## 1. Qualia




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



![figure 1](figure1.gif)
Figure 1:
vermilion, crimson, and turquoise patches





Three experiences of the imagined sort differ in their
phenomenology, or in "what it's like" to undergo them. What
it's like to see the crimson patch is not the same as what it's like to
see the turquoise patch, for example. Further--assuming you have
normal color vision--seeing the crimson patch is more similar,
in phenomenological respects, to seeing the 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 and turquoise patches lack. Your experience of the
vermilion patch has a quale \((Q\_{V})\) that your
experiences of the crimson and turquoise patches lack; likewise, your
experience of the turquoise patch has quale
\(Q\_{T}\). What about an experience of all three
patches, as when viewing the whole of figure 1? Which of
\(Q\_{C}, Q\_{V}\), and
\(Q\_{T}\) does that have? The answer usually
implicit in the literature is 'All three' (as opposed to
 'None').[1]
 This is probably the more natural way of
understanding qualia terminology, given the explanation so far, and is
the one adopted in this article.




In addition to the quale \(Q\_{C}\), your
experience of the crimson patch has quale
\(Q\_{R}\) which it shares with your experiences
of the vermilion patch, blood, fire trucks, strawberries, ripe
tomatoes, and so on. Your experience of the turquoise patch (in
isolation) lacks \(Q\_{R}\).




It must be emphasized that
'\(Q\_{C}\)', for example, is not
*explicitly defined* using color terminology.
'\(Q\_{C}\)' is not stipulated to be
an abbreviation of 'the property of being an experience of
something's looking crimson', for instance. Rather, the role of
descriptions like the latter is simply to draw attention to the salient
property that '\(Q\_{C}\)' is supposed
to be a name for, in much the same way that one might introduce the
unfamiliar name 'Eugene Cernan' by saying that it refers to
the last man to walk on the moon. In the jargon, the description
'the property of being an experience of something's looking
crimson' can be used to *fix the reference* of
'\(Q\_{C}\)'. (See the entry on
 reference.)




Qualia terminology can be introduced in a similar manner for other
sorts of visual experiences (seeing differently shaped patches, for
instance), for other perceptual modalities, for bodily sensations, and
for thoughts, imagery, emotions, and so forth. It is controversial
whether some of these mental events/states have qualia--in
particular, episodes of conscious thought, at least some of which seem
devoid of
 phenomenology.[2]




One might wonder why some special terminology is required.
Admittedly '\(Q\_{R}\)', for example,
is not *defined* in terms of 'red', but isn't
\(Q\_{R}\) in fact the property of 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 this identification.


### 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 that
experiences have qualia seems fairly
 harmless.[4]
 The innocent student
might well be puzzled, then, to learn of Frank Jackson's controversial
"knowledge argument for qualia" (Jackson 1982), and
Dennett's attempt to dismiss qualia as a philosopher's invention
(Dennett 1988). But on closer examination, much of this apparent
disagreement is merely terminological. On Jackson's use of the term,
qualia are properties of mental states "which no amount of purely
physical information includes" (1982, 273); on Dennett's, they
are "ineffable", "intrinsic",
"private", and "directly or immediately apprehensible
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
to distinguish from the present one is Dretske's. According to Dretske,
qualia include *colors*--properties of objects like
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 of *objects* of experiences; in this article
qualia are properties of *experiences.*




The American pragmatist C. I. Lewis introduced 'qualia'
into contemporary
 philosophy.[6]
 Qualia, he explains in *Mind and the
World Order*, are "recognizable qualitative characters of the
given" (1929, 121). According to Lewis, what is
"given" in experience are sense-data (although Lewis
himself preferred other terminology: see 55-7), not objects like
tomatoes. Goodman's well-known discussion of qualia in *The
Structure of Appearance* (1951) follows Lewis's use. Among
Jackson, Dennett, and Dretske, Dretske's use of 'qualia' is
the closest to Lewis's. Restricting attention to the case of veridical
perception, we may think of Dretske as basically agreeing with Lewis
about the characterization of qualia, but disagreeing with Lewis about
the given. When one sees that a tomato is red, according to Lewis a
sense-datum, not the tomato, is given; according to Dretske what is
given is the tomato. So, since a "recognizable qualitative
character" of the tomato is its color, Dretske thinks that colors
are examples of
 qualia.[7]


## 2. Inverted qualia scenarios




Let us say that a *scenario* is a (more-or-less detailed)
story, which may be possible or impossible. (So, for example, there is
a scenario in which someone squares the circle.) Corresponding to a
scenario is what we can call a *hypothesis*: that the scenario
is *possible*. So, for example, the hypothesis corresponding to
a circle-squaring scenario is false. There are a variety of
"inverted qualia" scenarios in the literature--almost 
always involving color perception--whose corresponding
hypotheses differ in plausibility. These hypotheses are used as
premises in a number of philosophical arguments, discussed in section 3
below.


### 2.1 A Simple Inverted Qualia Scenario




Consider the hue circle in figure 2, taken from the Natural Color
System color space, which is organized around the four hues red, green,
blue, and
 yellow.[8]
 These are the *unique* *hues*:
they have shades that are not perceptual mixtures of any other hue. For
example, there is a shade of green that is neither bluish nor
yellowish. The other hues are *binary*: all of their shades are
perceptual mixtures of two unique hues. For example, every shade of
purple is bluish and reddish. The four unique hues--yellow, red,
blue, green--come in two *opponent pairs*: red-green and
blue-yellow. Red is opposed to green in the sense that there are no
reddish-greens or greenish-reds; likewise there are no bluish-yellows
or yellowish-blues. The unique hues are equally spaced around the NCS
circle, and the other hues are spaced according to their perceptible
proportion of the unique hues. So, for example, the orange patch
equidistant from the unique yellow pole and unique red pole is equally
similar to both.



![figure 2](figure2.gif)
Figure 2:
NCS hue circle[9]





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



![figure 3](figure3.gif)
Figure 3:
the function \(I\)





Introduce another perceiver, Invert (you are Nonvert). Imagine you
are looking at scene \(S\): an arrangement of some fruits (see the
left-hand part of figure 4). Now take the apparent hues of objects in
\(S\), and transform them using the function \(I\). Use this
transformation to create a new scene \(S\_{I}\), exactly
like the old scene \(S\) except that it looks to have differently
colored "inverted" fruits (etc.). That is, if a banana
originally looks to have hue \(h\), in \(S\_{I}\) it
looks to have hue \(I(h)\). (See the right-hand part of
figure 4; notice that the greens in \(S\) are rather yellowish,
and hence get mapped to bluish-reds.) Then one simple inverted qualia
scenario is this: what it's like for Invert to look at \(S\) is
exactly the same as what it's like for Nonvert (i.e., you) to look at
\(S\_{I}\), and similarly for all other scenes that Invert
encounters. According to this scenario, if you look at the right-hand
part of figure 4, your experience is phenomenologically the same as
Invert's experience when she looks at the left-hand part of figure 4.
In qualia terminology: 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 hue
\(I(h)\) (with corresponding quale \(Q^\*\)), then
Invert's experience of \(O\_{1}\) has quale \(Q^\*\) and
her experience of \(O\_{2}\) has quale \(Q\). In this
sense Invert's qualia are 'inverted' with respect to
Nonvert's.



![figure 4](figure4.gif)
Figure 4:
180deg hue inversion





Because the example concerns color qualia, this sort of inverted
qualia scenario is usually described as a case of "spectrum
inversion". (Note that the 180deg inversion takes unique hues
to unique hues, and binary hues to binary hues. An inversion scenario
produced by a rotation of 45deg would take the unique hue red to the
binary hue orange; and so presumably would be behaviorally detectable:
see subsection 2.3.1 below.)




Philosophy is stuck with the terminology of 'spectrum
inversion', but it is potentially
 misleading.[10]
 First, a
spectrum inversion scenario sounds like one which inverts either the
spectrum or the colors of objects, but it actually inverts neither. In
a typical spectrum inversion scenario, the spectral band 650-700nm
remains red, and lemons remain
 yellow.[11]




Second, even when properly taken as an inversion of experiences, one
might suppose that the "spectrum inversion" function
corresponds to flipping the spectrum over. That is, using the
traditional names for the spectral bands, one might suppose the
function maps red to violet, orange to indigo, yellow to blue, green to
green, blue to yellow, indigo to orange, and violet to red. However,
this is not the usual sort of inversion scenario (red is not mapped to
green, for example). Further, this function is not defined for all
hues. Many hues--in particular, a large range of
"extra-spectral" purples--are not found in the
spectrum.


