Feelings and experiences vary widely. For example, I run my fingersover sandpaper, smell a skunk, feel a sharp pain in my finger, seem tosee bright purple, become extremely angry. In each of these cases, Iam the subject of a mental state with a very distinctive subjectivecharacter. There is something it islike for me to undergoeach state, some phenomenology that it has. Philosophers often use theterm ‘qualia’ (singular ‘quale’) to refer tothe introspectively accessible, phenomenal aspects of our mentallives. In this broad sense of the term, it is difficult to deny thatthere are qualia. Disagreement typically centers on which mentalstates have qualia, whether qualia are intrinsic qualities of theirbearers, and how qualia relate to the physical world both inside andoutside the head. The status of qualia is hotly debated in philosophylargely because it is central to a proper understanding of the natureof consciousness. Qualia are at the very heart of the mind-bodyproblem.

The entry that follows is divided into thirteen sections. The firstdistinguishes various uses of the term ‘qualia’. Thesecond addresses the question of which mental states have qualia. Thethird section brings out some of the main arguments for the view thatqualia are irreducible and non-physical. The remaining sections focuson functionalism and qualia, the explanatory gap, qualia andintrospection, representational theories of qualia, qualia asintrinsic, nonrepresentational properties, relational theories ofqualia, the issue of qualia and simple minds, and qualia and AI.

• 1. Uses of the Term ‘Qualia’
• 2. Which Mental States Possess Qualia?
• 3. Are Qualia Irreducible, Non-Physical Entities?
• 4. Functionalism and Qualia
• 5. Qualia and the Explanatory Gap
• 6. Qualia and Introspection
• 7. Representational Theories of Qualia
• 8. Qualia as Intrinsic, Nonrepresentational Properties of Experiences
• 9. Relational Theories of Qualia
• 10. Illusionism about Qualia
• 11. Russellian Monism about Qualia
• 12. Which Biological Creatures Undergo States with Qualia?
• 13. Qualia and AI
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Uses of the Term ‘Qualia’

(1) Qualia as phenomenal character. Consider your visual experience asyou stare at a bright turquoise color patch in a paint store. There issomething it is like for you subjectively to undergo that experience.What it is like to undergo the experience is very different from whatit is like for you to experience a dull brown color patch. Thisdifference is a difference in what is often called ‘phenomenalcharacter’. The phenomenal character of an experience is what itis like subjectively to undergo the experience. If you are told tofocus your attention upon the phenomenal character of your experience,you will find that in doing so you are aware of certain qualities.These qualities — ones that are accessible to you when youintrospect and that together make up the phenomenal character of theexperience are sometimes called ‘qualia’. C.S. Peirceseems to have had something like this in mind when he introduced theterm ‘quale’ into philosophy in 1866 (1866/1982, para223).

There are more restricted uses of the term ‘qualia’,however.

(2) Qualia as properties of sense data. Consider a painting of adalmatian. Viewers of the painting can apprehend not only its content(i.e., its representing a dalmatian) but also the colors, shapes, andspatial relations obtaining among the blobs of paint on the canvas. Ithas sometimes been supposed that being aware or conscious of a visualexperience is like viewing an inner, non-physical picture orsense-datum. So, for example, on this conception, if I see adalmatian, I am subject to a mental picture-like representation of adalmatian (a sense-datum), introspection of which reveals to me bothits content and its intrinsic, non-representational features(counterparts to the visual features of the blobs of paint on thecanvas). These intrinsic, non-representational features have beentaken by advocates of the sense-datum theory to be the soledeterminants of what it is like for me to have the experience. In asecond, more restricted sense of the term ‘qualia’, then,qualia are intrinsic, consciously accessible, non-representationalfeatures of sense-data and other non-physical phenomenal objects thatare responsible for their phenomenal character. Historically, the term‘qualia’ was first used in connection with the sense-datumtheory by C.I. Lewis in 1929. As Lewis used the term, qualia wereproperties of sense-data themselves.

(3) Qualia as intrinsic non-representational properties. There isanother established sense of the term ‘qualia’, which issimilar to the one just given but which does not demand of qualiaadvocates that they endorse the sense-datum theory. However sensoryexperiences are ultimately analyzed — whether, for example, theyare taken to involve relations to sensory objects or they areidentified with neural events or they are held to be physicallyirreducible events — many philosophers suppose that they haveintrinsic, consciously accessible features that arenon-representational and that are solely responsible for theirphenomenal character. These features, whatever their ultimate nature,physical or non-physical, are often dubbed ‘qualia’.

In the case of visual experiences, for example, it is frequentlysupposed that there is a range of visual qualia, where these are takento be intrinsic features of visual experiences that (a) are accessibleto introspection, (b) can vary without any variation in therepresentational contents of the experiences, (c) are mentalcounterparts to some directly visible properties of objects (e.g.,color), and (d) are the sole determinants of the phenomenal characterof the experiences. This usage of ‘qualia’ has becomeperhaps the most common one in recent years. Philosophers who hold orhave held that there are qualia, in this sense of the term, include,for example, Nagel (1974), Peacocke (1983) and Block (1990).

(4) Qualia as intrinsic, nonphysical, ineffable properties. Somephilosophers (e.g, Dennett 1987, 1991) use the term‘qualia’ in a still more restricted way so that qualia areintrinsic properties of experiences that are also ineffable,nonphysical, and ‘given’ to their subjects incorrigibly(without the possibility of error). Philosophers who deny that thereare qualia sometimes have in mind qualia as the term is used in thismore restricted sense (or a similar one). It is also worth mentioningthat sometimes the term ‘qualia’ is restricted to sensoryexperiences by definition, while on other occasions it is allowed thatif thoughts and other such cognitive states have phenomenal character,then they also have qualia. Thus, announcements by philosophers whodeclare themselves opposed to qualia need to be treated with somecaution. One can agree that there are no qualia in the last threesenses I have explained, while still endorsing qualia in the standardfirst sense.

In the rest of this entry, I use the term ‘qualia’ in thevery broad way I did at the beginning of the entry. So,I take it forgranted that there are qualia. Later on, in section 8, I discussspecifically the view of qualia as intrinsic, nonrepresentationalproperties.

2. Which Mental States Possess Qualia?

The following would certainly be included on my own list. (1)Perceptual experiences, for example, experiences of the sort involvedin seeing green, hearing loud trumpets, tasting liquorice, smellingthe sea air, handling a piece of fur. (2) Bodily sensations, forexample, feeling a twinge of pain, feeling an itch, feeling hungry,having a stomach ache, feeling hot, feeling dizzy. Think here also ofexperiences such as those present during orgasm or while runningflat-out. (3) Felt reactions or passions or emotions, for example,feeling delight, lust, fear, love, feeling grief, jealousy, regret.(4) Felt moods, for example, feeling elated, depressed, calm, bored,tense, miserable. (For more here, see Haugeland 1985, pp.230–235).

