The Problem of Perception is a pervasive and traditional problem aboutour ordinary conception of perceptual experience. The problem iscreated by the phenomena of perceptual illusion and hallucination: ifthese kinds of error are possible, how can perceptual experience bewhat we ordinarily understand it to be: something that enables directperception of the world? These possibilities of error challenge theintelligibility of our ordinary conception of perceptual experience;the major theories of experience are responses to this challenge.

• 1. Our Ordinary Conception of Perceptual Experience
  • 1.1 Starting Points
  • 1.2 Ordinary Objects
  • 1.3 Presentation
  • 1.4 Direct Realism
  • 1.5 The Character of Experience
  • 1.6 The Common Kind Claim
• 2. The Problem of Perception
  • 2.1 The Argument from Illusion
  • 2.2 The Argument from Hallucination
• 3. Theories of Experience
  • 3.1 The Sense-Datum Theory
    • 3.1.1 The Sense-Datum Theory in Outline
    • 3.1.2 The Sense-Datum Theory and the Problem of Perception
    • 3.1.3 The Sense-Datum Theory and our Ordinary Conception of Perceptual Experience
    • 3.1.4 The Sense-Datum Theory and Perception of the World
    • 3.1.5 Objections to the Sense-Datum Theory
  • 3.2 Adverbialism
    • 3.2.1 Adverbialism in Outline
    • 3.2.2 The Adverbialism and Qualia
    • 3.2.3 Objections to Adverbialism
    • 3.2.4 Adverbialism and the Problem of Perception
    • 3.2.5 Adverbialism and Our Ordinary Conception of Perceptual Experience
    • 3.2.6 Adverbialism and Perception of the World
  • 3.3 Intentionalism
    • 3.3.1 Intentionalism in Outline
    • 3.3.2 Sources of Intentionalism
    • 3.3.3 The Intentional Content of Perceptual Experience
    • 3.3.4 Intentionalism and the Problem of Perception
    • 3.3.5 Intentionalism and Perception of the World
    • 3.3.6 Intentionalism and our Ordinary Conception of Perceptual Experience
  • 3.4 Naive Realist Disjunctivism
    • 3.4.1 Naive Realism in Outline
    • 3.4.2 Naive Realism and the Problem of Perception
    • 3.4.3 The Development of Naive Realist Disjunctivism
    • 3.4.4 Naive Realism Disjunctivism and our Ordinary Conception of Perceptual Experience
• 4. Conclusion
• Bibliography
  • Further reading
• Academic Tools
• Other Internet Resources
• Related Entries

1. Our Ordinary Conception of Perceptual Experience

A.D. Smith claims that what most authors have in mind in talking aboutthe Problem of Perception is the “question of whether we canever directly perceive the physical world”, where “thephysical world” is understood in a realist way: as having“an existence that is not in any way dependent upon its being...perceived or thought about” (2002: 1). The arguments at theheart of the Problem of Perception challenge thisdirectrealist perspective on perceptual experience. But since thisperspective is embedded within ourordinary conception ofperceptual experience, the problem gets to the heart of our ordinaryways of thinking.

So, what is our ordinary conception of perceptual experience? And howdoes it embed a direct realist perspective?

1.1 Starting Points

We conceive of perceptual experiences as occurrences with phenomenalcharacter. The phenomenal character of an experience is what it islike for a subject to undergo it (Nagel (1974)). Our ordinaryconception of perceptual experience emerges from first-personalreflection on its character, rather than from scientificinvestigation; it is a conception of experience from a “purelyphenomenological point of view” (Broad 1952: 3–4). We’llpresent this conception by outlining what phenomenological reflectionsuggests first about theobjects (§1.2),structure (§1.3), andcharacter(§1.5) of experience, and then about the relation between veridical,illusory, and hallucinatory experiences, and in particular whetherthese cases form acommon kind (§1.6).

Let’s begin with P.F. Strawson’s idea that “maturesensible experience (in general) presents itself as, in Kantianphrase, an immediate consciousness of the existence of things outsideus” (1979: 97), and similarly McDowell’s idea thatperceptual experience appears to be an “openness to theworld” (1994: 111), conceived of as openness to mind-independentreality (1994: 25–26).

These ideas reflect the basic phenomenological observation thatperceptual experiences have objects, and more specifically directobjects: objects that are simply perceived or experienced, but not invirtue of the perception or experience of distinct, more“immediate”, objects.

Various authors appeal to a notion of directness in outlining ourordinary conception of perceptual experience, and the Problem ofPerception. A dissenting voice is Austin (1962), and for recentcritical discussion see Martin (2017). For further discussion of howto understand notions of direct and indirect perception, see Jackson(1977), Snowdon (1992), Foster (2000), Smith (2002), and Martin(2005).

This starting point gives rise to the following questions (cf. Martin1998: 176):

1. The Objects Question: what is the nature of the directobjects of experience?
2. The Structure Question: in what sense are experiencesdirectlyof their objects?

Let’s turn to the answers to these questions suggested byStrawson and McDowell’s remarks (for a more critical stance onthese remarks see Mackie (2020)).

1.2 Ordinary Objects

Strawson begins his argument by asking how someone might typicallyrespond to a request for a description of their current visualexperience. He says that it is natural to give the following kind ofanswer: “I see the red light of the setting sun filteringthrough the black and thickly clustered branches of the elms; I seethe dappled deer grazing in groups on the vivid greengrass…” (1979: 97). There are two ideas implicit in thisanswer. First, the description talks about objects which are thingsdistinct from experience. Second, the description is“rich”, describing the nature of the experience not merelyin terms of simple shapes and colours; but in terms of the familiarthings we encounter in the “lived world” in all theircomplexity (see also Heidegger (1977: 156)).

So, we can highlight the following answer to the Objects Question:

• Ordinary Objects: perceptual experiences aredirectly ofordinary mind-independent objects.

There are three things to clarify about this. First, it incorporatesrealism in that it appeals to the notion of a mind-independent objectof experience: one that doesn’t depend for its existence uponexperience. Second, it concerns familiar or ordinary objects, thingsthat we admit as part of common-sense ontology. Third, “objectof experience” is understood broadly to encompass perceptibleentities in mind-independent reality including ordinary materialobjects, but also features and other entities (e.g., events,quantities of stuff). When we talk of “ordinary objects”,“the world” etc, we take this as shorthand for: familiaror ordinary mind-independent perceptible entities.

Some writers have defended a thesis known as the transparency ofexperience (see Harman (1990); Speaks (2009); Tye (1992, 1995, 2000);Thau (2002); and for critical discussions, Martin (2002a), Smith(2008), Stoljar (2004) and Soteriou (2013)).Transparency is normally defined as the thesis thatintrospecting what it is like for a subject to have an experience doesnot reveal awareness of experiences themselves, but only of theirmind-independent objects. There are two claims here: (i) introspectionreveals the mind-independent objects of experience, and (ii)introspection does not reveal any features of anything else.

Transparency is similar toOrdinaryObjects. The latter claim does involve something like (i).But it does not involve (ii). And it is not obvious that (ii) is partof our ordinary conception of perceptual experience. After all, wereadily admit that an ordinary scene (e.g., a snow-covered churchyard)can look very different when one removes one’s glasses:one’s visual experience then becomes blurred. But thisphenomenal difference does not seem to derive from any apparentdifference in the objects of experience. Rather, it seems to be adifference in the way in which those objects are experienced. (See Tye(2000) and Gow (2019) for different responses. For further discussion,see Crane (2000), Smith (2008), Allen (2013), and French (2014). For adifferent challenge to (ii) and its ilk see Richardson (2010) andSoteriou (2013: Chapter 5), and French (2018)).

1.3 Presentation

What, then, about the Structure Question? Strawson speaks of themanner in which we directly experience objects as a matter of“immediate consciousness”, and McDowell talks of our“openness” to objects. Other notions commonly invoked hereinclude the idea that we are directly “acquainted” withobjects, we directly “apprehend” them, they are“given” to us, or directly “present to themind”. What these notions all aim to capture is the intuitiveidea that perceptual experience of an object involves a specialintimate perceptual relation to an object, a relation whichdifferentiates perceptual experiences from non-perceptual states ofmind which are similarly directed on the world (e.g., non-sensory,non-perceptual thoughts).

One function of this relation is to make objects present in such a waythat they can shape or mould the character of one’s experience.In virtue of this, perceptions of the world are unlike(non-perceptual) thoughts about the world: they are constrained by theobjects actually given. One’s perception of a snow-coveredchurchyard is responsive to how the churchyard is now, as one isperceiving it. But one’s (non-perceptual) thought need not be:in the middle of winter, one can imagine the churchyard as it is inspring, and one can think of it in all sorts of ways which are not theways it presently is.

In what follows we will use the notion of perceptual presentation tocapture this perceptual relation. We can thus highlight the followinganswer to the structure question:

• Presentation: perceptual experiences are directperceptual presentations of their objects.

In what follows, we use “direct presentation” forshort.

1.4 Direct Realism

Putting the pieces together, our ordinary conception of perceptualexperience involves:

• Direct Realist Presentation: perceptualexperiences aredirect perceptual presentations of ordinaryobjects.

If direct perceptual presentation of an ordinary object is a way ofdirectly perceiving it, then this gives us:

• Direct Realism: we can directly perceive ordinaryobjects.

1.5 The Character of Experience

We can now shed light on the phenomenal character of perceptualexperience. Consider, then, the following question:

3. The Character Question: what determines the phenomenal characterof experience?

We began with the basic phenomenological observation that perceptualexperiences are directly of things. A similarly basic observation isthat what it is like for us to experience is at least partly a matterof such things appearing certain ways to us. When we reflect upon whatdetermines what it is like to have an experience, we naturally beginwith what is presented to us, and how it is presented. This is why itis so natural for Strawson to describe his experience in terms of whathe perceives, and for Martin to say that “our awareness of whatan experience is like is inextricably bound up with knowledge of whatis presented to one in having such experience” (1998: 173).