### 2.2 Locke's Inverted Spectrum Scenario




Locke appears to have been the first to formulate explicitly an
inverted spectrum scenario. (An immediate precursor is 
Malebranche.[12]) 
In the chapter of the *Essay* titled
*Of True and False* Ideas, Locke writes:



> Neither would it carry any Imputation of *Falshood*
> to our simple *Ideas*, \(if\) by the different Structure of
> our Organs, it were so ordered, That *the same Object should produce
> in several Men's Minds different* Ideas at the same time;
> *v.g.* if the *Idea*, that a *Violet* produced in
> one Man's Mind by his Eyes, were the same that a *Marigold*
> produces in another Man's, and *vice versa*. For since
> this could never be known: because one Man's Mind could not pass into
> another Man's Body, to perceive, what Appearances were produced by
> those Organs; neither the *Ideas* hereby, nor the Names, would
> be at all confounded, or any *Falshood* be in either. For all
> Things, that had the Texture of a *Violet*, producing constantly
> the *Idea*, which he called *Blue*, and those which had
> the Texture of a *Marigold*, producing constantly the
> *Idea*, which he as constantly called *Yellow*, whatever
> those Appearances were in his Mind; he would be able as regularly to
> distinguish Things for his Use by those Appearances, and understand,
> and signify those distinctions, marked by the Names *Blue* and
> *Yellow*, as if the Appearances, or *Ideas* in his Mind,
> received from those two Flowers, were exactly the same, with the
> *Ideas* in other Men's Minds. (1689/1975, II, xxxii,
> 15)




Locke's description of this inverted spectrum scenario is laden with
his own commitment to "Ideas", which (on one
interpretation) are sense-data, some of which possess both color and
 shape.[13]
 On this view, spectrum inversion is a case
of "sense-datum inversion": when Invert looks at a violet
she becomes acquainted with the kind of sense-datum Nonvert is
acquainted with when he looks at a marigold. Setting this tendentious
theoretical gloss aside, Locke's scenario has three notable features.
First, it is a case of spectrum inversion *from birth*. Second,
it is a case of inversion *within the same linguistic
community.* Third, it is (or is naturally read as being) a case in
which Invert and Nonvert are behaviorally alike--a
*behaviorally undetectable* spectrum inversion.




Locke does not fill in the details of his scenario, so it is left
unclear whether, for example, the leaves of marigolds and violets would
produce "Red Ideas" in the mind of the inverted subject.
But suppose, reasonably enough, that Locke's scenario involved a
rotation of the hue circle. Locke evidently thought that the hypothesis
corresponding to his scenario was true: that his scenario 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 perceptually salient
dimension along which colors can vary: there are (usually taken to be)
two other dimensions, *saturation* and
 *lightness*.[14]
 A color is saturated to the extent to
which its hue is intense or vivid: pastels are desaturated, and
achromatic colors (blacks, whites, and grays) have no saturation.
Colors become lighter as they become less grayish or blackened.
Arranging the colors along these three dimensions produces a color
solid, an example of which is shown in figure 5:



![figure 5](figure5.gif)
Figure 5:
3D color space: the Munsell color solid[15]






The lightness dimension corresponds to the central vertical axis,
with white at the top. The hue and saturation dimensions correspond,
respectively, to the angle around the vertical axis, and to the
distance from it. Thus the shades of maximum saturation are on the
outside of the solid. Notice that the yellows have their maximum
saturation at higher levels of lightness than the reds and the blues.
So, assuming that Invert's judgments of the relations between colors
are--modulo the inversion--normal, a possible Lockean
180deg hue rotation scenario would be behaviorally detectable. Invert
would judge the maximally saturated colors she calls 'shades of
blue' to be lighter than the maximally saturated colors she calls
'shades of yellow'. Further, there are more distinguishable
hue steps between blue and red than there are between yellow and 
green--a fact that is reflected in the Munsell space, whose hue circle
has five hues equally spaced: red, yellow, green, blue, purple.
(Contrast the NCS space mentioned in the previous subsection.) Hence
the Lockean inversion function \(I\), assuming it is defined on
all hues, would map some distinct hues (in particular, some bluish
reds) to the same hue (in particular, the same yellowish green). The
range of \(I\) would therefore contain fewer hues than its domain.
Invert would not be able to distinguish some stimuli (those she calls
'bluish red') that Nonvert could tell apart, and so again
the inversion would be behaviorally detectable.


### 2.3 Other Inverted Spectrum Scenarios


#### 2.3.1 Behaviorally Undetectable Scenarios




As discussed in section 3 below, inverted spectrum scenarios have a
wide range of philosophical uses, and come in a correspondingly wide
range of flavors. It is not always required, for example, that Invert
and Nonvert are behaviorally alike. But suppose that a behaviorally
undetectable scenario is needed, and moreover one that is genuinely
possible. With the assumption that Invert is otherwise normal, we just
saw that Locke's behaviorally undetectable scenario is not possible.
Without relaxing the simple assumption about Invert, can we find 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
discussion of Locke's scenario shows that a scenario corresponding to a
rotation of the color solid around the lightness axis should be
avoided. However, as Palmer points out (1999a, 926), there are three
inversion scenarios that at least solve the problem posed by the light
and saturated yellows. These three scenarios correspond to,
respectively, a reversal of the red-green axis; a reversal of the
blue-yellow and black-white axes; and the previous two reversals taken
together: a reversal of the red-green, blue-yellow, and black-white
axes. These three scenarios are (approximately) illustrated in Figure 6
below.



![figure 6](figure6.gif)
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 perceptually
distinguishable shades between red and blue than there are between
green 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 (see figure 6). Similarly, desaturated bluish-red is
pink (qualitatively different from saturated bluish-red), whereas
desaturated greenish-yellow is similar to saturated greenish-yellow.
Again, red is a "warm" color, whereas blue is
"cool"--and perhaps this is not a matter of learned
associations with temperature (see Hardin 1997, 297-7). In any event,
there is clearly scope to resist the claim that one of Palmer's three
inversions would be behaviorally
 undetectable.[17]




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



> But even if our color experience is not in fact such that a
> mapping of this [behaviorally undetectable] sort is possible, it seems
> to me conceivable that it might have been--and that is what
> matters for our present philosophical purposes. For example, I think we
> know well enough what it would be like to see the world
> nonchromatically, i.e., in black, white, and the various shades of 
> grey--for we frequently do see it in this way in photographs, moving
> pictures, and television. And there is an obvious mapping of the
> nonchromatic shades onto each other which satisfies the conditions for
> inversion. In the discussion that follows I shall assume, for
> convenience, that such a mapping is possible for the full range of
> colors--but I do not think that anything essential turns on
> whether this assumption is correct. (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 only black-white rod vision) who is also a
vision scientist, see Nordby 1996 (Other Internet
 Resources).[19]




Here is Block trying the second strategy:



> [D]o the empirical issues really matter for the challenge
> that the possibility of an inverted spectrum poses for functionalism?
> My answer is: only in a subtle and indirect way. For if there *could
> be* creatures who have color experience or at least visual
> experience for whom the relevant empirical points do not apply, then
> functionalism is refuted even if *human* spectra cannot be
> inverted. For example, perhaps it is a consequence of the human genome
> that humans tend to be unwilling to give a name to light green, even
> though they are willing to give a name to light red
> ('pink'). Still, there *could* be people whose
> visual experience is similar if not identical to ours who find it
> equally natural to give names to light green as to light red. (Perhaps
> we could even genetically engineer humans to become so willing.) (Block
> 1999, 946; cf. Shoemaker 1982, 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 space
*must* be asymmetrical" (2000, 204) (that is, must lack
any symmetries); if so, both strategies are misguided (see also Dennett
1991, 389-98; 1993, 927; 1994).


#### 2.3.2 Intrapersonal and Interpersonal Scenarios




If a behaviorally undetectable spectrum inversion scenario is
possible, how do we know it does not actually obtain? There is a
temptation to say that we do not know--moreover, that we cannot
know. (For more discussion, see subsection 3.6 below.) And if we cannot
verify or falsify the claim that such a scenario does not obtain, then
according to the verificationist theory of meaning held by the logical
positivists (Ayer 1959) the scenario is meaningless. Indeed, the
logical positivists sometimes gave spectrum inversion as an example of
an unverifiable claim (Schlick 1932/3, 93, quoted in Shoemaker 1982,
339; see also Ayer 1936, 173-4, and Wittgenstein 1958, SS272).




