Qualia inversion thought experiments are ubiquitous in contemporaryphilosophy of mind (largely due to the influence of Shoemaker 1982 andBlock 1990). The most popular kind is one or another variant ofLocke’s hypothetical case of “spectrum inversion”,in which strawberries and ripe tomatoes produce visual experiences ofthe sort that are actually produced by grass and cucumbers, grass andcucumbers produce experiences of the sort that are actually producedby strawberries and ripe tomatoes, and so on. This entry surveys themain philosophical applications of what Dennett has called “oneof philosophy’s most virulent memes” (1991, 389).

Section 1 explains what “qualia” are supposed to be.Section 2 describes the many different sorts of “invertedqualia” (specifically, “inverted spectrum”) thoughtexperiments, including a close cousin that does not involve inversion.Section 3 discusses the major philosophical arguments that appeal tospectrum inversion.

This article is long and goes into intricate details that some readerswill wish to ignore. Those wanting a shorter introduction should readsection 1 (skipping subsection 1.1), section 2 (subsections 2.1, 2.2,2.3), and subsection 3.1. (Another shorter introduction is Ross 2020.)Those new to the topic should first read the entry onqualia.

• 1. Qualia
  • 1.1 Other uses of ‘qualia’
• 2. Inverted qualia scenarios
  • 2.1 A Simple Inverted Qualia Scenario
  • 2.2 Locke’s Inverted Spectrum Scenario
  • 2.3 Other Inverted Spectrum Scenarios
    • 2.3.1 Behaviorally Undetectable Scenarios
    • 2.3.2 Intrapersonal and Interpersonal Scenarios
    • 2.3.3 Inverted Earth
  • 2.4 Shifted Qualia
• 3. Spectrum Inversion in an Argument…
  • 3.1 …Against Behaviorism, Functionalism, and Physicalism
  • 3.2 …Against Representationalism
  • 3.3 …For Appearance Properties
  • 3.4 …For Modes of Presentation
  • 3.5 …For Relativism
  • 3.6 …For Skepticism About Others’ Minds
  • 3.7 …For the Explanatory Gap
  • 3.8 …For the Ineffability of Qualia
  • 3.9 ...For the Inconsistency of Content-Externalism, Representationalism, and Qualia-Internalism
  • 3.10 Summary: Required Features of Inverted Spectrum Scenarios
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Qualia

Qualia (singular ‘quale’), in a common modern usage, areproperties of experiences that type them in phenomenological respects.Imagine seeing three colored patches against a neutral background ingood light, one after the other. In particular, imagine seeing avermilion patch, then a crimson patch, and finally a turquoise patch.(Those with poor imaginations may consult Figure 1.)

Figure 1: vermilion, crimson, andturquoise patches

Three experiences of the imagined sort differ in their phenomenology,or in “what it’s like” to undergo them. Whatit’s like to see the crimson patch is not the same as whatit’s like to see the turquoise patch, for example.Further—assuming you have normal color vision—seeing thecrimson patch is more similar, in phenomenological respects, to seeingthe vermilion patch than it is to seeing the turquoise patch.

Thus your experience of the crimson patch has a quale (call it‘\(Q_{C}\)’) that your experiences of the vermilion andturquoise patches lack. Your experience of the vermilion patch has aquale \((Q_{V})\) that your experiences of the crimson and turquoisepatches lack; likewise, your experience of the turquoise patch hasquale \(Q_{T}\). What about an experience of all three patches, aswhen viewing the whole of figure 1? Which of \(Q_{C}, Q_{V}\), and\(Q_{T}\) does that have? The answer usually implicit in theliterature is ‘All three’ (as opposed to ‘None’).^[1] This is probably the more natural way of understanding qualiaterminology, given the explanation so far, and is the one adopted inthis article.

In addition to the quale \(Q_{C}\), your experience of the crimsonpatch has quale \(Q_{R}\) which it shares with your experiences of thevermilion patch, blood, fire trucks, strawberries, ripe tomatoes, andso on. Your experience of the turquoise patch (in isolation) lacks\(Q_{R}\).

It must be emphasized that ‘\(Q_{C}\)’, for example, isnotexplicitly defined using color terminology.‘\(Q_{C}\)’ is not stipulated to be an abbreviation of‘the property of being an experience of something’slooking crimson’, for instance. Rather, the role of descriptionslike the latter is simply to draw attention to the salient propertythat ‘\(Q_{C}\)’ is supposed to be a name for, in much thesame way that one might introduce the unfamiliar name ‘EugeneCernan’ by saying that it refers to the last man to walk on themoon. In the jargon, the description ‘the property of being anexperience of something’s looking crimson’ can be used tofix the reference of ‘\(Q_{C}\)’. (See the entryonreference.)

Qualia terminology can be introduced in a similar manner for othersorts of visual experiences (seeing differently shaped patches, forinstance), for other perceptual modalities, for bodily sensations, andfor thoughts, imagery, emotions, and so forth. It is controversialwhether some of these mental events/states have qualia—inparticular, episodes of conscious thought, at least some of which seemdevoid of phenomenology.^[2]

One might wonder why some special terminology is required. Admittedly‘\(Q_{R}\)’, for example, is notdefined in termsof ‘red’, but isn’t \(Q_{R}\) in fact the propertyof being an experience of something’s looking red?^[3] And if it is, why introduce another name? However, as discussed later(subsection 3.2), there is an argument against thisidentification.

1.1 Other uses of ‘qualia’

‘Qualia’ is an especially confusing piece of terminology,even by the standards of the profession that brought us‘realism’. In the sense just explained, the claim thatexperiences have qualia seems fairly harmless.^[4] The innocent student might well be puzzled, then, to learn of FrankJackson’s controversial “knowledge argument forqualia” (Jackson 1982), and Dennett’s attempt to dismissqualia as a philosopher’s invention (Dennett 1988). But oncloser examination, much of this apparent disagreement is merelyterminological. On Jackson’s use of the term, qualia areproperties of mental states “which no amount of purely physicalinformation includes” (1982, 273); on Dennett’s, they are“ineffable”, “intrinsic”,“private”, and “directly or immediatelyapprehensible in consciousness” (1988, 229; cf. Tye 2002, 447).And none of this is part of the official explanation of‘qualia’ in the previous section.

Another use of ‘qualia’ that is particularly important todistinguish from the present one is Dretske’s. According toDretske, qualia includecolors—properties of objectslike tomatoes, not experiences. This is because he explains qualia as“the ways objects phenomenally appear or seem” (1995, 73),and red is one way that tomatoes appear.^[5] Qualia, on Dretske’s use, are properties ofobjects ofexperiences; in this article qualia are properties ofexperiences.

The American pragmatist C. I. Lewis introduced ‘qualia’into contemporary philosophy.^[6] Qualia, he explains inMind and the World Order, are“recognizable qualitative characters of the given” (1929,121). According to Lewis, what is “given” in experienceare sense-data (although Lewis himself preferred other terminology:see 55–7), not objects like tomatoes. Goodman’s well-knowndiscussion of qualia inThe Structure of Appearance (1951)follows Lewis’s use. Among Jackson, Dennett, and Dretske,Dretske’s use of ‘qualia’ is the closest toLewis’s. Restricting attention to the case of veridicalperception, we may think of Dretske as basically agreeing with Lewisabout the characterization of qualia, but disagreeing with Lewis aboutthe given. When one sees that a tomato is red, according to Lewis asense-datum, not the tomato, is given; according to Dretske what isgiven is the tomato. So, since a “recognizable qualitativecharacter” of the tomato is its color, Dretske thinks thatcolors are examples of qualia.^[7]

2. Inverted qualia scenarios

Let’s say that ascenario is a (more-or-less detailed)story, which may be possible or impossible. (So, for example, there isa scenario in which someone squares the circle.) Corresponding to ascenario is what we can call ahypothesis: that the scenarioispossible. So, for example, the hypothesis corresponding toa circle-squaring scenario is false. There are a variety of“inverted qualia” scenarios in the literature—almostalways involving color perception—whose corresponding hypothesesdiffer in plausibility. These hypotheses are used as premises in anumber of philosophical arguments, discussed in section 3 below.Although color perception is the central example, there are inversionscenarios for other visual attributes, or attributes detectable byother sensory modalities (for audition, see the entry on auditoryperception,subsection 3.2.5).

2.1 A Simple Inverted Qualia Scenario

Consider the hue circle in figure 2, taken from the Natural ColorSystem color space, which is organized around the four hues red,green, blue, and yellow.^[8] These are theuniquehues: they have shades thatare not perceptual mixtures of any other hue. For example, there is ashade of green that is neither bluish nor yellowish. The other huesarebinary: all of their shades are perceptual mixtures oftwo unique hues. For example, every shade of purple is bluish andreddish. The four unique hues—yellow, red, blue,green—come in twoopponent pairs: red-green andblue-yellow. Red is opposed to green in the sense that there are noreddish-greens or greenish-reds; likewise there are no bluish-yellowsor yellowish-blues. The unique hues are equally spaced around the NCScircle, and the other hues are spaced according to their perceptibleproportion of the unique hues. So, for example, the orange patchequidistant from the unique yellow pole and unique red pole is equallysimilar to both.

Figure 2: NCS hue circle^[9]

Let \(I\) be the function that takes each shade to its opposing shade,thus rotating the hue circle 180°. \(I\) maps reds to greens,blues to yellows, bluish-greens to yellowish-reds, and so on (seefigure 3).

Figure 3: the function \(I\)

Introduce another perceiver, Invert (you are Nonvert). Imagine you arelooking at scene \(S\): an arrangement of some fruits (see theleft-hand part of figure 4). Now take the apparent hues of objects in\(S\), and transform them using the function \(I\). Use thistransformation to create a new scene \(S_{I}\), exactly like the oldscene \(S\) except that it looks to have differently colored“inverted” fruits (etc.). That is, if a banana originallylooks to have hue \(h\), in \(S_{I}\) it looks to have hueI(h). (See the right-hand part of figure 4; noticethat the greens in \(S\) are rather yellowish, and hence get mapped tobluish-reds.) Then one simple inverted qualia scenario is this: whatit’s like for Invert to look at \(S\) is exactly the same aswhat it’s like for Nonvert (i.e., you) to look at \(S_{I}\), andsimilarly for all other scenes that Invert encounters. According tothis scenario, if you look at the right-hand part of figure 4, yourexperience is phenomenologically the same as Invert’s experiencewhen she looks at the left-hand part of figure 4. In qualiaterminology: if an object \(O_{1}\) looks to have hue \(h\) to Nonvert(with \(Q\) being the corresponding quale of her experience), and\(O_{2}\) looks to have hueI(h) (with correspondingquale \(Q^*\)), then Invert’s experience of \(O_{1}\) has quale\(Q^*\) and her experience of \(O_{2}\) has quale \(Q\). In this senseInvert’s qualia are ‘inverted’ with respect toNonvert’s.

Figure 4: 180° hue inversion

Because the example concerns color qualia, this sort of invertedqualia scenario is usually described as a case of “spectruminversion”. (Note that the 180° inversion takes unique huesto unique hues, and binary hues to binary hues. An inversion scenarioproduced by a rotation of 45° would take the unique hue red to thebinary hue orange; and so presumably would be behaviorally detectable:see subsection 2.3.1 below.)

Philosophy is stuck with the terminology of ‘spectruminversion’, but it is potentially misleading.^[10] First, a spectrum inversion scenario sounds like one which invertseither the spectrum or the colors of objects, but it actually invertsneither. In a typical spectrum inversion scenario, the spectral band650–700nm remains red, and lemons remain yellow.^[11]

Second, even when properly taken as an inversion of experiences, onemight suppose that the “spectrum inversion” functioncorresponds to flipping the spectrum over. That is, using thetraditional names for the spectral bands, one might suppose thefunction maps red to violet, orange to indigo, yellow to blue, greento green, blue to yellow, indigo to orange, and violet to red.However, this is not the usual sort of inversion scenario (red is notmapped to green, for example). Further, this function is not definedfor all hues. Many hues—in particular, a large range of“extra-spectral” purples—are not found in thespectrum.

