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REDDISH GREEN
A CHALLENGE FOR MODAL CLAIMS ABOUT PHENOMENAL STRUCTURE
Juan Suarez & Martine Nida-Rümelin
Université de Fribourg, Switzerland
Abstract: We discuss two modal claims about the phenomenal structure of color
experiences in the light of empirical results: the claim that violet experiences are necessarily
experiences of a color that is for the subject on that occasion phenomenally composed of red
and blue (the modal claim about violet) and the claim that no subject can possibly have an
experience of a color that is for it then phenomenally composed of green and red (the modal
claim about reddish green). The modal claim about reddish green is undermined by empirical
results. We discuss whether these empirical results cast doubt on the other modal claims as
well. We argue that this not the case. Our argument is based on the thesis that the best
argument for the modal claim about violet is quite different from the best argument for the
modal claim about reddish green. To argue for this disanalogy we propose a reconstruction
of the best available justification for both claims.
1. Conceptual preliminaries and presuppositions
For a long time it has been accepted that red and green cannot combine to a new color in
experience in the way red and blue can combine to form an experience of violet. This natural
assumption has been challenged by the experiments of (Crane & Piantanida, 1983) and
(Billock, Gleason, & Tsou, 2001). The results of these experiments if taken at face value
show that it is possible for human beings to see a color that has a reddish and a greenish
component. We assume that what is at issue here is the question of whether red and green
can or cannot combine in experience to a new perceived color that is phenomenally
composed of red and green in the way violet is composed of red and blue or orange is
composed of red and yellow. To formulate the philosophical issues we are interested in will
require using the concept of phenomenal composition. Before we begin we have to say a few
words about how we understand the concept and we have to distinguish two related but
different concepts of phenomenal composition.
A few controversial assumptions will be
presupposed in the present paper (and are discussed in other places)1:
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(1) We will assume that the claim
(V) Violet is composed of red and blue.
is made true by a particular aspect of the subjective character of violet experiences. It is not
made true, in our view, by any fact concerning the mixture of pigments or the mixture of light.
(V) is true because things that look violet to a person look to that person in a particular way:
they look reddish and bluish and there is no other chromatic hue component present in the
color as it is perceived by the subject at issue. You may insist that (V) may be interpreted as
a claim about how to mix violet with pigments on a piece of paper. This may be true but this
possible interpretation of (V) is not the interpretation we will be interested in. There is a
reading of (V) – or so we claim – that is made true by phenomenal facts. This is why we call
the relation stated in (V) the relation of phenomenal composition.
(2) Claims like (V) about phenomenal composition are made true by phenomenal facts but
they are not made true by contingent phenomenal facts. They are true because violet is
necessarily experienced as being composed of red and blue. To claim that (V) is true in
general is to claim that no subject in counterfactual circumstances could have an experience
of something as violet without thereby having an experience of something as looking bluish
and reddish at the same time. So, according to the interpretation of (V) that we will
presuppose, (V) implies that it is constitutive of having an experience of violet that it is an
experience of a color that is seen as containing a reddish and a bluish component. This
modal claim has sometimes been invoked to argue that being phenomenally composed of
red and blue is a necessary property of colors.2 Contrary to this we claim that (V) in itself
(without any modal operator) is already a modal claim about violet experiences. We agree
that (V) is itself a necessary truth. We agree with Hardin that violet is necessarily
phenomenally composed of red and violet. But this then is to say that the color violet
necessarily has the property of being necessarily experienced in a particular way. This
analysis may look excessively complicated. We think the complication is unavoidable but we
will not try to defend this thesis here.
(3) To avoid confusion two notions of phenomenal composition have to be distinguished. The
first notion of phenomenal composition is the one used in (V). The second notion of
phenomenal composition is used to describe a particular aspect of the subjective character
of violet experiences (the relevant aspect we mentioned before). The fact that a particular
person sees a reddish and a bluish component when having an experience of violet is
expressed using the second concept. We will choose the locution "the object appears to the
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person in a color that looks phenomenally composed of red and blue to that person on that
occasion" to express the second concept. For our philosophical purposes it is important to be
able to give phenomenological descriptions of concrete color experiences that do not imply
modal claims about color experiences of the relevant type. It must be possible e.g. to claim
that for Mary something that looks violet to her on a particular occasion looks in a color that
has (in Mary's experience) a blue and a red component without thereby implying that what is
said here about Mary on that particular occasion has to be true of her in any other moment
when she has an experience of violet and has to be true for any subject that has an
experience of violet.
In a language that is appropriate to our philosophical purposes,
phenomenological descriptions concerning a particular violet experience should not logically
imply modal claims about the phenomenal character of violet experiences in general. It is
quite easy to see that this constraint cannot be met without a conceptual distinction of the
kind we just introduced. It can be argued that – given a number of substantial philosophical
assumptions – the distinction can be neglected after all. But these reasons for abandoning
the distinction cannot even be formulated without using the distinction itself.3
(4) We will presuppose a further controversial claim that might be called realism about
phenomenal composition (in the sense of the second notion). According to this claim a
person may actually have an experience of a color that looks composed of red and blue to
him or her on that occasion without noticing that this is so. A person may even have an
experience of a hue that is for her a binary hue (it contains for her two hue components) and
yet be convinced that there are no two hue components in the color as she perceives it and
vice versa. According to this view it is no contradiction to say that a person sees green as a
unique hue and yet seriously believes that she is thereby seeing a hue that is for her
phenomenally composed of blue and yellow.4 According to this realist thesis we can be
wrong about facts concerning phenomenal composition (in the sense of the second notion)
even with respect to our own color experiences and this even while having them and even
while directing our attention towards the relevant phenomenal aspect.
2. Modal Knowledge about Phenomenal Composition. A Problem Raised by Reddish
Greens
If claims like (V) are correctly interpreted as implying modal claims about the phenomenal
character of violet experiences then the following epistemological question arises: How can
we know that violet experiences have a certain phenomenal structure necessarily? It appears
to be quite unproblematic to assume that a person can know, by carefully attending to her
own violet experience while having it, that she is thereby having an experience of a color that
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looks to be composed of red and blue to her on that occasion. But how can she know that
this will be so again next time when she will have a violet experience? And how can she
know that no subject can ever have an experience of violet without thereby having an
experience of a color that looks to be phenomenally composed of red and blue for to that
subject on that occasion? How can a person rationally judge about violet experiences at
other times in other galaxies had by different sentient beings? Or is it maybe irrational to hold
the modal claim that is implied by claims like (V)?