The allegedly meaningless scenario is a case of
*inter*personal (or intersubjective) spectrum inversion: Invert
is spectrally inverted with respect to another person, Nonvert. But
there is another sort of inversion scenario, in which a single person's
qualia are inverted with respect to her qualia at an earlier time. As
Shoemaker notes (1982, 327), a case of *intra*personal (or
intrasubjective) spectrum inversion appears to have been first
discussed by Wittgenstein:



> Consider this case: someone says 'I can't understand
> it, I see everything red blue today and vice versa.' We answer
> 'it must look queer!' He says it does and, e.g., goes on to
> say how cold the glowing coal looks and how warm the clear (blue) sky.
> I think we should under these or similar circumstances be inclined to
> say that he saw red what we saw blue. And again we should say 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 behaviorally
undetectable interpersonal spectrum inversion scenario is not possible
(arguably for verificationist reasons), Shoemaker claims that once the
possibility of a Wittgensteinian *intra*personal inversion is
granted, there is an inexorable slide to the possibility of a
behaviorally undetectable *inter*personal scenario:



> ...if the color experience of a person can differ from
> that of others at some point during his career, it should be possible
> for such a difference to exist throughout a person's career. But if
> this a possibility, then it does seem perfectly coherent to suppose,
> and perfectly compatible with all the behavioral evidence we have about
> the experiences of others, that, in Wittgenstein's words, "one
> section of mankind has one sensation of red and another section
> another." (Shoemaker 1982,
>  329)[21]




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



**Step 1**: this is possible: an
"overnight" intrapersonal inversion, as in the quotation
from Wittgenstein.


**Step 2**: if (Step 1), then this is possible: an
"overnight" inversion followed by semantic adaptation
(applying 'red' to glowing coal, 'blue' to the
sky, etc.), but with memory of one's experiences before the inversion.
That is, one (re)learns to use color terminology like a normal person,
while remembering that one's experiences of glowing coal (etc.) used to
be very different. The inversion remains detectable, because one
asserts, for example, that one's experiences have drastically
changed.


**Step 3**: if (Step 2), then this is possible: an
"overnight" inversion followed by semantic adaptation,
followed by amnesia about one's past experiences, with the result that
one's pre- and post- inversion behavioral dispositions are the same. At
this step, one's behavior is just as it would have been if one had
simply been stricken with amnesia, with no prior inversion.


**Step 4**: if (Step 3), then this is possible: a
"from birth" behaviorally undetectable
*inter*personal inversion scenario.





Similar arguments starting from a Wittgensteinian intrapersonal
scenario can be given for the other kinds of interpersonal inversion
hypotheses 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), *inter*personal comparisons of qualia (unlike
*intra*personal comparisons) do not make sense. The
Frege-Schlick view could be supported on verificationist grounds; for
a more interesting line of defense, see Stalnaker 1999, 2006, and
Shoemaker 2006b and Block 2007, 103-7, for discussion. Since it makes
perfect sense (and indeed is often true) to say that tomatoes look red
to most people, a proponent of the Frege-Schlick view must deny, for
example, that \(Q\_{R}\) is the property of being
an experience of something's looking red (see section 1 above and
Stalnaker 1999, 225).


#### 2.3.3 Inverted Earth




Asymmetries in color space pose problems for step 3 of the previous
argument. But--especially for those with verificationist
sympathies--step 3 is problematic even if these concerns are
waived. 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 period of
amnesia you have no sense that anything is amiss--so perhaps
nothing is. Similar doubts can be raised about step 2: suppose you use
color terminology exactly as you did before the step 1 
inversion--that is, spontaneously on the basis of how things 
look--but you seem to recall that your past experiences were radically
different. Would you be confident that you hadn't misremembered your
past experiences? (See Dennett 1988; 1991, Ch. 12; 1993; 1994; and Rey
1992.)




Although Block thinks "that these criticisms can be defeated
on their 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 the consequent confusion,
semantic adaptation and amnesia, your eyes are fitted with "color
inverting lenses" and you are transported to another 
planet--Inverted Earth. This is a place just like Earth except that
each object has "the complementary color of [its counterpart] on
Earth. The sky is yellow, grass is red, fire hydrants are green,
etc." (1990, 60). The inhabitants also speak Color Inverted
English ('red' means *green*, 'blue'
means *yellow*, etc.). The right hand part of figure 4 above
displays a photograph of fruits taken on Inverted Earth with an
ordinary Earthly camera. (Despite the yellow sky, the illumination on
Inverted Earth is the same as it is on Earth. Note that achromatic
colors are not inverted--on Inverted Earth snow is white and
coal is
 black.)[23]
 Because of the inverting lenses--and 
ignoring complications such as those mentioned in subsection 
2.3.1--when you arrive on Inverted Earth you notice no visible change.
Your experience when you look at an arrangement of fruits on Inverted
Earth is phenomenologically the same as your previous experience of the
counterpart arrangement on Earth (see the left hand part of figure 4),
and conversation with the locals proceeds just as smoothly as it did
back on Earth. This scenario is therefore the converse of typical
inverted spectrum scenarios: instead of keeping the environment fixed
and varying the internal constitution of the subject, Inverted Earth
varies the environment and (due to the inverting lenses) keeps the
subject's internal constitution fixed. Block uses Inverted Earth in an
argument against functionalism and representationalism (see subsections
3.1 and 3.2
 below).[24]


### 2.4 Shifted Qualia




The qualia inversion scenarios discussed so far are merely
hypothetical--more cautiously, we do not know whether any of
them
 obtain.[25]
 There are, however, "shifted"
qualia scenarios that *actually* obtain. And, in fact, many of
the philosophical arguments that appeal to the possibility of an
inversion scenario can make do instead by appealing to the actual
shifted qualia scenario, hence avoiding potentially controversial
claims about possibility.




The shifted qualia scenario that is usually discussed 
concerns--unsurprisingly--color vision. There is a substantial
amount of variation between people classified as having
"normal" color vision by standard tests, due to differences
in the lens of the eye and photoreceptor pigments, among other factors.
In one experiment, introduced into the philosophical literature by
Hardin (1993, 79-80), Hurvich et al. (1968) found that the apparent
location of unique green for spectral lights among 50 subjects varied
from 490 to
 520nm.[26]
 This is a large range: 15nm either side of
unique green looks distinctly bluish or yellowish. For example, when
Smith looks at the third patch in figure 7 (in isolation), his
experience might have the quale that Jones's experience has when she
looks at the *fourth* patch in Figure 7, keeping the viewing
circumstances fixed. And when Smith looks at the fourth patch, his
experience might have the quale that Jones's experience has when she
looks at the *fifth* patch. Thus--at least over a small
range of hues--Jones's and Smith's color qualia are
"shifted" with respect to each other. Accordingly, this
sort of scenario can be described as a case of "shifted spectra"
(Block 1999). (NB: here we are assuming that the Frege-Schlick view
mentioned in subsection 2.3.2 is incorrect.)



![figure 7](figure7.gif)
Figure 7:
five patches: yellowish-green to bluish-green





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


## 3. Spectrum Inversion in an Argument...




Inversion scenarios--in particular, spectrum 
inversion--turn up in a wide range of philosophical arguments, which we
are now in a position to examine.


### 3.1 ...Against Behaviorism, Functionalism, and Physicalism



*Behaviorism* in the philosophy of mind is the view that the
mental is nothing over and above behavior (including dispositions to
behave). Any version of behaviorism implies that the mental supervenes
on behavior. That is: necessarily, two creatures who are behaviorally
alike are also mentally alike. Likewise, any version of
*functionalism* or *physicalism* implies that the mental
supervenes on, respectively, functional organization and physical
makeup. For the purposes of this subsection, it is not necessary to
get into the details of these theories. However, two points should be
noted. First, it should not be assumed that either behavior,
functional organization, or physical makeup is an intrinsic 
matter--the relevant sorts of behavioral, functional, and physical
properties may be extrinsic.
 In other words,
perfect duplicates may differ in behavioral, functional, or physical
 respects.[27]
 Second, as these theories are usually
understood, difference in behavioral respects implies difference in
functional respects, which in turn implies difference in physical
respects; none of the converse implications
 holds.[28]
 So the three
supervenience theses just mentioned are related as follows: the
behaviorist supervenience thesis implies the functionalist thesis,
which in turn implies the physicalist thesis.




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



**Argument Aa**

P1a.
The following spectrum inversion scenario is possible: Invert
and Nonvert are *behaviorally* alike, and are both looking at a
 tomato.[29]

Since P1a implies that the mental does not supervene on
behavior:



Ca.

Behaviorism is false.