2.2 Locke’s Inverted Spectrum Scenario

Locke appears to have been the first to formulate explicitly aninverted spectrum scenario. (An immediate precursor is Malebranche.^[12]) In the chapter of theEssay titledOf True andFalse Ideas, Locke writes:

Neither would it carry any Imputation ofFalshood to oursimpleIdeas, \(if\) by the different Structure of ourOrgans, it were so ordered, Thatthe same Object should produce inseveral Men’s Minds different Ideas at the same time;v.g. if theIdea, that aViolet produced inone Man’s Mind by his Eyes, were the same that aMarigold produces in another Man’s, andviceversâ. For since this could never be known: because oneMan’s Mind could not pass into another Man’s Body, toperceive, what Appearances were produced by those Organs; neither theIdeas hereby, nor the Names, would be at all confounded, oranyFalshood be in either. For all Things, that had theTexture of aViolet, producing constantly theIdea,which he calledBlue, and those which had the Texture of aMarigold, producing constantly theIdea, which he asconstantly calledYellow, whatever those Appearances were inhis Mind; he would be able as regularly to distinguish Things for hisUse by those Appearances, and understand, and signify thosedistinctions, marked by the NamesBlue andYellow,as if the Appearances, orIdeas in his Mind, received fromthose two Flowers, were exactly the same, with theIdeas inother Men’s Minds. (1689/1975, II, xxxii, 15)

Locke’s description of this inverted spectrum scenario is ladenwith his own commitment to “Ideas”, which (on oneinterpretation) are sense-data, some of which possess both color and shape.^[13] On this view, spectrum inversion is a case of “sense-datuminversion”: when Invert looks at a violet she becomes acquaintedwith the kind of sense-datum Nonvert is acquainted with when he looksat a marigold. Setting this tendentious theoretical gloss aside,Locke’s scenario has three notable features. First, it is a caseof spectrum inversionfrom birth. Second, it is a case ofinversionwithin the same linguistic community. Third, it is(or is naturally read as being) a case in which Invert and Nonvert arebehaviorally alike—abehaviorally undetectable spectruminversion.

Locke does not fill in the details of his scenario, so it is leftunclear whether, for example, the leaves of marigolds and violetswould produce “Red Ideas” in the mind of the invertedsubject. But suppose, reasonably enough, that Locke’s scenarioinvolved a rotation of the hue circle. Locke evidently thought thatthe hypothesis corresponding to his scenario was true: that hisscenario is possible. Was he right?

If we assume that Invert is otherwise like a normal human perceiver,then a major asymmetry in color space shows that Locke was incorrect.Hue (red, green, bluish-red, etc.) is not the only perceptuallysalient dimension along which colors can vary: there are (usuallytaken to be) two other dimensions,saturation andlightness.^[14] A color is saturated to the extent to which its hue is intense orvivid: pastels are desaturated, and achromatic colors (blacks, whites,and grays) have no saturation. Colors become lighter as they becomeless grayish or blackened. Arranging the colors along these threedimensions produces a color solid, an example of which is shown infigure 5:

Figure 5: 3D color space: the Munsellcolor solid^[15]

The lightness dimension corresponds to the central vertical axis, withwhite at the top. The hue and saturation dimensions correspond,respectively, to the angle around the vertical axis, and to thedistance from it. Thus the shades of maximum saturation are on theoutside of the solid. Notice that the yellows have their maximumsaturation at higher levels of lightness than the reds and the blues.So, assuming that Invert’s judgments of the relations betweencolors are—modulo the inversion—normal, a possible Lockean180° hue rotation scenario would be behaviorally detectable.Invert would judge the maximally saturated colors she calls‘shades of blue’ to be lighter than the maximallysaturated colors she calls ‘shades of yellow’. Further,there are more distinguishable hue steps between blue and red thanthere are between yellow and green—a fact that is reflected inthe Munsell space, whose hue circle has five hues equally spaced: red,yellow, green, blue, purple. (Contrast the NCS space mentioned in theprevious subsection.) Hence the Lockean inversion function \(I\),assuming it is defined on all hues, would map some distinct hues (inparticular, some bluish reds) to the same hue (in particular, the sameyellowish green). The range of \(I\) would therefore contain fewerhues than its domain. Invert would not be able to distinguish somestimuli (those she calls ‘bluish red’) that Nonvert couldtell apart, and so again the inversion would be behaviorallydetectable.

2.3 Other Inverted Spectrum Scenarios

2.3.1 Behaviorally Undetectable Scenarios

As discussed in section 3 below, inverted spectrum scenarios have awide range of philosophical uses, and come in a correspondingly widerange of flavors. It is not always required, for example, that Invertand Nonvert are behaviorally alike. But suppose that a behaviorallyundetectable scenario is needed, and moreover one that is genuinelypossible. With the assumption that Invert is otherwise normal, we justsaw that Locke’s behaviorally undetectable scenario is notpossible. Without relaxing the simple assumption about Invert, can wefind one that is?

Suppose we stay with the full range of normal human color experience,and so with the color solid as illustrated in figure 5. The discussionof Locke’s scenario shows that a scenario corresponding to arotation of the color solid around the lightness axis should beavoided. However, as Palmer points out (1999a, 926), there are threeinversion scenarios that at least solve the problem posed by the lightand saturated yellows. These three scenarios correspond to,respectively, a reversal of the red-green axis; a reversal of theblue-yellow and black-white axes; and the previous two reversals takentogether: a reversal of the red-green, blue-yellow, and black-whiteaxes. These three scenarios are (approximately) illustrated in Figure6 below.

Figure 6: three inversions: red-green(top right); blue-yellow/black-white (bottom left);red-green/blue-yellow/black-white (bottom right)

As noted in the previous subsection, there are more perceptuallydistinguishable shades between red and blue than there are betweengreen and yellow, which would make red-green inversion behaviorally detectable.^[16] And there are yet further asymmetries. Dark yellow is brown(qualitatively different from yellow), whereas dark blue is blue (seefigure 6). Similarly, desaturated bluish-red is pink (qualitativelydifferent from saturated bluish-red), whereas desaturatedgreenish-yellow is similar to saturated greenish-yellow. Again, red isa “warm” color, whereas blue is“cool”—and perhaps this is not a matter of learnedassociations with temperature (see Hardin 1997, 297–7). In anyevent, there is clearly scope to resist the claim that one ofPalmer’s three inversions would be behaviorally undetectable.^[17]

Faced with these difficulties, philosophers seeking a clearly possiblebehaviorally undetectable inversion scenario have either considered aperceiver with limited color vision (for instance black-white vision),or else a perceiver with alien/quasi color vision, where anyalien/quasi color space that represents perceptible similarities anddifferences is stipulated to have appropriate symmetries. Here isShoemaker trying the first strategy:

But even if our color experience is not in fact such that a mapping ofthis [behaviorally undetectable] sort is possible, it seems to meconceivable that it might have been—and that is what matters forour present philosophical purposes. For example, I think we know wellenough what it would be like to see the world nonchromatically, i.e.,in black, white, and the various shades of grey—for wefrequently do see it in this way in photographs, moving pictures, andtelevision. And there is an obvious mapping of the nonchromatic shadesonto each other which satisfies the conditions for inversion. In thediscussion that follows I shall assume, for convenience, that such amapping is possible for the full range of colors—but I do notthink that anything essential turns on whether this assumption iscorrect. (Shoemaker 1975a, 196; note omitted).

For some responses, see Tye 1995, 205, and Hilbert and Kalderon 2000,206. “Black-white” inversion is also discussed by Clark(1996) (Other Internet Resources), Myin (2001) and Broackes (2007),and was briefly mentioned by Wittgenstein (1977, III-84).^[18] For a short autobiography of a complete achromat (someone with onlyblack-white rod vision) who is also a vision scientist, see Nordby1996 (Other Internet Resources).^[19]

Here is Block trying the second strategy:

[D]o the empirical issues really matter for the challenge that thepossibility of an inverted spectrum poses for functionalism? My answeris: only in a subtle and indirect way. For if therecould becreatures who have color experience or at least visual experience forwhom the relevant empirical points do not apply, then functionalism isrefuted even ifhuman spectra cannot be inverted. Forexample, perhaps it is a consequence of the human genome that humanstend to be unwilling to give a name to light green, even though theyare willing to give a name to light red (‘pink’). Still,therecould be people whose visual experience is similar ifnot identical to ours who find it equally natural to give names tolight green as to light red. (Perhaps we could even geneticallyengineer humans to become so willing.) (Block 1999, 946; cf. Shoemaker1982, 336–8, and Levine 1991, 34–6.)

For some doubts about the second strategy, see Hardin 1997,299–300.

Hilbert and Kalderon argue that “every possible quality spacemust be asymmetrical” (2000, 204) (that is, must lackany symmetries); if so, both strategies are misguided (see alsoDennett 1991, 389–98; 1993, 927; 1994).

2.3.2 Intrapersonal and Interpersonal Scenarios

If a behaviorally undetectable spectrum inversion scenario ispossible, how do we know it does not actually obtain? There is atemptation to say that we do not know—moreover, that we cannotknow. (For more discussion, see subsection 3.6 below.) And if wecannot verify or falsify the claim that such a scenario does notobtain, then according to the verificationist theory of meaning heldby the logical positivists (Ayer 1959) the scenario is meaningless.Indeed, the logical positivists sometimes gave spectrum inversion asan example of an unverifiable claim (Schlick 1932/3, 93, quoted inShoemaker 1982, 339; see also Ayer 1936, 173–4, and Wittgenstein1958, §272).

The allegedly meaningless scenario is a case ofinterpersonal(or intersubjective) spectrum inversion: Invert is spectrally invertedwith respect to another person, Nonvert. But there is another sort ofinversion scenario, in which a single person’s qualia areinverted with respect to her qualia at an earlier time. As Shoemakernotes (1982, 327), a case ofintrapersonal (orintrasubjective) spectrum inversion appears to have been firstdiscussed by Wittgenstein:

Consider this case: someone says ‘I can’t understand it, Isee everything red blue today and vice versa.’ We answer‘it must look queer!’ He says it does and, e.g., goes onto say how cold the glowing coal looks and how warm the clear (blue)sky. I think we should under these or similar circumstances beinclined to say that he saw red what we saw blue. And again we shouldsay that we know that he means by the words ‘blue’ and‘red’ what we do as he has always used them as we do.(Wittgenstein 1968, 284; quoted in Shoemaker 1982, 327–8)^[20]

Although Wittgenstein seems to have thought that a behaviorallyundetectable interpersonal spectrum inversion scenario is not possible(arguably for verificationist reasons), Shoemaker claims that once thepossibility of a Wittgensteinianintrapersonal inversion isgranted, there is an inexorable slide to the possibility of abehaviorally undetectableinterpersonal scenario:

…if the color experience of a person can differ from that ofothers at some point during his career, it should be possible for sucha difference to exist throughout a person’s career. But if thisa possibility, then it does seem perfectly coherent to suppose, andperfectly compatible with all the behavioral evidence we have aboutthe experiences of others, that, in Wittgenstein’s words,“one section of mankind has one sensation of red and anothersection another.” (Shoemaker 1982, 329)^[21]

We can think of this sort of argument as proceeding in four steps (seeBlock 1990, Shoemaker 1996b):

Similar arguments starting from a Wittgensteinian intrapersonalscenario can be given for the other kinds of interpersonal inversionhypotheses discussed in section 3 below.

One might think that at least step 4 is unproblematic. However,according to the “Frege-Schlick view” (Shoemaker 1982,339),interpersonal comparisons of qualia (unlikeintrapersonal comparisons) do not make sense. TheFrege-Schlick view could be supported on verificationist grounds; fora more interesting line of defense, see Stalnaker 1999, 2006, andShoemaker 2006b and Block 2007, 103–7, for discussion. Since itmakes perfect sense (and indeed is often true) to say that tomatoeslook red to most people, a proponent of the Frege-Schlick view mustdeny, for example, that \(Q_{R}\) is the property of being anexperience of something’s looking red (see section 1 above andStalnaker 1999, 225).

2.3.3 Inverted Earth

Asymmetries in color space pose problems for step 3 of the previousargument. But—especially for those with verificationistsympathies—step 3 is problematic even if these concerns arewaived. Why be so sure that the “total adaptation”(semantic adaptation plus amnesia) doesn’t reinvert the qualia?After all, if you imagine being the subject yourself, after the periodof amnesia you have no sense that anything is amiss—so perhapsnothing is. Similar doubts can be raised about step 2: suppose you usecolor terminology exactly as you did before the step 1inversion—that is, spontaneously on the basis of how thingslook—but you seem to recall that your past experiences wereradically different. Would you be confident that you hadn’tmisremembered your past experiences? (See Dennett 1988; 1991, Ch. 12;1993; 1994; 2005, Ch. 4; 2013, Ch. 58, and Rey 1992.)