Our answer to these questions is that we can rationally judge that (V) is true. On our view
this implies the claim that we do have epistemic access to modal truths about phenomenal
composition (in the second sense). We will defend the view that a person who (a) judges on
the basis of carefully attending to her own violet experiences that she has an experience of a
color that is phenomenally composed of red and blue for her whenever she has an
experience of this type, does indeed have reason to (b) judge that having an experience of a
reddish and a bluish component is indeed constitutive of having an experience of violet. This
view involves the claim that we can rationally proceed from phenomenological observations
about our own experiences to modal claims about experiences of the relevant type in
general. How can we do this? What is the correct reconstruction of the steps involved in a
justification of the modal claims at issue? We will propose a justification of modal claims
about phenomenal composition (in the second sense of the term) in a moment. But there is a
potential danger for our view based on the case of reddish greens. We will now consider this
danger.
In certain cases, we claim, we can rationally form judgements about the necessary structure
of color experiences in general on the basis of phenomenological descriptions concerning
the phenomenal structure of our own actual color experiences. This is the view we defend
and the case we cited is the one about violet. However, the case of reddish greens seems to
show that we are easily led astray when we dare to proceed from phenomenological
descriptions of phenomenal structure to modal claims about phenomenal structure. It is a
true and quite obvious phenomenological fact about the phenomenal structure of our normal
human color perception that we never see a color that looks to be phenomenally composed
of red and green. If we try to imagine a color that is phenomenally composed of red and
green we do not succeed. In normal human color perception red and green are opponents in
Hering's sense: there is no hue ever seen by a real person in real life that is phenomenally
composed of red and green for that person on that occasion. We are tempted to conclude,
like in the case of violet, that this particular fact about the actual structure of our color
experience is a necessary truth about red and green. We are tempted to say something like
this: if some arbitrary subject under counterfactual circumstances sees a color that is for that
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subject phenomenally composed of two hues H1 and H2, then these hues are not green and
red. It is – so we are tempted to say – constitutive of red and green that they cannot be
combined in experience to a new hue in the way red and blue or red and yellow or blue and
green can.5
But there are empirical results that seem to show that this is false. These results cast doubt
on the claim that we have modal knowledge about phenomenal structure in the case of violet
and orange as well. Our modal judgement in the case of violet is based on knowledge about
the phenomenal structure of our actual experiences. Something very similar seems to go on
in the case of the apparently wrong modal judgement about red and green. Maybe then we
should admit that we simply do not have anything more but knowledge about actual
phenomenal structure and maybe we should withdraw opinion with respect to the
corresponding modal claims in general. To see if this is the conclusion to draw we will first
have a look on the relevant empirical results and their interpretation.
3. Empirical studies about reddish green
In a study by Crane and Piantanida6 subjects report seeing reddish-greens and yellowishblues. A variant of this experiment has been successfully conducted by Billock et al. 7 To our
knowledge no other similar experiments have been realized. The conditions in which these
studies have been made are very particular. It is highly unlikely that the perception of the socalled ‘novel colors’8 can happen outside a vision science lab. There are pertinent features
of the experiments which require some introduction to non-scientists. In this section we will
first introduce some of the relevant technical terms, and then describe the experiment.
3.1. A few technical terms
Stabilized images and filling in
The eye is rarely stationary for more than a few microseconds. In order to see, the
eye needs contrast, which is provided by constant, very fast movements of the eye called
saccades. This mechanism probably enables us to avoid seeing the blood vessels placed
between the retina and the visual scene.9 If the eye totally lacks contrast for a few seconds
then the image will fade out. This is what happens in the so-called ganzfeld phenomenon, in
which the contrast provided by the visible parts of the subject’s face is hidden from view. C L
Hardin describes an example of this phenomenon:
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"A subject’s eyes are covered with the two halves of a ping-pong ball and the room is
filled with a diffuse, shadowless colored light, pink for example. Within a couple of
minutes’ time, the color fades completely from view; subjects frequently claim that the
light has been turned off." (Hardin, 1993) p.22
A stabilized image is an image projected on part of the visual field which follows the
movements of the eye, so that the fading out of the image typical of the ganzfeld
phenomenon is restricted only to the stabilized portion of the visual field. This can be done
with contact lenses with a non-transparent part. In the experiments the stabilization is done
with an ‘eyetracker’, a device designed to stabilize images without using contact lenses with
non-transparent parts. Eyetrackers use the reflection of infrared light of the eye to track its
movements and project images onto it.10
If an image is stabilized on a part of the retina for a certain time, thus producing a sort
of 'informational hole' underlying the fading out phenomenon just described, then the brain
tends to complete the image by filling in something using the information of the surround.
The filling-in process is commonly taken to explain the fact that there is no perceived hole in
our visual field corresponding to the blind spot on the retina. The blind spot is the place in the
retina where the optic nerve exits the eye.
In this part of the retina there are no
photoreceptors, and therefore no visual information is received, and yet we do not notice this
informational hole except in very exceptional circumstances. 11 So-called scotomas (lesions
of the retina) can go unnoticed by the subject even when much larger than the blind spot.
This again is considered to be explainable by a filling in process.
Equiluminance
There are three types of photoreceptors that participate in color vision, individuated
by their sensitivity to different wavelengths. The S-cones are maximally sensible to short
wavelengths, the M to middle wavelengths and the L to long wavelengths. According to a
widely accepted model the ‘luminance pathway' processes the sum of the activity of the Land M- cones.12 It is assumed that two perceived surfaces are equiluminants when the
degree of activity in the luminance pathways produced by the surfaces is the same. In
psychophysics equiluminance is usually defined operationally: when under certain
circumstances perception of, e.g., the border between two different colored surface is
minimised the two surfaces are called equiluminants.13 Because of the inter-personal
differences of sensitivity to wavelengths even between normal subjects, two surfaces are
equiluminants relative to a subject, and the equiluminance of two surfaces must be
determined for subjects individually. Equiluminance between two chromatically different parts
of the visual field tend to produce perceptions of ‘problematic borders’, fading borders and a
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series of chromatic illusions. By mixing stabilized images to equiluminance, the likelihood that
the borders of the contours of the image fade are increased.
