never first perceive a throng of sensations’ as a claim about auditory attention—that in many cases we attend to the things that make sounds rather than the sounds themselves. That is consistent with the claim that it introspectively seems that my auditory experience could not be as it actually is were the sounds not present, but could be as it actually is were the things that I take to be making the sounds not making them. 8 

Dretske calls this a form of indirect perception: ‘Perception is indirect when one sees a fact by seeing objects other than those constitutive of the fact—objects that indicate, by their properties or behaviour, the fact in question’ (Dretske 2010: 56).

Audition   277 I might say ‘that man must be a giant’. What I say is true just in case the man who made those footprints is a giant. Hearing the sound made by a dog puts me in a position to think deferred demonstrative thoughts about the dog. It might be suggested that hearing the dog just is being in a position to think deferred demonstrative thoughts about it on the basis of hearing the sounds it makes. What this suggestion amounts to will depend on what account we give of deferred demonstrative reference. Evans suggested that ‘that man’, said whilst pointing at a footprint, functions as a descriptive phrase along the lines of ‘the man whose foot made that footprint’.9 Applied to hearing, the suggestion would be that hearing the sound made by a dog puts me in a position to think ‘that’s a dog’.10 My thought is equivalent to ‘the thing that is making that sound is a dog’. It is a thought about whatever is making the sound, and is true just in case that thing is a dog. There is an obvious problem with this suggestion. In hearing the sound made by the dog I might think ‘that dog might have been fierce’. Prima facie, my thought is about a particular dog, that it might have been fierce; but, according to the suggestion, my thought is about how the sound might have been, that it might have been made by a fierce dog. So my thought about the dog, on the basis of hearing its bark, is not equivalent to the descriptive phrase. This problem is a problem with deferred demonstrative reference generally.11 One solution would be to treat the descriptive component as rigid, along the lines of ‘the thing that is actually making that sound, whatever it is, is a dog’.12 There may be other better solutions,13 but there is a more serious problem with the deferred demonstrative account. There certainly are contexts in which we are prepared to say that someone hears what makes a sound simply in virtue of hearing a sound that it makes, in the way described by the deferred demonstrative account. We are prepared to say, for example, of a record being played on a stereo, that we hear ‘that record’. But hearing the things that make sounds cannot generally be explained in that way. One way to bring this out is to draw a contrast between two kinds of case. Suppose that I hear a dog in virtue of hearing the sound of its barking, that is, I hear the barking sound and so am in a position to demonstratively think about the thing making that sound. In contrast, suppose that the sound of a dog barking is the ringtone for my phone. When my phone rings I hear the phone in virtue of hearing the barking sound that it 9 

He argues that in such cases ‘the identification is by description’ (1982: 199). hearing the sound made by a dog puts me in a position to think ‘that’s a dog’, it is not itself sufficient for me to think that: further background capacities are required. In particular, I must be able to recognize the sound as the sound made by a dog. I think the fact that the deferred demonstrative account of hearing a sound source requires recognition is problematic, but there is not space here for further discussion. 11  See Borg (2002). 12  This kind of view seems to be what Martin has in mind when he says: ‘In the case of audition, the primary objects of demonstrative identification are sounds, associated with phrases such as “that barking” or “that noise”. One may pick out the source of the sound via picking out the sound itself—we might then understand the demonstrative expression “that dog” as involving deferred ostension, perhaps as the descriptive phrase, “the dog which is actually the source of this sound” ’ (Martin 1997: 93). 13  In fact a ‘rigidified description’ approach is not adequate as an account of deferred demonstrative reference in general (Borg 2009). Someone determined to defend this view of auditory perception might argue that, whatever the correct account of deferred demonstratives, it can be applied to the case of hearing. 10  Although