Further, when we reflect upon what determines what it is like for usto experience, we naturally begin with the ordinary objects that arepresented to us, and how they are presented or appear. This is why itis so natural for Strawson to describe his experience in terms of suchobjects, and why many find (at least component (i) of) Transparencyintuitive.

So, we can highlight the following answer to the CharacterQuestion:

• Direct Realist Character: the phenomenalcharacter of experience is determined, at least partly, bythedirect presentation of ordinary objects.

1.6 The Common Kind Claim

Perceptual experiences are not just veridical experiences: there areillusions and hallucinations too. What does phenomenologicalreflection say about how these cases relate to each other? Morespecifically:

4. The Common Kind Question: are veridical, illusory, andhallucinatory experiences fundamentally the same, do they form of acommon kind?

In the context of the Problem of Perception, these cases are usuallydistinguished as follows: a veridical experience is an experience inwhich an ordinary object is perceived, and where the object appears asit is; an illusory experience is an experience in which an ordinaryobject is perceived, and where the object appears other than it is; ahallucination is an experience which seems to the subject exactly likea veridical perception of an ordinary object but where there is nosuch perceived or presented object. (For illusions and hallucinationswhich don’t fit these forms, see Johnston (2011), and Batty andMacpherson (2016)).

Clearly, there are differences between these categories, but from aphenomenological point of view, these experiences seem the same in atleast this sense: for any veridical perception of an ordinary object,we can imagine a corresponding illusion or hallucination which cannotbe told apart or distinguished, by introspection, from the veridicalperception. This suggests the following answer to the Common KindQuestion:

• Common Kind Claim: veridical, illusory, andhallucinatory experiences (as) of an F are fundamentally the same;they form acommon kind.

Thus, a veridical, illusory, and hallucinatory experience, all alikein being experiences (as) of a churchyard covered in white snow, arenot merely superficially similar, they are fundamentally the same:these experiences have the same nature, fundamentally the same kind ofexperiential event is occurring in each case. Any differences betweenthem are external to their nature as experiences (e.g., to do with howthey are caused).

2. The Problem of Perception

The Problem of Perception is that if illusions and hallucinations arepossible, then perceptual experience, as we ordinarily understand it,is impossible. The Problem is animated by two central arguments: theargument from illusion (§2.1) and the argument from hallucination(§2.2). (A similar problem arises with reference to otherperceptual phenomena such as perspectival variation or conflictingappearances: see Burnyeat (1979) and the entry on sense-data). Forsome classic readings on these arguments, see Moore (1905, 1910);Russell (1912); Price (1932); Broad (1965); and Ayer (1940), seeSwartz (1965) for a good collection of readings. And for more recentexpositions see Snowdon (1992), Valberg (1992), Robinson (1994:Chapter 2), Smith (2002: Chapters 1 and 7), Martin (2006), Fish (2009:Chapter 2), Brewer (2011: Chapter 1) and Pautz (2021).

The two central arguments have a similar structure which we cancapture as follows:

1. In an illusory/hallucinatory experience, a subject is not directlypresented with an ordinary object.
2. The same account of experience must apply to veridical experiencesas applies to illusory/hallucinatory experiences.

Therefore,

3. Subjects are never directly presented with ordinary objects.

(C) contradicts Direct Realist Presentation, and thus our ordinaryconception of perceptual experience. And since Direct Realism seems tofollow from Direct Realist Presentation, the argument challengesDirect Realism too (for more on this see§3.2.6).

Representing the arguments in this basic form enables us to highlighttheir two major movements; what Paul Snowdon calls the base case, andthe spreading step (1992, 2005). In the base case a conclusion aboutjust illusory/hallucinatory experiences is sought: (A). In thespreading step, (B), this result is generalised so as to get (C). Thisgeneralising move works on these background assumptions: (a1) that (B)yields the claim that one is not directly presented with ordinaryobjects in veridical experiences (given (A)), and (a2) if one is notdirectly presented with such objects in even veridical experiences,one never is.

We’ll look at more complex versions of the argument shortly. Aswe’ll see, the main burden on the arguer from illusion is insupporting the relevant version of (A), whereas the main burden on thearguer from hallucination is in defending the relevant version of(B).

Now, the argument here is purely negative. But many philosophers havemoved from this to the further conclusion that since we are alwaysdirectly presented with something in perceptual experience, what weare presented with is a “non-ordinary” object (see§3.1.2).

2.1 The Argument from Illusion

Applying the above structure, the argument from illusion is:

1. In illusory experiences, we are not directly presented withordinary objects.
2. The same account of experience must apply to veridical experiencesas applies to illusory experiences.

Therefore,

3. We are never directly presented with ordinary objects.

Moving beyond the simple formulation, the argument is typicallypresented as involving these steps, for an arbitrary subject S:

1. In an illusion, it seems to S that something has a sensiblequality, F, which the ordinary object supposedly being perceived doesnot have.
2. When it seems to S that something has a sensible quality, F, thenthere is something directly presented to S which does have thisquality.
3. Since the ordinary object in question is, by hypothesis, not-F,then it follows that in an illusion, S is not directly presented withthe ordinary object supposedly being perceived.
4. The same account of experience must apply to both veridical andillusory experiences.

Therefore,

5. In veridical experience, S is not directly presented with theordinary object supposedly being perceived.
6. If S is not directly presented with the ordinary object supposedlybeing perceived in veridical experience, S is never directly presentedwith an ordinary object.

Therefore,

7. We are never directly presented with ordinary objects.

The most controversial premise here is premise (ii). The othersreflect intuitive ways of thinking about perceptual experience, orplausible assumptions. This is clear enough with (i) and (iv). Premise(i) articulates the operative conception of illusions. An example toillustrate is a case where a white wall looks yellow to you, inpeculiar lighting (Smith (2002: 25)). And premise (vi) reflects theintuitive idea that if we aren’t directly presented with theordinary objects we seem to perceive in veridical experiences, then wearen’t directly presented with ordinary objects at all. For itwould be implausible to relinquish the idea that we are directlypresented with the ordinary objects we seem to perceive in veridicalexperience, yet maintain that we can still somehow else be directlypresented with ordinary objects, e.g., with the idea thathallucinations are direct presentations of ordinary objects, or withthe idea that veridical experiences are direct presentations ofordinary objects just not those we seem to perceive.

But what about (iv)? On one way of interpreting this, it reflects theCommon Kind Claimapplied to veridical experiencesand illusions. Furthermore, various authors hold that (iv) issupported by the continuity between veridical experiences and illusoryexperience (Price (1932: 32), Ayer (1940: 8–9), Broad (1952: 9),Robinson (1994: 57), Smith (2002: 26–28): the fact that they may forma “continuous series” in which they “shade into oneanother” (Ayer (1940: 8–9)). This, it is held, supports the ideathat experiential differences between illusions and veridicalperceptions are differences of “degree and not of kind”(Ayer (1940: 8)).

Premise (ii) is a version of what Robinson calls the PhenomenalPrinciple:

If there sensibly appears to a subject to be something which possessesa particular sensible quality then there is something of which thesubject is aware which does possess that sensible quality (1994: 32).

C.D. Broad motivates this principle on explanatory grounds. In casesof perceptual experience things appear some ways rather than others tous. We need to explain this. Why does the penny look elliptical to youas opposed to some other shape? One answer is that there is somethingdirectly presented to you which is in fact elliptical. Thus, as Broadsays “If, in fact, nothing elliptical is before my mind, it isvery hard to understand why the penny should seem elliptical ratherthan of any other shape.” (1923: 240). Other philosophers havesimply taken the principle to be obvious. H.H. Price, for example,says that “When I say ‘this table appears brown tome’ it is quite plain that I am acquainted with an actualinstance of brownness” (1932: 63).

So much for the argument’s main premises. How is it supposed towork? Here we find the suggestion that it hinges on an application ofLeibniz’s Law of the Indiscernibility of Identicals (Robinson(1994: 32); Smith (2002: 25)). The point is that (i) and (ii) tell usthat in an illusory experience you are directly presented with an Fthing, but the ordinary object supposedly being perceived is not F,thus the F thing and the ordinary object are not identical, byLeibniz’s Law. On these grounds, the conclusion of the base caseis supposed to follow. And then the ultimate conclusion of theargument can be derived from its further premises.

But as French and Walters (2018) argue, this is invalid. (i), (ii) andLeibniz’s Law entail that in an illusory experience you aredirectly presented with an F thing which is non-identical to theordinary object supposedly being perceived. However, thisdoesn’t entail that in the illusion you are not directlypresented with the ordinary object. You might be directly presentedwith the ordinary object as well as the F thing. We should be carefulto distinguish not being directly presented with the ordinary objectfrom being directly presented with something which is not the ordinaryobject (e.g., between not being directly presented with the whitewall, and being directly presented with something that is not thewhite wall, e.g., a yellow entity). The argument is invalid inconflating these two ideas.

One option for fixing the argument is to introduce what French andWalters call theExclusion Assumption (cf., Snowdon(1992: 74)): If in an illusion of an ordinary object as F, a subjectis directly presented with an F thing non-identical to the ordinaryobject, then they are not also directly presented with the ordinaryobject.

This assumption bridges the gap between the conclusion actuallyachieved: namely, in an illusory experience S is directly presentedwith an F thing non-identical to the ordinary object, and the desiredconclusion (iii). But whether this assumption is defensible remains tobe seen. We leave this and the issue of validity aside and considerresponses from different theories of experience below.