Since behaviorism is not a popular position these days, this
application of an inverted qualia scenario is perhaps not so
interesting. And given the complications discussed in subsection 2.3.1,
there is even room for a behaviorist to resist. However, of
considerably more interest are similar arguments against functionalism
(and physicalism). Block and Fodor (1972), who invented the terminology
of 'inverted qualia', were the first to formulate an
inverted spectrum argument against functionalism, specifically Turing
machine functionalism as defended in Putnam
 1967.[30]
 Ignoring the details
of particular functionalisms, the argument is exactly parallel to the
one against behaviorism. (Similar remarks go for the inverted spectrum
argument against physicalism.) According to functionalism, mental
states are functional states: states defined by their causal role with
respect to inputs, outputs, and other states. So, according to
functionalism, necessarily, two creatures who are functionally alike
are also mentally alike. In order to complete the argument, an
appropriate inverted spectrum hypothesis must be established, where
Invert and Nonvert are functional duplicates.




The anti-functionalist analogue of argument Aa is:



**Argument Ab**

P1b

The following spectrum inversion scenario is possible: Invert
and Nonvert are *functionally* alike, and are both looking at a
tomato.


Since P1b implies that the mental does not supervene on functional
organization:



Cb.

Functionalism is false.



The possibility of a behaviorally undetectable inversion scenario
(P1a) can be motivated by appeal to the sorts of considerations
discussed in 2.3.1 above. However, in order to refute functionalism a
stronger inversion hypothesis (P1b) is needed. As Block and Fodor point
out, functionalism allows us to *deny* that "two organisms
are in the same psychological state whenever their behaviors and/or
behavioral dispositions are identical" (1972, 86), hence avoiding
the stock objections to behaviorism. The functionalist, then, has no
problem with behaviorally undetectable inversions. But why should she
concede the possibility of a *functionally* undetectable
inversion? The question can be made more pointed by observing that (a)
no one has ever articulated a detailed functionalist theory of any
mental state, and (b) any realistic version of such a theory would be
extremely
 complicated.[31]
 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
> counterarguments against the view that the 'inverted
> spectrum' [scenario] is conceptually coherent are not persuasive.
> If this is correct, it looks as though the possibility of qualia
> inversion poses a serious prima facie argument against functionalist
> accounts of the criteria for type identity of psychological states.
> (91)




Block and Fodor's apparent move from the "conceptual
coherence" of the inversion scenario to its possibility can be
questioned. Even though one cannot know a priori that not-p (that is, p
is conceptually coherent), p may yet be impossible. For example, one
cannot know a priori that gold does not have the atomic number 79, but
it is a necessary truth that gold has this atomic number. (This sort of
separation between conceptual coherence and possibility is not
uncontroversial, but is commonly
 accepted.[32])




In any case, there are other conceptually coherent scenarios that are
considerably more straightforward than an inverted spectrum scenario,
for example a scenario containing a conscious subject and a functional
duplicate who is not conscious at all (a "zombie", in the
philosophical sense). So if the move from conceptual coherence to
possibility is in fact legitimate, functionalism may be refuted by a
simpler argument that does not have an inversion hypothesis as a
premise. (Shoemaker is a notable dissenter on this point; he holds
that 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 argument
against functionalism might reply that the scenario's possibility does
not merely rest on its conceptual coherence. In addition--this
reply continues--there is a positive "Cartesian
intuition" that such an inversion scenario is possible (a
"clear and distinct idea" of the scenario, perhaps), and
this is prima facie evidence that it \(is\) possible.




However, Cartesian intuition, just like conceptual coherence, is not
a very discriminating weapon, tending to spread possibility over a wide
landscape (cf. Tye 2003, section 4). Cartesian intuition also tends to
certify the possibility of scenarios containing zombies, thinking
rocks, entirely disembodied minds (not even embodied in ectoplasm), and
so forth--all *impossibilities*, according to the
functionalist. So, as with conceptual coherence, any inverted spectrum
argument against functionalism that relies on Cartesian intuitions can
be converted into an equally plausible and simpler argument that makes
no mention of the inverted spectrum.




There is one other defense of the utility of inversion scenarios in
anti-functionalist arguments, namely that some of them are
*biologically* possible--and hence not as far fetched as
scenarios containing zombies or thinking rocks. If this is right, then
spectrum inversion would be of special significance, since we have a
firmer grip on possibilities that are closer to home.




Here is it is helpful to examine Block's Inverted Earth argument
against functionalism, which at a superficial glance might not seem to
stray beyond the constraints of Earthly biology. As we saw in
subsection 2.3.3, the Inverted Earth scenario is designed to avoid
certain objections to the usual argument from intrapersonal inversion
hypotheses to interpersonal inversion hypotheses. How is the scenario
turned into an argument against functionalism?




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



> An experience has [\(Q\_{R}\)] if [and
> only if] it functions in the right way--if it is caused by red
> things in the right circumstances, and used in thought about red things
> and action with respect to red things rightly. The functional roles I
> am talking about are what I call 'long-arm' roles, roles
> that include real things in the world as the inputs and outputs. They
> are to be distinguished from the 'short-arm' roles that
> functionalists sometimes prefer, roles that stop at the skin. (1990,
> 58, note
>  omitted)[33]




Block then tries to establish that after a suitable period of time
on Inverted Earth, your beliefs and judgments about the colors of
things would be *correct*: like the locals, you would believe
that fire 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
> Inverted Earth would dominate, and so your intentional contents would
> shift so as to be the same as those of the natives. Consider an analogy
> (supplied by Martin Davies): if you had a Margaret Thatcher
> recognitional capacity before your journey to Inverted Earth, and on
> arriving misidentify twin MT as MT, you are mistaken. But eventually
> your '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, and
make an effort to speak the local language; see Block 1996a, 42;
2003.)




This step of the argument appeals to *externalism* about
mental content (Putnam 1975, Burge 1979), specifically some sort of
causal covariational theory (see the entry
 externalism about mental content).
Putting the basic idea crudely: after a while on Inverted Earth certain
of your inner states that on Earth were reliably caused by the presence
of red things and thereby represented redness will instead be reliably
caused by the presence of green things, and thereby will come to
represent greenness.




This gives us an apparent counterexample against the "long
arm" functionalist theory. On Inverted Earth your experiences
have the functional role that the functionalist theory says is
necessary and sufficient for possessing
\(Q\_{R}\): they are "caused by red things in the
right circumstances, and used in thought about red things and action
with respect to red things rightly". But on Inverted Earth your
experiences with this functional role have
\(Q\_{G}\), not (or not always)
\(Q\_{R}\).




If we insist that the Inverted Earth scenario is constrained by
actual biology, can it still be maintained that your experiences caused
by red things on Inverted Earth have the
\(Q\_{R}\)-role? That is not clear, even if we
grant Block's claim about the "shift in intentional
contents" without a corresponding change in qualia. The problem
is twofold. First, because of asymmetries in color space and additional
complications (see footnote 23),
 to say nothing of the details of the
"inverting lenses", your total functional organization
would certainly change in various respects after traveling to a
biologically possible Inverted Earth. Second, Block's description of
the long-arm functional theory is highly schematic. It may be that a
suitably sophisticated and developed form of this theory would not have
the consequence that, on a biologically possible Inverted Earth, your
experiences caused by red things have the
\(Q\_{R}\)-role. Similar points go for an argument
against functionalism using a traditional inverted spectrum
scenario.




Unsurprisingly, Block does not rest very much--if 
any--weight on the biological possibility of the Inverted Earth
scenario:



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




This response concedes that the Inverted Earth argument against
functionalism may need to appeal to more-or-less outlandish
possibilities. And if it does, then since other possibilities not
involving inversions, and arguably no more outlandish, will do just as
well, it is doubtful that Inverted Earth-type scenarios have an
essential role to play in arguments against
 functionalism.[34]




The anti-physicalist inverted spectrum argument is:



**Argument Ac**

P1c.

The following spectrum inversion scenario is possible: Invert
and Nonvert are *physically* alike, and are both looking at a
tomato.

Since P1c implies that the mental does not supervene on physical
makeup:



Cc.

Physicalism is false.