278   Matthew Nudds makes, that is, I hear the barking sound and so am in a position to demonstratively think about the thing making that sound. The demonstrative account I have been considering treats these two cases in the same way: I hear the phone in just the same way that I hear the dog. But our intuitions are that the cases are different. The sound made by a dog’s barking seems naturally connected to the dog’s barking, it seems to ‘match’ or be appropriate to the barking, in a way that the sound when made by the phone is not.14 Made by the phone, the sound seems only arbitrarily connected to the phone; in fact, there seems to be something misleading or wrong about hearing that sound as made by my phone. It might be suggested that this sense of the sound being misleading is simply a consequence of the fact that I associate the kind of sound made by a dog barking with a dog and not with a telephone, and so am disposed to judge that whatever made the sound is a dog. This disposition would lead me to judge something false when the sound is made by the telephone, and that explains why hearing the sound made by the telephone seems misleading. There are two reasons for rejecting this suggestion. The first is that the sound seems misleading even when I know it is made by my telephone and I have no disposition to judge that it is made by a dog. The second is that mere association between a sound and what makes it, no matter how strong, is insufficient to explain the sense in which there is something non-arbitrary about the connection between hearing a sound and what produced it.

4  The representational account Part of what is involved in hearing the dog’s barking is that hearing the sound of its barking puts you in a position to hear it as a dog’s barking. The sound is not simply an effect of what made it, it is connected to what made it in such a way that it reveals or tells us something about the thing that made it. The reason the barking ringtone seems misleading is that what it seems to reveal or tell us is false. In a discussion of olfaction, Lycan suggests that olfactory experience has two kinds of content: ‘that smells represent adaptively significant environmental entities, and they also represent odors. In fact, they represent the environmental entities by representing odors. By smelling a certain familiar odor I also smell—veridically or not—a dog’ (Lycan 1996: 148). Whether or not this is true of olfaction, we can explain the relation between our experience of sounds and their sources by appealing to this kind of representational structure. It is plausible that our experiences of sounds represent adaptively significant sound sources as well as sounds,15 and that they represent sound sources by representing the sounds that they produce. If that’s right, we should think of auditory experience as having two kinds

14  My claim here is not a claim about recognition, but about something more fundamental. It could be that we come to recognize the phone on the basis of hearing the barking sound as well as, or better than, we can recognize the dog, but even were that the case there would be a difference between the way hearing the sound enables us to hear the dog and the way it puts us in a position to hear the phone. 15  By ‘adaptively significant sound sources’ I mean the sound sources that the auditory system evolved to perceive, and not, e.g., things that produce sounds by means of loudspeakers.

Audition   279 of content—as representing sounds and as representing the sources of sounds. So hearing a sound doesn’t simply put the perceiver in a position to think about the source of the sound, it involves an experience that represents the source as being some way. When the experience is veridical the perceiver hears the source as well as the sound. That would allow us to explain what is misleading about the sound of a dog barking when made by my telephone: in hearing the sound I have an experience that represents the barking of a dog; since there is no barking dog, the experience is non-veridical. In the rest of this chapter I spell out in more detail this representational account of auditory perception. I begin with the problem of explaining how auditory perception could represent sound sources. To understand that requires understanding, in outline at least, how sound sources produce sounds.

How sounds are produced Sounds are produced by anything that produces a suitable compression wave16 in an appropriate medium. Most commonly, sounds are produced by objects that have been caused to vibrate and whose vibration disturbs the surrounding air to produce a compression wave. Other kinds of events produce sounds too: the turbulent flow of air around an obstruction, or the sudden heating of air by a spark can produce compression waves in air, and we are familiar with the sounds—of the wind, of thunder, or the crackle of a spark—produced by these kinds of event. For the sake of simplicity I am going to consider only sounds produced by vibrating objects.17 We tend to conceive of vibrations as simple—as depicted by sine waves—but naturally occurring vibrations are never simple. For example, when a taut string is plucked it vibrates along its entire length with the maximum displacement occurring in the middle of the string. The wavelength of this vibration is twice the length of the string; its frequency18—the lowest frequency component of the string’s complex vibration—is known as the fundamental frequency of the vibration. The string also vibrates at three times the fundamental frequency, with a wavelength that corresponds to two-thirds the length of the string—imagine the string divided in three with each part vibrating—at five times the fundamental frequency—divide the string into five—and so on. These higher frequencies—the odd integer multiples of the fundamental frequency—are known as harmonics or partials of that fundamental. They correspond to the modes of 16  Since