Should we include any other mental states on the list? Galen Strawsonhas claimed (1994) that there are such things as theexperience of understanding a sentence, theexperience of suddenly thinking of something, of suddenlyremembering something, and so on. Moreover, in his view, experiencesof these sorts are not reducible to associated sensory experiencesand/or images. Strawson’s position here seems to be thatthought-experience is a distinctive experience in its own right. Hesays, for example: “Each sensory modality is an experientialmodality, and thought experience (in which understanding-experiencemay be included) is an experiential modality to be reckoned alongsidethe other experiential modalities” (p. 196). On Strawson’sview, then, some thoughts have qualia. (This is also the position ofHorgan and Tienson 2002.)

This view is controversial. One response is to claim that thephenomenal aspects of understanding derive largely from linguistic (orverbal) images, which have the phonological and syntactic structure ofitems in the subject’s native language. These images frequentlyeven come complete with details of stress and intonation. As we read,it is sometimes phenomenally as if we are speaking to ourselves.(Likewise when we consciously think about something without reading).We often “hear” an inner voice. Depending upon the contentof the passage, we may also undergo a variety of emotions andfeelings. We may feel tense, bored, excited, uneasy, angry. Onceall these reactions are removed, together with the images ofan inner voice and the visual sensations produced by reading, somewould say (myself included) that no phenomenology remains.

An alternative view is that when we hear words we understand, ourauditory experiences themselves represent meaning properties as wellas such properties as pitch, loudness, and timbre. These meaningproperties contribute to the phenomenal character of the auditoryexperiences and thus to their qualia. High-levelism of this sort aboutmeanings and perceptual experiences has been defended by Siegel (2006)and Bayne (2009). For an opposing view, see O’Callaghan(2011).

In any event, images and sensations of the above sorts are not alwayspresent in thought. They are notessential to thought.Consider, for example, the thoughts involved in everyday visualrecognition (or the thoughts of creatures without a naturallanguage).

What about desires, for example, my desire for a week’s holidayin Venice? It is certainly true that in some cases, there is anassociated phenomenal character. Often when we strongly desiresomething, we experience a feeling of being “pulled” or“tugged”. There may also be accompanying images in variousmodalities.

Should we include such propositional attitudes as feeling angrythat the house has been burgled or seeingthat thecomputer is missing on the list? These seem best treated ashybrid or complex states, one component of which is essentially aphenomenal state and the other (a judgment or belief) is not. Thus, inboth cases, there is a constituent experience that is the real bearerof the relevant quale or qualia.

3. Are Qualia Irreducible, Non-Physical Entities?

The literature on qualia is filled with thought-experiments of onesort or another. Perhaps the most famous of these is the case of Mary,the brilliant color scientist. Mary, so the story goes (Jackson 1982),is imprisoned in a black and white room. Never having been permittedto leave it, she acquires information about the world outside from theblack and white books her captors have made available to her, from theblack and white television sets attached to external cameras, and fromthe black and white monitor screens hooked up to banks of computers.As time passes, Mary acquires more and more information about thephysical aspects of color and color vision. (For a real life case of avisual scientist (Knut Nordby) who is an achromotope, see Sacks 1996,Chapter 1.) Eventually, Mary becomes the world’s leadingauthority on these matters. Indeed she comes to knowall thephysical facts pertinent to everyday colors and color vision.

Still, she wonders to herself: What do people in the outside worldexperience when they see the various colors? What is itlike for them to see red or green? One day her captorsrelease her. She is free at last to see things with their real colors(and free too to scrub off the awful black and white paint that coversher body). She steps outside her room into a garden full of flowers.“So, that is what it is like to experience red,” sheexclaims, as she sees a red rose. “And that,” she adds,looking down at the grass, “is what it is like to experiencegreen.”

Mary here seems to make some important discoveries. She seems to findout things she did not know before. How can that be, if, as seemspossible, at least in principle, she has all the physical informationthere is to have about color and color vision — if she knows allthe pertinent physical facts?

One possible explanation is that that there is a realm of subjective,phenomenal qualities associated with color, qualities the intrinsicnature of which Mary comes to discover upon her release, as sheherself undergoes the various new color experiences. Before she lefther room, she only knew the objective, physical basis of thosesubjective qualities, their causes and effects, and various relationsof similarity and difference. She had no knowledge of the subjectivequalities in themselves.

This explanation is not available to the physicalist. If what it islike for someone to experience red is one and the same as somephysical quality, then Mary already knowsthat while in herroom. Likewise, for experiences of the other colors. For Mary knowsall the pertinent physical facts. What, then, can the physicalistsay?

Some physicalists respond that knowing what it is like is know-how andnothing more. Mary acquires certain abilities, specifically in thecase of red, the ability to recognize red things by sight alone, theability to imagine a red expanse, the ability to remember theexperience of red. She doesnot come to know any newinformation, any new facts about color, any new qualities. This is theview of David Lewis (1990) and Lawrence Nemirow (1990).

The Ability Hypothesis, as it is often called, is more resilient thanmany philosophers suppose (see Tye 2000, Chapter One). But it hasdifficulty in properly accounting for our knowledge of what it is liketo undergo experiences of determinate hues while we are undergoingthem. For example, I can know what it is like to experience red-17, asI stare at a rose of that color. Of course, I don’t know the hueas red-17. My conception of it is likely justthat shade ofred. But I certainly know what it is like to experience the huewhile it is present. Unfortunately, I lack the abilities Lewis citesand so does Mary even after she leaves her cell. She is not able torecognize things that are red-17 as red-17 by sight. Given the wayhuman memory works and the limitations on it, she lacks the conceptred-17. She has no mental template that is sufficiently fine-grainedto permit her to identify the experience of red-17 when it comesagain. Presented with two items, one red-17 and the other red-18, in aseries of tests, she cannot say with any accuracy which experience herearlier experience of the rose matches. Sometimes she picks one; atother times she picks the other. Nor is she able afterwards to imaginethings as having hue, red-17, or as having that very shade of red therose had; and for precisely the same reason.

The Ability Hypothesis appears to be in trouble. An alternativephysicalist proposal is that Mary in her room lacks certainphenomenal concepts, certain ways of thinking about ormentally representing color experiences and colors. Once she leavesthe room, she acquires these new modes of thought as she experiencesthe various colors. Even so, the qualities the new concepts pick outare ones she knew in a different way in her room, for they arephysical or functional qualities like all others.

One problem this approach faces is that it seems to imply that Marydoes not really make a new discovery when she says, “So, that iswhat it is like to experience red.” Upon reflection, however, itis far from obvious that this is really a consequence. For it iswidely accepted that concepts or modes of presentation are involved inthe individuation of thought-contents, given one sense of the term‘content’ — the sense in which thought-content iswhatever information that-clauses provide that suffices for thepurposes of even the most demanding rationalizing explanation. In thissense, what I think, when I think that Cicero was an orator, is notwhat I think when I think that Tully was an orator. This is preciselywhy it is possible to discover that Cicero is Tully. The thought thatCicero was an orator differs from the thought that Tully was an oratornot at the level of truth-conditions — the same singularproposition is partly constitutive of the content of both — butat the level of concepts or mode of presentation. The one thoughtexercises the conceptCicero; the other the conceptTully. The concepts have the same reference, but they presentthe referent in different ways and thus the two thoughts can playdifferent roles in rationalizing explanation.