3.2. The experiment
There were 7 subjects in the experiment of Billock et al, the exact number of
observers participating in the experiment of Crane and Piantanida is not available.14 The
subjects were presented with a red and a green stripe on a black field, such that the red and
green stripes have a common border. In both experiments the red-green field was stabilized
with an eyetracker. This was done in order to provoke a filling-in process in which the
information from the non-stabilized parts of the image, i.e. the edges between the black field
and the red and green stripe, should be used. The idea is that the subjects perceive the
outer edges of the red and green stripes but not the common red-green edge. In the
experiments conducted by Billock et al. the two stripes were mixed to equiluminance for each
subject. Here is a list of the kinds of reports that were obtained in the two experiments:
(1) Homogenous mixture: Subjects report seeing a homogeneous color phenomenally
composed of red and green whose components are as clear and as compelling as the red
and blue components of a purple.15 (4 subjects out of 7)
(2) Gradient color: Subjects report seeing a gradient color that runs from red on one side to
green on the other with a large region in between that appears both red and green. (5
subjects out of 7)
(3) Special arrangements of the visual field: Subjects report seeing either (a) two color
stripes that seem to switch sides rapidly before fading out or regaining their places. (4
subjects out of 7) or they report seeing (b) the red and green stripes arranged horizontally
rather than vertically (1 subject out of 7)
(4) Blackouts: Subjects report that the visual field turns into black (like in the ganzfeld
phenomenon). (6 subjects out of 7)
(5) Transparency phenomenon: Subjects report that it looks as though the opponent
colors originate in two depth planes and as though they are seen one trough the other. (4
subjects out of 7)
(6) Dots: Subjects report that the visual field appears to be composed entirely of a regular
array of just resolvable red and green dots. (Number of subjects not available)
(7) Islands: Subjects report that the visual field appears as a number of islands of one color
on a background of the other color. (Number of subjects not available)
In almost each trial the subject reported more than one of the kinds of experiences
described in (1) to (7). In most trials where subjects reported having had experiences of the
kind (1) and (2), they also reported that these experiences were preceded by experiences of
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the kind described in (4) and (5). The hypothesis driving the experiments of Billock et al. is
that experiences such as those reported in (1) and (2) are more likely to occur if the two
stripes are equiluminant. This hypothesis was motivated by the findings of (Nerger,
Piantanida, & Larimer, 1993) who had shown that differences in luminance may lessen the
effects of filling in. Several trials increased the probability of reports like (1). Two subjects
reported independently after the experiment that “reddish-green and yellowish-blue colors
could now be imagined.” (Billock et al., 2001) p.2399
All but one of the seven subjects of Billock et al.’s study were expert psychophysicists,
including some researchers in vision. Crane and Piantanida participated as subjects in their
own experiment and so did two of the authors in Billock et al in their new version. Even
though the experimenters made efforts to ensure that the subjects had a large color
vocabulary, several subjects seem to have had difficulties in describing the phenomenon
they had experienced as is documented by the following two citations:
"Although most [of the subjects] reported that regardless of where they attended in
the field the color was simultaneously both red and green, some observers indicated
that although they were aware that what they were viewing was a color (that is, the
field was not achromatic), they were unable to name or describe the color. One of
these observers was an artist with a large color vocabulary." (Crane & Piantanida,
1983) p.1079
"Our subjects (like those in (Crane & Piantanida, 1983)) were tongue-tied in their
descriptions of these colors, using terms like “green with a red sheen” or “red with
green highlights.” (Billock et al., 2001)p.2398 [Here the authors are referring to
reports (2), (3), (5), (6), (7), above].
4. Current Interpretations of the Empirical Result
4.1. Taking the subjects reports at face value
To take the subject reports of Crane and Piantanida and Billock et al.’s studies at face
value is to take these reports as literally and accurately describing the experiences the
subjects were reporting. Subjects reporting percepts like (1) are thus taken to have had
experiences as of binary colors with a reddish and a greenish component in the case of
reddish-greens and with a bluish and a yellowish component in the case of yellowish-blues.
Here are a few at least prima facie reasons that can be advanced in favour of this
interpretation:
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(i)
The experiment of Crane and Piantanida has been repeated successfully by
Billock et al. and it has been modified in a way that increases the likelihood of
reports like (1) and (2).
(ii)
The only existing empirical theory which predicts the impossibility of novel colors,
standard opponence process theory, is controversial in its original unmodified
form and open to different interpretations that need not all imply the impossibility
of experiences of reddish greens.16 According to the models proposed by the
authors of the two experiments perception of novel colors is expected under some
special circumstances.
(iii)
Some of the subjects, including Piantanida and Billock, are vision scientists and
are expected to be experts in the use of color vocabulary. This is good reason to
take their reports at face value.
(iv)
The list of different reports given by the subjects supports the idea that the
subjects were trying to be precise in their description and to avoid ambiguities.
4.2. Scepticism about novel colors
This section discusses the possibility of not taking the subject reports at face value
and some reasons for doing so.
Crane and Piantanida’s findings were quite controversial at the time of their
publication.17 This was in part due to the fact that only some of Crane and Piantanida’s
subjects reported seeing novel colors. In the absence of other evidence, or a compelling
explanation of why only some of the subjects in the experiment reported having seen a
binary hue composed of red and green (or blue and yellow), it seems reasonable to be
careful about these reports. Another source of doubt is the reluctance of the subjects to
describe the colors as reddish-green.
Part of this reluctance may be explained by the
novelty of the experience and the fact that the subjects may have been prejudiced against
the possibility of novel colors. But the reluctance may also be explained by the quality of the
experiences itself, which some of the subjects described later to Larry Hardin as being dark
and muddy, adding that these two qualities make colors hard to judge.18
Some of the sceptical worries are answered in Billock et al.’s study. First, there is a
tentative explanation of why only some of the subjects of Crane and Piantanida’s study
reported seeing reddish-greens:
in order to see novel colors the stripes have to be
equiluminants and some training may be needed.19 Four out of seven of Billock et al.’s
subjects reported (1) and, according to Vince Billock20 “the colors we are talking about are
not muddy and the subjects have rich perceptual vocabularies. The only remaining reasons
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for having difficulties describing the effects are that the phenomena are novel and dynamic
(multistable).”
5. A further doubt about reddish greens (a speculation)
According to the realist view about phenomenal composition that we defend a person can
seriously judge that he or she has an experience of a hue that is phenomenally composed for
her at that moment in a particular way and yet thereby be wrong about the phenomenal
character of his or her own experience. For someone who accepts this view that explicitly
endorses fallibilism about phenomenal judgements it is quite natural to consider the
possibility that those subjects who described the color perceived in the laboratory as being
composed of red and green for them on this occasion were misdescribing their own
experience. In this section we briefly describe a way in which they might have gone wrong.