Although there is some controversy about just how science-fictional
anti-functionalist inversion scenarios need to be,
anti-*physicalist* inversion scenarios are usually supposed to
be very remote from actuality, and their possibility is hotly disputed.
Almost uncontroversially: if an inverted spectrum argument against
physicalism works at all, then a simple zombie scenario will equally
serve the
 purpose.[35]


### 3.2 ...Against Representationalism




It is widely held that perceptual experiences represent the
perceiver's environment as being a certain way. For example, the
experience of someone with normal color vision looking at figure 1
represents (inter alia) her environment as containing a crimson,
vermilion, and turquoise square. In the terminology of Chalmers 2004
(slightly adapted), a *representational property* is a property
of a mental state/event that specifies (perhaps only in part) the
state/event's representational content. For example, the property of
being a visual experience that represents that there is a crimson
square before one is a representational property (for a taxonomy of
representational properties, see Chalmers 2004, section 2). The basic
idea of *representationalism* or *intentionalism* is that
qualia are representational properties, or at least supervene on
representational properties. One advantage of representationalism is
that it appears to reduce "phenomenal consciousness" (Block
1995) to a certain kind of intentionality. Since the problem of
providing a naturalistic account of intentionality is often thought to
be tractable, representationalism brings the possibility of a
naturalistic account of consciousness (see, e.g., Dretske 1995, Lycan
1996, Tye 2000, and Speaks 2015).[36]




Spectrum inversion scenarios help to focus the dispute between
representationalists and their critics. (Actual cases of shifted
spectra can also serve: see Block 1999.) Any version of
representationalism is committed to the following thesis. Consider a
case of red-green spectrum inversion, and imagine Invert and Nonvert
are both looking at the red peppers depicted in figure 6, against a
neutral background. Nonvert's experience has
\(Q\_{R}\), while Invert's experience has
\(Q\_{G}\). Because the two experiences have
different qualia, any version of representationalism implies that, if
this scenario is possible, the two experiences differ in
representational content. Hence, if the foregoing scenario can be
filled out so that (a) the two experiences have the *same*
content and (b) the scenario is possible, then representationalism is
refuted.




How can these two desiderata be satisfied? Fortunately for the
anti-representationalist--or *phenomenist* (Block 
2003)--the usual ways of trying to secure (a) do not require Invert
and Nonvert to be behavioral duplicates (or, for that matter,
functional duplicates). The anti-representationalist can therefore
dismiss concerns that a behaviorally undetectable inversion scenario is
impossible.




The description of the anti-representationalist scenario is
typically completed with the following three features. First, Invert is
able to use her color vision to reidentify objects, distinguish objects
from their backgrounds, etc., with more-or-less the facility of
Nonvert. In Locke's phrase, Invert "would be able as regularly to
distinguish Things for [her] Use by those Appearances". Second,
Invert has been spectrally inverted from birth (or at least for a long
period of time). Third, Nonvert and Invert belong to the same
linguistic community: in particular, they use color vocabulary in the
same way, applying 'red' to tomatoes, 'yellow'
to bananas, and so forth.




Assume that this scenario is possible (for an argument that it isn't,
see Sundstrom 2002 and Gibbons 2005; for a reply see Littlejohn
2009). The three features just mentioned are intended to support the
view that this scenario is one in which, when Invert and Nonvert both
look at the fruits depicted in figure 6, their experiences have
the *same* representational properties. In particular (glossing
over a complication to be discussed in subsection 3.3 below), the
banana *looks yellow* to both Invert and Nonvert, the
strawberries *look red* to both, and so on. So, assuming that
bananas are yellow, strawberries are red, etc., neither Invert nor
Nonvert is suffering from some global color illusion. If this inverted
spectrum hypothesis is correct, then qualia do not supervene on
representational properties, and therefore representationalism is
false.




(Here is one way of putting the Inverted Earth version of this
argument (see subsections 2.3.3 and 3.1). After first arriving on
Inverted Earth, your word 'red' means *red*, and to
you the green peppers on Inverted Earth look red. But after a period of
acclimatization, you come to speak the language of the locals, and your
experiences come to represent correctly the colors of things--green 
peppers on Inverted Earth look green. Now compare your present
experience of a green pepper on Inverted Earth with your previous
experience of peppers of exactly that shade back on Earth. Same
content, but different qualia. Alternatively, the
anti-representationalist argument can proceed by exhibiting an example
of the converse: same qualia, but different content--see Block
1990, 64-7.)




The three features of the anti-representationalist scenario can
motivate the conclusion that Invert is not systematically misperceiving
the colors of things as follows. First, because Invert's color vision
is as useful as Nonvert's for discriminating and identifying objects,
surely it would be arbitrary to suppose that Invert's color vision, but
not Nonvert's, is the source of pervasive illusions. Second, because
Nonvert has been inverted since birth, a complicated system of causal
connections between the colors of objects in her environment and states
of her visual system has been in place for a long period. In
particular, there is a reliable causal connection between the presence
of a red object before Invert's eyes and a certain neural event
occurring in Invert; this sort of causal connection is plausibly
sufficient to bestow the property of representing redness on this type
of neural event. Third, because Invert and Nonvert belong to the same
linguistic community, Invert's word 'red' means
*red*. So when Invert says (as she does), 'Strawberries
look red to me', she means that strawberries *look red* to
her. So, if strawberries do not look red to her, Invert is
systematically in error about how things look, and this result is not
 credible.[37]




Naturally, each of these reasons for thinking that Invert is not
misperceiving the colors of objects can be questioned. Against the
first, one might dispute the claim that it would be arbitrary to
convict only Invert of error--after all, for all that's been
said, Nonvert and Invert might differ functionally, which is presumably
a relevant difference. Against the second, there are well-known
problems for the "causal covariational" account of mental
content that it assumes (see, e.g., Fodor 1992, Ch. 3). Finally,
against the third, it may be argued that the consequence that Invert is
mistaken about the content of her experience is not unacceptable (Tye
2002,
 451).[38]




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



**Argument B**

P1.

Neither Invert nor Nonvert is misperceiving the color of the
tomato.
P2.

The tomato is red (and not any other color).
Hence:



C1.

The tomato looks the same color (namely, red) to both Invert and
Nonvert.
P3.

If representationalism is true, then the phenomenal difference
between Invert and Nonvert is due to a difference in the colors that
their experiences represent the tomato as having.
Hence, from C1 and P3:



C2.

Representationalism is false.



Some of the dialectic surrounding P1 has been described. In the
following three subsections, other ways of resisting the argument will
be discussed.




If Argument B is sound, tomatoes look red to both Invert and
Nonvert, although the corresponding qualia are different. This is why
spectrum inversion was not described in subsection 2.1 as a case where
tomatoes *look green* to Invert (and *look red* to
Nonvert). If spectrum inversion is explained in these terms, the
thought experiment is 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 experience has \(Q\_{B}\) just in
case it has a certain *non*-representational property. Let us
stipulate that '\(B\)' refers to this non-representational property,
if such 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 an experience 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.[39]
 According to the sense-datum theorist, sense-data that are associated
with experiences of seeing the sky, lapis lazuli, cobalt glass, etc.,
have a distinctive property; the traditional sense-datum theorist took
this 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, according to the sense-datum theorist,
the phenomenist equation can be spelled out 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
no truck with sense-data, and typically leave the phenomenist equation
unadorned. However, the sense-datum theorist can offer the following
consideration 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 blue square. \(e\_{1}\) has color
qualia \(Q\_{B}\) and
\(Q\_{R}\), and also "spatial qualia",
which we can label '\(Q\_{Tr}\)' and
'\(Q\_{Sq}\)'. The reference of these
four bits of qualia terminology
('\(Q\_{B}\)',
'\(Q\_{R}\)',
'\(Q\_{Tr}\)', and
'\(Q\_{Sq}\)') has been fixed by, respectively,
experiences of 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
\(e\_{2}\) differ phenomenologically, and therefore differ
in qualia. So more qualia terminology is required: in particular, a
quale name whose reference is fixed by experiences of blue triangles
and red squares, and another name whose reference is fixed by
experiences of red triangles and blue squares. In a useful notation,
the first quale name is
'\(Q\_{Rx \amp Sq(x) \amp By \amp Tr(y)}\)',
 and the second is
'\(Q\_{Rx \amp Tr(x) \amp By \amp Sq(y)}\)'.
 Obviously further qualia names with ever-more complicated subscripts will be
needed.




Now notice that there are many entailment relations between
qualia-statements--for example, '\(e\) has
\(Q\_{Rx \amp Sq(x)}\)'
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. The orthodox representationalist and the sense-datum
theorist have simple accounts of these entailments in terms of the
structure of the *objects* of experiences (*apparent*
structure, for the representationalist; *actual* structure, for
the sense-datum theorist). Assuming representationalism:
'\(e\) has
\(Q\_{Rx \amp Sq(x)}\)'
(equivalently, '\(e\) is an experience of something's
looking red and square') clearly entails '\(e\) has
\(Q\_{Rx}\)' (equivalently, 'e is an
experience of something's looking red'). Assuming the sense-datum
theory: '\(e\) has
\(Q\_{Rx \amp Sq(x)}\)'
(equivalently, '\(e\) is a sensing of a red and square
sense-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 these
entailments, and it is not clear whether she is entitled to them at
 all.[40]


### 3.3 ...For Appearance Properties




Return to the anti-representationalist argument of the previous
subsection:



**Argument B**

P1.