it is possible to produce very high and very low frequency compression waves that are not detected by the ears, it is tempting to say that a compression wave must be produced that has a frequency within an audible frequency range. But that’s not quite true: because of the non-linearity of the transmission of high-frequency compression waves in air, an ultrasonic compression wave may produce an audible sound (see Westervelt 1963; Yang et al. 2005). The possibility of producing sounds in this way is a further reason to doubt the adequacy of the event view of sounds (discussed in section 4.1.1). 17 Sounds produced by vibrating objects are, arguably, fundamental to understanding auditory perception, and our experience of sounds produced in other ways can be explained in terms of our experience of such sounds. 18 The frequency with which the string vibrates is inversely proportional to the wavelength, and proportional to the velocity of the wave. The velocity of the wave depends on the tension of the string and its mass; changing the tension therefore changes the fundamental frequency of the vibration and the pitch of the sound produced.

280   Matthew Nudds vibration of the string, and it vibrates in all these modes simultaneously.19 Any complex vibration can be analysed into a number of simple harmonic frequency components. The vibration of an object can be analysed into frequency components corresponding to the object’s modes of vibration. We can think of the overall vibration of the string—or of any object—as the complex vibration that results from superimposing all its different modes of vibration.20 When an object is struck, the impact causes it to vibrate. Whereas a string vibrates in one dimension, objects vibrate in two or three dimensions. Objects therefore have many more possible modes of vibration than a string. Many things determine the character of an object’s vibration—the number and proportion of different frequency components and the way they change over time—including its physical properties. The size of an object will determine the lowest frequency at which it vibrates; its shape will determine the spectral composition of its vibration.21 The time it takes for the object to return to equilibrium is determined by how quickly it decays or loses energy (due to the internal friction of the object, and air resistance). Heavily damped vibrations decay rapidly, whereas lightly damped vibrations are prolonged. The speed and manner in which a vibration decays—damping may alter the spectral composition of the vibration over time—varies with the composition of the object.22 The nature of the event or process that causes the vibration also affects the character of the vibration. Whether the object was struck once or repeatedly, whether it was scraped or scratched, affects the time-course of the vibration. The force with which an object is struck affects the spectral composition as well as the amplitude of the resulting vibration (the relative intensity of the higher-frequency

19 

A plucked string will vibrate at a number of different frequencies, but not all of these frequencies will be present in equal amounts. Where along its length it is plucked will alter the harmonic structure of the overall vibration. If it is plucked in the middle, the first harmonic is strongly excited; however, the second mode of vibration vibrates around the centre point of the string, and is not excited. To excite the second mode, the string must be plucked off-centre at a position a quarter of the way from the end. Plucking in the middle excites the odd modes, and off-centre the even modes. So the relative harmonic structure of the vibration of the string will vary according to how it is plucked (and the resultant sound will vary—being ‘brighter’ or ‘stronger’). Plucked strings behave slightly differently to strings caused to vibrate by other means. For a detailed discussion, see Fletcher and Rossing (1998: sections 2.7–2.11). 20  Two sine waves can be combined to produce a complex waveform which is simply the result of summing the amplitudes of the two waves at each moment of time. Complex waveforms can be combined in the same way. Conversely, any complex waveform can be analysed into a number of component sine waves of various frequencies and amplitudes which, when added together in the correct phase, produce the analysed wave (this process of analysis is known as Fourier analysis. Details can be found in any textbook on vibrations (e.g. French 1971: chs 2 and 6). The complex compression wave that is detected by our ears instantiates a vibration that is equivalent to a set of phase related sine wave components of differing frequency and amplitude. Many psychoacoustic theories suppose that the auditory system must perform some equivalent of a Fourier analysis. 21  Differences in geometrical properties of objects affect the way that they vibrate, but they do so only in virtue of being correlated with the mechanical properties of those objects; it is likely that the auditory system detects or tracks mechanical rather than geometrical properties of objects. Further work needs to be done to discover which mechanical properties the auditory system detects or tracks. See Carello et al. (2005: 14 ff). 22  How much damping different materials produce very clearly affects the character of the sound an object makes when it is struck—for example, wood, which is heavily damped, makes a thunking sound, whereas metal, which is less damped, rings.