2.2 The Argument From Hallucination

The argument from hallucination relies on the possibility ofhallucinations as understood above. Such hallucinations are not likereal drug-induced hallucinations or hallucinations suffered by thosewith certain mental disorders. They are rather supposed to be merelypossible events. For example, suppose you are now having a veridicalperception of a snow-covered churchyard. The assumption thathallucinations are possible means that you could have an experiencewhich is subjectively indistinguishable—that is,indistinguishable by you, “from the inside”—from averidical perception of a snow-covered churchyard, but where there isin fact no churchyard presented or there to be perceived. The claimthat such hallucinations are possible is widely accepted but notindisputable (see Austin (1962) and Masrour (2020)). For more onhallucinations, see Macpherson and Platchias (2013).

The argument from hallucination runs as follows:

1. In hallucinatory experiences, we are not directly presented withordinary objects
2. The same account of experience must apply to veridical experiencesas applies to hallucinatory experiences.

Therefore,

3. We are never directly presented with ordinary objects.

Unlike with the argument from illusion, the base case doesn’trely on the Phenomenal Principle:(A) simply fallsout of what hallucinations are supposed to be.

The spreading step can be interpreted in terms of theCommonKind Claim, applied to veridical experiences andhallucinations. Accepting (B) understood in this way puts a constrainton what can be said about the nature of veridical experience: whatevercan be said had better be able to apply to hallucinations too. Theargument is that, given (A), this then rules out an account ofveridical experiences as direct presentations of ordinary objects. Butthen (C) follows (given that if we are not directly presented withordinary objects in veridical experience, we never are).

With the argument understood in this way, we can see the power of theProblem of Perception. (A) is intuitive, and (B) is part of ourordinary conception of perceptual experience, yet what follows, (C),contradicts another aspect of our ordinary conception (DirectRealist Presentation). Thus, the very intelligibility of ourordinary conception of perceptual experience is threatened.

Now it might be argued that theCommon Kind Claimapplied to veridical perceptions and hallucinations is not asplausible as it is when applied to veridical perceptions andillusions. For veridical and illusory experiences are more naturallygrouped together anyway, unlike veridical perceptions andhallucinations. For, at least before we encounter the argument fromillusion, veridical perceptions and illusions are both naturallythought of as direct presentations of ordinary objects (it’sjust that in illusory cases the presented objects appear other thanthey are). However, as noted above, from aphenomenologicalpoint of view, hallucinations too seem as though they are directpresentations of ordinary objects:from the subject’sperspective a hallucination as of an F cannot be distinguishedfrom a veridical experience of an F. This is why it seems so plausibleto think of them as fundamentally the same.

Even so, theCommon Kind Claim applied to veridicalperceptions and hallucinations is controversial, and rejecting it iscentral to thedisjunctivist response to the Problem ofPerception that we will consider later (§3.4).

3. Theories of Experience

A number of philosophical theories of experience have emerged asresponses to the Problem of Perception, or in relation to suchresponses. Here we consider the sense-datum theory (§3.1), adverbialism (§3.2), intentionalism (§3.3), and naive realist disjunctivism (§3.4). In this exposition we do not consider much the possibility of hybridviews. The way these positions relate to the Problem of Perception ismapped most clearly in Martin (1995, 1998, 2000).

We present these theories as operating on two levels. On Level 1, theytell us about the nature of experience. With the exception ofadverbialism (for reasons that will emerge shortly), this can beinvestigated by considering the stance of each theory on the nature ofthe objects of experience, and the structure of our experience ofobjects. On Level 2, they tell us how what is said at the first levelbears on the explanation of the character of experience. We alsoconsider how each theory addresses the common kind question.

In what follows, we’ll work with the example of a visualexperience of a snow-covered churchyard. To simplify, we will discussthe character of this experience in terms of one aspect of it: thingslooking white to a subject. The question at Level 1 is: what is thenature of such an experience? Does it involve the direct presentationof objects, or not? If so, what sorts of objects? If not, how are weto understand the nature of this experience? The question at Level 2is: what is it about the nature of this experience that explains whythings look any way at all to someone, and why they look,specifically, white?

3.1 The Sense-Datum Theory

3.1.1 The Sense-Datum Theory in Outline

What does the sense-datum theorist say at Level 1? On this theory,whenever a subject has a sensory experience, there is something whichis presented to them. This relational conception of experience issometimes called an “act-object” conception, since itposits a distinction between the mental act of being presented withsomething, and the object presented. More precisely, the sense-datumtheorist holds that an experience in which something appears F to S,where F is a sensible quality (e.g., whiteness), consists in S beingdirectly presented with something which actually is F (e.g. a whitething). They thus endorse the aforementionedPhenomenalPrinciple. The sense-datum theorist calls these objects ofperception “sense-data”.

Understood in this way, a sense-datum is justwhatever it isthat you are directly presented with that instantiates the sensiblequalities which characterise the character of your experience. Thisinvolves no further claim about thenature of sense-data,though as we’ll see shortly, sense-datum theorists do go on tomake further claims about the nature of sense-data.

What about Level 2? With respect to our example, the sense-datumtheorist claims that things appearing any way at all to you consistsin the fact that you are directly presented with a sense-datum, andthings appearing white to you consists in the fact that you aredirectly presented with a white sense-datum. The character of yourexperience is explained by an actual instance of whiteness manifestingitself in experience.

The sense-datum theorist endorses theCommon KindClaim. So, a veridical experience in which something appearswhite to you consists in your being directly presented with a whitesense-datum; but so do corresponding illusory and hallucinatoryexperiences. These experiences have the same nature.

3.1.2 The Sense-Datum Theory and the Problem of Perception

The sense-datum theorist endorses the following negative claim:

1. We are never directly presented with ordinary objects.

They accept this on the basis of the arguments from illusion andhallucination. However, the intended contrast with Direct RealistPresentation usually involves a stronger claim:

2. We are only ever directly presented withsense-data,which are non-ordinary objects.

This involves a positive claim about what weare directlypresented with, given that we are never directly presented withordinary objects. And it embeds a claim about the nature of sense-datathat goes beyond that outlined above: now sense-data are understood asnon-ordinary objects.

Sense-datum theorists divide over exactly how to understand sense-datainsofar as they are non-ordinary. Some early sense-datum theorists(such as Moore) initially took sense-data to be mind-independent, butpeculiar non-physical objects. Later theorists treat sense-data asmind-dependent entities (Robinson (1994)). This is how the theorytends to be understood in literature from second half of the 20thcentury on.

Sense-datum theorists have developed more positive Problem ofPerception style reasoning to support these additional ideas. Forinstance, Macpherson (2013: 12–13) outlines a more complicated versionof the argument from hallucination than that above which concludesthat “All perceptual experience, hallucinatory andnon-hallucinatory, involves awareness of a mind-dependent, nonphysicalobject—a sense-datum”. And some sense-datum theorists haveattempted to support non-ordinary sense-data outside of the context ofthe Problem of Perception (see Jackson (1977) and Lowe (1992)).

From now on when we speak of “sense-data” we will meannon-ordinary sense-data, and when we speak of the “sense-datumtheory” we have in mind a theory that endorses not just (1) but(2).

3.1.3 The Sense-Datum Theory and Our Ordinary Conception of Perceptual Experience

The sense-datum theorist agrees with some aspects of our ordinaryconception of perceptual experience. They endorse theCommonKind Claim. They also endorsePresentation– the idea that the direct objects of experience areperceptually presented to us. It’s just that they don’tagree that the direct objects of experience are ordinary objects– they are non-ordinary sense-data. They thus rejectOrdinary Objects, and henceDirect RealistPresentation, andDirect RealistCharacter.

3.1.4 The Sense-Datum Theory and Perception of the World

Is the sense-datum theory a theory on which we completely lose contactwith the world, a theory on which we cannot perceive the world?

Though it is possible for a sense-datum theorist to accept this, amore popular position has been one on which we still have some form ofperception of the world, just not direct perception. That is, thesense-datum theorist can say that we indirectly perceive ordinaryobjects: we perceive them by being directly presented with sense-data.A sense-datum theorist who says this is known as an indirect realistor representative realist (see the entry onepistemological problems of perception). The task for such a sense-datum theorist is to spell out how thedirect presentation of sense-data can lead to indirect perception ofordinary objects. This is something early sense-datum theoristspursued by asking how sense-data are related to ordinary objects. Atheorist who denies that we perceive mind-independent objects at all,directly or indirectly, but only sense-data construed as mentalentities, is known as a phenomenalist or an idealist (see Foster(2000), see Crane and Farkas (2004: Section 2) for an introduction tothe subject; and the entry onidealism).

3.1.5 Objections to the Sense-Datum Theory

The sense-datum theory was widely rejected in the second half of the20th century, though it still had its occasional champions (e.g.,Jackson (1977), O’Shaughnessy (2000, 2003), Lowe (1992),Robinson (1994), Foster (2000)). A number of objections have been madeto the theory. Some of these are objections specifically to theindirect realist version: for example, the claim that the theory givesrise to an unacceptable “veil of perception” between mindand world. The idea is that sense-data “interpose”themselves between perceivers and ordinary objects, and thereforeproblematise our perceptual, cognitive, and epistemic access to theworld. In response, the indirect realist can say that sense-data arethe medium by which we perceive ordinary objects, and no more create a“veil of perception” than the fact that we use words totalk about things creates a “veil of words” between us andwhat we talk about. (For recent discussion see Silins (2011)).

A common objection is to attack thePhenomenalPrinciple (see Barnes (1944–5); Anscombe (1965)). Theobjection is that thePhenomenal Principle isfallacious. It is not built into the meaning of “somethingappears F to one” that “one is directly presented with anF thing”. Defenders of the sense-datum theory can respond thatthe Phenomenal Principle is not supposed to be a purelylogical inference; it is not supposed to be true simply becauseof the logical form or semantic structure of “appears” andsimilar locutions. Rather, it is true because of specificphenomenological facts about perceptual experience. But this justmeans that theorists who reject the Phenomenal Principle are notdisagreeing about whether the Phenomenal Principle involves a fallacyor about some semantic issue, but rather about the nature ofexperience itself.