The possibility we consider is a highly speculative. But the speculation might illustrate the
following more general point: even in the apparently simple case of phenomenal composition
of colors it can be very difficult to find an adequate and unbiased phenomenological
description. The error theory we will describe is not meant to be a serious proposal of an
alternative interpretation of the empirical results. To be a serious proposal it would have to be
tested by further especially designed experiments.
According to the speculation we will now present subjects that described the hue they
perceived as being composed (for them on that occasion) of red and green confused what
we will call apparent simultaneous presence of red and green on a surface with phenomenal
composition of red and green. We have to explain the phenomenal difference that we have in
mind.
It will help to first remember that some subjects of the experiment described their
experiences as being of two layers, one green, the other red, one behind the other, “as if
looking through a green glass on a red surface”. According to this description the two
surfaces appeared to be located at different distances and the hues of the two layers did not
mix into one as they do in phenomenal composition. Now what would happen if the apparent
difference in location where to disappear, all other qualitative aspects remaining the same?
Is there some possible experience that is adequately described in this way: it is like an
experience of looking through a green glass on a red surface but the two surfaces do not
appear to be at different places, so that we could say equally well that the experience is like
looking through a red glass on a green surface (although both descriptions are in a way
inappropriate since they suggest an apparent difference in location). It is in fact possible to
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produce this kind of experience by a simple experiment with goggles with one red and one
green glass. When looking at a white surface with these goggles an experience of this kind
may occur: (a) it is like seeing a greenish surface and a reddish surface, (b) the colors of the
two surfaces do not mix into one as they do in phenomenal composition and (c) the two
surfaces are one in the sense that they appear to be located at the same place.21 If we
assume that there are possible color experiences that are appropriately described by (a) - (c)
and that do occur when confronted with red through one eye and green through the other at
the same time, then it is quite natural to speculate that those subjects who described their
experience as being an experience of phenomenal composition of red and green really had
an experience of this quite special kind. The speculation provides a plausible error theory
explaining what then would be a phenomenological misdescription: since there is no
information about difference in location phenomenally present it may well appear to be
appropriate to say that the apparent surface appears to be both reddish and greenish.
However, despite the fact that the two hue components are seen ‘at the same place’ they do
not mix into a new hue quality (if description (b) is correct). If this speculation is correct then
the experiences that have been misdescribed as experiences of reddish green require for the
formation of new phenomenal concepts for their appropriate phenomenological description.
They require the distinction between phenomenal composition of two hues and apparent
simultaneous presence of two hues on one and the same surface. According to this
distinction it is possible to see a surface as being both reddish and greenish without having
an experience of a color that is (for the subject on that occasion) phenomenally composed of
red and green.
6. The philosophical challenge
But let us assume now that the strongest interpretation of the experimental results is correct
and that some subjects really saw a new hue that is never experienced under normal
circumstances and that was phenomenally composed of red and green for them then. It
follows that red and green are not incompatible in the sense of the following definition:
Definition: The hues H1 and H2 are incompatible iff
(IC) It is impossible that a subject has an experience of a hue that is phenomenally
composed of H1 and H2 for him or her then.
On the basis of one's own experiences of red and green it is however tempting to believe that
red and green are incompatible in this sense. Phenomenological reflection on the particular
character of red and green seems to reveal that these two hues cannot possibly mix into a
new hue in any possible experience. Phenomenological reflection seems to support the
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particular modal claim about red and green at issue. However, according to the present
interpretation of the empirical results, we have to accept that the modal claim has been
shown to be false by empirical investigation. We thus seem to be forced to conclude that
phenomenological reflection is unreliable as a source of modal knowledge about
phenomenal structure. Given this consequence we have reason to doubt other modal claims
that are based on phenomenological reflection as well. We have reason to doubt, for
example, that violet is composed of red and blue (if the claim is interpreted in the way we
proposed).
In what follows we will argue that this doubt would be an overreaction. The possibility of
experiences of reddish greens or bluish yellows should not be taken to justify general
scepticism about phenomenologically based modal knowledge with respect to the structure
of color experience. To justify this claim we have to show that there is a relevant disanalogy
between the violet case and the reddish green case. We have to show that the best
justification available for the modal claim that no one can have an experience of violet
without thereby having an experience of a color that is then for that subject phenomenally
composed of red and green is different in structure and stronger than the best available
argument for the modal claim that no one can ever have an experience of a color that is for
that subject on that occasion phenomenally composed of red and green.
7. How to justify the modal claim about violet experiences
To see that the best justification for the claim we defend (modal claim about violet) is quite
different in structure from the best justification of the modal claim that is challenged by the
empirical results at issue (modal claim about reddish greens) we have to propose first a
reconstruction of the first justification. We have to give an answer to the following questions:
Why are we justified in believing that no subject can have an experience of violet without
thereby having an experience of a hue that is (for the subject on that occasion)
phenomenally composed of red and blue? What are the different steps involved in the
justification? What are the premises we need to accept if we take the claim to be true? What
are our reasons to accept these premises?
7.1. Phenomenal criteria of concept application
In preparation to our answer to these questions we have to say a few words about the
application of phenomenal concepts to one's own experiences. When learning the color
language we learn not only to apply color concepts to colored objects but also to apply color
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sensation words to types of sensations or experiences. These two conceptual capacities are
of course closely related. For the present purposes we will focus on the second capacity. A
subject who has acquired the concept of a violet experience has a number of capacities. The
subject will consider an experience as falling under the concept just in case it is a violet
experience (the concept of course has vague boundaries) and the subject will be able to
imagine violet experiences and the subject will be able to consider the possibility that other
subjects have this type of experience too. When somebody has learned to apply the concept
of violet experiences correctly to his or her own experiences then he or she has learned to
distinguish violet experiences from other types of experiences by their phenomenal
character. He or she has learned to distinguish experiences according to a certain
phenomenal criterion. In a sense the person then has learned to apply a certain criterion.
But to talk of a 'phenomenal criterion' may be risky in this context. If we say that a person
applies a particular phenomenal criterion in her use of the concept of violet sensations we
wish to say - simply - that she recognizes a certain phenomenal commonality (something all
and only violet experiences have in common) and that she applies the concept as a result of
her recognition of this commonality. We presuppose here that violet experiences do have
something in common and that what they have in common concerns the phenomenal
character. In some cases the subject who applies a certain phenomenal criterion in her use
of a phenomenal concept does not have any other concept that she could use to describe
the criterion that she thereby applies. If for example, a person should say what criterion she
applies when applying the concept "red experience" to her own experiences, then the person
would not be able to say anything informative about the criterion without again using the
concept of a red experience. The best she could probably say is that she calls an experience
of her own a red experience just in case it is an experience of a color with a strongly
prevailing red component. So at least the concept of a red component has to be used in the
description of the phenomenal criterion applied by a person who masters the concept of a
red experience. The same holds for the third person perspective. If A describes the
phenomenal criterion applied by B when using her concept of a red sensation, then A will
have to talk of a prevailing red component in the color experienced by B again. However, no
danger of any problematic circularity arises. There is no need to describe the phenomenal
criterion applied in applications of the concept of a red experience in any independent way.