Audition   281 harmonics of a vibration typically increases when an object is struck with greater force).23 Finally, what, if any, parts of the object are held fixed or are touching other objects and surfaces, affects the character of its vibration by changing which modes of vibration are excited and how they are damped. Because the character of the object’s vibration is determined by the nature of the object and its interactions with other objects, the vibration embodies or carries information about the object and its interaction with other objects. When a vibrating object is immersed in a suitable medium, its vibration produces a compression wave in that medium. As this compression wave propagates through the medium it interacts with and is reflected by objects and surfaces in the environment, and the reflections propagate in turn. These reflections carry information about objects and obstructions in the environment, so the compression waves that reach the ears carry information about the environment, in addition to information about the objects that produce sounds. All this information is, in principle at least, recoverable.24

The event view of sounds An obvious question to ask is what the relation is between sounds and objects’ vibrations. I have described objects and vibrations as producing sounds, but a number of writers have defended the view that sounds are identical to, or supervene on, objects’ vibrations. Casati and Dokic, for example, defend an event view of sounds, according to which ‘sounds are monadic events happening to material objects. This means that sounds are located at their sources, and are identical with, or at least supervene on, the relevant physical processes in them’ (Casati and Dokic 2011: 98).25 O’Callaghan defends a similar view: ‘particular sounds are events . . . [they] are the events in which a medium is disturbed or changed or set into motion in a wave-like way by the motions of bodies. Events such as collisions and vibrations of objects cause the sound events’ (O’Callaghan 2007: 36). Both think sounds supervene on a vibratory event or process occurring in an object, but they differ as to whether sounds should be identified with that event or process, or with the event that is that vibratory event disturbing the medium, and so over whether the existence of sounds depends on the presence of a medium.26 In what follows that difference won’t matter. If the event view of sounds is correct, then it would be reasonable to suppose that an account of auditory perception should begin with an explanation of how we perceive 23 

See Chowning (1999: 270). How much information the auditory system can recover is an unresolved empirical question. For a useful survey of the relation between an object’s properties and the way it vibrates, see Lufti (2008). The information is, in principle, recoverable and, although relatively little systematic research has been done, it is evident that our auditory system can recover at least some of it: it is evident, that is, that we can perceive the sources of sounds and their properties. This was first emphasized by Gaver (1993a, 1993b). For a recent survey of much of this evidence, see Carello et al. (2005). The mechanisms involved in the perception of sound source location are relatively well understood (for a survey, see, e.g., Schnupp et al. 2011: ch. 5; Blauert 1997). There have been a number of studies that show that we can perceive spatial properties of the environment in which sounds are produced (e.g. Rosenblum et al. 2000; Rosenblum et al. 2005, 2007). 25  See also Casati and Dokic (2004, 2011). 26  It is a consequence of O’Callaghan’s view that sounds do not exist in a vacuum: a tuning fork struck in a vacuum vibrates, but makes no sound because there is no medium to be set in motion; Casati and Dokic think that striking the tuning fork makes a sound, but that in a vacuum the sound cannot be heard. 24 

282   Matthew Nudds sound events, and that an explanation of our perception of the sources of sounds should be in terms of the perception of those sound events. In fact, the direction of explanation goes the other way. It is not possible to explain how we perceive sounds other than in terms of our perception of the sources of sounds.