Neither Invert nor Nonvert is misperceiving the color of the
tomato.
P2.

The tomato is red (and not any other color).
Hence:



C1.

The tomato looks the same color (namely, red) to both Invert and
Nonvert.
P3.

If representationalism is true, then the phenomenal difference
between Invert and Nonvert is due to a difference in the colors that
their experiences represent the tomato as having.
Hence, from C1 and P3:



C2.

Representationalism is false.



Representationalists usually resist P1. But there are other options.
According to Shoemaker, the flaw in the argument is not P1, but rather
P3. In addition to representing colors, Shoemaker thinks that visual
experiences represent other ("colorlike") properties that
we do not have words for in English, and which he calls *appearance
 properties*.[41]
 On this view, both Invert and Nonvert's
experiences represent the tomato as *red*. However, Invert's
experience also represents the tomato as having a certain salient
appearance property (call it
'\(AP\_{G}\)'), while Nonvert's
experience represents the tomato as having a certain salient appearance
property \((AP\_{R})\). It is this
representational difference between Invert and Nonvert that accounts
for the phenomenological difference between their experiences. One may,
then, view Shoemaker's main argument for appearance properties as
proceeding from P1, P2, and representationalism (i.e., not-C2), to the
conclusion that P3 is false.




What are the appearance properties \(AP\_{G}\)
and \(AP\_{R}\)? Since Shoemaker thinks that it
is implausible that Invert is systematically misperceiving the colors,
it is not surprising that he also thinks that neither Nonvert nor
Invert is systematically misperceiving the appearance 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
"currently producing [a \(Q\_{R}\)]
experience in someone related to it in a certain way, namely someone
viewing it under normal lighting conditions" (254), and
similarly for \(AP\_{G}\) (see also Shoemaker
1994a). This secures the result that the tomato has
\(AP\_{R}\) when Nonvert is looking at it; as
Shoemaker notes, it implies that the tomato lacks
\(AP\_{R}\) when it is not being perceived. This
account of appearance properties has been substantially revised and
developed in Shoemaker's later work. According to Shoemaker 2002,
appearance properties include *dispositions* to produce certain
experiences in certain perceivers (a suggestion that was considered
but rejected in Shoemaker 1994a, b). Shoemaker 2006a revises the
account further; for discussion, see Egan 2006 and Speaks 2015, ch. 22.




Thau (2002, Ch. 5) holds a similar view, but there are some
important differences. First, Thau's argument does not turn on the need
to secure spectrum inversion without misrepresentation, and instead
deploys an adaptation of Jackson's (1982) thought experiment concerning
black-and-white Mary. (See the entry on
 qualia: the knowledge argument.)
 Second, because Thau is not concerned to
ensure that neither Invert nor Nonvert is misperceiving the tomato, he
does not try to argue that the tomato has both
\(AP\_{G}\) and \(AP\_{R}\),
leaving the question unexamined. Third, Thau's argument for appearance
properties commits him to the view that they cannot be named (222-5);
Shoemaker is not so committed. Finally, Thau does not think, unlike
Shoemaker, that colors are visually represented (211). According to
Thau, beliefs about the colors of things are based on experiences that
represent objects as having appearance properties. These beliefs are
justified, Thau argues, because there is a correlation between an
object's having color \(C\) and its looking to have
*AP\(\_{C}\)* (235-6).


### 3.4 ...For Modes of Presentation




An illustration of "Frege's puzzle" is this. It is
apparently possible to believe that Michael Caine is a Cockney, while
not believing that Maurice Micklewhite is a Cockney. But how can this
be, since Michael Caine and Maurice Micklewhite are the same
individual?




According to many philosophers, appearances are not misleading, and
the two beliefs really are different: specifically, they represent the
very same individual, the beloved star of *Alfie*, in different
ways, or under different modes of presentation. On this view, the
propositional content of a belief is a Fregean Thought, with modes of
presentation as constituents--as opposed to a structured
Russellian proposition, with objects and properties as
 constituents.[42]
 Put differently but connectedly, the
example shows that the names 'Michael Caine' and
'Maurice Micklewhite' have different *Fregean
senses*--their semantic values cannot simply be their
referents.




A similar issue arises in the philosophy of perception (see, e.g.,
Boghossian and Velleman 1991, Peacocke 2001, Thau 2002). When one looks
at a cucumber, does the propositional content of one's experience have
a constituent that is a "mode of presentation" of greenness
(a neo-Fregean view) or does it instead simply contain the property
greenness itself? Using the familiar ordered pair notation for
propositional content (see, e.g., Thau 2002, 83), and ignoring issues
about whether the cucumber itself is associated with a mode of
presentation, the dispute may be put as follows. On the neo-Fregean
view, the content of one's experience of the cucumber is \(\langle\)the
cucumber, \(\mathrm{MOP\_{greenness}} \rangle\); on the neo-Russellian view, the
content of one's experiences is \(\langle\)the cucumber, greenness\(\rangle\).




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



P3.

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


As explained in subsection 3.3, one may resist P3 by claiming that
color experience represents appearance properties. That
amounts to a defense of representationalism by introducing a
distinction "at the level of reference". However, P3 may
also be denied by introducing a distinction "at the level of
sense". On this view, the difference between Invert and Nonvert
is like the difference--as the Fregean has it--between
Ian, who believes that Michael Caine is a Cockney, and Nan, who
believes that Maurice Micklewhite is a Cockney. On this Fregean view of
the content of perception, the difference between Invert's and
Nonvert's experiences is that they represent the very same property,
namely redness, in different ways, or under different modes of
presentation.




Thau 2002 argues against modes of presentation (and also points out
the close connections between the inverted spectrum and Frege's
puzzle). Chalmers 2004 and Block 2007 defend a Fregean view.


### 3.5 ...For Relativism




We are not quite finished with Argument B:



**Argument B**

P1.

Neither Invert nor Nonvert is misperceiving the color of the
tomato.
P2.

The tomato is red (and not any other color).
Hence:



C1.

The tomato looks the same color (namely, red) to both Invert and
Nonvert.
P3.

If representationalism is true, then the phenomenal difference
between Invert and Nonvert is due to a difference in the colors that
their experiences represent the tomato as having.
Hence, from C1 and P3:



C2.

Representationalism is false.



So far, reasons to reject P1 and P3 have been discussed. But one
might also question the step from P1 and P2 to C1. As an analogy,
suppose that Hare is on a train, looking at a tomato in his lunchbox,
and that Tortoise is on the platform, looking at the tomato as the
train speeds by. Both Hare and Tortoise have normal vision, in
particular, normal visual motion perception. Consider the following
argument.



**Argument B\***

P1\*.

Neither Hare nor Tortoise is misperceiving the motion of the
tomato.
P2\*.

The tomato is moving (not stationary).
Hence:



C1\*.

The tomato looks to be moving to both Hare and Tortoise.



Since the tomato is moving *relative to Tortoise*, and is not
moving *relative to Hare*, if P2\* is true, it must not be taken
to mean that the tomato is moving relative to Hare. Assume, then, that
P2\* is given the following true interpretation: the tomato is moving
relative to Tortoise. However, Hare does not have to perceive that the
tomato is moving relative to Tortoise in order to perceive (correctly)
the tomato's motion--perceiving it as *not* moving
relative to himself will also suffice. Hence, Hare's and Tortoise's
experiences can both be veridical, despite representing the tomato's
motion differently, which is to say that Argument B\* is invalid.




One might diagnose a similar mistake in Argument B, and thus endorse
*relativism* about color. According to relativism the tomato is
not red *simpliciter*: rather, it is red relative to Nonvert
(not green relative to Nonvert), and green relative to Invert (not red
relative to Invert). In other words, the tomato is simultaneously
*red-for-Nonvert* and *green-for-Invert*. Since, on this
view, the tomato looks red-for-Nonvert to Nonvert, and red-for-Invert
to Invert, both their experiences are veridical, despite representing
the tomato differently.




What is this property of being red-for-Nonvert? The usual answer is
something along the lines of the account of appearance properties in
Shoemaker 2002: something is red-for-Nonvert iff it is disposed to
cause experiences with \(R\) in perceivers of Nonvert's kind. And
this, of course, is essentially the "secondary quality"
account of color that many find in Locke. Sometimes relativism is
combined with representationalism (McGinn 1983, Tye 1994), but it
arguably fits more naturally with phenomenism (McLaughlin 2003, Cohen
2004).