It appears then that there is no difficulty in holding both that Marycomes to know some new things upon her release, while already knowingall the pertinent real-world physical facts, even though the newexperiences she undergoes and their introspectible qualities arewholly physical. In an ordinary, everyday sense, Mary’sknowledge increases. And that, it may be contended, is all thephysicalist needs to answer the Knowledge Argument. (The term‘fact’, it should be mentioned, is itself ambiguous.Sometimes it is used to pick out real-world states of affairs alone;sometimes it is used for such states of affairs under certainconceptualizations. When we speak of the physical facts above, weshould be taken to refer either to physical states of affairs alone orto those states of affairs under purely physical conceptualizations.For more on ‘fact’, see Tye 1995.)

Some philosophers insist that the difference between the old and thenew concepts in this case is such that there must be a difference inthe world between the properties these concepts stand for or denote(Jackson 1993, Chalmers 1996). Some of these properties Mary knew inher cell; others she becomes cognizant of only upon her release. Thisis necessary for Mary to make a real discovery: she must come toassociate with the experience of red new qualities she did notassociate with it in her room. The physicalist is committed to denyingthis claim; for the new qualities would have to be non-physical.

The issues here are complex. What the physicalist really needs tosettle the issue is a theory of phenomenal concepts (a theory, thatis, of the allegedly special concepts that are deployed from the firstperson point of view when we recognize our experiences as being ofsuch-and-such subjective types) which is itself compatible withphysicalism. There are proposals on offer (see, for example, Hill1991, Loar 1990, Levine 2000, Sturgeon 2000, Perry 2001, Papineau2002, Tye, 2003), but there is as yet no agreement as to the form sucha theory should take, and some philosophers contend that a propertheory of phenomenal concepts shows that no satisfactory answer can begiven by the physicalist to the example of Mary’s Room (Chalmers1999). Another possibility is that the very idea of a phenomenalconcept, conceived of as a concept very different in how it functionsfrom concepts applied elsewhere, is itself confused. On this view,physicalists who have appealed to phenomenal concepts to handle theexample of Mary’s Room have been barking up the wrong tree (Tye2009).

Another famous anti-reductionist thought-experiment concerning qualiaappeals to the possibility of zombies. A philosophical zombie is amolecule by molecule duplicate of a sentient creature, a normalhuman-being, for example, but who differs from that creature inlackingany phenomenal consciousness. For me, as I lie on thebeach, happily drinking some wine and watching the waves, I undergo avariety of visual, olfactory, and gustatory experiences. But my zombietwin experiences nothing at all. He has no phenomenal consciousness.Since my twin is an exact physical duplicate of me, his innerpsychological states will befunctionally isomorphic with myown (assuming he is located in an identical environment). Whateverphysical stimulus is applied, he will process the stimulus in the sameway as I do, and produce exactly the same behavioral responses.Indeed, on the assumption that non-phenomenal psychological states arefunctional states (that is, states definable in terms of their role orfunction in mediating between stimuli and behavior), my zombie twinhas just the same beliefs, thoughts, and desires as I do. He differsfrom me only with respect to experience. For him, there is nothing itis like to stare at the waves or to sip wine.

The hypothesis that there can be philosophical zombies is not normallythe hypothesis that such zombies arenomically possible, thattheir existence is consistent with the actual laws of nature. Ratherthe suggestion is that zombie replicas of this sort are at leastimaginable and hence metaphysically possible.

Philosophical zombies pose a serious threat to physicalist views ofqualia. To begin with, if zombie replicas are metaphysically possible,then there is a simple argument that seems to show that phenomenalstates are not identical with internal, objective, physical states.Suppose objective, physical stateP can occur withoutphenomenal stateS in some appropriate zombie replica (in themetaphysical sense of ‘can’ noted above). IntuitivelyS cannot occur withoutS. Pain, for example, cannotbe felt without pain. So,P has a modal propertySlacks, namely the property ofpossibly occurring withoutS. So, by Leibniz’ Law (the law that for anythingx and for anythingy, ifx is identicalwithy thenx andy shareall thesame properties),S is not identical withP.

Secondly, if a person microphysically identical with me, located in anidentical environment (both present and past), can lackanyphenomenal experiences, then facts pertaining to experience andfeeling, facts about qualia, are not necessarily fixed or determinedby the objective microphysical facts. And this the physicalist cannotallow, even if she concedes that phenomenally conscious states are notstrictly identical with internal, objective, physical states. For thephysicalist, whatever her stripe, must at least believe that themicrophysical facts determine all the facts, that any world that wasexactly like ours inall microphysical respects (down to thesmallest detail, to the position of every single boson, for example)would have to be like our world in all respects (having identicalmountains, lakes, glaciers, trees, rocks, sentient creatures, cities,and so on).

One well-known physicalist reply to the case of zombies (Loar 1990) isto grant that they are conceptually possible, or at least that thereis noobvious contradiction in the idea of a zombie, whiledenying that zombies are metaphysically possible. Since theanti-physicalist argument requires metaphysical possibility —mere conceptual possibility will not suffice — it now collapses.That conceptual possibility is too weak for theanti-physicalist’s purposes (at least without furtherqualification and argument) is shown by the fact that it isconceptually possible that I am not Michael Tye (that I am an impostoror someone misinformed about his past) even though, given the actualfacts, it is metaphysically impossible.

4. Functionalism and Qualia

Functionalism is the view that individual qualia have functionalnatures, that the phenomenal character of, e.g., pain is one and thesame as the property of playing such-and-such a causal orteleofunctional role in mediating between physical inputs (e.g., bodydamage) and physical outputs (e.g., withdrawal behavior). On this view(Lycan 1987), qualia are multiply physically realizable. Inner statesthat are physically very different may nonetheless feel the same. Whatis crucial to what it is like is functional role, not underlyinghardware.

There are two famous objections to functionalist theories of qualia:the Inverted Spectrum and the Absent Qualia Hypothesis. The first movein the former objection consists in claiming that you might see redwhen I see green and vice-versa; likewise for the other colors so thatour color experiences are phenomenally inverted. This does not sufficeto create trouble for the functionalist yet. For you and I are surelyrepresentationally different here: for example, you have a visualexperience that represents red when I have one that represents green.And that representational difference brings with it a difference inour patterns of causal interactions with external things (and therebya functional difference).

This reply can be handled by the advocate of inverted qualia byswitching to a case in which we both have visual experiences with thesame representational contents on the same occasions while stilldiffering phenomenally. Whether such cases are really metaphysicallypossible is open to dispute, however. Certainly, those philosopherswho are representationalists about qualia (see Section 7) would denytheir possibility. Indeed, it is not even clear that such cases areconceptually possible (Harrison 1973, Hardin 1993, Tye 1995). Butleaving this to one side, it is far from obvious that there would nothave to be some salient fine-grained functional differences betweenus, notwithstanding our gross functional identity.