In the violet case, however, we do have other phenomenal concepts that we can use to
describe the phenomenal criterion that we implicitly apply when using the phenomenal
concept of violet experiences. We can describe the criterion simply by saying that we call an
experience a violet experience just in case it is an experience of a color with the hue violet.
But we can also say the same in another way: we can say that we call an experience a violet
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experience just in case it is an experience of a color that has for the subject on that occasion
a red component and a blue component where none of the two prevails too much. (What
would be "too much" is of course again vague.) So in the case of violet we can describe the
phenomenal criterion we apply when using the concept of the type of experience at issue in
terms of phenomenal composition.
It should be noted that, according to the realist and fallibilist view we defend, we may be
wrong about the phenomenal criterion we actually apply. Strictly speaking we express only a
hypothesis about the phenomenal criterion we actually apply when we say that we call an
experience an experience of violet just in case the condition just mentioned about
phenomenal composition is satisfied. The hypothesis might be wrong. A person may be
convinced that the phenomenal criterion for the application of the concept of a green
experience can be described as follows: the experience is an experience of a color that is for
the subject at issue phenomenally composed of blue and yellow. Yet, green is a unique
hue.22 So this is a false description of the phenomenal criterion we actually apply. So
although we are in a sense directly aware of the phenomenal criterion that we apply we may
nonetheless be wrong about the criterion (we may misconceptualize the criterion). In the
present case the misconception of the phenomenal criterion is due to a false
phenomenological description of one's own color experiences. A person who believes that
the phenomenal criterion for green experiences is the one just mentioned will believe that
she appropriately describes her own green experiences as experiences of a binary color, a
color that appears (for her on these occasions) composed of blue and yellow.
How then can we rationally form a hypothesis about the phenomenal criterion that we
actually apply in the case of a given phenomenal concept of types of color experiences? Our
answer is that it is possible to rationally form a hypothesis of this kind on the basis of
phenomenological reflex ion on one's own color experiences. By carefully attending to the
subjective character of those experiences I learned to call violet, I am able to find out what
they have in common and to express what they have in common in terms of phenomenal
composition. Why is it allowed to base this general hypothesis on observations of my own
single case? The answer is, in our view: we are entitled to assume that we did learn to use
the concept of violet experiences appropriately in this sense: we learned to apply the same
phenomenal criterion that is applied by other people as well when they use their phenomenal
concept they express using the term "violet experience". Of course, here again, there is room
for a mistake. If I am pseudonormal then what I call violet experiences is what other people
call experiences of bluish green (or greenish blue). I then have not learned to use the term
"violet experiences" correctly and I then associate the wrong phenomenal concept with the
phenomenal term.23 Under normal circumstances however - or so we assume - we are
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justified in the belief that we express the same phenomenal concept when using the term
"violet experience" as other competent users of our language with normal color vision. This is
to say that we apply the same phenomenal criterion when using the phenomenal concept we
associate with the term as they do. But if we are entitled to believe that the phenomenal
criterion is the same, then we are justified to believe that a description of the phenomenal
criterion we actually apply in our own case is appropriate if and only if the description is also
appropriate as a description of the criterion applied by others when using the concept they
associate with the relevant term. Therefore we can arrive at justified claims about the
phenomenal criterion applied in uses of the concept of violet experiences in general by
carefully attending to our own single case.
7.2. Actual and counterfactual cases of color experiences
Until now we have been talking about the application of phenomenal concepts to actual color
experiences only. We have not yet been talking about possible color experiences of other
sentient beings in counterfactual circumstances. We have to turn to counterfactual cases
however since the claim we wish to justify is a modal claim about all possible violet
experiences. At this point it is important to see that phenomenal concepts are special in the
following respect: the criterion for their application to counterfactual cases is the same as the
criterion for their application to actual cases. If it is correct, for example, that a person who
masters the concept of violet experiences applies the concept to all and only those
experiences where the subject has an experience of a color that is phenomenally composed
of red and blue (with none of the two components prevailing too much), then an experience
in counterfactual circumstances counts as an experience of this particular type just in case it
fulfils this phenomenal criterion. For a subject in counterfactual circumstances to fall under
the concept of having a violet experience it is necessary and sufficient that it has an
experience that fulfils precisely that phenomenal criterion actually applied by people who
have the concept in the real world with respect to their own color experiences. The reason is
that to fall under a particular phenomenal type is to fulfil a particular phenomenal criterion.
There is nothing else that is essential for having a given phenomenal property. There is a
particular aspect of the phenomenal character that is necessary and sufficient for actual
experiences to fall under the type "violet experiences". If some being in counterfactual
circumstances or in some other part of this universe has an experience with this particular
phenomenal aspect then the experience is ipso facto an experience of violet. In other words:
It is only this particular aspect of the experience that is essential for being a violet
experience.24
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Note that what we just claimed for the case of phenomenal concepts is not generally true for
all concepts. In many cases, as has been pointed out in the literature about natural kind
terms, the criterion of application in the real world (the way we pick out what falls under the
concept in the real world) may not coincide with the criterion of application in our thoughts
about counterfactual circumstances. Many philosophers admit that we pick out the liquid
water in the actual world by properties of water that are not essential to water. In other
words: the properties that a liquid must have to fall under our concept of water in the real
world are properties that a liquid in counterfactual circumstances might lack although it is
appropriately considered as being water. The parallel claim is false for phenomenal
concepts: if a certain phenomenal criterion has to be fulfilled by an actual experience to fall
under our concept of a violet experience, then no experience in counterfactual circumstances
that fails to satisfy this criterion falls under the concept of a violet experience.25 It follows that
any claim about the phenomenal criterion we apply to actual experiences when using a
particular phenomenal concept is also true as a claim about the criterion for counterfactual
cases. Therefore the following conditional holds: If CR is the phenomenal criterion for
application of the phenomenal concept C to actual experiences then nothing in
counterfactual circumstances falls under C unless it fulfils CR. For the case of violet the
conditional reads as follows: If it is true that the phenomenal criterion for correct applications
of the concept of violet experiences is that the experience at issue is of a color that is for the
person at issue on the given occasion phenomenally composed of red and blue (where none
of the two components prevails too much), then no being in counterfactual circumstances
has an experience of violet unless it has an experience of a color that is for it on that
occasion phenomenally composed of red and blue. This is of course the result we wanted.