Although Block thinks “that these criticisms can be defeated ontheir own terms” (1990, 61), his “Inverted Earth”scenario is designed to sidestep them. (See Block 1990, 1996a, 2003.)^[22] Instead of considering an “overnight” inversion and theconsequent confusion, semantic adaptation and amnesia, your eyes arefitted with “color inverting lenses” and you aretransported to another planet—Inverted Earth. This is a placejust like Earth except that each object has “the complementarycolor of [its counterpart] on Earth. The sky is yellow, grass is red,fire hydrants are green, etc.” (1990, 60). The inhabitants alsospeak Color Inverted English (‘red’ meansgreen,‘blue’ meansyellow, etc.). The right hand partof figure 4 above displays a photograph of fruits taken on InvertedEarth with an ordinary Earthly camera. (Despite the yellow sky, theillumination on Inverted Earth is the same as it is on Earth. Notethat achromatic colors are not inverted—on Inverted Earth snowis white and coal is black.)^[23] Because of the inverting lenses—and ignoring complications suchas those mentioned in subsection 2.3.1—when you arrive onInverted Earth you notice no visible change. Your experience when youlook at an arrangement of fruits on Inverted Earth isphenomenologically the same as your previous experience of thecounterpart arrangement on Earth (see the left hand part of figure 4),and conversation with the locals proceeds just as smoothly as it didback on Earth. This scenario is therefore the converse of typicalinverted spectrum scenarios: instead of keeping the environment fixedand varying the internal constitution of the subject, Inverted Earthvaries the environment and (due to the inverting lenses) keeps thesubject’s internal constitution fixed. Block uses Inverted Earthin an argument against functionalism and representationalism (seesubsections 3.1 and 3.2 below).^[24]

2.4 Shifted Qualia

The qualia inversion scenarios discussed so far are merelyhypothetical—more cautiously, we do not know whether any of them obtain.^[25] There are, however, “shifted” qualia scenarios thatactually obtain. And, in fact, many of the philosophicalarguments that appeal to the possibility of an inversion scenario canmake do instead by appealing to the actual shifted qualia scenario,hence avoiding potentially controversial claims about possibility.

The shifted qualia scenario that is usually discussedconcerns—unsurprisingly—color vision. There is asubstantial amount of variation between people classified as having“normal” color vision by standard tests, due todifferences in the lens of the eye and photoreceptor pigments, amongother factors. In one experiment, introduced into the philosophicalliterature by Hardin (1993, 79–80), Hurvich et al. (1968) foundthat the apparent location of unique green for spectral lights among50 subjects varied from 490 to 520nm.^[26] This is a large range: 15nm either side of unique green looksdistinctly bluish or yellowish. For example, when Smith looks at thethird patch in figure 7 (in isolation), his experience might have thequale that Jones’s experience has when she looks at thefourth patch in Figure 7, keeping the viewing circumstancesfixed. And when Smith looks at the fourth patch, his experience mighthave the quale that Jones’s experience has when she looks at thefifth patch. Thus—at least over a small range ofhues—Jones’s and Smith’s color qualia are“shifted” with respect to each other. Accordingly, thissort of scenario can be described as a case of “shiftedspectra” (Block 1999). (NB: here we are assuming that theFrege-Schlick view mentioned in subsection 2.3.2 is incorrect.)

Figure 7: five patches: yellowish-greento bluish-green

Notice that if a behaviorally undetectable scenario is wanted, anactual case of shifted spectra will not fit the bill.

3. Spectrum Inversion in an Argument…

Inversion scenarios—in particular, spectrum inversion—turnup in a wide range of philosophical arguments, which we are now in aposition to examine.^[27]

3.1 …Against Behaviorism, Functionalism, and Physicalism

Behaviorism in the philosophy of mind is the view that themental is nothing over and above behavior (including dispositions tobehave). Any version of behaviorism implies that the mental superveneson behavior. That is: necessarily, two creatures who are behaviorallyalike are also mentally alike. Likewise, any version offunctionalism orphysicalism implies that the mentalsupervenes on, respectively, functional organization and physicalmakeup. For the purposes of this subsection, it is not necessary toget into the details of these theories. However, two points should benoted. First, it should not be assumed that either behavior,functional organization, or physical makeup is an intrinsicmatter—the relevant sorts of behavioral, functional, andphysical properties may be extrinsic. In other words, perfectduplicates may differ in behavioral, functional, or physical respects.^[28] Second, as these theories are usually understood, difference inbehavioral respects implies difference in functional respects, whichin turn implies difference in physical respects; none of the converseimplications holds.^[29] So the three supervenience theses just mentioned are related asfollows: the behaviorist supervenience thesis implies thefunctionalist thesis, which in turn implies the physicalistthesis.

If some behaviorally undetectable inverted spectrum hypothesis iscorrect, then there could be a pair of creatures who are behaviorallyalike but mentally different: Invert and Nonvert are in differentmental states when they each look at a tomato, and are behaviorallyalike. Hence, if the inverted spectrum hypothesis is correct,behaviorism is false. This gives us an argument againstbehaviorism:

Since behaviorism is not a popular position these days, thisapplication of an inverted qualia scenario is perhaps not sointeresting. And given the complications discussed in subsection2.3.1, there is even room for a behaviorist to resist. However, ofconsiderably more interest are similar arguments against functionalism(and physicalism). Block and Fodor (1972), who invented theterminology of ‘inverted qualia’, were the first toformulate an inverted spectrum argument against functionalism,specifically Turing machine functionalism as defended in Putnam 1967.^[31] Ignoring the details of particular functionalisms, the argument isexactly parallel to the one against behaviorism. (Similar remarks gofor the inverted spectrum argument against physicalism.) According tofunctionalism, mental states are functional states: states defined bytheir causal role with respect to inputs, outputs, and other states.So, according to functionalism, necessarily, two creatures who arefunctionally alike are also mentally alike. In order to complete theargument, an appropriate inverted spectrum hypothesis must beestablished, where Invert and Nonvert are functional duplicates.

The anti-functionalist analogue of argument Aa is:

The possibility of a behaviorally undetectable inversion scenario(P1a) can be motivated by appeal to the sorts of considerationsdiscussed in 2.3.1 above. However, in order to refute functionalism astronger inversion hypothesis (P1b) is needed. As Block and Fodorpoint out, functionalism allows us todeny that “twoorganisms are in the same psychological state whenever their behaviorsand/or behavioral dispositions are identical” (1972, 86), henceavoiding the stock objections to behaviorism. The functionalist, then,has no problem with behaviorally undetectable inversions. But whyshould she concede the possibility of afunctionallyundetectable inversion? The question can be made more pointed byobserving that (a) no one has ever articulated a detailedfunctionalist theory of any mental state, and (b) any realisticversion of such a theory would be extremely complicated.^[32] In favor of the possibility of a functionally undetectable inversion,Block and Fodor offer its “conceptual coherence”:

It seems to us that the standard verificationist counterargumentsagainst the view that the ‘inverted spectrum’ [scenario]is conceptually coherent are not persuasive. If this is correct, itlooks as though the possibility of qualia inversion poses a seriousprima facie argument against functionalist accounts of the criteriafor type identity of psychological states. (91)

Block and Fodor’s apparent move from the “conceptualcoherence” of the inversion scenario to its possibility can bequestioned. Even though one cannot know a priori that not-p (that is,p is conceptually coherent), p may yet be impossible. For example, onecannot know a priori that gold does not have the atomic number 79, butit is a necessary truth that gold has this atomic number. (This sortof separation between conceptual coherence and possibility is notuncontroversial, but is commonly accepted.^[33])

In any case, there are other conceptually coherent scenarios that areconsiderably more straightforward than an inverted spectrum scenario,for example a scenario containing a conscious subject and a functionalduplicate who is not conscious at all (a “zombie”, in thephilosophical sense). So if the move from conceptual coherence topossibility is in fact legitimate, functionalism may be refuted by asimpler argument that does not have an inversion hypothesis as apremise. (Shoemaker is a notable dissenter on this point; he holdsthat while inverted spectrum scenarios are conceptually coherent,zombie scenarios are not. See Shoemaker 1975a, 1981, 1991.)

A defender of the utility of an inversion scenario in an argumentagainst functionalism might reply that the scenario’spossibility does not merely rest on its conceptual coherence. Inaddition—this reply continues—there is a positive“Cartesian intuition” that such an inversion scenario ispossible (a “clear and distinct idea” of the scenario,perhaps), and this is prima facie evidence that itispossible.

However, Cartesian intuition, just like conceptual coherence, is not avery discriminating weapon, tending to spread possibility over a widelandscape (cf. Tye 2021, section 4). Cartesian intuition also tends tocertify the possibility of scenarios containing zombies, thinkingrocks, entirely disembodied minds (not even embodied in ectoplasm),and so forth—allimpossibilities, according to thefunctionalist. So, as with conceptual coherence, any inverted spectrumargument against functionalism that relies on Cartesian intuitions canbe converted into an equally plausible and simpler argument that makesno mention of the inverted spectrum.

There is one other defense of the utility of inversion scenarios inanti-functionalist arguments, namely that some of them arebiologically possible—and hence not as far fetched asscenarios containing zombies or thinking rocks. If this is right, thenspectrum inversion would be of special significance, since we have afirmer grip on possibilities that are closer to home.

Here is it is helpful to examine Block’s Inverted Earth argumentagainst functionalism, which at a superficial glance might not seem tostray beyond the constraints of Earthly biology. As we saw insubsection 2.3.3, the Inverted Earth scenario is designed to avoidcertain objections to the usual argument from intrapersonal inversionhypotheses to interpersonal inversion hypotheses. How is the scenarioturned into an argument against functionalism?

The brand of functionalism (about qualia) that Block sets out torefute is this:

An experience has [\(Q_{R}\)] if [and only if] it functions in theright way—if it is caused by red things in the rightcircumstances, and used in thought about red things and action withrespect to red things rightly. The functional roles I am talking aboutare what I call ‘long-arm’ roles, roles that include realthings in the world as the inputs and outputs. They are to bedistinguished from the ‘short-arm’ roles thatfunctionalists sometimes prefer, roles that stop at the skin. (1990,58, note omitted)^[34]

Block then tries to establish that after a suitable period of time onInverted Earth, your beliefs and judgments about the colors of thingswould becorrect: like the locals, you would believe thatfire hydrants are green, the sky is yellow, and so on:

[A]ccording to me, after enough time has passed on Inverted Earth,your embedding in the physical and linguistic environment of InvertedEarth would dominate, and so your intentional contents would shift soas to be the same as those of the natives. Consider an analogy(supplied by Martin Davies): if you had a Margaret Thatcherrecognitional capacity before your journey to Inverted Earth, and onarriving misidentify twin MT as MT, you are mistaken. But eventuallyyour ‘That’s MT’ judgements get to be about twin MT,and so become right after having started out wrong. If you were[transported] at age 15, by the time 50 years have passed, you use‘red’ to mean green, just as the natives do. (64)

(We can also add that you know that you are on Inverted Earth, andmake an effort to speak the local language; see Block 1996a, 42;2003.)

This step of the argument appeals toexternalism about mentalcontent (Putnam 1975, Burge 1979), specifically some sort of causalcovariational theory (see the entryexternalism about mental content). Putting the basic idea crudely: after a while on Inverted Earthcertain of your inner states that on Earth were reliably caused by thepresence of red things and thereby represented redness will instead bereliably caused by the presence of green things, and thereby will cometo represent greenness.

This gives us an apparent counterexample against the “longarm” functionalist theory. On Inverted Earth your experienceshave the functional role that the functionalist theory says isnecessary and sufficient for possessing \(Q_{R}\): they are“caused by red things in the right circumstances, and used inthought about red things and action with respect to red thingsrightly”. But on Inverted Earth your experiences with thisfunctional role have \(Q_{G}\), not (or not always) \(Q_{R}\).

If we insist that the Inverted Earth scenario is constrained by actualbiology, can it still be maintained that your experiences caused byred things on Inverted Earth have the \(Q_{R}\)-role? That is notclear, even if we grant Block’s claim about the “shift inintentional contents” without a corresponding change in qualia.The problem is twofold. First, because of asymmetries in color spaceand additional complications (seefootnote 23), to say nothing of the details of the “inverting lenses”,your total functional organization would certainly change in variousrespects after traveling to a biologically possible Inverted Earth.Second, Block’s description of the long-arm functional theory ishighly schematic. It may be that a suitably sophisticated anddeveloped form of this theory would not have the consequence that, ona biologically possible Inverted Earth, your experiences caused by redthings have the \(Q_{R}\)-role. Similar points go for an argumentagainst functionalism using a traditional inverted spectrumscenario.