Shoemaker did not block Argument B in this straightforward fashion
because he finds relativism implausible. As he puts it in a review of
McGinn 1983:



> Suppose...that overnight we all undergo
> intrasubjective 'spectrum inversion'...It cannot
> seriously be maintained that the result of the change would be that
> henceforth grass \(is\) red, port wine green, etc. And it is
> plausible that, once we were accustomed to the change, we would no
> longer say that grass *looks* red (for it would look the way we
> had become accustomed to having green things look). This point is even
> clearer if we imagine that we undergo intrasubjective inversion one at
> a time rather than all of us at once. (1986, 411)




Like the argument for appearance properties, the argument for
relativism can be made by appeal to shifted spectra (see, in
particular, Cohen 2004). Averill 1992 argues for a version of
relativism using physically possible intrapersonal shifted spectra
scenarios, involving a slight change in the eye, or in the
 atmosphere.[43]


### 3.6 ...For Skepticism About Others' Minds




The "inverted spectrum" quotation from Locke in
subsection 2.2 above continues:



> I am nevertheless very apt to think, that the sensible
> Ideas, produced by any Object in different Men's Minds, are most
> commonly very near and undiscernibly alike. For which Opinion, I think,
> there might be many Reasons offered: but that being besides my present
> Business, I shall not trouble my Reader with them; but only mind him,
> that the contrary Supposition, if it could be proved, is of little use,
> either for the Improvement of our Knowledge, or Conveniency of Life;
> and so we 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
is not at all clear what reasons may be offered. Malebranche was of the contrary opinion: 



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




Let \(p\) be the claim that when others look at ripe tomatoes, their
experiences have \(Q\_{R}\). Let \(S\) be a
spectrum inversion scenario with 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:



**Argument C**

P1.

One's evidence about others' behavior and use of color words
does not favor \(p\) over \(S\).
P2.

One has no other evidence that favors \(p\) over \(S\).
P3.

If one's evidence does not favor \(p\) over \(S\), one does not know \(p\).
Therefore:



C.

One does not know \(p\).



Although philosophers have generally not been impressed by similar
arguments for skepticism about the external world, there is little
consensus on the status of arguments along the above lines. For
example, Block writes: "I claim we simply do not know whether
spectrum inversion obtains or not" (1990, 57). Argument C is less
threatening than some other skeptical arguments because, even if sound,
generalizations of it to skepticism about other kinds of mental states
are implausible. For example, a parallel argument against one's
knowledge of other's beliefs would have a dubious first premise.




P1 will be denied by an orthodox representationalist. Setting a
controversial skepticism about testimony aside, presumably one can know
on the basis of testimony that tomatoes look red to many people. (See
Shoemaker 1982, 334.) So, since orthodox representationalism equates
\(Q\_{R}\) with the property of being an
experience of something's looking red, one may know on the basis of
testimony that when others look at tomatoes, their experiences have
\(Q\_{R}\).




Some philosophers think that the fact that others are biologically
similar to oneself is an important piece of evidence for their mental
similarity (see, e.g., Hill 1991, Ch. 9), and P2 might be denied on
these grounds (see, e.g., Papineau 2002, 132). For more discussion, see
Block
 2002.[44]


### 3.7 ...For the Explanatory Gap




Many philosophers think there is an "explanatory gap"
(Levine 1983, 2001) between physical facts and facts about conscious
experience. On this view, even if consciousness is a physical
phenomenon, it cannot be given a physical explanation. Inverted
spectrum 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
> "\(G\ldots\)" When we consider the qualitative
> character of our visual experiences when looking at ripe McIntosh
> apples, as opposed to looking at ripe cucumbers, the difference is not
> explained by appeal to \(G\) and \(R\). For \(R\)
> doesn't really explain why I have the one kind of qualitative
> experience--the kind I have when looking at McIntosh 
> apples--and not the other. As evidence for this, note that 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. (Levine 1983,
> 356-7)




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



**Argument D**

P1.

If a physical theory \(T\) explains the fact that we have
experiences with \(Q\_{R}\) when looking at
McIntosh apples, and experiences with \(Q\_{G}\)
when looking at cucumbers, then it is not imaginable that the explanans
holds without the explanandum. That is, it is not imaginable that
\(T\) holds and we do not have experiences with
\(Q\_{R}\) when looking at McIntosh apples
(etc.).
P2.

A red-green spectrum inversion scenario in which \(T\)
holds is imaginable.
Hence:



C.

No physical theory explains the fact that we have experiences
with \(Q\_{R}\) when looking at McIntosh apples,
and experiences with \(Q\_{G}\) when looking at
cucumbers.



Notice that Argument D does not have as a premise a spectrum
inversion *hypothesis*--that a certain spectrum inversion
scenario is *possible*. All the argument requires is that the
spectrum inversion scenario is *imaginable*. Indeed, since
Levine is a physicalist, he thinks that this scenario is *not*
possible.




What is the intended interpretation of 'imagine' in P1
and P2? (In the literature 'conceive' is used
interchangeably.) The usual answer (Levine 2001, Ch. 2) is this:
\(p\) is imaginable iff not-\(p\) is not *a priori*.
On this interpretation, P1 amounts to this: it is *a priori*
that if the explanans holds, so does the explanandum; that is, that the
explanans *a priori* entails the explanandum. This can be
motivated by appeal to the "deductive-nomological" model of
explanation (see Hempel 1965, and the entry on
 scientific explanation);
 this
model is controversial, and in fact Levine rejects it, but he argues
that there is a broader motivation:



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




One might resist Argument D by denying P2 (for some ammunition, see
Hardin 1987; 1993, 134-42; for a reply see Levine 1991; see also Hardin
1991). A much more common response is to deny P1 (Block and Stalnaker
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 on
the basis of an argument related to Argument D, although somewhat more
complicated (2001, Ch. 3). And in any case, just like the inverted
spectrum argument against behaviorism, functionalism and physicalism
(see subsection 3.1 above), inverted spectrum scenarios are not playing
an essential role in the case for the gap, and indeed Levine 2001 leans
more heavily on "absent qualia" scenarios: "The
conceivability of zombies...is the principal manifestation 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 some suspicion. Assume
that spectrum inversion does *not* occur, and consider a
counterfactual situation in which, as Block puts it,
"*spectrum inversion is rife*" (1990, 55). Suppose
that philosophers in this counterfactual situation introduced qualia
terminology in the way it was introduced in section 1. If their qualia
terminology is meaningless, then it is hard to see why our terminology
is better off--we use
'\(Q\_{R}\)' just as it is used in
the counterfactual situation. If, on the other hand, their qualia
terminology is meaningful, then presumably
'\(Q\_{R}\)', as they use it, refers
to something other than a quale. (Since spectrum inversion is rife,
their use of '\(Q\_{R}\)' is not
associated with any particular quale.) Again, given the overlap in
use, why suppose that our word
'\(Q\_{R}\)' is any different? Either
way: '\(Q\_{R}\)' does not refer to a
quale. There is a threat, then, that qualia cannot be named in a
public language--that they are *ineffable* (cf. Dennett
1988, 228-9). Indeed, that seems to be Block's opinion: "if an
inverted spectrum is possible, then experiential contents that can be
expressed in public language (for example, *looking red*) are
not qualitative contents, but rather intentional contents"
(1990, 55; see also Block 2007, 73-4). ("Qualitative
contents" are qualia that are not representational properties:
see subsection 3.2.)




Frege held a version of the ineffability view. One of his theses in
*The Foundations of Arithmetic* is that arithmetic is
"objective", which he explains as follows:



> What is objective...is what is subject to laws, what
> can be conceived and judged, what is expressible in words. What is
> purely intuitable is not communicable. To make this clear, let us
> suppose two rational beings such that projective properties and
> relations are all they can intuit--the lying of three points on
> a line, of four points on a plane, and so on; and let what the one
> intuits as plane appear to the other as a point, and vice versa, so
> that what for the one is the line joining two points for the other is
> the line of intersection of two planes, and so on with the one
> intuition always dual to the other. In these circumstances they could
> understand one another quite well and would never realize the
> difference between their intuitions, since in projective geometry every
> proposition has its dual counterpart; any disagreements over points of
> aesthetic appreciation would not be conclusive evidence. Over all
> geometrical theorems they would be in complete agreement, only
> interpreting the words in terms of their respective intuitions. With
> the word 'point', for example, one would connect one
> intuition and the other another. We can therefore still say that this
> word has for them an objective meaning, provided only that by this
> meaning we do not understand any of the peculiarities of their
> respective intuitions. (1884/1953, SS26)




This is an inverted spatial qualia scenario. According to Frege, the
inversion would not show up in the semantics of words: both Nonvert and
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 color
terminology.