Sound events and sound-producing events If you simultaneously scratch and tap a reverberant rough surface such as the aluminium cover of a laptop, you will hear two sounds: the scratching sound, which lasts as long as your scratching, and the almost instantaneous sound of the tap. If the tap occurs half way through the scratching, then you will hear the sound of the tap at the same time as you hear the sound of the scratching. The two sounds are produced simultaneously by a single object (the lid of the laptop). If you tap a reverberant object, such as a metal lampshade, twice in quick succession you will hear two successive sounds. Tapping the shade produces a ‘ringing’ sound that begins almost instantaneously and then fades away gradually (but still quite quickly). If the taps are close enough together, you will hear the second sound begin before the first sound has quite faded away. The two successive (but overlapping) sounds are produced by a single object (the lampshade). In reflecting on these examples we should be careful to distinguish the putative sound events (the events that the event view says are identical to sounds) from the events that cause them. The tap on the lampshade is a brief, almost instantaneous, event; that tap causes the lampshade to ‘ring’—to vibrate—for several seconds; the sound we hear begins with the tap, but lasts as long as the vibration—the ‘ringing’—lasts. The tap on the lampshade is not the putative sound event; it causes the sound event—the ‘ringing’ vibration of the shade. The scratching and the tapping on the laptop cause the lid to vibrate; that vibration dies away almost instantaneously, but the sounds we hear result from the vibration of the lid caused by the scratching and tapping. The tapping and scratching events are not the putative sound events; they are events that cause the putative sound events. We can call such causing events ‘sound-producing events’. In both of the examples we hear two sounds. According to the event view, we perceive two sound events occurring in the object (or setting the medium into motion). How might these events be individuated, that is, what makes it the case that the objects each instantiate two vibratory events, rather than a single event (or more than two events)? When an object makes a sound, the object goes from a state of equilibrium; it vibrates for a period of time; and eventually it returns to a state of equilibrium. So there is a vibratory event or process that begins when the object goes from a state of equilibrium and ends when the object returns to a state of equilibrium. This event can be individuated relative to the object to which it occurs: it is the event that consists in the object undergoing a vibratory process. The two examples show that putative sound events cannot be understood in this way. In the first example, the object goes from a state of equilibrium when it is scratched and returns to a state of equilibrium only after the scratching has stopped. The tap occurs during this time, when the object is already vibrating. If the sound-event is the event that begins when the object goes from a state of equilibrium and ends when the object returns to a state of equilibrium then the object undergoes a single vibratory event that comprises

Audition   283 both the scratching and the tapping. In the second example, the second tap occurs before the ringing produced by the first tap has died away. So the object goes from a state of equilibrium when it is first tapped and returns to a state of equilibrium only after the ringing produced by the second tap has died away. So, again, if the sound-event is the event that begins when the object goes from a state of equilibrium and ends when the object returns to a state of equilibrium, then the object undergoes a single vibratory event that comprises both taps. Since in both cases we hear two sounds, the sounds we hear are not identical with vibratory events individuated in this way. Can we say that the objects instantiate two vibratory events because they instantiate two vibrations—that we can individuate two vibrations qua vibrations? I described how a vibrating object has many modes of vibration. There is no intrinsic connection between these different modes other than that they are modes of vibration of the same object.27 That means that we can represent the object’s vibration as the complex vibration produced by the superimposition of the frequency components corresponding to all of its excited modes of vibration, or we can equally well represent it simply as a list of individual frequency components corresponding to each mode, or as some combination of components. The difference is just a difference in the way we represent the ways in which the object is vibrating. There is no physical basis for grouping frequency components, considered as such, in one way rather than another, and so no physical basis for individuating two vibrations instantiated by the object, rather than a single complex vibration or many individual modes of vibration. We can’t individuate sound events in terms of objects’ vibrations or in terms of vibrations as such; but we can individuate sound events in terms of what caused or excited the different modes of vibration of an object. In both examples the modes of vibration were caused or excited by one or other of the two sound-producing events. We can pick out modes of vibration according to which of the sound-producing events caused them, and can individuate two complex vibrations made up of the frequency components corresponding to the modes picked out in this way. That gives us a way—in fact, the only way—of individuating two vibrations, and hence two putative sound events, instantiated by the objects. If that’s right then two things follow. The first is that there can be no way of saying what sounds there are other than in terms of what produced them,28 and hence no account of our perception of sounds that is independent of an account of our perception of sound-producing events. The second is that an account of auditory perception needs to explain how the auditory system can track sound-producing events in a way that doesn’t depend on tracking sounds. In the following sections I provide such an explanation and show how it supports the representational account of auditory perception.

27  If a vibrating string is touched, the modes of vibration for which the point of touching is a node will continue unaffected whilst those for which it is an anti-node will be damped (French 1971: 167); in principle one can change the amplitude of any one mode without affecting the others; this demonstrates that modes of vibration are independent of one another (French 1971: 196). There may, however, be non-linearities in the movement of parts of an object so that the different modes of vibration are not strictly independent of each other, but that won’t help solve the individuation problem. 28  Or what would normally produce them: there may be cases of hearing a sound that was not in fact produced by a sound-producing event. I discuss such cases below.