We have justified the step from a claim about a phenomenal criterion as it is applied in actual
cases to the modal claim at issue about all possible experiences.
7.3. Summary of the proposed reconstruction
In our thoughts we use phenomenal concepts to attribute phenomenal properties to other
people or to other sentient beings. We use the phenomenal concept of having a violet
experience to attribute the phenomenal property of having a violet experience. In many
cases we can use language to express what we think. We use the predicate "has a violet
experience" in order to attribute the property of having a violet experience under its
phenomenal conceptualization. This does not mean that a person who does not have the
phenomenal concept of a violet experience cannot use the corresponding phenomenal term
to attribute a certain phenomenal property. A blind person may lack the phenomenal concept
of a violet experience and yet use the term "violet experience" with the intention to ascribe a
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particular phenomenal property to another person. Yet, there is a close relationship between
the phenomenal concept of having violet experiences and the corresponding phenomenal
predicate "has a violet experience". We can describe the relation as follows: If a person
thinks that some X has a violet experience and thereby uses the phenomenal concept of
violet experiences, then that person would use the sentence "X has a violet experience"
correctly if she used it to express that thought. To have a name for this relation between
phenomenal concepts and phenomenal predicates we will say that the concept is associated
with the predicate and we will thereby presuppose something like the following definition:
Definition: A phenomenal concept C is the concept associated with the phenomenal
predicate PP just in case the following condition is fulfilled: If a person A has the thought that
X has the property P and conceptualizes the property P via the phenomenal concept C and if
A expresses this thought saying "X has P", then A uses PP correctly.
According to this definition what phenomenal concept is associated to a particular
phenomenal term depends on what concept is involved in a thought that can be correctly
expressed using the term. With this terminological preliminary in place we can reformulate
and summarize the argument developed in the two preceding sections.
The justification of the modal claim that no sentient being can have an experience of violet
without thereby having an experience of a color that is for it then phenomenally composed of
red and blue can now be formulated in the form of an argument. (Since phenomenological
descriptions of one's own experiences play a role we will formulate the argument in the first
person.)
Premise 1 (hypothesis about my own phenomenal criterion):
The phenomenal criterion for my application of my phenomenal concept to my own
experiences can be formulated as follows: I accept something as being a violet experience
just in case it is an experience of a color that is for me then phenomenally composed of red
and violet (where none of the two prevails too much).
Premise 1 expresses a phenomenological description. A person who accepts that premise
accepts a certain phenomenological description of all those experiences he or she subsumes
under the phenomenal concept of violet experiences.
Premise 2 (assumption of correct language use):
My phenomenal concept of having violet experiences is the concept associated with the
predicate "has violet experiences".
This premise is meant to imply:
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Consequence 1: My phenomenal criterion for the application of my phenomenal concept of
violet experiences coincides with the phenomenal criterion for the concept associated with
the term "has a violet experience".
Premise 1 and consequence 1 imply:
Consequence 2 (correct application of the corresponding term): An actual experience
falls under the phenomenal concept associated with the predicate "has a violet experience"
iff the subject at issue has an experience of a color that is phenomenally composed of red
and blue for it then (where none of the two components prevails too much).
Premise 3 (counterfactual extension of phenomenal concepts): In the case of
phenomenal concepts the phenomenal criterion of application to actual experiences
coincides with the phenomenal criterion of application to counterfactual cases.
Consequence 2 and premise 3 imply:
Consequence 3 (the modal claim formulated in terms of concept application): No
experience of a being in counterfactual circumstances falls under the phenomenal concept of
having violet experiences unless it has an experience of a color that is for it then
phenomenally composed of red and blue.
We arrived, almost, at the modal claim we wanted to justify. We still have to get rid of talk of
concept application since we wish to talk of the type of experience itself. To do this we simply
have to assume that what falls under the phenomenal concept of violet experiences in
counterfactual circumstances is a violet experience.
Premise 4 (link between concept application and the exemplification of the
corresponding property in counterfactual circumstances): A being (in counterfactual
circumstances) falls under the concept of having a violet experience iff it has a violet
experience.
We now can conclude (using premise 4 and consequence 3):
Consequence 5 (the modal claim about violet experiences): Necessarily, if a being has
an experience of violet it has an experience of a color that is for it then phenomenally
composed of red and blue.26
We normally are in an epistemic position where is justified to assume the first two premises.
Premise 3 is a general conceptual truth concerning phenomenal concepts and premise 4 is
trivial. So the modal claim at issue has been shown to be justified (for every person in a
normal epistemic situation). Of course this does not exclude the possibility of error. We
cannot be certain that our phenomenological description of our own experiences is correct
(we might be wrong about the phenomenal criterion we apply, premise 1 may be false).
Premise 2 might be false too. No singular person can exclude that he or she is a deviant
color perceiver and that her or she systematically misunderstands phenomenal terms for that
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reason. However, there normally is no good reason for this doubt. In the normal case it is
possible to form rationally justified belief about modal claims concerning phenomenal
composition in color experiences of a given type. A person can (a) form a hypothesis about
the relevant phenomenal criterion for her own application of the phenomenal concept of the
type of color experience at issue. He or she can then (b) assume that this criterion coincides
with the phenomenal criterion of application for the phenomenal concept associated with the
corresponding predicate and (c) conclude that this criterion coincides with the criterion of
application for that concept in counterfactual cases. Step (a) involves a phenomenological
analysis of one's own experiences of the relevant type, step (b) presupposes conformity of
one's own understanding of a phenomenal term with the understanding of competent
speakers of the language and (c) uses a conceptual fact about phenomenal concepts.27
8. How to justify the modal claim about reddish greens
Does the case of reddish greens undermine the modal claim about violet? The possibility of
experiencing reddish greens would undermine the modal claim we just defended if the best
justification for the intuitively plausible modal claim that it is impossible to experience a
reddish green were relevantly similar to the justification we gave for the modal claim about
violet. If that justification looks very much like the one we gave for the modal claim about
violet then (given the empirical results reported above) we have reason to doubt the
argument that led to the modal claim about violet as well. To see if this is the case we have
to find a justification for the modal thesis about reddish green that is plausibly the best
candidate for a rational reconstruction of the reasons we have for believing in that claim.