> The word 'white' ordinarily makes us think of a
> certain sensation, which is, of course, entirely subjective; but even
> in ordinary everyday speech, it often bears, I think, an objective
> sense. When we call snow white, we mean to refer to an objective
> quality which we recognize, in ordinary daylight, by a certain
> sensation. If the snow is being seen in a coloured light, we take that
> into account in our judgement and say, for instance, 'It
> *appears* red at present, but it \(is\) white.' Even
> a colour-blind man can speak of red and green, in spite of the fact
> that he does not distinguish between these colors in his sensations; he
> recognizes the distinction by the fact that others make it, or perhaps
> by making a physical experiment. Often, therefore, a colour word does
> not signify our subjective sensation, which we cannot know to agree
> with anyone else's (for obviously calling things by the same name does
> not guarantee as much), but rather an objective quality.
> (SS26)




Although Frege seems to concede that *sometimes* a color word
"signifies our subjective sensation", the general drift of
the argument points to a much stronger conclusion, that our subjective
sensations are simply not "expressible in words". A related
example is Wittgenstein's "beetle in the box":



> 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 at *his*
> beetle.--Here it would be quite possible for everyone to have
> something different in his box. One might even imagine such a thing
> constantly changing.--But suppose the word 'beetle'
> had a use in these people's language?--If so it would not be
> used as the name of a thing. The thing in the box has no place in the
> language game at all; not even as a 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, SS293)




(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, has
normal color vision, is a member of our linguistic community, and uses
qualia terminology ('\(Q\_{R}\)',
'\(Q\_{G}\)', etc.), as introduced in
section 1 above. Further suppose that spectrum inversion does not in
fact occur.




Now consider a counterfactual spectrum inversion scenario in which
"spectrum inversion is rife". Invert has been spectrally
inverted with respect to some other members of his community since
birth, all of whom use color terminology in much the same way. Nonvert
is spectrally inverted with respect to his neighbor Invert, but--comparing 
this scenario with the actual scenario described in the
previous paragraph--is not spectrally inverted with respect to
Humbert. Further suppose that Nonvert and his neighbor Invert use
qualia terminology as introduced in section 1 above. Assume as a
suppressed premise that this scenario is possible.




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



**Argument E**

P1.

'\(Q\_{R}\)', as Invert uses
it, and '\(Q\_{R}\)', as Nonvert uses
it, refer (if at all) to the same property.
P2.

'\(Q\_{R}\)', as Invert uses
it, does not refer to \(X\).
Hence:



C1.

'\(Q\_{R}\)', as Nonvert uses
it, does not refer to \(X\).
P3.

'\(Q\_{R}\)', as Humbert uses
it, and '\(Q\_{R}\)', as Nonvert uses
it, refer (if at all) to the same property.

Hence, from C1 and P3:



C2.

'\(Q\_{R}\)', as Humbert uses
it, does not refer to \(X\).



Since the rest of us are in no better position than Humbert, C2
leads inevitably to the conclusion that
'\(Q\_{R}\)',
'\(Q\_{G}\)', etc., as introduced in
the manner of section 1, do not in fact refer to qualia. One might view
Argument E as showing that certain salient aspects of our mental lives
are linguistically elusive (as Frege apparently did); alternatively,
one might follow Wittgenstein and conclude that the very idea of qualia
rests on a conceptual confusion.




In fact, C2 does not imply that qualia are *completely*
unspeakable--it does not, that is, imply that \(no\)
expression refers to \(X\) (i.e., the quale distinctive of
Humbert's experiences of red things). Indeed, if the sentence to the
right of 'C2' succeeds in expressing a truth, then
'\(X\)' (and so 'the quale distinctive of Humbert's
experiences of red things') refers to \(X\). If Argument E
is as far as we can go, then the moral seems to be that particular
qualia can only be picked out 'by description'--they
cannot be referred to by semantically simple expressions, such as
'\(Q\_{R}\)' and
 '\(Q\_{G}\)'.[45]
 But--bearing
in mind Wittgenstein's remark that "the box might even be
empty"--one might attempt to extend the argument to show
that even the word 'qualia' itself is devoid of
significance.




However, Argument E is not obviously sound. The premise in need of
most defense is
 P3.[46]
 When qualia terminology was introduced in
section 1, it was tacitly presupposed that spectrum inversion was
*not* rife. In Invert's and Nonvert's community, that
presupposition is false, and so it should not be surprising if the
attempt to introduce '\(Q\_{R}\)' into
their public language fails. But in Humbert's community the
presupposition is *true*; so why wouldn't
'\(Q\_{R}\)', as the members of this
community use it, successfully refer to the quale distinctive of
Humbert's experiences of red
 things?[47]


### 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
subsections 3.1 and 3.2. Premise P1 of our much-scrutinized 
Argument B--'Neither Invert nor Nonvert is misperceiving the color of
the tomato'--was supported, in part, by a particular
externalist theory of perceptual content. According to the externalist,
some representational properties of subjects, like the property of
believing that water is wet, or that arthritis is painful, or the
property of having an experience of something's looking red, are
extrinsic: these properties are not necessarily shared between perfect
duplicates (or even less-than-perfect duplicates with perfectly
duplicated
 brains).[48]
 Smith may believe that water is wet, yet
twin-Smith on Putnam's Twin Earth does not believe that water is wet.
The tomato may look red to Jones, yet not to twin-Jones on Inverted
Earth. (In an alternative scenario, twin-Jones has just been created by
happenstance in a swamp: see Davidson 1987.)




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




Finally, representationalism (see subsection 3.2 above) is--if 
not as popular as the previous two claims--at least defended
by many contemporary philosophers.




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



**Argument F**

P1.

Representational properties are extrinsic.
P2.

Representationalism is true (for simplicity, in the simple form
of subsection 3.2 above: \(Q\_{C}\) = the property
of being an experience of something's looking to have color
\(C)\).
P3.

Qualia are intrinsic.



Consider the representational property of having an experience of
something's looking red. By P1, this property is extrinsic, and so
there is a possible world \(w\) in which a subject \(x\) has
this property and \(y\)--a perfect duplicate of 
\(x\)--lacks it. Solely for illustration, we may take \(w\) to be
a possible world in which Nonvert and his twin Invert are both looking
at a tomato in a white bowl (but perhaps the twins are on different
planets). Nonvert is having an experience of something's looking red,
and Invert is not; more specifically: (i) the tomato looks red, and
nothing looks green, 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 twins whose experiences do not share qualia; in other words,
qualia are not intrinsic. 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 scenario
in which duplicate perceivers are spectrally inverted. This spectrum
inversion hypothesis is ruled out by P3, and P3 is of course consistent
with Argument F's conclusion.




Argument F shows that either content-externalism, representationalism,
or qualia-internalism should be rejected. For a discussion of this
problem, see Egan and John 2003 (Other Internet Resources); Dretske
(1995, Ch. 5) argues against P3 (see also Tye 1995, 150-5; 2002,
Ch. 6; Lycan 1996, 115-7; and Noe 2005, Ch. 7); P1 is
denied in Chalmers 2004.




Relatedly, McGinn (1989, 58-94) runs a "spatially Inverted
Earth" argument against what he calls 'strong
externalism' about perceptual content (a particular kind of
externalism); Davies (1997) adapts McGinn's example to argue for
externalism about perceptual content. Both sides of the
"externalism/internalism" debate as encapsulated in
Argument F presuppose that it is possible to keep a perceiver's
internal constitution fixed while greatly varying the environment; this
assumption is critically examined in Hurley 1998, Chs. 7, 8, and Myin
2001.


### 3.10 Summary: Required Features of Inverted Spectrum Scenarios




|  |  |
| --- | --- |
| **Conclusion** | **Required features of scenario** |
| Behaviorism is false. | Behaviorally undetectable inversion. |
| Functionalism is false. | Functionally undetectable inversion. |
| Physicalism is false. | Physically undetectable inversion. |
| Representationalism is false. | Inversion with no misperception (so a behaviorally undetectable
inversion is not required); in addition, lifelong inversion and same
linguistic community. Shifted spectra might do as well. |
| There are appearance properties. | As immediately above ("Representationalism is
false"). |
| There are perceptual modes of presentation. | As immediately above. |
| Color relativism is true. | As immediately above. |
| One does not know about others' qualia. | Inversion that is not ruled out by one's actual evidence about
others' behavior and use of color words. |
| There is an explanatory gap. | Inversion that obtains together with the actual physical theory of
color experiences; the scenario does not need to be possible, only
imaginable. |
| Qualia are ineffable. | Inverted and noninverted subjects in same community, with the use
of qualia terminology similar to the actual use. |
| Content-externalism, representationalism, and qualia-internalism
are inconsistent. | Inverted subjects who are perfect duplicates; this scenario is not
assumed to be possible. |