Another influential objection to sense-data comes from the prevailingnaturalism of contemporary philosophy. Naturalism (or physicalism)says that the world is entirely physical in its nature: everythingthere is supervenes on the physical, and is governed by physical law.Many sense-datum theorists are committed to the claim thatnon-ordinary sense-data are mind-dependent: objects whose existencedepends on the existence of states of mind. Is this consistent withnaturalism? If so, the challenge is to explain how an object can bebrought into existence by the existence of an experience, and how thisis supposed to be governed by physical law.

Many contemporary sense-datum theorists, however, will not be moved bythis challenge, since they are happy to accept the rejection ofnaturalism as a consequence of their theory (Robinson (1994), Foster(2000)). On the other hand, one might think that there is no conflicthere with naturalism, as long as experiences themselves are part ofthe natural order. But if sense-data are non-ordinary in beingmind-independent butnon-physical, then it is much less clearhow naturalism can be maintained (cf., what Martin (2004, 2006) calls“experiential naturalism” which serves as a constraint ontheories of experience and rules out some but not all forms of thesense-datum theory).

For other objections to the sense-datum theory, including the worrythat it must admit “indeterminate” sense-data (e.g., onthe basis of seeing a speckled hen, which appears to have a number ofspeckles but no definite number), see the entry onsense-data.

3.2 Adverbialism

3.2.1 Adverbialism in Outline

Part of the point of adverbialism, as defended by Ducasse (1942) andChisholm (1957) is to do justice to the phenomenology of experiencewhilst avoiding the dubious metaphysical commitments of thesense-datum theory. The only entities which the adverbialist needs toacknowledge are subjects of experience, experiences themselves, andways these experiences are modified. Let us explain.

At Level 1, the adverbialist rejects thePhenomenal Principleand the whole idea that experience consists in being directlypresented with perceptible entities. For the adverbialist, whensomeone has an experience of something white, something like whitenessis instantiated, but in the experience itself, not a presented thing.This is not to say that the experience is white, but rather that theexperience ismodified in a certain way, the way we can call“perceiving whitely”. The canonical descriptions ofperceptual experiences, then, employ adverbial modifications of theperceptual verbs: instead of describing an experience assomeone’s “visually sensing a white sphere”, thetheory says that they are “visually sensing whitely andspherely”. This is why this theory is called the“adverbial theory”; but it is important to emphasize thatit is more a theory about the nature of experience itself than it is asemantic analysis of sentences describing experience.

It is also intended as a theory of the character of experience (Level2). The adverbialist claims that things appearing white to youconsists in yousensing whitely. It is because you aresensing insome way that explains why things appear a certainway to you at all, and it is the fact that you are sensingwhitely that explains why things appearwhite toyou, rather than some other way. The character of your experience isexplained by the specific “white” way in which yourexperience is modified.

The adverbialist endorses the Common Kind Claim. So,a veridical experience in which something appears white to you,consists in you sensing whitely, but so do corresponding illusory andhallucinatory experiences: these experiences have the same nature.

3.2.2 Adverbialism and Qualia

When used in a broad way, “qualia” picks out whateverqualities a state of mind has which constitute the state ofmind’s having the phenomenal character it has. In this broadsense, any phenomenally conscious state of mind has qualia. (This isthe way the term is used in, e.g., Chalmers (1996)). Used in a narrowway, however, qualia are non-intentional, intrinsic properties ofexperience: properties which have no intentional or representationalaspects whatsoever. To use Gilbert Harman’s apt metaphor, qualiain this sense are “mental paint” properties (1990). Harmanrejects mental paint, but the idea of experience as involving mentalpaint is defended by Block (2004)).

It is relatively uncontroversial to say that there are qualia in thebroad sense. It can be misleading, however, to use the term in thisway, since it can give rise to the illusion that the existence ofqualia is a substantial philosophical thesis when in fact it issomething which will be accepted by anyone who believes in phenomenalcharacter. (Hence Dennett’s (1991) denial of qualia can seembewildering if “qualia” is taken in the broad sense). Itis controversial to say that there are qualia in the narrow sense,though, and those who have asserted their existence have thereforeprovided arguments and thought-experiments to defend this assertion(see Block (1997), Peacocke (1983: Chapter 1), Shoemaker (1990)). Inwhat follows, “qualia” will be used exclusively in thenarrow sense.

As noted, adverbialism is committed to the view that experiencingsomething white, for example, involves your experience being modifiedin a certain way: experiencing whitely. A natural way to understandthis is in terms of the idea that the experience is an event, and themodification of it is a property of that event. Since this property isboth intrinsic (as opposed to relational or representational) andphenomenal then this way of understanding adverbialism is committed tothe existence of qualia.

3.2.3 Objections to Adverbialism

An important objection to adverbialism is the “Many PropertyProblem” proposed by Frank Jackson (1975). Consider someone whosenses a brown square and a green triangle simultaneously. Theadverbialist will characterize this state of mind as “sensingbrownly and squarely and greenly and triangularly”. But how canthey distinguish the state of mind they are describing in this wayfrom that of sensing a brown triangle and a green square? Thecharacterization fits that state of mind equally well. Obviously, whatis wanted is a description according to which the brownness“goes with” the squareness, and the greenness “goeswith” the triangularity. But how is the adverbialist to do thiswithout introducing objects of experience—the things which arebrown and green respectively—or a visual field with a spatialstructure? The challenge is whether the adverbialist can properlyaccount for the spatial structure and complexity in what is given invisual experience. See Tye (1984), Breckenridge (2018: Chapter 10),and D’Ambrosio (2019) for adverbialist responses to thischallenge. For a helpful overview, see Fish (2010: Chapter 3).

A further challenge is that adverbialism is “incapable of doingjustice to the most obvious and indeed essential phenomenological factabout perceptual consciousness… namely… itsobject-directness” (Butchvarov (1980: 272)). Recall here thebasic phenomenological observation we began with: perceptualexperiences are directly of things.

As we’ve seen, at Level 1, the adverbialist denies thatperceptual experiences are direct presentations of objects. And atLevel 2, in explaining character, the adverbialist assigns no role tothe direct presentation of things, just ways of sensing. But then ifit is an aspect of the phenomenology of experience that ourexperiences have direct objects, then it is not clear that theadverbialist has the resources to capture this. For the adverbialist,to capture your experience of a snow-covered churchyard we invokeseeing whitely not seeing a whitething. How, then, can weexplain whyphenomenologically, your experience is directlyof a white thing – or even why it seems to be object-directed inthis way? Butchvarov’s charge is that the adverbialistdoesn’t have the resources to answer these questions. (SeeD’Ambrosio (2019) for a recent adverbialist attempt to capturesomething like object-directness).

3.2.4 Adverbialism and the Problem of Perception

The argument from illusion relies on thePhenomenalPrinciple. In rejecting this, the adverbialist thus rejectsthe argument. But what about the argument from hallucination? Thisdoes not rely on the Phenomenal Principle. The adverbialist accepts(A). And they also accept (B) in the form of theCommon KindClaim. (C) follows (given assumptions (a1) and (a2)). Forthis reason, the adverbialist must rejectDirect RealistPresentation. So, like the sense-datum theorist, theadverbialist must admit that we are never directly presented withordinary objects, not even in veridical experience.

3.2.5 Adverbialism and our Ordinary Conception of Perceptual Experience

Like the sense-datum theorist, though the adverbialist accepts some ofour ordinary conception of perceptual experience (theCommonKind Claim), they reject other aspects of it. The argumentfrom hallucination forces them to rejectDirect RealistPresentation (and thereforeDirect RealistCharacter). Underlying this is the adverbialist’srejection ofPresentation, and arguablyOrdinary Objects too. They rejectPresentation in denying that experiences have arelational structure. And given our discussion of Butchvarov’schallenge, it seems as though they must reject (or at leastdon’t have the resources to accept)OrdinaryObjects. For it is unclear how they can validate thephenomenological claim that experiences are of objects, let alonedirectly of ordinary objects.

So, even though adverbialism arises as a response to the sense-datumtheory, given its almost wholesale rejection of our ordinaryconception of perceptual experience, it is unclear how much of animprovement the approach is in the broader dialectic of the Problem ofPerception.

3.2.6 Adverbialism and Perception of the World

One response to this is that we should not suppose that the only wayto articulate direct realism is through the claim we’ve labelledDirect Realist Presentation. There is another way toarticulate it which, it might be suggested, enables the adverbialistto account for direct perception of the world. Consider, then:

• Direct Realist Presentation: perceptualexperiences are direct perceptual presentations of ordinaryobjects.

This entailsDirect Realism – that we candirectly perceive ordinary objects – on the assumption thatbeing directly perceptually presented with an ordinary object is a wayof directly perceiving it. On this way of thinking, direct perceptionof an ordinary object is built into perceptual experience itself.However, one might reject this claim about experience (asadverbialists do), and still hold that we can have direct perceptionof an ordinary object. How?

Instead of thinking of direct perception of the world as builtinto experience, we can think of direct perception of theworld as builtout of experience together with thesatisfaction of other conditions. This idea is usually developedthrough acausal theory of perception (Grice 1961): whereperception of an object is analysed in terms of (i) experience of anordinary object (conceived as something which is not sufficient forperception), and (ii) the satisfaction of a causal condition whichrequires that the experience be caused by the object (in a non-deviantway). This is a causal theory ofdirect perception on theassumption that the account doesn’t involve any perceptualintermediaries.