284   Matthew Nudds

Transmission and detection If you are in proximity to a vibrating object the compression wave it produces will affect your ears. The ears function to capture and filter29 the compression wave, and to detect the different frequency components that compose it.30 The output of each ear is a state31 that encodes time-varying information about each of the frequency components that make up the vibration instantiated by the compression wave that reaches the cochlea or inner ear. The proximal state that encodes this signal serves as the input to subsequent auditory processing. Although the output of each ear is a proximal state that encodes the detected pattern of frequency components over time, what we hear are individual sounds and their sources. That means the auditory system must transform the proximal state into a representation of putative sound events and their causes. Doing that involves solving what is, in effect, an auditory under-determination problem. The compression wave that reaches our ears is normally produced by many different things—different sounds events—simultaneously producing sounds. The compression waves produced by these events interact with each other—in constructive or destructive ways, in ways that may obscure of mask frequency components—with surrounding objects, and with the medium, so that the compression wave that reaches and is detected by the ears is, at any moment, the result of the additive combination of the compression waves produced by all the putative sound events occurring in the immediate environment. Compression waves reflected (and re-reflected) by surrounding objects and surfaces reach the ears fractionally later in time than the original, and reflections of the early part of a compression wave may combine and interfere with later parts of that wave, so that the compression wave that reaches and is detected by the ears is temporally ‘smeared’. There is nothing intrinsic to a particular frequency component that marks it as having been produced by one sound event rather than another, and nothing intrinsic to each of a set of components that marks it as having been produced by a single sound event simultaneously with other components. There is no one-to-one mapping of the pattern of frequency components detected by the ears onto the sound events that produced them. That pattern is consistent with any number of different sound events: any number of different events could have produced the pattern of frequency components detected by the ears. How, then, does the auditory system work out what sound events actually produced the 29 

Parts of the ear function in a mechanical way to alter the sound wave. In particular, parts of the outer ear (or pinna) function to differentially reflect certain frequency components in such a way that the compression wave is selectively amplified and filtered. The filtering plays a role in sound source localization, particularly in determining the elevation of the source, and whether it came from in front of or behind the listener. The ear canal has characteristic resonances that, again, selectively filter the compression wave. See Rosowski (2010). 30  Having passed through the ear canal, the filtered compression wave passes into the cochlea, and causes the basilar membrane to vibrate. Different parts of the basilar membrane vibrate in response to different frequencies; its surface is covered with sensitive hairs, organized in such a way that different hairs move in response to different frequency components of the compression wave. The displacement of these hairs produces activity in associated neurons. For a survey, see Hackney and Furness (2010); a good introduction to the way the ear functions is Schnupp et al. (2011: ch. 3). 31  It would be more accurate, given the dynamic nature of this output, to characterize it as a process. It is common practice to refer to the stages in perceptual processing as states and for ease of exposition I will do the same.

Audition   285 frequency components it detects? It does so by working out what sound-producing events would best explain the pattern of frequency components detected by the ears.

Representing sound-producing events The auditory system transforms the pattern of frequency components encoded by the proximal state into a representation of sound-producing events and it does this by, in effect, making assumptions about the way the frequency components were produced and transmitted. For example, the vibration that is produced by a single sound-producing event—by the striking of an object, say—is made up of frequency components that will normally be related to each other in specific ways. The frequency components will share temporal properties, in particular they will start at the same time and be phase related; they will tend to change in similar ways over time, decaying steadily and at a similar rate; they will be harmonically related; new frequency components will not suddenly appear (and existing components will not suddenly disappear). It is unlikely (but not impossible) that frequency components produced by distinct sound-producing events will be related in these ways. Therefore, if frequency components detected by the auditory system are related in these ways, they are likely to result from a single sound-producing event. The auditory system can exploit this fact to determine what sound-producing events are occurring at any time: given the particular pattern of frequency components detected, the auditory system produces a representation of the sound-producing events that would best explain that pattern.32 If the frequency components were produced normally, then the best explanation will be correct, and the representation will be veridical. The frequency components of vibrations that result from a sequence of soundproducing events—from footsteps, for example—or from a temporally extended event or process—from a car engine, a dog barking, or a scratching—will be related to one another over time in characteristic ways. For example, a sequence of sound-producing events—such as footsteps—will produce frequency components with similar harmonic and temporal structures; and a temporally extended event or process—such as a scratching—will produce a vibration whose components will change in ways that are constrained by the nature of the event or process—they will not radically or suddenly change in their harmonic structure, for example. The auditory system can exploit these relationships amongst frequency components to determine how sound-producing events are related over time: given the pattern of frequency components detected over time, the auditory system produces a representation of the temporally extended sound-producing events, and sequences of sound-producing events, that would best explain that pattern. Again, if the frequency components were produced normally, the representation will be veridical. In some cases, the production of a representation of sound-producing events draws on knowledge of the properties of object or event that produced the sound. Such top-down processes are likely to be involved in the perception of many temporally structured events, 32  That the auditory system tends to treat components that share these features as having a single source has been experimentally demonstrated. My discussion here draws on Bregman (1990: esp. ch. 3), to which the reader should refer for details of the empirical support for the claims in the text. See also Schnupp et al. (2011: ch. 6).