It may be appear as though we are able to judge that red and green cannot possibly combine
to a new hue just by attending to the particular quality of red and green. Given their intrinsic
quality (somebody might say) it is evident that they cannot be present in the sense of
phenomenal composition in the experience of one hue. If this is the way to justify our belief in
the modal claim at issue about reddish greens, then the way we arrive at the modal thesis is
quite direct. According to the present view about how the claim could be justified a person
who has the phenomenal concept of having red experiences and the phenomenal concept of
having green experiences and who understand the notion of phenomenal composition can
see (intuit) that there is no possible hue such that a person could have an experience of that
hue and thereby have an experience of a color that is phenomenally composed of red and
green. According to this proposal, the modal claim about reddish greens is justified by what
has been called rational intuition: understanding the notions involved suffices for the capacity
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to have the modal insight.28 Let us call this view about the best justification of the modal claim
about reddish green the rational intuition view (about the claim).
According to the rational intuition view the best justification of the modal claim about reddish
green is quite different in structure from the best justification of the modal claim about violet.
According to that view understanding the notions involved makes the modal claim compelling
or intuitively attractive. A person who understands the concepts involved cannot but intuit
that the modal claim is true. According to our reconstruction of the way the modal claim
about violet can be justified, the situation is more complicated and involves a number of
different steps. There are no analogous steps present in the justification of the modal claim
about reddish greens according to the rational intuition view. No premise about the
phenomenal criterion of application of phenomenal concepts plays any significant role. There
is thus no premise needed that would be analogous to the first premise of the above
argument. The first premise in that argument is the result of phenomenal reflection on
particular color experiences belonging to the kind in question. It is clear that the case for the
modal claim about violet cannot start with a phenomenological description of experiences of
the type we call green experiences or the type we call red experiences. That green cannot
combine in the way at issue with red is nothing that can be part of a phenomenological
description of a green experience. By carefully attending to violet experiences we are able to
discern a reddish component. If we discern the reddish component, then we have been able
to isolate (in reflection) a particular aspect of the phenomenal character of experiences of the
relevant kind. By contrast, the impossibility of green to combine with red is not an aspect of
the subjective quality of the experience of green in itself. Therefore, phenomenological
reflection in the strict sense of finding out what phenomenal aspect experiences of a
particular kind have in common is not the starting point for any possible justification of the
modal claim about reddish greens.
Let us turn to the second premise. A person who asserts the modal claim at issue wishes to
say something about red and green experiences. Red and green experiences are those
experiences that are attributed in thought using the phenomenal concepts associated with
the term "red experiences" and "green experiences". If a person has reason to doubt that he
or she understands the terms "red experiences" and "green experiences" correctly then she
cannot use her conceptually based intuition to judge the truth of the modal claim (that is of
course formulated using the linguistic terms "red experience" and "green experience").
Therefore, on the rational intuition view, a justification of the modal claim has to include an
assumption analogous to premise 2 in the above argument. So here we find a parallel. The
parallel, however, is a trivial one.
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In the argument for the modal claim about violet the conceptual claim about phenomenal
concepts, premise 3, plays a prominent role. There is no such step involved in the
justification of the modal claim about reddish greens if the rational intuition view is the one to
adopt. We do not, in that case, first form a hypothesis about phenomenal criteria of concept
application to actual cases and then generalize to counterfactual cases (using premise 3),
since there is no hypothesis about phenomenal application to actual cases involved in the
first place. Rather, according to the rational intuition view, we go on directly to a claim about
counterfactual cases by modal intuition based on concept understanding.
We conclude that - according to the rational intuition view and presupposing the above
justification concerning the violet case as the best justification available - there is no
structural similarity between the two justifications. The two justifications are fundamentally
different. Therefore, the empirical results that undermine the impossibility claim about reddish
greens cannot undermine the necessity claim about violet.
To arrive at this result we assumed, however, that the rational intuition view is the one to
accept. But there might be a better justification of the modal claim about reddish green that is
also more similar in structure to the argument given for the modal claim about violet. If this
were true, then the empirical results about reddish greens would undermine the necessity
claim about violet after all. How could a justification of this kind look like?
A justification of this kind might start with the observation that (a) by carefully attending to our
own color experiences we can find out that we never have an experience of a hue that is
phenomenally composed for us then of green and red and (b) that whenever we try to
imagine an experience of a hue that is phenomenally composed of red and green we do not
succeed in fulfilling that imaginative task. The first observation, however, is a bad starting
point. There simply is no rational way from the observation that we do not ever have an
experience of a color that is for us then phenomenally composed in a particular way to the
belief that necessarily no subject can ever have an experience of a color that is for him or her
then phenomenally composed in the way at issue. More to the point, no premise analogous
to premise 3 can help to get from the observation about actual cases to the claim about
counterfactual cases. Premise 3 can help to make that step only if we have a
phenomenological description of concrete actual cases as a starting point. But the
observation mentioned in (a) does not provide a phenomenological description of actual
cases. So maybe our incapacity mentioned in (b) is a better starting point. But how can we
rationally conclude from the mere fact that we are unable to imagine a reddish green to the
modal claim that it is impossible to experience a reddish green? Maybe somebody can come
up with a convincing justification of this step. If so, however, it certainly will not have the
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structure of the argument for the modal claim about violet. Again, no premise similar to
premise 3 can possibly be used in an argument defending the step from our incapacity of
imagination to the relevant impossibility claim. The reason is the same as before. Premise 3
can help if we can start with a phenomenological description of actual experiences that
belong to a particular kind. But the observed incapacity mentioned in (b) does not provide a
phenomenological description of actual cases.
Our main point here is not to attack the modal claim about reddish green or to show that it is
irrational to hold that claim. We rather would like to be neutral on this point for the moment.
What the discussion should show is this: there is a fundamental disanalogy between the best
way to justify the modal claim about violet and the best way to justify the modal claim about
reddish green. Therefore, it would be a mistake to think that the empirical results about
reddish greens can challenge the modal claim about violet (and other similar claims about
phenomenal composition).
9. Objections
First objection
Simplifying a bit we may say that the above argument implies the following claim: A person
who forms (on the basis of carefully attending to her own color experiences) the belief that all
her violet experiences are experiences of a color that is for him or her then phenomenally
composed of red and blue has reason to believe that nothing can count as a violet
experience unless it has that particular property. But now imagine the case of a person,
Rosa, who for some contingent reason never sees any yellowish red but only pure red or
bluish red. When Rosa carefully attends to her own color experiences she will observe that
all her red experiences have the following property: they are either an experience of a unique
hue or they contain a bluish component. Can she rationally conclude that all experiences of
red necessarily have that particular property? Intuitively it seems that she cannot and
obviously the conclusion would be false. But the case seems to be perfectly parallel to the
violet case. So something must have gone wrong.