Consider a computational example. For any two numerical inputs,M andN, a given computer always produces as outputsthe product ofM andN. There is a second computerthat does exactly the same thing. In this way, they are functionallyidentical. Does it follow that they are running exactly the sameprogram? Of course, not! There are all sorts of programs that willmultiply together two numbers. These programs can differ dramatically.At one gross level the machines are functionally identical, but atlower levels the machines can be functionally different.

In the case of you and me, then, the opponent of inverted qualia canclaim that, even if we are functionally identical at a coarse level— we both call red things ‘red’, we both believethat those things are red on the basis of our experiences, we both arecaused to undergo such experiences by viewing red things, etc. —there are necessarily fine-grained differences in our internalfunctional organization. And that is why our experiences arephenomenally different.

Some philosophers will no doubt respond that it is still imaginablethat you and I are functionally identical inall relevantrespects yet phenomenally different. But this claim presents a problemat least for those philosophers who oppose functionalism but whoaccept physicalism. For it is just as easy to imagine that there areinverted qualia in molecule-by-molecule duplicates (in the sameexternal, physical settings) as it is to imagine inverted qualia infunctional duplicates. If the former duplicates are reallymetaphysically impossible, as the physicalist is committed toclaiming, why not the latter? Some further convincing argument needsto be given that the two cases are disanalogous. As yet, to my mind,no such argument has been presented. (Of course, this response doesnot apply to those philosophers who take the view that qualia areirreducible, non-physical entities. However, these philosophers haveother severe problems of their own. In particular, they face theproblem of phenomenal causation. Given the causal closure of thephysical, how can qualia make any difference? For more here, see Tye1995, Chalmers 1996).

The absent qualia hypothesis is the hypothesis that functionalduplicates of sentient creatures are possible, duplicates thatentirely lack qualia. For example, one writer (Block 1980) asks us tosuppose that a billion Chinese people are each given a two-way radiowith which to communicate with one another and with an artificial(brainless) body. The movements of the body are controlled by theradio signals, and the signals themselves are made in accordance withinstructions the Chinese people receive from a vast display in the skywhich is visible to all of them. The instructions are such that theparticipating Chinese people function like individual neurons, and theradio links like synapses, so that together the Chinese peopleduplicate the causal organization of a human brain. Whether or notthis system, if it were ever actualized, wouldactuallyundergo any feelings and experiences, it seems coherent to supposethat it might not. But if this is a real metaphysical possibility,then qualia do not have functional essences.

One standard functionalist reply to cases like the China-body systemis to bite the bullet and to argue that however strange it seems, theChina-body system could not fail to undergo qualia. The oddness ofthis view derives, according to some functionalists (Lycan 1987), fromour relative size. We are each so much smaller than the China-bodysystem that we fail to see the forest for the trees. Just as acreature the size of a neuron trapped inside a human head might wellbe wrongly convinced that there could not be consciousness there, sowe too draw the wrong conclusion as we contemplate the China-bodysystem. It has also been argued (e.g., by Shoemaker 1975) that anysystem that was a full functional duplicate of one of us would have tobe subject to all the same beliefs, including beliefs about its owninternal states. Thus the China-Body system would have to believe thatit experiences pain; and if it had beliefs of this sort, then it couldnot fail to be the subject of some experiences (and hence some stateswith phenomenal character). If this reply is successful (for anupdated version of this reply and a new related thought experiment,see Tye 2006), what it shows is that the property of having somephenomenal character or other has a functional essence. But it doesnot show that individual qualia are functional in nature. Thus onecould accept that absent qualia are impossible while also holding thatinverted spectra are possible (see, e.g., Shoemaker 1975).

5. Qualia and the Explanatory Gap

Our grasp of what it is like to undergo phenomenal states is suppliedto us by introspection. We also have an admittedly incomplete grasp ofwhat goes on objectively in the brain and the body. But there is, itseems, a vast chasm between the two. It is very hard to see how thischasm in our understanding could ever be bridged. For no matter howdeeply we probe into the physical structure of neurons and thechemical transactions which occur when they fire, no matter how muchobjective information we come to acquire, we still seem to be leftwith something that we cannot explain, namely, why and howsuch-and-such objective, physical changes, whatever they might be,generate so-and-so subjective feeling, or any subjective feeling atall.

This is the famous “explanatory gap” for qualia (Levine1983, 2000). Some say that the explanatory gap is unbridgeable andthat the proper conclusion to draw from it is that there is acorresponding gap in the world. Experiences and feelings haveirreducibly subjective, non-physical qualities (Jackson 1993; Chalmers1996, 2005). Others take essentially the same position on the gapwhile insisting that this does not detract from a purely physicalistview of experiences and feelings. What it shows rather is that somephysical qualities or states are irreducibly subjective entities(Searle 1992). Others hold that the explanatory gap may one day bebridged but we currently lack the concepts to bring the subjective andobjective perspectives together. On this view, it may turn out thatqualia are physical, but we currently have no clear conception as tohow they could be (Nagel 1974). Still others adamantly insist that theexplanatory gap is, in principle, bridgeable but not by us or by anycreatures like us. Experiences and feelings are as much a part of thephysical, natural world as life, digestion, DNA, or lightning. It isjust that with the concepts we have and the concepts we are capable offorming, we are cognitively closed to a full, bridging explanation bythe very structure of our minds (McGinn 1991).

Another view that has been gaining adherents of late is that there isa real, unbridgeable gap, but it has no consequences for the nature ofconsciousness and physicalist or functionalist theories thereof. Onthis view, there is nothing in the gap that should lead us to anybifurcationin the world between experiences and feelings onthe one hand and physical or functional phenomena on the other. Therearen’t two sorts of natural phenomena: the irreduciblysubjective and the objective. The explanatory gap derives from thespecial character of phenomenalconcepts. These conceptsmislead us into thinking that the gap is deeper and more troublesomethan it really is.

On one version of this view, phenomenal concepts are just indexicalconcepts applied to phenomenal states via introspection (see Lycan1996). On an alternative version of the view, phenomenal concepts arevery special, first-person concepts different in kind from all others(see Tye 2003). This response to the explanatory gap obviously bearsaffinities to the second physicalist response sketched in Section 3 tothe Knowledge Argument. Unfortunately, if the appeal to phenomenalconcepts by the physicalist is misguided, then it cannot be used tohandle the gap.

There is no general agreement on how the gap is generated and what itshows.

6. Qualia and Introspection

In the past, philosophers have often appealed directly tointrospection on behalf of the view that qualia are intrinsic,non-intentional features of experiences. Recently, a number ofphilosophers have claimed that introspection reveals no such qualities(Harman 1990, Dretske 1995, Tye 1995, 2000). Suppose you are facing awhite wall, on which you see a bright red, round patch of paint.Suppose you are attending closely to the color and shape of the patchas well as the background. Now turn your attention from what you seeout there in the world before you to your visual experience. Focusuponyour awareness of the patch as opposed tothepatch of which you are aware. Do you find yourself suddenlyacquainted with new qualities, qualities that are intrinsic to yourvisual experience in the way that redness and roundness are qualitiesintrinsic to the patch of paint? According to some philosophers, theanswer to this question is a resounding ‘No’. As you lookat the patch, you are aware of certain features out there in theworld. When you turn your attention inwards to your experience ofthose features, you are awarethat you are having anexperience of a certain sort but you awareof the very samefeatures; no new features of your experience are revealed. In thisway, your visual experience is transparent or diaphanous. When you tryto examine it, you see right through it, as it were, to the qualitiesyou were experiencing all along in being a subject of the experience,qualities your experience isof.