Unsurprisingly, Block does not rest very much—ifany—weight on the biological possibility of the Inverted Earthscenario:

But what if the facts of human physiology get in the way of the caseas I described it? My response is the same as the one mentionedearlier (based on Shoemaker’s rebuttal of Harrison), namely thatit is possible for there to be a race of people very much like us,with color vision, and color sensations, but whose physiology does notrule out the case described (or spectrum inversion). The functionalistcan hardly be satisfied with the claim that our experiences arefunctional states but the other race’s experiences are not.(1990, 64)

This response concedes that the Inverted Earth argument againstfunctionalism may need to appeal to more-or-less outlandishpossibilities. And if it does, then since other possibilities notinvolving inversions, and arguably no more outlandish, will do just aswell, it is doubtful that Inverted Earth-type scenarios have anessential role to play in arguments against functionalism.^[35]

The anti-physicalist inverted spectrum argument is:

Although there is some controversy about just how science-fictionalanti-functionalist inversion scenarios need to be,anti-physicalist inversion scenarios are usually supposed tobe very remote from actuality, and their possibility is hotlydisputed. Almost uncontroversially: if an inverted spectrum argumentagainst physicalism works at all, then a simple zombie scenario willequally serve the purpose.^[36]

3.2 …Against Representationalism

It is widely held that perceptual experiences represent theperceiver’s environment as being a certain way. For example, theexperience of someone with normal color vision looking at figure 1represents (inter alia) her environment as containing a crimson,vermilion, and turquoise square. In the terminology of Chalmers 2004(slightly adapted), arepresentational property is a propertyof a mental state/event that specifies (perhaps only in part) thestate/event’s representational content. For example, theproperty of being a visual experience that represents that there is acrimson square before one is a representational property (for ataxonomy of representational properties, see Chalmers 2004, section2). The basic idea ofrepresentationalism orintentionalism is that qualia are representationalproperties, or at least supervene on representational properties. Oneadvantage of representationalism is that it appears to reduce“phenomenal consciousness” (Block 1995) to a certain kindof intentionality. Since the problem of providing a naturalisticaccount of intentionality is often thought to be tractable,representationalism brings the possibility of a naturalistic accountof consciousness (see, e.g., Dretske 1995, Lycan 1996, Tye 2000, andSpeaks 2015).^[37]

Spectrum inversion scenarios help to focus the dispute betweenrepresentationalists and their critics. (Actual cases of shiftedspectra can also serve: see Block 1999.) Any version ofrepresentationalism is committed to the following thesis. Consider acase of red-green spectrum inversion, and imagine Invert and Nonvertare both looking at the red peppers depicted in figure 6, against aneutral background. Nonvert’s experience has \(Q_{R}\), whileInvert’s experience has \(Q_{G}\). Because the two experienceshave different qualia, any version of representationalism impliesthat, if this scenario is possible, the two experiences differ inrepresentational content. Hence, if the foregoing scenario can befilled out so that (a) the two experiences have thesamecontent and (b) the scenario is possible, then representationalism isrefuted.

How can these two desiderata be satisfied? Fortunately for theanti-representationalist—orphenomenist (Block2003)—the usual ways of trying to secure (a) do not requireInvert and Nonvert to be behavioral duplicates (or, for that matter,functional duplicates). The anti-representationalist can thereforedismiss concerns that a behaviorally undetectable inversion scenariois impossible.

The description of the anti-representationalist scenario is typicallycompleted with the following three features. First, Invert is able touse her color vision to reidentify objects, distinguish objects fromtheir backgrounds, etc., with more-or-less the facility of Nonvert. InLocke’s phrase, Invert “would be able as regularly todistinguish Things for [her] Use by those Appearances”. Second,Invert has been spectrally inverted from birth (or at least for a longperiod of time). Third, Nonvert and Invert belong to the samelinguistic community: in particular, they use color vocabulary in thesame way, applying ‘red’ to tomatoes, ‘yellow’to bananas, and so forth.

Assume that this scenario is possible (for an argument that itisn’t, see Sundström 2002 and Gibbons 2005; for a reply seeLittlejohn 2009). The three features just mentioned are intended tosupport the view that this scenario is one in which, when Invert andNonvert both look at the fruits depicted in figure 6, theirexperiences have thesame representational properties. Inparticular (glossing over a complication to be discussed in subsection3.3 below), the bananalooks yellow to both Invert andNonvert, the strawberrieslook red to both, and so on. So,assuming that bananas are yellow, strawberries are red, etc., neitherInvert nor Nonvert is suffering from some global color illusion. Ifthis inverted spectrum hypothesis is correct, then qualia do notsupervene on representational properties, and thereforerepresentationalism is false.

(Here is one way of putting the Inverted Earth version of thisargument (see subsections 2.3.3 and 3.1). After first arriving onInverted Earth, your word ‘red’ meansred, and toyou the green peppers on Inverted Earth look red. But after a periodof acclimatization, you come to speak the language of the locals, andyour experiences come to represent correctly the colors ofthings—green peppers on Inverted Earth look green. Now compareyour present experience of a green pepper on Inverted Earth with yourprevious experience of peppers of exactly that shade back on Earth.Same content, but different qualia. Alternatively, theanti-representationalist argument can proceed by exhibiting an exampleof the converse: same qualia, but different content—see Block1990, 64–7.)

The three features of the anti-representationalist scenario canmotivate the conclusion that Invert is not systematicallymisperceiving the colors of things as follows. First, becauseInvert’s color vision is as useful as Nonvert’s fordiscriminating and identifying objects, surely it would be arbitraryto suppose that Invert’s color vision, but not Nonvert’s,is the source of pervasive illusions. Second, because Nonvert has beeninverted since birth, a complicated system of causal connectionsbetween the colors of objects in her environment and states of hervisual system has been in place for a long period. In particular,there is a reliable causal connection between the presence of a redobject before Invert’s eyes and a certain neural event occurringin Invert; this sort of causal connection is plausibly sufficient tobestow the property of representing redness on this type of neuralevent. Third, because Invert and Nonvert belong to the same linguisticcommunity, Invert’s word ‘red’ meansred.So when Invert says (as she does), ‘Strawberries look red tome’, she means that strawberrieslook red to her. So,if strawberries do not look red to her, Invert is systematically inerror about how things look, and this result is not credible.^[38]

Naturally, each of these reasons for thinking that Invert is notmisperceiving the colors of objects can be questioned. Against thefirst, one might dispute the claim that it would be arbitrary toconvict only Invert of error—after all, for all that’sbeen said, Nonvert and Invert might differ functionally, which ispresumably a relevant difference. Against the second, there arewell-known problems for the “causal covariational” accountof mental content that it assumes (see, e.g., Fodor 1992, Ch. 3).Finally, against the third, it may be argued that the consequence thatInvert is mistaken about the content of her experience is notunacceptable (Tye 2002, 451).^[39]

It will be useful to set out the anti-representationalist argumentmore carefully. Assume as a suppressed premise that the invertedspectrum scenario just described is possible, and suppose that Invertand Nonvert are both looking at a ripe tomato in good light:

Some of the dialectic surrounding P1 has been described. In thefollowing three subsections, other ways of resisting the argument willbe discussed.

If Argument B is sound, tomatoes look red to both Invert and Nonvert,although the corresponding qualia are different. This is why spectruminversion was not described in subsection 2.1 as a case where tomatoeslook green to Invert (andlook red to Nonvert). Ifspectrum inversion is explained in these terms, the thought experimentis quite unsuitable for anti-representationalist purposes.

According to the (orthodox) representationalist, an experience has\(Q_{B}\), say, just in case it is an experience that represents blue.According to the phenomenist who endorses Argument B, an experiencehas \(Q_{B}\) just in case it has a certainnon-representational property. Let us stipulate that‘\(B\)’ refers to this non-representational property, ifsuch a thing exists. Then the two views may be put as follows:

Phenomenism
\(Q_{B} = B\) (a certain nonrepresentational property).

Orthodox representationalism
\(Q_{B}\) = property of visually representing blue (i.e., being anexperience of something’s looking blue).

The sense-datum theory is usually taken to be a form of phenomenism;it will be treated as such here.^[40] According to the sense-datum theorist, sense-data that are associatedwith experiences of seeing the sky, lapis lazuli, cobalt glass, etc.,have a distinctive property; the traditional sense-datum theorist tookthis property to be the color blue (see, e.g., Moore 1953, 30, n.2),but let us speak more neutrally and call it ‘blue´’(Peacocke 1983, Ch. 1). Then, accordingto the sense-datum theorist, the phenomenist equation can be spelledout more informatively thus:

Sense-data theory
\(Q_{B} = B\) = being a sensing of a blue´sense-datum.

Orthodox phenomenists (for instance Block and Levine) have notruck with sense-data, and typically leave the phenomenist equationunadorned. However, the sense-datum theorist can offer the followingconsideration in her favor.

Imagine two experiences: first, an experience (call it‘\(e_{1}\)’) of a blue triangle next to a red square;second, an experience \((e_{2})\) of a red triangle next to a bluesquare. \(e_{1}\) has color qualia \(Q_{B}\) and \(Q_{R}\), and also“spatial qualia”, which we can label‘\(Q_{Tr}\)’ and ‘\(Q_{Sq}\)’. The referenceof these four bits of qualia terminology (‘\(Q_{B}\)’,‘\(Q_{R}\)’, ‘\(Q_{Tr}\)’, and‘\(Q_{Sq}\)’) has been fixed by, respectively, experiencesof blue objects, experiences of red objects, experiences of triangles,and experiences of squares. \(e_{2}\), of course, also has \(Q_{B},Q_{R}, Q_{Tr}\), and \(Q_{Sq}\). Yet \(e_{1}\) and \(e_{2}\) differphenomenologically, and therefore differ in qualia. So more qualiaterminology is required: in particular, a quale name whose referenceis fixed by experiences of blue triangles and red squares, and anothername whose reference is fixed by experiences of red triangles and bluesquares. In a useful notation, the first quale name is ‘\(Q_{Rx\amp Sq(x) \amp By \amp Tr(y)}\)’, and the second is‘\(Q_{Rx \amp Tr(x) \amp By \amp Sq(y)}\)’. Obviouslyfurther qualia names with ever-more complicated subscripts will beneeded.

Now notice that there are many entailment relations betweenqualia-statements—for example, ‘\(e\) has \(Q_{Rx \ampSq(x)}\)’ entails ‘\(e\) has \(Q_{Rx}\)’, and‘\(e\) has \(Q_{Rx \amp Tr(x) \amp By \amp Sq(y)}\)’entails ‘\(e\) has \(Q_{Rx \amp Sq(y)}\)’, and so on. Theorthodox representationalist and the sense-datum theorist have simpleaccounts of these entailments in terms of the structure of theobjects of experiences (apparent structure, for therepresentationalist;actual structure, for the sense-datumtheorist). Assuming representationalism: ‘\(e\) has \(Q_{Rx \ampSq(x)}\)’ (equivalently, ‘\(e\) is an experience ofsomething’s looking red and square’) clearly entails‘\(e\) has \(Q_{Rx}\)’ (equivalently, ‘e isan experience of something’s looking red’). Assuming thesense-datum theory: ‘\(e\) has \(Q_{Rx \amp Sq(x)}\)’(equivalently, ‘\(e\) is a sensing of a red and squaresense-datum’) clearly entails ‘\(e\) has \(Q_{Rx}\)’(equivalently, ‘\(e\) is a sensing of a red sense-datum’).The orthodox phenomenist cannot give a similar explanation of theseentailments, and it is not clear whether she is entitled to them at all.^[41]

3.3 …For Appearance Properties

Return to the anti-representationalist argument of the previoussubsection:

Representationalists usually resist P1. But there are other options.According to Shoemaker, the flaw in the argument is not P1, but ratherP3. In addition to representing colors, Shoemaker thinks that visualexperiences represent other (“colorlike”) properties thatwe do not have words for in English, and which he callsappearance properties.^[42] On this view, both Invert and Nonvert’s experiences representthe tomato asred. However, Invert’s experience alsorepresents the tomato as having a certain salient appearance property(call it ‘\(AP_{G}\)’), while Nonvert’s experiencerepresents the tomato as having a certain salient appearance property\((AP_{R})\). It is this representational difference between Invertand Nonvert that accounts for the phenomenological difference betweentheir experiences. One may, then, view Shoemaker’s main argumentfor appearance properties as proceeding from P1, P2, andrepresentationalism (i.e., not-C2), to the conclusion that P3 isfalse.