The adverbialist might suggest that they can embrace this: bycombining their theory ofexperience with a causal analysisof direct perception. Thus, they can hold that when you have anexperience of a snow-covered churchyard, if this experience isappropriately caused by an ordinary white thing (e.g., some snow),this is what directly perceiving such an object amounts to (given thatno perceptual intermediaries are involved).

However, whether the adverbialist is entitled to this way of makingsense of direct perceptual contact with the world hinges on whetherthey can make sense of the idea of an experienceof an ordinaryobject. But as we have seen in considering Butchvarov’schallenge, it is unclear whether the adverbialist can do this. It isthus unclear whether the adverbialist can really make sense of clause(i).

In response, the adverbialist might offer a causal analysis ofexperiences being of objects. They might thus attempt to fall back onthe idea that an experience in which you sense whitely is anexperience “of” a white thing insofar as it is causallyrelated to a white thing (or, insofar as it is of a type, instances ofwhich are typically caused by white things). However, as Butchvarovargues, the fact that “x is causally related to S’ssensing in a certain way can no more reasonably be described asS’s being conscious of [i.e. having a conscious experience of] xthan the fact that the presence of carbon monoxide in the air iscausally related to S’s having a headache can be described asS’s being conscious of [having a conscious experience of] carbonmonoxide” (1980: 273).

Even if the adverbialistis able to sustain such a causalform of direct realism, it is very different from the phenomenologicalform of direct realism embedded in our ordinary conception ofperceptual experience. It is thus unlikely to satisfy a direct realistsensitive to the phenomenological concerns which give rise to ourordinary conception of perceptual experience.

3.3 Intentionalism

3.3.1 Intentionalism in Outline

The intentionalist holds that we directly experience ordinary objects.The distinguishing feature of the view is a specific conception of themanner in which experiences are directly of ordinary objects: here theintentionalist appeals to intentionality conceived of as a form ofmental representation (hence it is also sometimes called therepresentationalist theory of experience).“Intentionality” is a term with its origins in scholasticphilosophy (see Crane (1998b)), but its current use derives fromBrentano (1874), who introduced the term “intentionalinexistence” for the “mind’s direction upon itsobjects”. Intentional inexistence, or intentionality, issometimes explained as the “aboutness” of mental states(see the entries onFranz Brentano,representational theories of consciousness andintentionality).

At Level 1, then, the intentionalist holds that to experience asnow-covered churchyard is todirectly perceptually representsuch an object (i.e. to represent such an object but not in virtue ofrepresenting another more “immediate” object). At Level 2,this is put to work in explaining phenomenal character. In relation toour example, why is this a case of things appearing any way at all toyou, and why is it a case of things appearing white to you? Here theintentionalist appeals to the experience’s directly representingthings in a certain way, and specifically to experience’sdirectly representing whiteness in the environment, to account forthis. The character of your experience is explained by the specificway in which your experience directly represents the world.

Critics of intentionalism have argued that it does not adequatelydistinguish perceptual experience from other forms of intentionality,and therefore does not manage to capture what is distinctive aboutexperience (Robinson (1994: 164)). One objection of this kind is thatthe aforementioned intentionalist explanation of character isinadequate. The worry is that believing that something is the case,for example, or hoping that something is the case, are both forms ofmental representation, but neither state of mind has any“feel” or phenomenal character to call its own. (Words orimages may come to mind when mentally representing something in thisway, but it is not obvious that these are essential to the states ofmind themselves.) So, the challenge is that if there is nothing aboutrepresentation as such which explains the character of an experience,how is experience supposed to be distinguished from mere thought?

There are a number of ways an intentionalist can respond. One issimply to take it as a basic fact about perceptual intentionality thatit has phenomenal character (see Kriegel (2013)). After all, eventhose who believe in qualia have to accept that some states of mindhave qualia and some do not, and that at some point the distinctionbetween mental states which are phenomenally conscious, and thosewhich are not, just has to be accepted as a brute fact. Anotherresponse is to say that in order to fully explain the phenomenalcharacter of perceptual experience, we need to treat experience asinvolving non-intentional qualia as well as intentionality (seePeacocke (1983: Chapter 1); Shoemaker (1996); Block (1997)). There is,accordingly, a dispute between these intentionalists who accept qualia(like Block and Shoemaker) and those who don’t (like Harman(1990) or Tye (1992)). (For more on this see the entries onqualia andinverted qualia. Additional readings are: Block (2005) (2010), Egan (2006), Hilbertand Kalderon (2000), Marcus (2006), Shoemaker (1990), Speaks (2015),Spener (2003), and Tye (2000)).

Intentionalists endorse theCommon Kind Claim. So, averidical experience of churchyard covered in white snow, consists indirect representation of such a scene, but so do correspondingillusory and hallucinatory experiences: these experiences have thesame nature.

Like adverbialists, the intentionalist has no need to postulatenon-ordinary perceptible entities in the cases of illusion andhallucination. It is not generally true that when a representationrepresents something (as being F), there has to actually be something(which is F). Thus, for the intentionalist, experience isrepresentational in a way that contrasts with it beingrelational/presentational. Experience does not genuinely have anact-object structure. This is in keeping with a standard tradition inthe theory of intentionality which treats it as non-relational (thetradition derives from Husserl (1900/1901); for discussion see Zahavi(2003: 13–27). So, for the intentionalist, since it is not ofthe essence of experience or its character that it is relational, itis not of its essence that it is a relation to a sense-datum.

3.3.2 Sources of Intentionalism

Some of the most influential (at least partial) intentional theoriesare Anscombe (1965), Armstrong (1968), Pitcher (1970), Peacocke(1983), Harman (1990), Tye (1992, 1995), Dretske (1995), Lycan (1996);for more recent accounts, see Byrne (2001), Siegel (2010), Pautz(2010) and the entry onthe contents of perception.

Within analytic philosophy, intentionalism is a generalisation of anidea presented by G.E.M. Anscombe (1965), and the “belieftheories” of D.M. Armstrong (1968) and George Pitcher (1970).(Within the phenomenological tradition intentionality and perceptionhad always been discussed together: see the entry onphenomenology.) Anscombe had drawn attention to the fact that perceptual verbssatisfy the tests for non-extensionality or intensionality (see theentry onintensional transitive verbs). For example, just as ‘Vladimir is thinking about Pegasus’is an intensional context, so ‘Vladimir has an experience as ofa pink elephant in the room’ is an intensional context. Inneither case can we infer that there exists something Vladimir isthinking about, or that there is exists something he is experiencing.This is the typical manifestation of intensionality. Anscombe regardedthe error of sense-datum and naive realist theories as the failure torecognise this intensionality. (Her own example was the allegedintensionality of ‘see’, but this is controversial.)

Armstrong and Pitcher argued that perception is a form of belief.(More precisely, they argued that it is the acquisition of a belief,since an acquisition is a conscious event, as perceiving is; ratherthan a state or condition, as belief is.) Belief is an intentionalstate in the sense that it represents the world to be a certain way,and the way it represents the world to be is said to be itsintentional content. Perception, it was argued, is similarly arepresentation of the world, and the way it represents the world to beis likewise its intentional content. The fact that someone can have aperceptual experience of something as F, without there being any thingwhich is F was taken as a reason for saying that perception is just aform of belief-acquisition.

Certain cases put pressure on this. For instance, consider the famousMüller-Lyer illusion in which two lines of equal length lookunequal. You can experience this even if you know (and thereforebelieve) that the lines are the same length. If perception were simplythe acquisition of belief, then this would be a case of explicitlycontradictory beliefs: you believe that the lines are the same lengthand that they are different lengths. But this is surely not the rightway to describe this situation. (Armstrong recognized this, andre-described perception as a “potential belief”; thismarks a significant retreat from the original claim).

The belief theory (and related theories, like the judgement theory ofCraig (1976)) is a specific version of the intentional theory. But itis not the most widely accepted version (though see Glüer (2009)for a recent defence; and Byrne (forthcoming)). Intentionalism is,however, not committed to the view that perceptual experience isbelief; experience can be asui generis kind of intentionalstate or event (Martin (1993)).

3.3.3 The Intentional Content of Perceptual Experience

Intentionalists hold that what is in common between veridicalexperiences and indistinguishable hallucinations/illusions is theirintentional content: roughly speaking, how the world isrepresented as being by the experiences. Many intentionalists holdthat the sameness of phenomenal character in perception andhallucination/illusion is exhausted or constituted by this sameness incontent (see Tye (2000), Byrne (2001)). But this latter claim is notessential to intentionalism (see the discussion of intentionalism andqualia above). What is essential is that the intentional content ofperception explains (whether wholly or partly) its phenomenalcharacter.

The intentional content of perceptual experience is sometimes called“perceptual content” (see the entry onthe contents of perception). What is perceptual content? A standard approach to intentionalitytreats all intentional states as propositional attitudes: states whichare ascribed by sentences of the form “S ___ that p” where‘S’ is to be replaced by a term for a subject,‘p’ with a sentence, and the ‘___’ with apsychological verb. The distinguishing feature of the propositionalattitudes is that their content—how they represent the world tobe—is something which is assessable as true or false. Hence thecanonical form of ascriptions of perceptual experiences is: “Sperceives/experiences that p”. Perceptual experience, on thiskind of intentionalist view, is a propositional attitude (see Byrne(2001), Siegel (2010)).