This point holds good, according to the philosophers above, even ifyou are hallucinating and there is no real patch of paint on the wallbefore you. Still you have an experienceof there being apatch of paint out there with a certain color and shape. It’sjust that this time your experience is a misrepresentation. And if youturn your attention inwards to your experience, you will‘see’ right through it again to those very samequalities.

These observations suggest that qualia, conceived of as theimmediately ‘felt’ qualitiesof experiences ofwhich we are cognizant when we attend to them introspectively, do notreally exist. The qualities of which we are aware are not qualities ofexperiences at all, but rather qualities that, if they are qualitiesof anything, are qualities of things in the world (as in the case ofperceptual experiences) or of regions of our bodies (as in the case ofbodily sensations). This is not to say that experiences do not havequalia. The point is that qualia are not qualities of experiences.This claim, which will be developed further in the next section, iscontroversial and some philosophers deny outright the thesis oftransparency with respect to qualia (see Block 1991, 2000; Stoljar2004; Nida-Rümelin 2007). According to Block, for example, qualiaare not presented to us in introspection as intrinsic, non-intentionalproperties of our experiences. Still it does not follow from this thatwe are not introspectively acquainted with such properties. For we doknow on the basis of introspection what it is like to undergo a visualexperience of blue, say. So, if what a state is like is a matter ofwhich intrinsic, non-intentional properties it tokens, then obviouslywe are introspectively aware of properties of this sort (in the de resense of ‘of’). On this view, whether qualia areproperties of experiences (in particular, intrinsic, non-intentionalproperties) is a theoretical matter. Introspection does not settle thematter one way or the other.

7. Representational Theories of Qualia

Talk of the ways things look and feel is intensional. If I have a redafter-image as a result of a flashbulb going off, the spot I‘see’ in front of the photographer’s face looks red,even though there is no such spot. If I live in a world in which alland only things that are purple are poisonous, it is still the casethat an object that looks purple to me does not thereby look poisonous(in the phenomenal sense of ‘looks’). If I feel a pain ina leg, I need not even have a leg. My pain might be a pain in aphantom limb. Facts such as these have been taken to provide furthersupport for the contention that some sort of representational accountis appropriate for qualia.

If qualia are not qualities of experiences, as some philosophersmaintain on the basis of an appeal to introspection, and the onlyqualities revealed in introspection are qualities represented byexperiences (qualities that, in the perceptual case, if they belong toanything, belong to external things), a natural representationalproposal is that qualia are really representational contents ofexperiences into which the represented qualities enter. This wouldalso explain why we talk of experiences *having* qualia or *having* aphenomenal character. For the representational content of anexperience is something the experience has; just as meaning issomething a word has. Moreover, just as the meaning of a word is not aquality the word possesses, so the phenomenal character of anexperience is not a quality the experience possesses.

If qualia are representational contents, just which contents arethese? Obviously there can be differences in the representationalcontents of experiences without any phenomenal difference. If you andI see a telescope from the same viewing angle, for example, then evenif I do not recognize it as a telescope and you do (so that ourexperiences differ representationally at this level), the way thetelescope looks to both of us is likely pretty much the same (in thephenomenal sense of ‘looks’). Likewise, if a child isviewing the same item from the same vantage point, her experience willlikely be pretty similar to yours and mine too. Phenomenally, ourexperiences are all very much alike, notwithstanding certainhigher-level representational differences. This, according to somerepresentationalists, is because we all have experiences thatrepresent to us the same 3-D surfaces, edges, colors, andsurface-shapes plus a myriad of other surface details.

The representation we share here has a content much like that of the 21/2-D sketch posited by David Marr in his famous theory of vision(1982) to which further shape and color information has been appended(for details, see Tye 1995). This content is plausibly viewed asnonconceptual. It forms the output of the early, largely modularsensory processing and the input to one or another system ofhigher-level cognitive processing. Representationalists sometimesclaim that it is here at this level of content that qualia are to befound (see Dretske 1995, Tye 1995, 2000; for an opposingrepresentational view, see McDowell 1994).

One worry for this view is that if qualia are to be handled in termsof representational content, then there had better be a content thatis shared by veridical visual experiences and their hallucinatorycounterparts. Disjunctivists have disputed the supposition that thereis a common content (see, e.g., Hinton 1973, Martin 1997, Snowdon1990). Perhaps veridical experiences have only singular contents andhallucinatory experiences have gappy contents or no content at all(for an extended discussion of visual experience and content, seePautz 2010, Siegel 2011).

An alternative possibility is that qualia are properties representedby experiences. On this view, there need be no common content sharedby veridical experiences and their hallucinatory counterparts. Itsuffices that the same properties be represented. Of course, such aview requires that a further account be provided of what it is thatmakes a property represented by an experience a quale.

Some philosophers try to ground qualia in modes of representationdeployed by experiences within their representational contents. On oneversion of this view, visual experiences not only represent theexternal world but also represent themselves (for a recent collectionof essays elaborating this view, see Kriegel and Williford 2006). Forexample, my current visual experience of a red object not onlyrepresents the object as red (this is my focal awareness) but alsorepresents itself as red (this is normally a kind of peripheralawareness I have of my experience). When I introspect, the experiencealone provides me with awareness of itself — no higher orderthought is necessary. What the experience is like for me is supposedlyits redness, where this is a mode of representation my experience usesto represent real world redness.

This view is incompatible with the phenomenon of transparency (seesection 6) and it is very close to the classic qualiaphile view,according to which when the subject introspects, she is aware of thetoken experience and its phenomenal properties. The new twist is thatthis awareness uses the token experience itself and one of itscontents.

Representationalists about qualia are often also externalists aboutrepresentational content (but not always — see, for example,Chalmers 2004). On this view, what a given experience represents ismetaphysically determined at least, in part, by factors in theexternal environment. Thus, it is usually held, microphysical twinscan differ with respect to the representational contents of theirexperiences. If these differences in content are of the right sortthen, according to the wide representationalist, microphysical twinscannotfail to differ with respect to the phenomenalcharacter of their experiences. What makes for a difference inrepresentational content in microphysical duplicates is some externaldifference, some connection between the subjects and items in theirrespective environments. The generic connection is sometimes called‘tracking’, though there is no general agreement as to inwhat exactly tracking consists.

On wide representationalism, qualia (like meanings) ain’t in thehead. The classic, Cartesian-based picture of experience and itsrelation to the world is thus turned upside down. Qualia are notintrinsic qualities of inner ideas of which their subjects aredirectly aware, qualities that are necessarily shared by internalduplicates however different their environments may be. Rather, theyare representational contents certain inner states possess, contentswhose nature is fixed at least in part by certain external relationsbetween individuals and their environments (Byrne and Tye 2006; for anopposing but still representationalist view, see Pautz 2006).