What are the appearance properties \(AP_{G}\) and \(AP_{R}\)? SinceShoemaker thinks that it is implausible that Invert is systematicallymisperceiving the colors, it is not surprising that he also thinksthat neither Nonvert nor Invert is systematically misperceiving theappearance properties. The tomato, then, has both \(AP_{G}\) and\(AP_{R}\). In Shoemaker 1994b, \(AP_{R}\) is said to be (where\(Q_{R}\) “is the quale that characterizes [Nonvert’s]experience of red things”) the property of “currentlyproducing [a \(Q_{R}\)] experience in someone related to it in acertain way, namely someone viewing it under normal lightingconditions” (254), and similarly for \(AP_{G}\) (see alsoShoemaker 1994a). This secures the result that the tomato has\(AP_{R}\) when Nonvert is looking at it; as Shoemaker notes, itimplies that the tomato lacks \(AP_{R}\) when it is not beingperceived. This account of appearance properties has beensubstantially revised and developed in Shoemaker’s later work.According to Shoemaker 2002, appearance properties includedispositions to produce certain experiences in certainperceivers (a suggestion that was considered but rejected in Shoemaker1994a, b). Shoemaker 2006a and 2019 revise the account further; fordiscussion, see Egan 2006, Speaks 2015, ch. 22, and Block 2019.

Thau (2002, Ch. 5) holds a similar view, but there are some importantdifferences. First, Thau’s argument does not turn on the need tosecure spectrum inversion without misrepresentation, and insteaddeploys an adaptation of Jackson’s (1982) thought experimentconcerning black-and-white Mary. (See the entry onqualia: the knowledge argument.) Second, because Thau is not concerned to ensure that neither Invertnor Nonvert is misperceiving the tomato, he does not try to argue thatthe tomato has both \(AP_{G}\) and \(AP_{R}\), leaving the questionunexamined. Third, Thau’s argument for appearance propertiescommits him to the view that they cannot be named (222–5);Shoemaker is not so committed. Finally, Thau does not think, unlikeShoemaker, that colors are visually represented (211). According toThau, beliefs about the colors of things are based on experiences thatrepresent objects as having appearance properties. These beliefs arejustified, Thau argues, because there is a correlation between anobject’s having color \(C\) and its looking to haveAP\(_{C}\) (235–6).

3.4 …For Modes of Presentation

An illustration of “Frege’s puzzle” is this. It isapparently possible to believe that Michael Caine is a Cockney, whilenot believing that Maurice Micklewhite is a Cockney. But how can thisbe, since Michael Caine and Maurice Micklewhite are the sameindividual?

According to many philosophers, appearances are not misleading, andthe two beliefs really are different: specifically, they represent thevery same individual, the beloved star ofAlfie, in differentways, or under different modes of presentation. On this view, thepropositional content of a belief is a Fregean Thought, with modes ofpresentation as constituents—as opposed to a structuredRussellian proposition, with objects and properties as constituents.^[43] Put differently but connectedly, the example shows that the names‘Michael Caine’ and ‘Maurice Micklewhite’ havedifferentFregean senses—their semantic values cannotsimply be their referents.

A similar issue arises in the philosophy of perception (see, e.g.,Boghossian and Velleman 1991, Peacocke 2001, Thau 2002). When onelooks at a cucumber, does the propositional content of one’sexperience have a constituent that is a “mode ofpresentation” of greenness (a neo-Fregean view) or does itinstead simply contain the property greenness itself? Using thefamiliar ordered pair notation for propositional content (see, e.g.,Thau 2002, 83), and ignoring issues about whether the cucumber itselfis associated with a mode of presentation, the dispute may be put asfollows. On the neo-Fregean view, the content of one’sexperience of the cucumber is \(\langle\)the cucumber,\(\mathrm{MOP_{greenness}} \rangle\); on the neo-Russellian view, thecontent of one’s experiences is \(\langle\)the cucumber,greenness\(\rangle\).

Recall the third premise of argument B (see the previous twosubsections):

P3.

If representationalism is true, then the phenomenal differencebetween Invert and Nonvert is due to a difference in the colors thattheir experiences represent the tomato as having.

As explained in subsection 3.3, one may resist P3 by claiming thatcolor experience represents appearance properties. That amounts to adefense of representationalism by introducing a distinction “atthe level of reference”. However, P3 may also be denied byintroducing a distinction “at the level of sense”. On thisview, the difference between Invert and Nonvert is like thedifference—as the Fregean has it—between Ian, who believesthat Michael Caine is a Cockney, and Nan, who believes that MauriceMicklewhite is a Cockney. On this Fregean view of the content ofperception, the difference between Invert’s and Nonvert’sexperiences is that they represent the very same property, namelyredness, in different ways, or under different modes ofpresentation.

Thau 2002 argues against modes of presentation (and also points outthe close connections between the inverted spectrum and Frege’spuzzle). Chalmers 2004 and Block 2007, 2019, defend a Fregeanview.

3.5 …For Relativism

We are not quite finished with Argument B:

So far, reasons to reject P1 and P3 have been discussed. But one mightalso question the step from P1 and P2 to C1. As an analogy, supposethat Hare is on a train, looking at a tomato in his lunchbox, and thatTortoise is on the platform, looking at the tomato as the train speedsby. Both Hare and Tortoise have normal vision, in particular, normalvisual motion perception. Consider the following argument.

Since the tomato is movingrelative to Tortoise, and is notmovingrelative to Hare, if P2* is true, it must not be takento mean that the tomato is moving relative to Hare. Assume, then, thatP2* is given the following true interpretation: the tomato is movingrelative to Tortoise. However, Hare does not have to perceive that thetomato is moving relative to Tortoise in order to perceive (correctly)the tomato’s motion—perceiving it asnot movingrelative to himself will also suffice. Hence, Hare’s andTortoise’s experiences can both be veridical, despiterepresenting the tomato’s motion differently, which is to saythat Argument B* is invalid.

One might diagnose a similar mistake in Argument B, and thus endorserelativism about color. According to relativism the tomato isnot redsimpliciter: rather, it is red relative to Nonvert(not green relative to Nonvert), and green relative to Invert (not redrelative to Invert). In other words, the tomato is simultaneouslyred-for-Nonvert andgreen-for-Invert. Since, on thisview, the tomato looks red-for-Nonvert to Nonvert, and red-for-Invertto Invert, both their experiences are veridical, despite representingthe tomato differently.

What is this property of being red-for-Nonvert? The usual answer issomething along the lines of the account of appearance properties inShoemaker 2002: something is red-for-Nonvert iff it is disposed tocause experiences with \(R\) in perceivers of Nonvert’s kind.And this, of course, is essentially the “secondaryquality” account of color that many find in Locke. Sometimesrelativism is combined with representationalism (McGinn 1983, Tye1994), but it arguably fits more naturally with phenomenism(McLaughlin 2003, Cohen 2004).

Shoemaker did not block Argument B in this straightforward fashionbecause he finds relativism implausible. As he puts it in a review ofMcGinn 1983:

Suppose…that overnight we all undergo intrasubjective‘spectrum inversion’…It cannot seriously bemaintained that the result of the change would be that henceforthgrass \(is\) red, port wine green, etc. And it is plausible that, oncewe were accustomed to the change, we would no longer say that grasslooks red (for it would look the way we had become accustomedto having green things look). This point is even clearer if we imaginethat we undergo intrasubjective inversion one at a time rather thanall of us at once. (1986, 411)

Like the argument for appearance properties, the argument forrelativism can be made by appeal to shifted spectra (see, inparticular, Cohen 2004). Averill 1992 argues for a version ofrelativism using physically possible intrapersonal shifted spectrascenarios, involving a slight change in the eye, or in the atmosphere.^[44]

3.6 …For Skepticism About Others’ Minds

The “inverted spectrum” quotation from Locke in subsection2.2 above continues:

I am nevertheless very apt to think, that the sensible Ideas, producedby any Object in different Men’s Minds, are most commonly verynear and undiscernibly alike. For which Opinion, I think, there mightbe many Reasons offered: but that being besides my present Business, Ishall not trouble my Reader with them; but only mind him, that thecontrary Supposition, if it could be proved, is of little use, eitherfor the Improvement of our Knowledge, or Conveniency of Life; and sowe need not trouble our selves to examine it. (1689/1975, II, xxxii,15)

It is regrettable that Locke did not trouble his Reader, because it isnot at all clear what reasons may be offered. Malebranche was of thecontrary opinion:

Yet I believe that it never, or almost never, happens that people seeblack or white other than as we see them, though they may not seemequally black or white to them. But as for the intermediate colors,such as red, yellow, blue, and especially those compounded from thesethree, I do not think there are many people who have exactly the samesensation of them. (1674–5/1997, I, 13, VI)

Let \(p\) be the claim that when others look at ripe tomatoes, theirexperiences have \(Q_{R}\). Let \(S\) be a spectrum inversion scenariowith the following simple feature: when others look at ripe tomatoes,their experiences have \(Q_{G}\), not \(Q_{R}\). (So \(p\) and \(S\)are incompatible.) Consider the following skeptical argument:

Although philosophers have generally not been impressed by similararguments for skepticism about the external world, there is littleconsensus on the status of arguments along the above lines. Forexample, Block writes: “I claim we simply do not know whetherspectrum inversion obtains or not” (1990, 57). Argument C isless threatening than some other skeptical arguments because, even ifsound, generalizations of it to skepticism about other kinds of mentalstates are implausible. For example, a parallel argument againstone’s knowledge of other’s beliefs would have a dubiousfirst premise.

P1 will be denied by an orthodox representationalist. Setting acontroversial skepticism about testimony aside, presumably one canknow on the basis of testimony that tomatoes look red to many people.(See Shoemaker 1982, 334.) So, since orthodox representationalismequates \(Q_{R}\) with the property of being an experience ofsomething’s looking red, one may know on the basis of testimonythat when others look at tomatoes, their experiences have\(Q_{R}\).

Some philosophers think that the fact that others are biologicallysimilar to oneself is an important piece of evidence for their mentalsimilarity (see, e.g., Hill 1991, Ch. 9), and P2 might be denied onthese grounds (see, e.g., Papineau 2002, 132). For more discussion,see Block 2002.^[45]

3.7 …For the Explanatory Gap

Many philosophers think there is an “explanatory gap”(Levine 1983, 2001) between physical facts and facts about consciousexperience. On this view, even if consciousness is a physicalphenomenon, it cannot be given a physical explanation. Invertedspectrum scenarios often play a role in arguments for the gap:

Let’s call the physical story for seeing red “\(R\)”and the physical story for seeing green “\(G\ldots\)” Whenwe consider the qualitative character of our visual experiences whenlooking at ripe McIntosh apples, as opposed to looking at ripecucumbers, the difference is not explained by appeal to \(G\) and\(R\). For \(R\) doesn’t really explain why I have the one kindof qualitative experience—the kind I have when looking atMcIntosh apples—and not the other. As evidence for this, notethat it seems just as easy to imagine \(G\) as to imagine \(R\)underlying the qualitative experience that is in fact associated with\(R\). The reverse, of course, also seems quite imaginable. (Levine1983, 356–7)

The argument for the gap suggested by Levine 1983 can be set out asfollows:

Notice that Argument D does not have as a premise a spectrum inversionhypothesis—that a certain spectrum inversion scenarioispossible. All the argument requires is that the spectruminversion scenario isimaginable. Indeed, since Levine is aphysicalist, he thinks that this scenario isnotpossible.

What is the intended interpretation of ‘imagine’ in P1 andP2? (In the literature ‘conceive’ is usedinterchangeably.) The usual answer (Levine 2001, Ch. 2) is this: \(p\)is imaginable iff not-\(p\) is nota priori. On thisinterpretation, P1 amounts to this: it isa priori that ifthe explanans holds, so does the explanandum; that is, that theexplanansa priori entails the explanandum. This can bemotivated by appeal to the “deductive-nomological” modelof explanation (see Hempel 1965, and the entry onscientific explanation); this model is controversial, and in fact Levine rejects it, but heargues that there is a broader motivation:

From the brief survey of current theories of scientific explanationjust presented, I think the following claim can be justified: in agood scientific explanation, the explanans either entails theexplanandum, or it entails a probability distribution over a range ofalternatives, among which the explanandum resides. (2001, 74)

One might resist Argument D by denying P2 (for some ammunition, seeHardin 1987; 1993, 134–42; for a reply see Levine 1991; see alsoHardin 1991). A much more common response is to deny P1 (Block andStalnaker 1999; for a reply see Chalmers and Jackson 2001).