But intentionalism is not committed to the view that experience is apropositional attitude. For one thing, it is controversial whether allintentional states are propositional attitudes (see Crane (2001:Chapter 4)). Among the intentional phenomena there are relations likelove and hate which do not have propositional content; and there arealso non-relational states expressed by the so-called“intensional transitive” verbs like seek, fear, expect(see the entry onintensional transitive verbs). All these states of mind have contents which are not, on the face ofit, assessable as true or false. If I am seeking a bottle ofinexpensive Burgundy, what I am seeking—the intentional contentof my seeking, or the intentional object under a certain mode ofpresentation—is not something true or false. Some argue thatthese intentional relations and intentional transitives are analysableor reducible to propositional formulations (see Larson (2003) for anattempt to defend this view of intensional transitives; and Sainsbury(2010) for a less radical defence). But the matter is controversial;and it is especially controversial where experience is concerned. Forwe have many ways of talking about experience which do notcharacterize its content in propositional terms: for example,“Vladimir sees a snail on the grass”, or “Vladimiris watching a snail on the grass” can be distinguished from thepropositional formulation “Vladimir sees that there is a snailon the grass” (for discussion of watching, see Crowther2009).

There are those who follow Dretske (1969) in claiming that thesesemantical distinctions express an important distinction between“epistemic” and “non-epistemic” seeing.However, the view that perceptual content is non-propositional is notthe same as the view that it is “non-epistemic” inDretske’s sense. For ascriptions of non-epistemic seeing areintended to be fully extensional in their object positions, but notall non-propositional descriptions of perception need be (for example,some have argued that “Macbeth saw a dagger before him”does not entail “there is a dagger which Macbeth saw”: cf.Anscombe (1965)). The question of whether perceptual experience has apropositional content is far from being settled, even for those whothink it has intentional content (see McDowell (2008); Crane(2009)).

Another debate about the content of perceptual experience is whetherit is object-dependent, or object-independent (see Soteriou (2000) andSchellenberg (2018: Part II); and for a more general discussion, seeChalmers (2006)). An object-dependent content is a content whichconcerns a particular object, and is such that it cannot be thecontent of a state of mind unless that object exists (McDowell (1987)and Brewer (1999)). An object-independent content is one whose abilityto be the content of any intentional state is not dependent on theexistence of any particular object (Davies (1992) and McGinn(1989)).

The intentionalist holds that the content that is common to veridicalexperiences and subjectively indistinguishable hallucinations isobject-independent: since such hallucinations occur in the absence ofobjects for such content to depend upon. However, as Martin (2002b)argues, drawing on (Burge 1991), the intentionalist can still appealto the idea thatparticular veridical experiences haveparticular object-dependent contents in addition to theobject-independent contents they share with subjectivelyindistinguishable hallucinations.

The objects of intentional states are sometimes called“intentional objects” (Crane (2001: Chapter 1)). What arethe intentional objects of perceptual experience, according tointentionalists? In the case of veridical perception, the answer issimple: ordinary objects like the churchyard, the snow etc. But whatshould be said about the hallucinatory case? Since this case is bydefinition one in which there is no ordinary object being perceived,how can we even talk about something being an “object ofexperience” here? As noted above, intentionalists say thatexperiences are representations; and one can represent what does notexist (see Harman (1990), Tye (1992)). This is certainly true; butisn’t there any more to be said? For how does a representationof a non-existent churchyard differ from a representation of anon-existent cat, say, when one of those is hallucinated? The statesseem to have different objects; but neither of these objects exist(see the entrynonexistent-objects).

One proposal is that the objects of hallucinatory experience are theproperties which the hallucinated object is presented as having(Johnston (2004)). Another answer is to say that these hallucinatorystates of mind have intentional objects which do not exist (Smith(2002: Chapter 9)). Intentional objects in this sense are not supposedto be entities or things of any kind. When we talk about perceptionand its “objects” in this context, we mean the word in theway it occurs in the phrase “object of thought” or“object of attention” and not as it occurs in the phrase“physical object”. An intentional object is always anobject for a subject, and this is not a way of classifying things inreality. An intentionalist need not be committed to intentionalobjects in this sense; but if they are not, then they owe an accountof the content of hallucinatory experiences.

How does the content of perceptual experience differ from the contentof other intentional states? According to some intentionalists, onemain difference is that perception has “non-conceptual”content. The basic idea is that experience involves a form of mentalrepresentation which is in certain ways less sophisticated than therepresentation involved in (say) belief. For example, having thebelief that the churchyard is covered in snow requires that you havethe concept of a churchyard. This is what it means to say that beliefhas conceptual content: to have the belief with the content that a isF requires that you possess the concept a and the concept F. So, tosay that experience has non-conceptual content is to say thefollowing: for you to have an experience with the content that a is Fdoes not require that you have the concept of a and the concept F. Theidea is that your perceptual experience can represent the world asbeing a certain way—the “a is F” way—even ifyou do not have the concepts that would be involved in believing thata is F. (For a more detailed version of this definition, see Crane(1998a) and Cussins (1990); for a different way of understanding theidea of non-conceptual content, see Heck (2000) and Speaks (2005). Theidea of non-conceptual content derives from Evans (1982); there aresome similar ideas in Dretske (1981); see Gunther (2002) for acollection of articles on this subject. Other support fornon-conceptual content can be found in Bermúdez (1997);Peacocke (1992); Crowther (2006); for opposition see Brewer (1999) andMcDowell (1994)).

3.3.4 Intentionalism and the Problem of Perception

The intentionalist rejects the argument from illusion as it hinges onthePhenomenal Principle which they reject. For theintentionalist, an illusory experience in which you see a white wallas yellow is not a case in which you are directly presented with ayellow sense-datum, but a case in which a white wall is directlyrepresented as being yellow.

However, the intentionalist must accept the argument fromhallucination. They accept (A), and they also accept (B) in the formof theCommon Kind Claim. (C) follows (given (a1) and(a2)). Thus, like sense-datum theorists and adverbialists,intentionalists rejectDirect Realist Presentation,and admit that we are not ever directly presented with ordinaryobjects, not even in veridical experience.

3.3.5 Intentionalism and Perception of the World

In response to this, the intentionalist can suggest that although theyrejectDirect Realist Presentation, they do notrejectDirect Realism. They can suggest that theformer is not the only way to understand the latter. As we saw above,another way to understandDirect Realism is with acausal understanding of direct perception.

As we noted above, it is unclear whether theadverbialist isentitled to this, since it is unclear how the adverbialist can makesense of the object-directedness of experience. But the intentionalistdoesn’t face this problem. The object-directedness of experienceis at the heart of their approach. Even though intentionalism deniesthat experiences involve the direct presentation of ordinary objects,it (a) respects and is motivated by the phenomenological observationthat experiences are directly of ordinary objects, and (b) offers analternative account of the manner in which experiences are directly ofordinary objects. As we’ve seen, instead of presentation, theintentionalist appeals to representation.

Thus, the intentionalist can maintain that when you see a snow-coveredchurchyard for what it is you dodirectly perceive asnow-covered churchyard. This isnot because your experienceitself directly presents you with a snow-covered churchyard. Itdoesn’t. After all, your experience is of such a kind that itcould occur in a hallucination, where it wouldn’t directlypresentany ordinary object. It is rather because yourexperience directly perceptually represents the presence of asnow-covered churchyard and is non-deviantly caused by the churchyardin question. This is what direct perception amounts to for theintentionalist

3.3.6 Intentionalism and our Ordinary Conception of Perceptual Experience

A concern about adverbialism that we raised above, from theperspective of one who wants to uphold our ordinary conception ofperceptual experience, is that (a) it rejects our ordinary conceptionof perceptual experience almostwholesale, and (b)adverbialist causal direct realism, even if it could be made to work,doesn’t seem to compensate for that: it isn’t sensitiveenough to the phenomenological concerns that motivate our ordinaryconception of perceptual experience. In contrast, intentionalism seemsto fare better on both scores.

First, strictly speaking, the intentionalist must reject our ordinaryconception of perceptual experience. Even though they accept theCommon Kind Claim, they rejectDirect RealistPresentation. Underlying this is not rejection ofOrdinary Objects but ofPresentation. But even here, their rejection ofPresentation is not too radical. For intentionalists can say thatexperiences arequasi-presentational. The appeal torepresentation enables this. For when you directly perceptuallyrepresent the snow-covered churchyard, it certainly seems to you as ifa churchyard is directly present to you, even if it is not (as youare, say, hallucinating). As we noted above, it is not clear from theresources the adverbialist offers how they can account for how it evenseems as if an object is present to you. How does perceivingwhitely make it seem as if a white thing is present to you?

Similarly, though strictly speaking the intentionalist must rejectDirect Realist Character, the departure from this isnot too radical. For instead, the intentionalist holds that thecharacter of experience is determined, at least partly, by the directperceptual representation of ordinary objects. It is not as ifordinary objects and their apparent presence drops out of the pictureon the intentionalist account of phenomenal character. The account issimilar toDirect Realist Character, just stripped ofthe genuine relationality.

Finally, the causal direct realist story that the intentionalistoffers is intelligible in the way that it arguably isn’t for theadverbialist. And although it invokes causal notions, this is not tothe exclusion of a corephenomenological understanding ofdirect experience of an object, which the intentionalist accounts forwith the notion of direct perceptual representation.

Intentionalism, then, is aDirect Realist theorywhich upholds some of our ordinary conception of perceptualexperience, and insofar as it rejects aspects of our ordinaryconception, it does so in a non-radical way, sensitive to thephenomenological concerns that motivate this conception in the firstplace.

3.4 Naive Realist Disjunctivism

3.4.1 Naive Realism in Outline

Consider the veridical experiences involved in cases where yougenuinely perceive objects as they actually are. At Level 1, naiverealists hold that such experiences are, at least in part, directpresentations of ordinary objects. At Level 2, the naive realist holdsthat things appear a certain way to you because you are directlypresented with aspects of the world, and – in the case we arefocusing on – things appear white to you, because you aredirectly presented with some white snow. The character of yourexperience is explained by an actual instance of whiteness manifestingitself in experience.