Representationalism, as presented so far, is an identity thesis withrespect to qualia: qualia are supposedly one and the same as certainrepresentationalcontents. Sometimes it is held instead thatqualia are one and the same as certain representationalproperties of experiences (or properties represented inexperiences); and sometimes it is is argued that theserepresentational properties are themselves irreducible (Siewert 1998).There is also a weaker version of representationalism, according towhich it is metaphysically necessary that experiences exactly alikewith respect to their representational contents are exactly alike withrespect to their qualia. Obviously, this supervenience thesis leavesopen the further question as to the essential nature of qualia.

For further discussion, see Section 3 of the entry onrepresentational theory of consciousness. Objections to representationalism are covered in the nextsection.

8. Qualia as Intrinsic, Nonrepresentational Properties of Experiences

As noted in section 1, the term ‘qualia’ is sometimes usedfor intrinsic nonrepresentational, consciously accessible propertiesof experience. Representationalists deny that there are qualia in thissense, while identifying qualia in the broad sense (that is, qualia asphenomenal character) with representational properties. However, somephilosophers hold that there are qualia in the sense of intrinsicnonrepresentational properties of experience. These philosophers denyrepresentationalism, and identify qualia in the broad sense withintrinsic nonrepresentational properties of experience. This view isthe subject of the present section.

As noted earlier, some philosophers deny that experience istransparent. They claim that introspection does not show thatexperiences lack introspectible, intrinsic, nonrepresentationalproperties. Further, they insist that representationalism encountersdecisive objections. These objections may be seen as making up onepillar in the main foundation for the view that experiences havequalia, conceived of now as intrinsic, nonrepresentational properties.The second pillar consists in what is sometimes called “thecommon kind assumption”, namely that veridical and hallucinatoryexperiences sometimes share the same phenomenal character (have thesame qualia). This assumption is accepted by all the advocates of theviews discussed so far but it is denied by advocates of relationaltheories of qualia (see section 9).

Objections to representational views of qualia often take the form ofputative counter-examples. One class of these consists of cases inwhich, it is claimed, experiences have the same representationalcontent but different phenomenal character. Christopher Peacockeadduces examples of this sort in his 1983. According to some (e.g.,Block 1990, Shoemaker forthcoming), the Inverted Spectrum alsosupplies an example that falls into this category. Another class ismade up of problem cases in which allegedly experiences have differentrepresentational contents (of the relevant sort) but the samephenomenal character. Ned Block’s Inverted Earth example (1990)is of this type. The latter cases only threaten strongrepresentationalism, the former are intended to refuterepresentationalism in both its strong and weaker forms.Counter-examples are also sometimes given in which supposedlyexperience of one sort or another is present but in which there is nostate with representational content. Swampman (Davidson 1986) —the molecule by molecule replica of one of us, formed accidentally bythe chemical reaction that occurs in a swamp when a partiallysubmerged log is hit by lightning — is one such counter-example,according to some philosophers. But there are more mundane cases.Consider the exogenous feeling of depression. That, it may seem, hasno representational content. Likewise, the exogenous feeling ofelation. Yet these experiences certainly differ phenomenally.

There isn’t space to go through all these objections. We brieflydiscuss just one: Inverted Earth. Inverted Earth is an imaginaryplanet, on which things have complementary colors to the colors oftheir counterparts on Earth. The sky is yellow, grass is red, ripetomatoes are green, and so on. The inhabitants of Inverted Earthundergo psychological attitudes and experiences with invertedintentional contents relative to those of people on Earth. They thinkthat the sky is yellow, see that grass is red, etc. However, they callthe sky ‘blue’, grass ‘green’, ripe tomatoes‘red’, etc. just as we do. Indeed, in all respectsconsistent with the alterations just described, Inverted Earth is asmuch like Earth as possible.

In Block’s original version of the tale, mad scientists insertcolor-inverting lenses in your eyes and take you to Inverted Earth,where you are substituted for your Inverted Earth twin ordoppelganger. Upon awakening, you are aware of no difference, sincethe inverting lenses neutralize the inverted colors. You think thatyou are still where you were before. What it is like for you when yousee the sky or anything else is just what it was like on earth. Butafter enough time has passed, after you have become sufficientlyembedded in the language and physical environment of Inverted Earth,your intentional contents will come to match those of the otherinhabitants. You will come to believe that the sky is yellow, forexample, just as they do. Similarly, you will come to have a visualexperience that represents the sky as yellow. For the experientialstate you now undergo, as you view the sky, is the one that, in you,now normally tracks yellow things. So, the later you will come to besubject to inner states that are intentionally inverted relative tothe inner states of the earlier you, while the phenomenal aspects ofyour experiences will remain unchanged.

Perhaps the simplest reply that can be made with respect to thisobjection is to deny that there really is any change in normaltracking with respect to color, at least as far as your experiencesgo. “Normal”, after all, has both teleological andnonteleological senses. If what an experience normally tracks is whatnature designed it to track, what it has as its biological purpose totrack, then shifting environments from Earth to Inverted Earth willmake no difference to normal tracking and hence no difference to therepresentational contents of your experiences. The sensory state thatnature designed in your species to track blue in the setting in whichyour species evolved will continue to do just that even if throughtime, on Inverted Earth, in that alien environment, it is usuallycaused in you by looking at yellow things.

The suggestion that tracking is teleological in character, at leastfor the case of basic experiences, goes naturally with the plausibleview that states like feeling pain or having a visual sensation of redare phylogenetically fixed (Dretske 1995). However, it encountersserious difficulties with respect to the Swampman case mentionedabove. On a cladistic conception of species, Swampman is not human.Indeed, lacking any evolutionary history, he belongs to no species atall. His inner states play no teleological role. Nature did not designany of them to do anything. So, if phenomenal character is a certainsort of teleo-representational content, as some representationalistshold, then Swampman has no experiences and no qualia. This, for manyphilosophers, isvery difficult to believe.

There are alternative replies available (see Lycan 1996, Tye 2000) inconnection with the Inverted Earth problem. These involve eitherdenying that qualia do remain constant with the switch to InvertedEarth or arguing that a non-teleological account of sensory contentmay be elaborated, under which qualia stay the same.

As noted above, the second pillar in the foundation of the view thatqualia are intrinsic, nonrepresentational properties of experiences isthe common kind assumption. Those philosophers who accept thisassumption see it (in the perceptual case) as providing the simplest,best explanation of the fact that hallucinations and veridicalperceptions sometimes seem exactly alike to their subjects. It isgranted, of course, that it does not follow that there is somethingcommon between hallucinations and perceptions in such cases from thefact that they seem alike. Nonetheless, it is a challenge to those whoreject this assumption (see section 9) to provide a betterexplanation.