286   Matthew Nudds including those involved in speech, and in the perception of familiar ‘meaningful’ sounds, such as the sound of a dog’s barking, of footsteps, of a car’s engine, and so on.33 The assumptions made by the auditory system about how the frequency components it detects were produced will, in normal circumstances, lead to veridical representation of the sound-producing events that in fact produced them. But sometimes the assumptions are false. In such cases, the representation of sound-producing events is non-veridical—a misrepresentation. For example, if two sound-producing events of the same kind involving the same kind of objects occur at exactly the same time, the resulting compression wave will have frequency components that stand in relationships to each other that normally only obtain between components that result from a single sound-producing event. The auditory system will assume that the frequency components were normally produced by a single sound-producing event, and so will (mis)represent the existence of a single event rather than two events. During the evolution of the auditory system, such errors are likely to have been rare. But with the advent of artificially reproduced and recorded sound, they have become commonplace. Stereo loudspeakers provide a familiar example of how the assumptions made by the auditory system can be false. Two loudspeakers—playing, for example, a recording of a drum being struck—produce a pattern of frequency components that stand in relationships to each other that would normally obtain only if they were produced by a sequence of sound-producing events involving a single object. The auditory system assumes that they were produced normally, and the resulting state (mis)represents the existence of a sequence of events—drum beats—involving a single object, when in fact the frequency components resulted from rather different events involving two distinct objects—two loudspeakers.34 The result is that we seem to hear a drum being struck. Stereo loudspeakers work because they produce a pattern of frequency components that would normally result from a number of different sound-producing events—from different musical instruments being struck, plucked, bowed, and so on. The auditory system assumes these frequency components were produced in the normal way and so (mis)represents the sound-producing events from which they would normally have resulted, rather than the events involving the loudspeakers that, in fact, produced them with the result that we seem to hear several different musical instruments being played.35

Representing sounds I have described how the auditory system transforms the pattern of frequency components it detects into a representation of sound-producing events. What is the connection 33  Bregman calls this kind of top-down process ‘schema-based segregation’ (1990: 395 ff., 665 ff.); it contrasts with what Bregman calls ‘primitive stream segregation’ (1990: 38 ff.) which is bottom-up and exploits invariable properties of the subject’s environment. 34  One of the most striking features of stereo loudspeakers is that the sounds they produce seem to come from locations in space at which there is no sound source. There is disagreement about how this phenomenon should be interpreted and what its significance is for the nature of sounds (for opposing views see, O’Callaghan 2007: ch. 3 and Nudds 2009). This disagreement turns on what account should be given of the spatial content of auditory experience. For a survey of empirical work relevant to such an account, see Blauert (1997). 35  Musical instruments playing together can produce similar kinds of misrepresentation or illusion. See Ball (2010) for examples of how composers have exploited this fact in producing musical works.