Naive realists thus assign an important explanatory role to the worlditself in explaining the character of veridical experiences. But thisdoesn’t mean that they are committed to the idea that suchcharacter isfully explained or exhausted by the presentedworld. Naive realists admit that even holding fixed presented aspectsof the world there can be variation in the character of experience.This is worked out in different (but compatible) ways by differenttheorists. One approach is to note how variations in theperceiver can make for variations in the character ofexperience (Logue (2012a)). Another is to highlight athird-relatum (of the relation of presentation) whichencapsulates various conditions of perception such as one’sspatiotemporal perspective and the operative perceptual modality,where variation in such conditions can make for variation inphenomenal character (Campbell (2009), Brewer (2011)). Finally, somesuggest that there can be variation in theway ormanner in which one is related to perceived objects whichmakes a difference to phenomenal character (Soteriou (2013), Campbell(2014), French and Phillips (2020)). For further discussion see French(2018).

For the naive realist, insofar as experience and experientialcharacter is constituted by a direct perceptual relation to aspects ofthe world, it is not constituted by the representation of such aspectsof the world. This is why many naive realists describe the relation atthe heart of their view as anon-representational relation.This doesn’t mean that experiences must lack intentionalcontent, but it means that (a) insofar as appeal is made topresentation to explain character, no appeal is made to intentionalcontent for that purpose, and (b) what is fundamental to experience issomething which itself cannot be explained in terms of representingthe world: a primitive relation of presentation. (For furtherdiscussion of naive realism as a non-representational view, see thearticles in Part Three of Brogaard (2014)).

The other theories we have considered all endorse theCommonKind Claim. We’ve noted that naive realism applies tothe veridical experiences involved in genuine perception, but does itapply more widely? Though naive realists may extend their approach toillusions, they typically deny that it applies to hallucinations andso reject theCommon Kind Claim. Naive realists whodeny theCommon Kind Claim aredisjunctivists. We call such a positionnaive realistdisjunctivism. Let’s explore these ideas now.

3.4.2 Naive Realism and the Problem of Perception

There are various different naive realist approaches to illusion (seee.g., Fish (2009: Chapter 6), Brewer (2008, 2011: Chapter 5), Kalderon(2011), Genone (2014), French and Phillips (2020)). When it comes tothe argument from illusion, the naive realist (like theintentionalist) rejects thePhenomenal Principle. Sohow does naive realism differ from intentionalism about illusions? Intwo respects: first, naive realists can maintain that illusoryexperiences are fundamentallydirect presentations of theworld. Second, the naive realist can explain the character of suchillusory experiences without appeal to intentional content, butinstead by appealing to the direct presentation of ordinary objects.Consider, for example, the approach developed by Brewer:

visually relevant similarities are those that ground and explain theways that the particular physical objects that we are acquainted within perception look. That is to say, visually relevant similarities aresimilarities by the lights of visual processing of various kinds...very crudely, visually relevant similarities are identities in suchthings as the way in which light is reflected and transmitted from theobjects in question, and the way in which the stimuli are handled bythe visual system, given its evolutionary history and our sharedtraining during development (2011: 103)... in a case of visualillusion in which a mind-independent physical object, o, looks F,although o is not actually F, o is the direct object of visualperception from a spatiotemporal point of view and in circumstances ofperception relative to which o has visually relevant similarities withparadigm exemplars of F although it is not actually an instance of F(2011: 105).

So though o may not itself be F, it can exist in certain conditions,C, such that it has visually relevant similarities to paradigm Fthings and in that sense it will objectively look F, or look like an Fthing—that is, it will itself have a property, a look or anappearance, independently of anyone actually seeing it (see alsoMartin (2010), Kalderon (2011), Antony (2011), and Genone (2014) onobjective looks). If o is then seen in C, o itself will look F toyouin perception. Brewer spells this all out in more detail,and with various examples. One is seeing a white piece of chalk asred. The chalk is seen in abnormal illumination conditions such thatthe white piece of chalk itself looks like a paradigm red piece ofchalk—it has “visually relevant similarities with aparadigm piece of chalk, of just that size and shape” (2011:106). Given that it is seen in those conditions, it looks red to you,even though it is not in fact red. Here, then, we have an account ofillusions in which we appeal to objects and the ways those objectsare, not the ways they are represented to be, in explainingcharacter.

What about the argument from hallucination? The naive realist thinksthat at least veridical experiences are direct presentations ofordinary objects. They thus reject the conclusion (C) of the argument.But typically, naive realists accept (A). They therefore block theargument by rejecting the spreading step (B), understood in terms oftheCommon Kind Claim applied to veridical andhallucinatory experiences.

Such a naive realist reasons as follows: suppose that when you see asnow-covered churchyard for what it is, you have an experience whichis in its nature a relation between you and ordinary objects. But asubjectively indistinguishable hallucinatory experience does not havesuch a nature. For such a hallucination could occur in the absence ofany relevant worldly items (e.g., in the lab of a scientistmanipulating your brain, in a world with no white things). Instead oftaking (B) and these facts about hallucination to ground the rejectionof naive realism, the naive realist instead rejects (B): even thoughthe hallucination as of a snow-covered churchyard is subjectivelyindistinguishable from a veridical experience of such a scene, it isnot of the same fundamental kind. (For a more nuanced formulation ofthe naive realist reasoning here, see Martin (2004), (2006). Raleigh(2014) and Ali (2018) advocate a naïve realist position whichkeeps theCommon Kind Claim but rejects (A) and hencethe understanding of hallucinations we are operating with here. Seealso Masrour (2020) who argues that it is an open question whetherhallucinations are possible.).

In blocking the argument from hallucination in this way the naiverealist endorsesdisjunctivism. This theory was firstproposed by Hinton (1973) and was later developed by P.F. Snowdon(1979, 1990), John McDowell (1982, 1987) and M.G.F. Martin (2002,2004, 2006). Disjunctivism is not best construed as it is by one ofits proponents, as the view “that there is nothing literally incommon” in veridical perception and hallucination, “noidentical quality” (Putnam (1999: 152)). For both the veridicalperception of an F and a subjectively indistinguishable hallucinationof an F are experiences which are subjectively indistinguishable froma veridical perception of an F. What disjunctivists deny is that whatmakes it true that these two experiences are describable inthis way is the presence of the same fundamental kind of mental state.Disjunctivists reject what J.M. Hinton calls “the doctrine ofthe ‘experience’ as the common element in a givenperception” and an indistinguishable hallucination (Hinton(1973: 71)). The most fundamental common description of both states,then, is a merely disjunctive one: the experience is either a genuineperception of an F or a mere hallucination as of an F. Hence thetheory’s name.

3.4.3 The Development of Naive Realist Disjunctivism

The disjunctivist rejects theCommon Kind Claim.Underlying this is a rejection of what Martin (2004, 2006) calls the“common kind assumption”, namely:

• (CKA) whatever fundamental kind of mental eventoccurs when you veridically perceive, the very same kind of eventcould occur were you undergoing a subjectively indistinguishablehallucination.

But is the disjunctivist’s rejection of(CKA)plausible? The disjunctivist can note how the fact that ahallucination is subjectively indistinguishable from a veridicalexperience does notentail that they are of the samefundamental kind, even if it does suggest this.

However, some argue that even if such an appeal to subjectiveindistinguishability is not enough to establish(CKA), it is nonetheless well supported by acausal argument (Robinson (1985)). We can suppose that whenyou see the snow-covered churchyard for what it is, there is someproximal cause of this experience: the experience is preceded by acertain sort of brain state B. But now we can imagine a situation inwhich we bring about B thus producing an experience in you, yet whereB is not brought about through any interaction between you and asnow-covered churchyard—e.g., in laboratory conditions. In thisscenario you have an hallucinatory experience as of a snow-coveredchurchyard. It is plausible to suppose that these experiences are ofthe very same kind given that they have the same proximal cause.

The point here is that(CKA) looks like a plausibleprinciple forcausally matching veridical and hallucinatoryexperiences – veridical and hallucinatory experiences with thesame proximal cause. This way of motivating(CKA)appeals to a same-cause, same-effect principle:

• Causal Principle 1: an event e1 is of the same kind as an event e2if event e1 is produced by the same kind of proximate causal conditionas e2 (Nudds 2009: 336).

Is this the end of the road for the naive realist disjunctivist, then?Not quite, since as Martin argues, the naive realist should rejectthis principle:

On [the naive realist] conception of experience, when one isveridically perceiving the objects of perception are constituents ofthe experiential episode. The given event could not have occurredwithout these entities existing and being constituents of it; in turn,one could not have had such a kind of event without there beingrelevant candidate objects of perception to be apprehended. So, evenif those objects are implicated in the causes of the experience, theyalso figure non-causally as essential constituents of it... Merepresence of a candidate object will not be sufficient for theperceiving of it, that is true, but its absence is sufficient for thenon-occurrence of such an event. The connection here is [one] of aconstitutive or essential condition of a kind of event. (2004:56–57).

Martin’s point is that the naive realist may well admit thepossibility of veridical experiences and causally matchinghallucinations, but they will resist the idea that sameness ofproximal cause implies sameness of the kind of experience involved.This is because there arenon-causal constitutive conditionsfor the occurrence of the veridical experience which are not satisfiedin the hallucinatory case.

However, Martin suggests that the arguer from hallucination candevelop their case against naive realism further. This developmentinvolves an argument with two stages. First, a modified causalargument: thereverse causal argument, and second thescreening-off problem.

The modified causal argument involves a modified causal principle:

• Causal Principle 2: an event e1 is of the same kind K as an evente2 if event e1 is produced by the same kind of proximate causalcondition as e2 in circumstances that do not differ in any non-causalconditions necessary for the occurrence of an event of kind K (Nudds2009: 337).