9. Relational Theories of Qualia

Relational theories of qualia typically begin with the naive realistthesis that in normal circumstances perceivers are directly aware ofthe objects around them and various properties that they have. It isthen proposed that since perceivers are also directly aware of whattheir experiences are like, the phenomenal character of theirexperiences in such cases is to be understood in terms of the relevantobjects and their properties along with the viewpoint from which theyare being observed. More precisely, it is urged that the phenomenalcharacter is constituted by the objects that the perceiver sees, someof their properties and how they are arranged relative to theviewer (Campbell 2002).

In later work, Campbell (2009) allows that the viewer’s‘standpoint’ needs to be factored into phenomenalcharacter too. The standpoint a perceiver occupies includes much morethan just the egocentric frame of the perceiver. It includes the sensemodality used to perceive, the time and place of the perceiving aswell as the distance from the perceived object, the orientation of theperceiver relative to the object, and the temporal dynamics of theexperience. Consciousness of an object, for Campbell, now consists ina three-place relation between a perceiver, an object, and astandpoint. With what exactly phenomenal character itself is to beidentified, on this proposal, is unclear.

Bill Brewer (2011) agrees with Campbell that a third relatum is neededin naïve realist accounts of perceptual experience, where thethird relatum includes the sense modality of the experience, thespatio-temporal point of view, and other relevant circumstances ofperception but he does not specify what exactly these circumstancesare. William Fish (2009) takes a similar position, arguing that thethird element should include idiosyncrasies of the perceiver’svisual system as well as attentional facts about the perceiver sincetwo ordinary perceivers viewing the same object from the same positionmay nonetheless differ in the character of their visual experiences,depending upon how good their eyesight is (for example) and how theydistribute their attention.

Of course, when one is (completely) hallucinating, there are noobjects that one sees. So, relationism cannot allow that thephenomenal character in this case is the same as in the veridicalcase. Accordingly, relationists reject what was called in the lastsection “the common kind assumption”. One possible viewconsistent with relationism is that in hallucinatory cases thephenomenal character is a matter of the representational content ofthe experience, as is claimed on some versions of representationalism.Another view, held by some relationists, is that there is nothing moreto the phenomenal character of a hallucinatory experience — forexample, an experience of a red triangle — than its beingindiscriminable or indistinguishable from a veridical experience of ared triangle (Martin 2004, Fish 2009). On this view, in giving amental characterization of a hallucinatory experience, there isnothing more to be said than that it has a certain relational andepistemological property, namely that of being indiscriminable fromthe relevant perceptual experience.

Sometimes relationists try to motivate their view by arguing thatsince the seen objects are constituents of veridical visualexperiences and they are not in the case of hallucinatory experiences,the experiences in the two cases must themselves be different.However, even if this is correct, it does not follow that they cannotshare the same phenomenal character. What follows is rather that ifthey do share a common phenomenal character, then the consciousexperiences are not to be individuated (solely) by that phenomenalcharacter.

One problem facing Martin’s relational account of hallucinatoryphenomenal character is that of cognitively unsophisticatedperceivers. Dogs can hallucinate but they lack the cognitivewherewithal to judge that their hallucinatory experiences of bones arethe same or different from their veridical experiences of squirrels.In at least one clear sense of ‘indiscriminable’, then,their hallucinatory experiences of bones are indiscriminable to themfrom their veridical experiences of squirrels. But the phenomenalcharacter of these experiences is certainly different. (For adiscussion of this problem and a response to it, see Martin 2004. Forcriticisms, see Siegel 2008.)

Another problem for the relational view is that it cannot easilyhandle cases of normal misperception, for example, the Muller-Lyerillusion. Campbell tells us that idiosyncrasies of the perceiver mayaffect phenomenal character, but he has no account to offer of casesin which something looks other than it is even to normal observers innormal circumstances. Here the scene before the eyes fails to capturethe phenomenology. Brewer says that illusions are to be accounted forin terms of visually relevant similarities to paradigms of a kind ofwhich the perceived object is not an instance. In the case of theMuller-Lyer, the paradigm is a pair of lines one longer and moredistant than its plane, the other shorter and less distant. Thisproposal encounters various potential difficulties (Pautz 2010). Forexample, in the waterfall illusion, the water appears to be moving andnot moving at the same time. Here there are no suitable paradigms inthe real world. (See the entry onthe disjunctive theory of perception.)

10. Illusionism about Qualia

According to illusionists (Dennett 2019, 2020; Frankish 2016; Kammerer2021), conscious experience is an illusion. It certainly seems to usthat conscious experiences, and thus qualia (at least in sense (1) ofthe four senses distinguished at the beginning of this entry) exist,but in reality there are no such things. Qualia are like Santa Clausand the Easter Bunny (Dennett 2020). It is not being denied here thatthrough the use of our senses, we genuinely encounter a wide range ofqualities, for example, in perception, colors, auditory qualities suchas pitch and loudness, various textures and aromas. But the qualitiesso encountered are not properties of experiences; for we do notgenuinely undergo any experiences. To be sure, when we introspect, itcertainly seems to us that we are the subjects of experiences withwidely varying phenomenal character. But we are wrong.

There is a possible weaker version of this view under which it is onlyqualia in senses (2)–(4) that are being repudiated. And in somepassages, some adherents of illusionism seem inclined to endorse thisalternative. Frankish, for example, holds that we are under anillusion in thinking that when we introspect, we come across special,private qualities. But he also says that consciousness is a matter ofbeing related to the world in various informational and reactive ways.This suggests that he holds that consciousness really does exist andthus also qualia in sense (1). Still, there are other passages inFrankish that endorse the unqualified line, and overall he seems toaccept the strong illusionist view.

This position is not easy to take seriously; for what could be moreobvious than the existence of conscious experience? Adherents of theview may respond that introspection simply leads us astray. On thebasis of introspection, we believe that we undergo experiences (stateswith qualia in sense (1)), but the beliefs so formed are false. Whatwould help strong illusionism here is a theory of introspection whichcan explain the apparent absurdity of the view. Such a theory isproposed in Kammerer 2021.

11. Russellian Monism about Qualia

Russellian Monism (RM) gets its name from a view Bertrand Russell heldin 1927 and that he himself called ‘neutral monism’. Thekey idea of this view is that the fundamental entities inmicro-reality have intrinsic natures not specified in microphysics,natures made up of properties (known as quiddities), some of which arecrucial to consciousness and conscious states. The standard reductiveversion holds that the relevant properties are themselves genuinelyconscious properties (that is, qualia) of various sorts. Advocatesinclude for example, Grover Maxwell (1978), David Chalmers (1995 and1997), Dan Stoljar (2001 and 2006), Galen Strawson (2006), and BarbaraMontero (2010). An alternative version of Russellian Monism has itthat the relevant properties are only proto-phenomenal. On oneinteresting version of this view (panqualityism), these properties arenot genuinely phenomenal since they are unexperienced but they arenonetheless of the same kind as the phenomenal qualities present inour experiences of pain or color (Coleman 2006, 2015). It is aconsequence of this view that the latter qualities themselves arequalities of a sort that are only contingently experienced. What makesthese qualities qualia just is the fact that they are experienced.