Audition   287 between this representation of sound-producing events and the sounds we experience? In transforming a detected pattern of frequency components into a representation of sound-producing events, the auditory system determines what sound producing events are likely to be responsible for those frequency components. In doing this it ‘allocates’ the frequency components it detects to these different events. If, for example, the auditory system produces a representation of two sound-producing events it allocates all the frequency components it detects to one or other of these events, and if it allocates a component to one event it cannot allocate it to the other. This makes good ecological sense. There must be some event that is responsible for each of the frequency components detected by the ears; so any representation of purported sound-producing events will be incorrect if the events represented cannot explain all the frequency components detected. One way to think about the transformation of the pattern of frequency components into a representation of sound-producing events is as a process that works out how best to allocate frequency components to sound-producing events: how many events are required in order to explain all the detected frequency components, where the explanation is constrained by the requirement that components allocated to the same event should be related to one another in ways that make it likely that they were produced by that event. Our experience of sounds is the result of the way frequency components are allocated to sound-producing events. How many sounds we experience is determined by how many sound-producing events the detected frequency components are allocated to; how those sounds appear is determined (at least in part) by the particular combination of frequency components allocated to each sound-producing event. For example, if all the frequency components detected by the auditory system are allocated to a single sound-producing event, then we experience a sound corresponding to that sound-producing event. The appearance of the sound is (at least partly) determined by the frequency components allocated to that source. If those same frequency components were allocated to two sound producing events,36 then we would experience two sounds corresponding to the two sound-producing events. The appearance of each sound would be different to the appearance of the single sound because each sound would result from a different combination of frequency components. The transformation that produces a representation of sound-producing events therefore results in an experience of sounds corresponding to the represented sound-producing events. The evidence for this is empirical. By manipulating the properties of frequency components we can manipulate the way they are transformed by the auditory system to produce representations of different sound-producing events, and so change the number and character of the sounds a listener experiences corresponding to those events.37 An illustration of some of the phenomena that I have been discussing is provided by the patterns of tone glides—sounds that change in pitch in a linear fashion—that result from hearing different groups’ frequency components. Suppose a rising tone glide is played at the same time as a falling tone glide. They can be experienced in one of two ways: either as 36 

This could be done by, e.g., introducing a spatial separation between the two groups of components and by introducing a temporal offset between them. 37  See Bregman (1990). Many of the same principles apply to grouping in music, and Diana Deutsch (1999) describes several examples of how changes in grouping change what musical sounds, and what sequences of musical sounds, are heard.

288   Matthew Nudds a sound that rises and then falls in pitch and a sound that falls and then rises, so that they seem to approach one another and then ‘bounce’ apart; or as a sound that steadily rises in pitch and a sound that steadily falls in pitch, so that they appear to ‘cross’ one another. In both cases the auditory system represents two sound-producing events. By altering the combinations of frequency components, it is possible to alter the way they are allocated to the sound-producing events. In the simplest case, the two tones are each made up of a single frequency component, one that increases in frequency whilst the other decreases. These result in an experience of sounds that ‘bounce’. The auditory system assumes that frequency components that are closer in frequency are likely to be the result of the same sound-producing event. However, if some harmonic structure is added to one of the tones, so that it comprises a fundamental and two higher harmonics, the result is an experience of sounds that cross. The auditory system assumes that frequency components with the same harmonic structure are likely to have been produced by a single event, and those with different harmonic structure are very unlikely to have been produced by a single event even when they are closer in pitch. There are many variations on this simple experiment,38 all of which can be explained in accordance with the same principles. The auditory system represents the sound producing events that best explain the frequency components detected by the ears, the frequency components are allocated to these events, and the sounds we experience are the result of this allocation. The result, when things go as they should, is that the auditory system veridically represents the sound-producing events in our environment and we experience sounds corresponding to these events: sounds that were in fact produced by them. This account of how auditory perception functions supports the representational view, according to which auditory perception represents sound sources by representing the sounds they produce. However, it suggests a significant revision to that view. What sounds we experience is a consequence of the way the auditory system transforms the frequency components it detects into a representation of sound-producing events. So the claim that auditory perception represents sound sources by representing the sounds they produce should not be understood as a claim about explanation, that is, that we can explain how we perceive sound sources by appeal to our perception of sounds.39 The auditory system does not represent sounds and then determine what produced those sounds; it determines what sound-producing events there are and that process results in an experience of sounds corresponding to those events. In fact, we saw that sound events cannot be individuated independently of sound-producing events, so there could be no explanation of sound perception other than in terms of the perception of sound-producing events. This reverses the 38  See, e.g., Tourgas and Bregman (1985); more complex examples (e.g. Tourgas and Bregman 1990; Kanafuka et al. 1996) can be explained in the same way. 39 Do sounds carry information about their sources? The pattern of frequency components that determine an experience of a sound carries information about the source of the sound. That pattern also determines the acoustic appearance of the sound. However, th