One exegetical complication is that Levine himself now denies P1,while continuing to maintain the existence of the explanatory gap onthe basis of an argument related to Argument D, although somewhat morecomplicated (2001, Ch. 3). And in any case, just like the invertedspectrum argument against behaviorism, functionalism and physicalism(see subsection 3.1 above), inverted spectrum scenarios are notplaying an essential role in the case for the gap, and indeed Levine2001 leans more heavily on “absent qualia” scenarios:“The conceivability of zombies…is the principalmanifestation of the explanatory gap” (79).

3.8 …For the Ineffability of Qualia

The introduction of ‘\(Q_{R}\)’, ‘\(Q_{G}\)’,and so forth, at the start of this article might have occasioned somesuspicion. Assume that spectrum inversion doesnot occur, andconsider a counterfactual situation in which, as Block puts it,“spectrum inversion is rife” (1990, 55). Supposethat philosophers in this counterfactual situation introduced qualiaterminology in the way it was introduced in section 1. If their qualiaterminology is meaningless, then it is hard to see why our terminologyis better off—we use ‘\(Q_{R}\)’ just as it is usedin the counterfactual situation. If, on the other hand, their qualiaterminology is meaningful, then presumably ‘\(Q_{R}\)’, asthey use it, refers to something other than a quale. (Since spectruminversion is rife, their use of ‘\(Q_{R}\)’ is notassociated with any particular quale.) Again, given the overlap inuse, why suppose that our word ‘\(Q_{R}\)’ is anydifferent? Either way: ‘\(Q_{R}\)’ does not refer to aquale. There is a threat, then, that qualia cannot be named in apublic language—that they areineffable (cf. Dennett1988, 228–9). Indeed, that seems to be Block’s opinion:“if an inverted spectrum is possible, then experiential contentsthat can be expressed in public language (for example,lookingred) are not qualitative contents, but rather intentionalcontents” (1990, 55; see also Block 2007, 73–4).(“Qualitative contents” are qualia that are notrepresentational properties: see subsection 3.2.)

Frege held a version of the ineffability view. One of his theses inThe Foundations of Arithmetic is that arithmetic is“objective”, which he explains as follows:

What is objective…is what is subject to laws, what can beconceived and judged, what is expressible in words. What is purelyintuitable is not communicable. To make this clear, let us suppose tworational beings such that projective properties and relations are allthey can intuit—the lying of three points on a line, of fourpoints on a plane, and so on; and let what the one intuits as planeappear to the other as a point, and vice versa, so that what for theone is the line joining two points for the other is the line ofintersection of two planes, and so on with the one intuition alwaysdual to the other. In these circumstances they could understand oneanother quite well and would never realize the difference betweentheir intuitions, since in projective geometry every proposition hasits dual counterpart; any disagreements over points of aestheticappreciation would not be conclusive evidence. Over all geometricaltheorems they would be in complete agreement, only interpreting thewords in terms of their respective intuitions. With the word‘point’, for example, one would connect one intuition andthe other another. We can therefore still say that this word has forthem an objective meaning, provided only that by this meaning we donot understand any of the peculiarities of their respectiveintuitions. (1884/1953, §26)

This is an inverted spatial qualia scenario. According to Frege, theinversion would not show up in the semantics of words: both Nonvertand Invert use the word ‘point’ with the same meaning,despite associating very different “intuitions” with it.In the next paragraph, Frege makes a similar claim about colorterminology.

The word ‘white’ ordinarily makes us think of a certainsensation, which is, of course, entirely subjective; but even inordinary everyday speech, it often bears, I think, an objective sense.When we call snow white, we mean to refer to an objective qualitywhich we recognize, in ordinary daylight, by a certain sensation. Ifthe snow is being seen in a coloured light, we take that into accountin our judgement and say, for instance, ‘Itappears redat present, but itis white.’ Even a colour-blind mancan speak of red and green, in spite of the fact that he does notdistinguish between these colors in his sensations; he recognizes thedistinction by the fact that others make it, or perhaps by making aphysical experiment. Often, therefore, a colour word does not signifyour subjective sensation, which we cannot know to agree with anyoneelse’s (for obviously calling things by the same name does notguarantee as much), but rather an objective quality. (§26)

Although Frege seems to concede thatsometimes a color word“signifies our subjective sensation”, the general drift ofthe argument points to a much stronger conclusion, that our subjectivesensations are simply not “expressible in words”. Arelated example is Wittgenstein’s “beetle in thebox”:

Suppose everyone had a box with something in it: we call it a‘beetle’. No one can look into anyone else’s box,and everyone says he knows what a beetle is only by looking athis beetle.—Here it would be quite possible foreveryone to have something different in his box. One might evenimagine such a thing constantly changing.—But suppose the word‘beetle’ had a use in these people’slanguage?—If so it would not be used as the name of a thing. Thething in the box has no place in the language game at all; not even asa something: for the box might even be empty. No, one can‘divide through’ by the thing in the box; it cancels out,whatever it is. (1958, §293)

(Notice that Wittgenstein imagines “absent beetles”,corresponding to an “absent qualia” scenario.)

Here is one argument suggested by these passages.

Suppose that Humbert is semantically (and otherwise) competent, hasnormal color vision, is a member of our linguistic community, and usesqualia terminology (‘\(Q_{R}\)’, ‘\(Q_{G}\)’,etc.), as introduced in section 1 above. Further suppose that spectruminversion does not in fact occur.

Now consider a counterfactual spectrum inversion scenario in which“spectrum inversion is rife”. Invert has been spectrallyinverted with respect to some other members of his community sincebirth, all of whom use color terminology in much the same way. Nonvertis spectrally inverted with respect to his neighbor Invert,but—comparing this scenario with the actual scenario describedin the previous paragraph—is not spectrally inverted withrespect to Humbert. Further suppose that Nonvert and his neighborInvert use qualia terminology as introduced in section 1 above. Assumeas a suppressed premise that this scenario is possible.

Let ‘\(X\)’ abbreviate the definite description ‘thequale distinctive of Humbert’s experiences of red things’(by hypothesis, this definite description is coextensive with‘the quale distinctive of Nonvert’s experiences of redthings in the counterfactual inversion scenario’).

Since the rest of us are in no better position than Humbert, C2 leadsinevitably to the conclusion that ‘\(Q_{R}\)’,‘\(Q_{G}\)’, etc., as introduced in the manner of section1, do not in fact refer to qualia. One might view Argument E asshowing that certain salient aspects of our mental lives arelinguistically elusive (as Frege apparently did); alternatively, onemight follow Wittgenstein and conclude that the very idea of qualiarests on a conceptual confusion.

In fact, C2 does not imply that qualia arecompletelyunspeakable—it does not, that is, imply that \(no\) expressionrefers to \(X\) (i.e., the quale distinctive of Humbert’sexperiences of red things). Indeed, if the sentence to the right of‘C2’ succeeds in expressing a truth, then‘\(X\)’ (and so ‘the quale distinctive ofHumbert’s experiences of red things’) refers to \(X\). IfArgument E is as far as we can go, then the moral seems to be thatparticular qualia can only be picked out ‘bydescription’—they cannot be referred to by semanticallysimple expressions, such as ‘\(Q_{R}\)’ and ‘\(Q_{G}\)’.^[46] But—bearing in mind Wittgenstein’s remark that “thebox might even be empty”—one might attempt to extend theargument to show that even the word ‘qualia’ itself isdevoid of significance.

However, Argument E is not obviously sound. The premise in need ofmost defense is P3.^[47] When qualia terminology was introduced in section 1, it was tacitlypresupposed that spectrum inversion wasnot rife. InInvert’s and Nonvert’s community, that presupposition isfalse, and so it should not be surprising if the attempt to introduce‘\(Q_{R}\)’ into their public language fails. But inHumbert’s community the presupposition istrue; so whywouldn’t ‘\(Q_{R}\)’, as the members of thiscommunity use it, successfully refer to the quale distinctive ofHumbert’s experiences of red things?^[48]

3.9 ...For the Inconsistency of Content-Externalism, Representationalism, and Qualia-Internalism

Externalism about beliefs and other propositional attitudes,and also about perceptual experiences, was alluded to in subsections3.1 and 3.2. Premise P1 of our much-scrutinized ArgumentB—‘Neither Invert nor Nonvert is misperceiving the colorof the tomato’—was supported, in part, by a particularexternalist theory of perceptual content. According to theexternalist, some representational properties of subjects, like theproperty of believing that water is wet, or that arthritis is painful,or the property of having an experience of something’s lookingred, are extrinsic: these properties are not necessarily sharedbetween perfect duplicates (or even less-than-perfect duplicates withperfectly duplicated brains).^[49] Smith may believe that water is wet, yet twin-Smith on Putnam’sTwin Earth does not believe that water is wet. The tomato may look redto Jones, yet not to twin-Jones on Inverted Earth. (In an alternativescenario, twin-Jones has just been created by happenstance in a swamp:see Davidson 1987.)

It is also widely held that qualia areintrinsic (see, e.g.,Block 1990, 68). (More exactly: properties of subjects likehavingan experience with quale Q, are intrinsic.) If Jones is having anexperience with quale \(Q\), then there is no possible world w inwhich twin-Jones is not having an experience with quale \(Q\).

Finally, representationalism (see subsection 3.2 above) is—ifnot as popular as the previous two claims—at least defended bymany contemporary philosophers.

Now consider the following argument (cf. Byrne and Hilbert 1997b,271–2):

Consider the representational property of having an experience ofsomething’s looking red. By P1, this property is extrinsic, andso there is a possible world \(w\) in which a subject \(x\) has thisproperty and \(y\)—a perfect duplicate of \(x\)—lacks it.Solely for illustration, we may take \(w\) to be a possible world inwhich Nonvert and his twin Invert are both looking at a tomato in awhite bowl (but perhaps the twins are on different planets). Nonvertis having an experience of something’s looking red, and Invertis not; more specifically: (i) the tomato looks red, and nothing looksgreen, to Nonvert; (ii) the tomato looks green, and nothing looks red,to Invert. By P2, Nonvert’s experience has \(Q_{R}\) (and not\(Q_{G})\); conversely for Invert. So Nonvert and Invert are twinswhose experiences do not share qualia; in other words, qualia are notintrinsic. By P3, contradiction. Hence:

C.

At least one of P1, P2, and P3 is false.

Notice that Argument F does not assume the possibility of a scenarioin which duplicate perceivers are spectrally inverted. This spectruminversion hypothesis is ruled out by P3, and P3 is of courseconsistent with Argument F’s conclusion.

Argument F shows that either content-externalism, representationalism,or qualia-internalism should be rejected. Dretske (1995, Ch. 5) arguesagainst P3 (see also Tye 1995, 150–5; 2002, Ch. 6; Lycan 1996,115–7; and Noë 2005, Ch. 7); P1 is denied in Chalmers2004.

Relatedly, McGinn (1989, 58–94) runs a “spatially InvertedEarth” argument against what he calls ‘strongexternalism’ about perceptual content (a particular kind ofexternalism); Davies (1997) adapts McGinn’s example to argue forexternalism about perceptual content. Both sides of the“externalism/internalism” debate as encapsulated inArgument F presuppose that it is possible to keep a perceiver’sinternal constitution fixed while greatly varying the environment;this assumption is critically examined in Hurley 1998, Chs. 7, 8, andMyin 2001.