There is debate about whether RM is really a physicalist view. Onething at least is clear: RM differs from the usual forms ofphysicalism in its reliance on quiddities and its assertion thatspecific quiddities are crucial to macro-conscious states. Of course,if the Russellian monist holds that some quiddities are genuinelyphenomenal properties, then some physical things will have subjectiveproperties as well as objective ones. And this might lead some to denythat RM is really a form of physicalism. Still, this seems to me averbal dispute about how to use the term‘physicalism’.

Russellian monists can say that they agree with dualists about theconceivability (and indeed metaphysical possibility) of zombies.Zombies are conceivable, they can claim, since it is conceivable thatthere are beings the same as us except for the phenomenally relevantquiddities. These beings are structurally, functionally, andbehaviorally just like us but they lack any conscious states.

The quiddities generally that are phenomenally relevant are verydifferent from macro-phenomenal properties; for it would be absurd tohold that quarks feel pains and itches and experience colors. So howare our qualia related to micro-qualia? This question poses thecombination problem for the Russellian monist about macro-qualia (seehere Goff 2006, Coleman 2014, Lewtas 2013, Roelofs 2019, Tye 2021). Ifour qualia are simple, then there is real emergence and reductiveRussellian Monism is false. On the other hand, if our qualia aregenerated from combinations of micro-qualia, then why is it that ourqualia seem (in some cases at any rate) so simple, so utterly lackingin components? To date, there is no agreed upon solution to thecombination problem.

12. Which Biological Creatures Undergo States with Qualia?

Do frogs have qualia? Or fish? What about honey bees? Somewhere downthe phylogenetic scale phenomenal consciousness ceases. But where? Itis sometimes supposed that once we begin to reflect upon much simplerbeings than ourselves — snails, for example — we are leftwith nothing physical or structural that we could plausibly take tohelp us determine whether they are phenomenally conscious (Papineau1994). There is reallyno way of our knowing if spiders aresubject to states with qualia, as they spin their webs, or if fishundergo any phenomenal experiences, as they swim about in the sea.

Representationalism has the beginnings of an answer to the abovequestions. If what it is for a state to have phenomenal character is(very roughly) that it be a state that (i) carries information aboutcertain features, internal or external, and (ii) is such that thisinformation stands ready and available to make a direct difference tobeliefs and desires (or belief- and desire-like states), thencreatures that are incapable of reasoning, of changing their behaviorin light of assessments they make, based upon information provided tothem by sensory stimulation of one sort or another, are notphenomenally conscious. Tropistic organisms, on this view, feel andexperience nothing. They have no qualia. They are full-fledgedunconscious automata or zombies, rather as blindsight subjects arerestricted unconscious automata or partial zombies with respect to arange of visual stimuli.

Consider, for example, the case of plants. There are many differentsorts of plant behavior. Some plants climb, others eat flies, stillothers catapult out seeds. Many plants close their leaves at night.The immediate cause of these activities is something internal to theplants. Seeds are ejected because of the hydration or dehydration ofthe cell walls in seed pods. Leaves are closed because of watermovement in the stems and petioles of the leaves, itself induced bychanges in the temperature and light. These inner events or states aresurely not phenomenal. There is nothing it is like to be a Venus FlyTrap or a Morning-Glory.

The behavior of plants is inflexible. It is genetically determinedand, therefore, not modifiable by learning. Natural selection hasfavored the behavior, since historically it has been beneficial to theplant species. But it need not be now. If, for example, flies start tocarry on their wings some substance that sickens Venus Fly Traps forseveral days afterwards, this will not have any effect on the plantbehavior with respect to flies. Each Venus Fly Trap will continue tosnap at flies as long as it has the strength to do so.

Plants do not learn from experience. They do not acquire beliefs andchange them in light of things that happen to them. Nor do they haveany desires. To be sure, we sometimes speak as if they do. We say thatthe wilting daffodils are just begging to be watered. But we recognizefull well that this is a harmless façon de parler. What we meanis that the daffodilsneed water. There is here nogoal-directed behavior, no purpose, nothing that is the result of anylearning, no desirefor water.

Plants, on the representational view, are not subject to any qualia.Nothing that goes on inside them is poised to make a direct differenceto what they believe or desire, since they have no beliefs ordesires.

Reasoning of the above sort can be used to make a case that eventhough qualia do not extend to plants and paramecia, qualia are verywidely distributed in nature (see Tye 1997, 2000). Of course, such acase requires decisions to be made about the attribution of beliefsand desires (or belief- and desire-like states) to much simplercreatures. And such decisions are likely to be controversial in somecases. Moreover, representationalism itself is a very controversialposition. The general topic of the origins of qualia is not one onwhich philosophers have said a great deal. (For a general,wide-ranging discussion of this issue that is neutral on the nature ofqualia, see Tye 2016, also Godfrey-Smith 2020, Birch 2024.)

13. Qualia and AI

One possible reaction to the view that machines might experiencequalia is simple: silicon chips are the wrong sort of stuff to supportqualia. Phenomenal consciousness is a biological phenomenon. But whysuppose that? In the biological world, creatures as physically diverseas octopi, bees, fish, and human beings have been credited with havingfeelings of various sorts. The brains of these creatures are verydifferent physically. Why not then machines too? There is also a wellknown argument which purports to show that silicon chips can supportqualia (Chalmers 1995b).This argument asks you to imagine the neuronsin your own visual cortex being replaced one by one with silicon chipswith precisely the same local functions as the neurons they replace.In the final case, every neuron in the system has been replaced by achip, and there are no biochemical mechanisms playing an essentialrole. This, it seems, would not change any of your beliefs, includingyour beliefs about your own experiences (for functionally everythingwould be as before). If this is right, it seems that you would have tocontinue to be subject to states with visual qualia, since it isplausible to suppose that you could not continue to believe that youwere subject to visual experiences and yet on the inside have no suchphenomenal states at all.

What about actual machines? One extreme view is that some LargeLanguage Models are already conscious, since they can talk as if theyare conscious, including, for example, talking about engaging intrade-offs of the sort characteristic in humans in some cases of pain(Keeling et al 2024). However, talking about trade-offs and actuallyengaging in them are two entirely different things. It is the capacityto do the latter (for example, if one is hungry, continuing to hold onto a very hot plate to get the food on it even though one is feelingpain from the heat) that is relevant to actual agreed upon cases ofpain. A more plausible suggestion is that we first try to decidewhether the machine shows any glimmers of intelligence, since in theanimal world wherever we find consciousness, we find at least somebasic level of intelligence. We then look at overall behavioralpatterns. If a multi-modal robot, using a network of internal cellslike those found in Large Language Models but capable of taking a muchbroader range of inputs, produces the same pattern of complexbehaviors as we do when we feel pain (for example, responding tobodily damage via sensors, withdrawing from damaging stimuli andprotecting itself from them, engaging in trade-offs, producing facialexpressions like those of people in pain), and it does so viacognitive states that interact as ours do in such circumstances, thenthat at least gives us reason to prefer the view that it feels pain tothe denial of that view. On this view, the attribution of qualia torobots is much like the attribution of qualia to nonhuman animals.

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Acknowledgments

The editors would like to thank Pat Hayes for bringing a corruption ofthe text to our attention.