(Martin’s own modified causal principle is more complicated thanthis in allowing for indeterministic causation. We gloss over thisimportant complication here). Take N to be the fundamental kind whichcharacterizes a veridical experience of a snow-covered churchyard,according to the naive realist. Does Causal Principle 2 allow us tosay that N is present in the causally matching hallucinatory case, as(CKA) predicts? No. For the hallucination is producedin circumstances that differ in non-causal conditions necessary forthe occurrence of Ngiven how the naive realist understandsN: in the circumstances in which the hallucination occurs thereis no appropriate object of perception, but the presence of such anobject is necessary for the occurrence of N.

So how does Causal Principle 2 help the arguer from hallucination? Wehave to run an argument in “the reverse direction, from whatmust be true of cases of causally matching hallucinations, to whatmust thereby be true of the veridical perceptions they match”(Martin 2006: 368). That is, take a hallucination as of a snow-coveredchurchyard h, and suppose that h is of some fundamental kind H. Now wecan apply Causal Principle 2 to show that H is present in a causallymatchingveridical experience of a snow-covered churchyard,v. For now v is produced by the same kind of proximal cause incircumstances where there is no difference in the non-causalconditions necessary for the occurrence of an event of kind H. This isbecause all that is necessary for an occurrence of H is some braincondition, which is present in the circumstances in which v is broughtabout. This reverse causal argument does not show that v is not offundamental kind N. What it does show, however, is that whateverfundamental kind is present in a hallucinatory case will also bepresent in a causally matching veridical case. So even if v isfundamentally N it is also H. That is, we have the Reverse Common KindAssumption:

• (RCKA) Whatever fundamental kind of event occurswhen you hallucinate, the very same kind of event also occurs in acausally matching veridical experience.

But now we run into thescreening-off problem. There issomething it is like for you to have an hallucinatory experience as ofa snow-covered churchyard, and the experience seems to relate you to asnow-covered churchyard. This fact about the hallucinatory experienceis grounded in its being of kind H. But now if an experience of thatkind is present in the veridical case, it is difficult to see how whatthe naive realist says is fundamental to that case, N, is doinganything by way of explaining what it is like for a subject to havethe experience. The presence of H in the veridical case seems to makeN explanatorily redundant, or “screen off” N’sexplanatory role, contra the ambitions of naive realism. (For moredetailed expositions of this two-stage argument see Martin (2004),Byrne and Logue, (2008), Hellie (2013) and Soteriou (2014: Chapter6)).

The most widely discussed naive realist response to this argument isthat of Martin (2004, 2006). Though there are now a range of differentnaive realist responses available, some of which integrate criticaldiscussion of Martin’s own approach (see Allen (2015), Logue(2012b, 2013), Fish (2009: Chapter 4), Hellie (2013), Moran (2019),Sethi (2020)).

Martin argues that the screening-off stage of the argument is onlyproblematic if we accept a positive, non-derivative account ofcausally matching hallucinations. On such an account, hallucinationshave a positive nature which doesn’t derive from that ofveridical perception: a nature that can be specified independently ofany reference to veridical perception. For instance, hallucinationsare direct presentations of sense-data, or representations of ordinaryobjects. Instead, Martin suggests, the disjunctivist should conceiveof causally matching hallucinations in a purely negative epistemicway: such a hallucination as of an F is a state of mind which is notintrospectively knowably not a veridical perception of an F. Whatmakes it the case that your hallucinatory experience is as of asnow-covered churchyard, with a certain sort of phenomenal character,is just that it is an occurrence which cannot be discriminated, byintrospection alone, from a veridical perception of a snow-coveredchurchyard. The particular subjective perspective that a hallucinatorhas in a causally matching hallucination as of a snow-coveredchurchyard is explained just by the obtaining of this negativeepistemic condition, not by anything more positive such as a relationto a white sense-datum or the representation of white snow (c.f.,Dancy (1995: 425)). On such a view, causally matching hallucinationsare derivative: specifying their nature requires essential referenceto the basic case of veridical perception.

If we accept Martin’s account of causally matchinghallucinations, then we can see how H can be present in both thehallucinatory and the veridical case: since trivially a veridicalexperience of a snow-covered churchyard is indiscriminable from averidical experience of a snow-covered churchyard. But what aboutscreening off? Does H have a nature which means that the presence of Hin the veridical case threatens the explanatory power of N? Itdoesn’t, Martin argues, since H’s explanatory force isderivative or dependent: it is parasitic on that of N. As Martin noteswith his own example:

But if that is so [if H screens off the explanatory role of N], thenthe property of being a veridical perception of a tree [i.e. N] neverhas an explanatory role, since it is never instantiated without theproperty of being indiscriminable from such a perception beinginstantiated as well. But if the property of being a veridicalperception lacks any explanatory role, then we can no longer show thatbeing indiscriminable from a veridical perception has the explanatoryproperties which would screen off the property of being a veridicalperception (2004: 69).

Here, then, is a summary of this complex dialectic: theargumentfrom hallucination seems to disprove naive realism, but the naiverealist appeals todisjunctivism in response. However, thecausal argument puts pressure on disjunctivism, by supportingthecommon kind assumption. In response, the naive realistrejects the key principle of this argument (Causal Principle 1). Butthen a two-stage argument consisting of thereverse causalargument and thescreening-off problem attempts to showthat: (1) the fundamental kind of experience present in hallucinationis also present in causally matching veridical experience, and (2)this undermines the naive realist idea that the character of veridicalexperience is shaped by the directly presented world. In response,Martin accepts a form of naive realism which embraces disjunctivism(in the form of the claim that causally matching veridical andhallucinatory experiences are fundamentally different). But which alsoaccepts (as per the reverse causal argument) that there is a commonelement across the cases, for the hallucinatory kind is present inveridical cases too. But since he conceives of this common element ina derivative, and purely negative epistemic way, he blocks theargument at the second stage, rejecting screening off.

Naturally, then, much subsequent critical discussion has focused onMartin’s negative epistemic conception of hallucination. Furtherdiscussion and development of Martin’s approach is to be foundin Nudds (2009, 2013) and Soteriou (2014: Chapter 6). For criticism ofMartin’s approach see Hawthorne and Kovakovich (2006), Farkas(2006), Sturgeon (2008), Siegel (2004, 2008), and Robinson (2013). SeeBurge (2005) for a general and polemical attack on disjunctivism. Formore on disjunctivism, see Haddock and Macpherson (eds.) (2008), Byrneand Logue (eds.) (2009), Macpherson and Platchias (eds.) (2013) andthe entry onthe disjunctive theory of perception.

3.4.4 Naive Realist Disjunctivism and Our Ordinary Conception of Perceptual Experience

According to naive realist disjunctivists, at least veridicalexperiences are directly of ordinary objects (OrdinaryObjects), and are direct presentations of their objects(Presentation). Naive realist disjunctivists thusmaintainDirect Realist Presentation, and henceDirect Realism for at least veridical experiences– indeed they maintainDirect Realism withoutthe need for any appeal to a causal theory of direct perception.Further, naive realist disjunctivists hold that the phenomenalcharacter of such experiences is determined, at least in part, by thedirect presentation of ordinary objects (Direct RealistCharacter). The only aspect of our ordinary conception ofperceptual experience which naive realist disjunctivists rejectoutright is theCommon Kind Claim.

4. Conclusion

Sense-datum theorists and adverbialists depart substantially from ourordinary conception of perceptual experience. Advocates of each viewwill argue, in their different ways, that this is a consequence ofresponding adequately to the Problem of Perception.

Intentionalists and naive realist disjunctivists disagree, and argue,in different ways, that we can respond to the Problem of Perceptionwithout departing substantially from our ordinary conception ofperceptual experience: by maintainingDirect Realismin some form, and maintaining or at least being sensitive to many ofthe specific phenomenological components of our ordinary conception ofperceptual experience.

Whilst the debate between sense-datum theorists and adverbialists (andbetween these and other theories) is not as prominent as it once was,the debate between intentionalists and naive realist disjunctivists isa significant ongoing debate in the philosophy of perception: a legacyof the Problem of Perception that is arguably “the greatestchasm” in the philosophy of perception (Crane (2006)). Thequestion, now, is not so muchwhetherto be a direct realist,buthow to be one.

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Further reading

Any serious attempt to master the literature on the problem ofperception should include a reading of Anscombe (1965), Armstrong(1968: Chapter 10), Dretske (1969), Jackson (1977), Martin (2002),Moore (1905), Peacocke (1983: Chapter 1), Robinson (1994), Russell(1912), Smith (2002), Snowdon (1992), Strawson (1979), Tye (1992), andValberg (1992a). Useful collections: Swartz (1965), Dancy (1988),Noë and Thompson (2002), Gendler and Hawthorne (2006), Haddockand Macpherson (2008), Byrne and Logue (2009), Nanay (2010), andBrogaard (2014). Matilal (1986) explores how issues around the Problemof Perception and theories of experience play out in Classical Indianphilosophy.

For discussion of how the problem of perception, somewhat differentlyconstrued, arises in the senses other than vision, see Perkins (1983).There is much literature on non-visual perception, not all of itaddressing the problem of perception, but much of it will be relevantto considering the problem of perception in non-visual modalities: onsounds, see Nudds (2001), O’Callaghan (2007), Nudds andO’Callaghan (2009); on smell, see Batty (2011), Richardson(2013a, 2013b); on touch, see O’Shaughnessy (1989), Martin(1992) and Fulkerson (2014); for the senses in general, see Nudds(2003), Macpherson (2011, 2011a) and Stokes, Matthen, and Briggs(2015)). On multisensory perception, see O’Callaghan (2019).

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Acknowledgments

We are very grateful to Tim Bayne, David Chalmers, Katalin Farkas,Mike Martin and Susanna Siegel for their comments on previous versionsof this entry. For discussion thanks to Arif Ahmed, Joshua Gert, AnilGomes, Penelope Mackie, and Lee Walters.