3.10 Summary: Required Features of Inverted Spectrum Scenarios

Bibliography

• Allen, K., 2010, “Locke and the Nature of Ideas”,Archiv für Geschichte der Philosophie, 92:236–255.
• Averill, E. W., 1992, “The Relational Nature ofColor”,Philosophical Review, 101: 551–88.
• Ayer, A. J., 1936,Language, Truth and Logic, London:Victor Gollancz; page reference is to the 1971 reprint, Harmondsworth,England: Pelican Books.
• –––, (ed.), 1959,Logical Positivism,New York: The Free Press.
• Bayne, T., and Michelle M. (eds.), 2011,CognitivePhenomenology, Oxford: Oxford University Press.
• Block, N., 1980, “Troubles with Functionalism”, inReadings in Philosophy of Psychology, Vol. 1, N. Block (ed.),Cambridge, MA: Harvard University Press, pp. 268–305.
• –––, 1990, “Inverted Earth”,Philosophical Perspectives, 4: 53–79.
• –––, 1995, “On a Confusion about aFunction of Consciousness”,Behavioral and BrainSciences, 18: 227–47.
• –––, 1996a, “Mental Paint and MentalLatex”,Philosophical Issues, 7: 19–49.
• –––, 1996b, “Functionalism”, inThe Encyclopedia of Philosophy Supplement, D. Borchert (ed.),New York: Macmillan, pp. 756–61.
• –––, 1999, “Sexism, Racism, Ageism and theNature of Consciousness”, inPhilosophical Topics, 26(1&2).
• –––, 2002, “The Harder Problem ofConsciousness”,Journal of Philosophy, 94:1–35.
• –––, 2003, “Mental Paint”, inReflections and Replies: Essays on the Philosophy of TylerBurge, M. Hahn and B. Ramberg (eds.), Cambridge, MA: MIT Press,pp. 165–200.
• –––, 2007, “Wittgenstein andQualia”,Philosophical Perspectives, 21:73–115.
• –––, 2019, “Sydney Shoemaker onTransparency and the Inverted Spectrum”, inBlockheads!Essays on Ned Block’s Philosophy of Mind and Consciousness,A. Pautz and D. Stoljar (eds.), Cambridge, MA: MIT Press, pp.481–86.
• Block, N. and Fodor, J., 1972, “What Psychological StatesAre Not”,Philosophical Review, 81: 159–81.
• Block, N. and Stalnaker, R., 1999, “Conceptual Analysis,Dualism, and the Explanatory Gap”,Philosophical Review108: 1–46.
• Boghossian, P., and Velleman, J. D., 1991, “PhysicalistTheories of Color”,Philosophical Review, 100:67–106. Reprinted in Byrne and Hilbert 1997a.
• Brenner, W. H., 2015, “From Inverted Spectra to ColorlessQualia: A Wittgensteinian Critique”,PhilosophicalInvestigations, 38(4): 360–81.
• Browning, J., 2024, “The History of Qualia and C.I.Lewis’ Role in it”,British Journal for the History ofPhilosophy, 32(1): 173–93.
• Broackes, J., 2007, “Black and White and the InvertedSpectrum”,Philosophical Quarterly, 57:161–75.
• –––, 2010, “What Do the Color BlindSee?”, inColor Ontology and Color Science, J. Cohenand M. Matthen (eds.), Cambridge, MA: MIT Press, pp.291–405.
• Burge, T., 1979, “Individualism and the Mental”,Midwest Studies in Philosophy, 4: 73–121.
• Byrne, A., 2001, “Intentionalism Defended”,Philosophical Review, 110: 199–240.
• –––, 2002, “Something About Mary”,Grazer Philosophische Studien, 63: 123–40.
• Byrne, A., and Hilbert, D. R., 1997a,Readings on Color,Volume 1: The Philosophy of Color, Cambridge, MA: MIT Press.
• –––, 1997b, “Colors andReflectances”, in Byrne and Hilbert 1997a, pp.263–288.
• –––, 2003a, “Color Realism and ColorScience”,Behavioral and Brain Sciences, 26:3–21.
• –––, 2003b, “Color Realism Redux”,Behavioral and Brain Sciences, 26: 52–63.
• –––, 2010, “How Do Things Look to theColor-Blind?”, inColor Ontology and Color Science, J.Cohen and M. Matthen (eds.), Cambridge, MA: MIT Press, pp.295–90.
• Campbell, N., 2000, “Physicalism, Qualia Inversion, andAffective States”,Synthese, 124: 239–55.
• Canfield, J., 2001, “Ned Block, Wittgenstein, and theInverted Spectrum”,Philosophia, 37:691–712.
• Carruthers, P., 2000,Phenomenal Consciousness,Cambridge: Cambridge University Press.
• Casati, R., 1990, “What is Wrong in InvertingSpectra?”Theoria, 10: 183–86.
• Chalmers, D., 1995, “Absent Qualia, Fading Qualia, DancingQualia”, inConscious Experience, T. Metzinger (ed.),Ferdinand-Schoningh: Paderborn, pp. 309–328.
• –––, 1996,The Conscious Mind, Oxford:Oxford University Press.
• –––, 2002,Philosophy of Mind, Oxford:Oxford University Press.
• –––, 2004, “The Representational Characterof Experience”, inThe Future for Philosophy, B. Leiter(ed.), Oxford: Oxford University Press, pp. 153–81.
• Chalmers, D., and Jackson, F., 2001, “Conceptual Analysisand Reductive Explanation”,Philosophical Review, 110:315–61.
• Churchland, P. M., and Churchland, P. S., 1981,“Functionalism, Qualia, and Intentionality”,Philosophical Topics, 12: 121–46.
• Clark, A., 1985, “Spectrum Inversion and the ColorSolid”,Southern Journal of Philosophy, 23:431–43.
• –––, 1993,Sensory Qualities, Oxford:Oxford University Press.
• –––, 2000,A Theory of Sentience,Oxford: Oxford University Press.
• Cohen, J., 2001, “Color, Content, and Fred: On a ProposedReductio of the Inverted Spectrum Hypothesis”,PhilosophicalStudies, 103: 121–44.
• –––, 2004, “Color Properties and ColorAscriptions: A Relationalist Manifesto”,PhilosophicalReview, 113: 451–506.
• Cole, D. J., 1990, “Functionalism and InvertedSpectra”,Synthese, 82: 207–22.
• Crane, T., 2000, “The Origins of Qualia”, inHistory of the Mind-Body Problem, T. Crane and S. Patterson(eds.), London: Routledge, pp. 169–194.
• Davidson, D., 1987, “Knowing One’s Own Mind”,Proceedings and Addresses of the American PhilosophicalAssociation, 60: 441–58. Reprinted in Davidson, 2001,Subjective, Intersubjective, Objective, Oxford: OxfordUniversity Press.
• Davies, M., 1997, “Externalism and Experience”, inThe Nature of Consciousness, N. Block, O. Flanagan and G.Güzeldere (eds.), Cambridge, MA: MIT Press, pp.309–327.
• Dennett, D. C., 1988, “Quining Qualia”, inConsciousness and Contemporary Science, A. Marcel and E.Bisiach (eds.), Oxford: Oxford University Press, pp. 226–246;page reference is to the reprint in Chalmers 2002.
• –––, 1991,Consciousness Explained,Boston: Little, Brown.
• –––, 1993, “The Message is: There is noMedium”,Philosophy and PhenomenologicalResearch, 53: 919–31.
• –––, 1994, “Instead of Qualia”, inConsciousness in Philosophy and Cognitive Neuroscience, A.Revonsuo and M. Kamppinen (eds.), Hillsdale, NJ: Lawrence Erlbaum, pp.129–39.
• –––, 2005,Sweet Dreams, Cambridge, MA:MIT Press.
• –––, 2013,Intuition Pumps And Other Toolsfor Thinking, New York: Norton.
• Donhauser, J., 2017, “Invisible Disagreement: an InvertedQualia Argument for Realism”,Philosophical Studies,174: 593–606.
• –––, 2024, “An Inverted Qualia Argumentfor Direct Realism”,Topoi, 43: 211–219.
• Dretske, F., 1995,Naturalizing the Mind, Cambridge, MA:MIT Press.
• Egan, A., 2006, “Appearance Properties?”,Noûs, 40: 495–521.
• Fodor, J., 1992,A Theory of Content and Other Essays,Cambridge, MA: MIT Press.
• Ford, J., 2011, “Tye-dyed Teleology and the InvertedSpectrum”,Philosophical Studies, 156:267–81.
• Frege, G., 1884 [1953],The Foundations of Arithmetic,Oxford: Blackwell.
• Gert, B., 1965, “Imagination and Verifiability”,Philosophical Studies, 16: 44–47.
• –––, 2017,Primitive Colors, Oxford:Oxford University Press.
• Gibbons, J., 1965, “Qualia: They’re not what theyseem”,Philosophical Studies, 126: 397–428.
• Goodman, N., 1951,The Structure of Appearance,Cambridge, MA: Harvard University Press.
• Hardin, C. L., 1987, “Qualia and Materialism: Closing theExplanatory Gap”,Philosophy and PhenomenologicalResearch, 48: 281–98.
• –––, 1991, “Reply to Levine’s‘Cool Red’”,Philosophical Psychology, 4:41–50.
• –––, 1993,Color for Philosophers(expanded edition), Indianapolis: Hackett.
• –––, 1997, “Reinverting theSpectrum”, inReadings on Color, Volume 1: The Philosophy ofColor, A. Byrne and D. R. Hilbert (eds.), Cambridge, MA: MITPress, pp. 289–312.
• –––, 1999a, “Color Quality andStructure”, inToward a Science of Consciousness III: TheThird Tucson Discussions and Debates, S. Hameroff, A. Kaszniak,D. Chalmers, (eds.), Cambridge, MA: MIT Press, pp. 65–74.
• –––, 1999b, “Color Relations and the Powerof Complexity”,Behavioral and Brain Sciences, 22:963–4.
• –––, 2003, “A Spectral Reflectance DothNot a Color Make”,Journal of Philosophy, 100:191–202.
• Harman, G., 1982, “Conceptual Role Semantics”,Notre Dame Journal of Formal Logic, 23: 242–56.
• –––, 1990, “The Intrinsic Quality ofExperience”,Philosophical Perspectives, 4:31–52.
• Harrison, B., 1967, “On Describing Colors”,Inquiry, 10: 38–52.
• –––, 1973,Form and Content, Oxford:Blackwell.
• Harvey, J., 1979, “Systematic Transposition ofColours”,Australasian Journal of Philosophy, 57:211–19.
• Hellie, B., 2004, “Inexpressible Truths and the Allure ofthe Knowledge Argument”, inThere’s Something aboutMary, P. Ludlow, Y. Nagasawa, and D. Stoljar (eds.), Cambridge,MA: MIT Press, pp. 333–364.
• Hempel, C., 1965, “Aspects of Scientific Explanation”,inAspects of Scientific Explanation and other Essays in thePhilosophy of Science, C. Hempel, New York: Free Press, pp.331–496.
• Hendriks, P., 2024, “From P-Zombies to SubstanceDualism”,Journal of Consciousness Studies,31(11–12): 110–121.
• Hilbert, D. R., and Kalderon, M., 2000, “Color and theInverted Spectrum”, inColor Perception: Philosophical,Psychological, Artistic, and Computational Perspectives, S. Davis(ed.), Oxford: Oxford University Press, pp. 187–214.
• Hill, C., 1991,Sensations: A Defense of TypeMaterialism, Cambridge: Cambridge University Press.
• Horgan, T., 1984, “Functionalism, Qualia, and the InvertedSpectrum”,Philosophy and Phenomenological Research,44: 453–70.
• Horgan, T., and Tienson, J., 2002, “The Intentionality ofPhenomenology and the Phenomenology of Intentionality”, inPhilosophy of Mind, D. Chalmers (ed.), Oxford: OxfordUniversity Press, pp. 520–33.
• Hurley, S. L., 1998,Consciousness in Action, Cambridge,MA: Harvard University Press.
• Hurvich, L. M., Jameson, D., and Cohen, J. D., 1968, “TheExperimental Determination of Unique Green in the Spectrum”,Perceptual Psychophysics, 4: 65–8.
• Jacovides, M., 1999, “Locke’s ResemblanceTheses”,Philosophical Review, 108: 461–96.
• Jackson, F., 1977,Perception, Cambridge: CambridgeUniversity Press.
• –––, 1982, “Epiphenomenal Qualia”,Philosophical Quarterly, 32: 127–36. Reprinted inChalmers 2002.
• –––, 1998,From Metaphysics to Ethics: ADefense of Conceptual Analysis, Oxford: Oxford UniversityPress.
• Johnsen, B. C., 1986, “The Inverted Spectrum”,Australasian Journal of Philosophy, 64: 471–6.
• –––, 1993, “The Intelligibility ofSpectrum Inversion”,Canadian Journal of Philosophy,23: 631–36.
• Kaiser, P. K., and Boynton, R. M., 1996,Human ColorVision, Washington, DC: Optical Society of America.
• Kay, P., 1999, “Asymmetries in the Distribution of Compositeand Derived Basic Color Categories”,Behavioral and BrainSciences, 22: 957–8.
• Keeley, B., 2019, “The Early History of the Quale and itsRelation to the Senses”, inRoutledge Companion toPhilosophy of
  Psychology, S. Robins, J. Symons, and P. Calvo (eds.), London:Routledge, pp. 71–89.
• Kirk, R., 1982, “Goodbye to Transposed Qualia”,Proceedings of the Aristotelian Society, 82:33–44.
• –––, 1994,Raw Feeling, Oxford: OxfordUniversity Press.
• Kuehni, R. G., 2003,Color Space and Its Divisions: ColorOrder from Antiquity to the Present, Hoboken, NJ: Wiley.
• Levine, J., 1983, “Materialism and Qualia: The ExplanatoryGap”,Pacific Philosophical Quarterly, 64:354–61; page reference is to the reprint in Chalmers 2002.
• –––, 1988, “Absent and Inverted QualiaRevisited”,Mind and Language, 3: 271–87.
• –––, 1991, “Cool Red”,Philosophical Psychology, 4: 27–40.
• –––, 2001,Purple Haze: The Puzzle ofConsciousness, Oxford: Oxford University Press.
• Lewis, C. I., 1929,Mind and the World Order, New York:Scribner’s.
• Lewis, D., 1980, “Mad Pain and Martian Pain”, inReadings in Philosophy of Psychology, Vol. 1, N. Block,(ed.), Cambridge, MA: Harvard University Press, pp. 216–22.
• –––, 1986,On the Plurality of Worlds,Oxford: Blackwell.
• Littlejohn, C., 2009, “On the Coherence of Inversion”,Acta Analytica, 24: 127–37.
• Locke, J., 1689/1975,Essay Concerning HumanUnderstanding, Oxford: Oxford University Press.
• Lycan, W. G., 1973, “Inverted Spectrum”,Ratio, 15: 315–19.
• –––, 1987,Consciousness, Cambridge,MA: MIT Press.
• –––, 1996,Consciousness andExperience, Cambridge, MA: MIT Press.
• MacLaury, R. E., 1999, “Asymmetry Among Hering PrimariesThwarts the Inverted Spectrum Argument”,Behavioral andBrain Sciences, 22: 960–61.
• Macpherson, F., 2005, “Colour Inversion Problems forRepresentationalism”,Philosophy and PhenomenologicalResearch, 70: 127–52.
• Malebranche, N. 1674–5 [1997],The Search AfterTruth, T. Lennon and P. Olscamp (eds. and trans.), Cambridge:Cambridge University Press.
• Marcus, E., 2006, “Intentionalism and the Imaginability ofthe Inverted Spectrum”,Philosophical Quarterly, 56:321–39.
• Mausfeld, R., 2003, “‘Colour’ as Part of theFormat of Different Perceptual Primitives: the Dual Coding ofColour”, inColour Perception: Mind and the PhysicalWorld, R. Mausfeld and D. Heyer (eds.), Oxford: Oxford UniversityPress, pp. 381–430.
• McGinn, C., 1983,The Subjective View, Oxford: OxfordUniversity Press.
• –––, 1989,Mental Content, Oxford:Blackwell.
• McLaughlin, B., 2003, “The Place of Color in Nature”,inColour Perception: Mind and the Physical World, R.Mausfeld and D. Heyer (eds.), Oxford: Oxford University Press, pp.475–502.
• Meyer, U., 2000, “Do Pseudonormal Persons Have InvertedQualia? Scientific Hypotheses and PhilosophicalInterpretations”,Facta Philosophica, 2:309–25.
• Mollon, J., Pokorny, J., and Knoblauch, K. (eds.), 2003,Normal and Defective Colour Vision, Oxford: Oxford UniversityPress.
• Moore, G. E., 1953,Some Main Problems of Philosophy,London: George Allen & Unwin.
• Myin, E., 2001, “Color and the DuplicationAssumption”,Synthese, 129: 61–77.
• Nida-Rümelin, M., 1996, “Pseudonormal Vision: An ActualCase of Qualia Inversion?”,Philosophical Studies, 82:145–57. Reprinted in Chalmers 2002.
• –––, 1999, “Intrinsic PhenomenalProperties in Color Vision Science: A Reply to Peter Ross”,Consciousness and Cognition, 8: 571–74.
• Noë, A., 2005,Action in Perception, Cambridge, MA:MIT Press.
• Palmer, S., 1999a, “Color, Consciousness, and theIsomorphism Constraint”,Behavioral and Brain Sciences,22: 923–43.
• –––, 1999b, “On Qualia, Relations, andStructure in Color Experience”,Behavioral and BrainSciences, 22: 976–85.
• Papineau, D., 2002,Thinking About Consciousness, Oxford:Oxford University Press.
• Peacocke, C., 1983,Sense and Content, Oxford: OxfordUniversity Press.
• –––, 1988, “The Limits of Intelligibility:A Post-Verificationist Proposal”,Philosophical Review,97: 463–96.
• –––, 2001. “Does Perception have aNonconceptual Content?”,Journal of Philosophy, 98:239–64.
• Piantanida, T. P., 1974, “A Replacement Model of X-linkedRecessive Colour Vision Defects”,Annals of HumanGenetics, 37: 393–404.
• Putnam, H., 1967, “Psychological Predicates”, inArt, Mind and Religion, W. Capitan and D. Merrill (eds.),Pittsburgh: University of Pittsburgh Press, pp. 37–48..Reprinted as “The Nature of Mental States” in Putnam,1975,Mind, Language, and Reality, Cambridge: CambridgeUniversity Press.
• –––, 1975, “The Meaning of‘Meaning’”,Minnesota Studies in the Philosophyof Science, 7: 131–93; reprinted in Putnam, 1975,Mind,Language, and Reality, Cambridge: Cambridge UniversityPress.
• –––, 1981,Reason, Truth and History,Cambridge: Cambridge University Press.
• Ren, H., 2016, “Inverted Earth Revisited”,Erkenntnis, 81: 1093–107.
• Rey, G., 1992, “Sensational Sentences Switched”,Philosophical Studies, 68: 289–319.
• –––, 1998, “A Narrow RepresentationalistAccount of Qualitative Experience”,PhilosophicalPerspectives, 12: 435–58.
• Robinson, H., 1994,Perception, London: Routledge.
• Ross, P. W., 1999a, “Color Science and Spectrum Inversion:Further Thoughts”,Consciousness and Cognition, 8:566–70.
• –––, 1999b, “Color Science and SpectrumInversion: A Reply to Nida-Rümelin”,Consciousness andCognition, 8: 575–76.
• –––, 2020, “Spectrum Inversion”, inRoutledge Handbook of Philosophy of Colour, D. Brown and F.Macpherson (eds.), London: Routledge.
• Russell, B., 1927,The Analysis of Matter, London: KeganPaul, Trench, Trubner & Co. Ltd.
• Sacks, O., 1997,The Island of the Colorblind, New York:Knopf.
• Schlick, M., 1932/3, “Positivism and Realism”,Erkenntnis, 3; page reference is to the reprint in Ayer1959.
• Schoettle, T., 2009, “How I Learned to Stop Worrying andLove the Inverted Spectrum”,Pacific PhilosophicalQuarterly, 90: 98–115.
• Shoemaker, S., 1975a, “Functionalism and Qualia”,Philosophical Studies, 27: 291–315. Reprinted inShoemaker 1984.
• –––, 1975b, “Phenomenal Similarity”,Critica, 7: 3–37. Reprinted in Shoemaker 1984.
• –––, 1981, “Absent Qualia AreImpossible”,Philosophical Review, 90: 581–99.Reprinted in Shoemaker 1984.
• –––, 1982, “The Inverted Spectrum”,Journal of Philosophy, 79: 357–81; page reference is tothe reprint in Shoemaker 1984.
• –––, 1984,Identity, Cause, and Mind,Cambridge: Cambridge University Press.
• –––, 1986, “Review of Colin McGinn’sThe Subjective View”,Journal of Philosophy,83: 407–13.
• –––, 1991, “Qualia andConsciousness”,Mind, 100: 507–24. Reprinted inShoemaker 1996a.
• –––, 1994a, “Phenomenal Character”,Noûs, 28: 21–38.
• –––, 1994b, “Self-Knowledge and‘Inner-Sense’”,Philosophy and PhenomenologicalResearch, 54: 249–314; page reference is to the reprint inShoemaker 1996a.
• –––. 1996a,The First-Person Perspective andOther Essays, Cambridge: Cambridge University Press.
• –––, 1996b,“Intersubjective/Intrasubjective”, in Shoemaker 1996a, pp.141–154.
• –––, 2002, “Content, Character, andColor”, Whitehead lectures, Harvard University.
• –––, 2006a, “On the Ways ThingsAppear”, inPerceptual Experience, T. Gendler and J.Hawthorne (eds.), Oxford: Oxford University Press, pp.461–480.
• –––, 2006b, “The Frege-SchlickView”, inContent and Modality, J. Thomson and A. Byrne(eds.), Oxford: Oxford University Press, pp. 18–33.
• –––, 2019, “Phenomenal Character andPhysicalism”, inBlockheads! Essays on Ned Block’sPhilosophy of Mind and Consciousness, A. Pautz and D. Stoljar(eds.), Cambridge, MA: MIT Press, pp. 459–79.
• Speaks, J., 2011, “Spectrum Inversion Without a Differencein Representation is Impossible”,PhilosophicalStudies, 156: 339–61.
• –––, 2015,The Phenomenal and theRepresentational, Oxford: Oxford University Press.
• Stalnaker, R., 1987,Inquiry, Cambridge, MA: MITPress.
• –––, 1999, “Comparing Qualia AcrossPersons”,Philosophical Topics, 26: 385–405; pagereference is to the reprint in Stalnaker, 2003,Ways a World MightBe, Oxford: Oxford University Press.
• –––, 2006, “Shoemaker,‘Frege-Schlick View’” (A Response to Shoemaker), inContent and Modality, J. Thomson and A. Byrne (eds.), Oxford:Oxford University Press, pp. 254–57.
• Strawson, G., 1989, “Red and ‘Red’”,Synthese, 78: 193–232.
• –––, 1994,Mental Reality, Cambridge,MA: MIT Press.
• Sundström, P., 2002, “An Argument Against SpectrumInversion”, inPhysicalism, Consciousness and Modality:Essays in the Philosophy of Mind, S. Lindström and S.Sundström (eds.), Umeå: The Department of Philosophy andLinguistics, pp. 65–94.
• Taylor, D., 1966, “The Incommunicability of Content”,Mind, 75: 527–41.
• Thau, M., 2002,Consciousness and Cognition, Oxford:Oxford University Press.
• Thompson, B., 2008, “Representationalism and theConceivability of Inverted Spectra”,Synthese, 160:203–13.
• Tye, M., 1994, “Qualia, Content, and the InvertedSpectrum”,Noûs, 28: 159–83.
• –––, 1995,Ten Problems ofConsciousness, Cambridge, MA: MIT Press.
• –––, 2000,Consciousness, Color, andContent, Cambridge, MA: MIT Press.
• –––, 2002, “Visual Qualia and VisualContent Revisited”, inPhilosophy of Mind, D. Chalmers(ed.), Oxford: Oxford University Press, pp. 447–456.
• –––, 2021, “Qualia”,TheStanford Encyclopedia of Philosophy (Fall 2021 Edition), EdwardN. Zalta (ed.), URL = <https://plato.stanford.edu/archives/fall2021/entries/qualia/>.
• Westphal, J., 1991,Colour: A Philosophical Introduction,Oxford: Blackwell.
• White. S., 1994, “Color and Notional Content”,Philosophical Topics, 22: 471–503.
• Wittgenstein, L., 1958,Philosophical Investigations,Oxford: Blackwell.
• –––, 1968, “Notes for Lectures on‘Private Experience’ and ‘Sense-data’”,Philosophical Review, 77: 275–320.
• –––, 1977,Remarks on Colour, Berkeley:University of California Press.

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Online Manuscripts

• Clark, A., 1996, “Inversions Spectral and Bright”, comments on Melinda Campbell, Meetings of the Society for Philosophy& Psychology, San Francisco.
• Nordby, K., 1996, “Vision in a Complete Achromat: A Personal Account”.

Web Pages and Web Sites

• A Glossary of Color Science, compiled by Alex Byrne (MIT) and David R. Hilbert (University ofIllinois/Chicago).
• Rolf Kuehni’s article onColor Spaces.
• Wikipedia entry on theMunsell color system.
• Eric Schwitzgebel’sSound-Color Qualia Inversion Contest.

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Acknowledgments

For advice and assistance I am very grateful to Jonathan Cohen, TylerDoggett, Andy Egan, Rachel Faith, Ned Hall, Elizabeth Harman, DavidHilbert, Jim John, Fiona Macpherson, and Daniel Stoljar.