Answering the first objection
The objection rests on a misunderstanding of the first step in the argument. To form a
hypothesis about a phenomenal criterion is not the same as the observation of something
that all experiences of a particular type have in common. Suppose that a person, we will call
her Violetta, never sees any violet except for a few rare occasions where she is presented
with violet stars of different shades painted on a white surface. Suppose somebody tries to
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teach the term "violet experience" to Violetta. There are two possibilities: either Violetta
understands the explanation and forms the phenomenal concept associated with the term
violet or she does not. If she does understand the explanation then she would apply that
concept to every violet experience. In this case, if somebody were to present an object to
Violetta that looks violet and circular, then Violetta would consider it to be one further case of
a violet experience. If this first possibility is realized, Violetta would be aware of the fact that
she herself actually never had (and might not ever have in the future) any violet experience
that is not at the same time an experience of something with the shape of a star. However,
Violetta would also be aware of the fact that the shape is irrelevant for the application of the
phenomenal concept that she has been taught. The example illustrates that we have to
distinguish - as said before - between the observation of a commonality between all
experiences of a particular type that somebody has ever had or has in his or her entire lifetime and the forming of a hypothesis about the adequate phenomenal criterion. If however,
Violetta did not understand the explanation, then she may have formed a different concept.
The phenomenal concept of the experience of something that looks both violet and starformed. In this case she would not be willing to apply her newly acquired concept to the
experience of a violet elephant.
Let us now turn to the case of Rosa. In Rosa's case we have to distinguish the same two
possibilities: (a) Rosa has the concept of a violet experience and believes correctly that this
concept is the one associated with the term "violet experience". (b) Rosa has the concept of
an experience of red or bluish red and she believes incorrectly that this is the concept
associated with the term "violet experience". If the possibility (a) is realized, then Rosa will
actually classify violet experiences according to the phenomenal criterion mentioned before.
She would subsume an experience of her own under her phenomenal concept of a violet
experience if and only if it is an experience of a color that is phenomenally composed of red
and blue (where none of the two components prevails too much). Rosa has the phenomenal
concept of a violet experience only if she would apply that concept in this way. This
possibility can be subdivided in two further possibilities:
(aa) When reflecting upon her own violet experiences Rosa is able to find out that the
criterion she applies when classifying them as violet experiences is the one mentioned
before. She then will accept premise 1 despite her special and slightly impoverished
experiential background. If this is the case under consideration, then Rosa poses no problem
for the argument. Her special situation will entail no epistemic mistake and she will rationally
arrive at the correct modal conclusion.
(ab)
When reflecting upon her own violet experiences Rosa will come up with a false
hypothesis about the phenomenal criterion that she actually applies. Although she would
classify slightly yellowish reds as experiences of red if she ever had this kind of color
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experience she is not aware of this fact. In this case Rosa will introduce a false premise. The
premise corresponding to premise 1 in the above argument in her corresponding argument
would be false. This possibility however provides no argument against the proposed
reconstruction. False premises may lead to false conclusions. Of course a person may
construct an argument of the above structure and yet arrive at a false conclusion if she
introduces at one step a false premise.
Let me no return to the possibility mentioned above under (b). Rosa then has not acquired
the concept of red experiences on the basis of her red experiences but another phenomenal
concept that is narrower (it only includes experiences of particular shades of red). In this
case Rosa may arrive at the wrong conclusion mentioned in the objection. But this will be
due to another mistake: she will believe, incorrectly, that her phenomenal concept at issue is
the concept associated with the term "red experiences". Again, Rosa's case poses no
problem. She arrives at a false conclusion although she uses a good type of argument for the
simple reason that she introduces at one point a false premise. (The premise corresponding
to premise 2 in her argument would be false).
Second objection
Despite the differences between the two justifications there is a common element that makes
them sufficiently similar for the empirical results about reddish green to undermine the modal
claim about violet as well. Let us assume that the rational intuition view is rejected and that
we are left with the imagination argument as the best argument for the modal claim about
reddish green. Then the common element is the role of imagination in both arguments.
Obviously in the second argument (for the impossibility claim concerning reddish green)
imagination plays a crucial role. From the fact that we cannot imagine an experience of a
color that is phenomenally composed of red and green we conclude that no experience of
this kind is possible. In the first argument, as it has been presented, no imaginative act
seems to be important at any point. A closer look upon the argument, however, reveals that
imagination does play an important role in the justification at issue. We see this if we have a
closer look at the way we arrive at premise 1. How can I find out that my phenomenal
criterion for applying my concept of a violet experience is appropriately described in the way
that has been proposed? It is not sufficient to consider actual cases of experiences that I had
in the past. I have to form an opinion about how I would react to imagined cases as well.
(This is what we learned from the answer to the first objection. Rosa can form an appropriate
hypothesis about the criterion she applies only by considering new cases that she never has
been confronted with.) So we do have to rely on our capacity to imagine color experiences.
To form a belief that we can state as premise 1, we have to be sure that (a) if we were
confronted with a color that is not phenomenally composed in the relevant way, than we
would not consider it as falling under the concept and that (b) if we were confronted with a
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color that is composed in the right way, then we would subsume it under the concept. To test
(a) and (b) by imagination we cannot do anything else but this: we try to imagine an
experience of a color that is phenomenally composed in the right way and that we would not
count as falling under the concept and we try to imagine an experience of a color that is
composed in the right way but that we would not consider as falling under the concept. If we
fail in both imaginative acts, then we accept premise 1. This is - it seems - the best and only
way to justify premise 1. But if so, then imagination and in particular the incapacity to imagine
an experience with certain properties, is crucial for the first argument just like it is crucial for
the second and so the analogy is re-established.
Answer to the second objection
We must admit that imagination plays a role in the justification of premise 1 in the way
described in the objection. However, this role of imagination is quite different from the role of
imagination in the justification of the modal claim about reddish green. In the case of
justifying premise 1 of the argument for the modal claim about violet imagination is necessary
to test one's own phenomenal criteria of concept application. If we do not succeed in
imagining a hue experience that fulfils a certain criterion but that we would not count as
falling under a particular concept and vice versa, then we have reason to believe that we
found the criterion that we actually apply. The test is not infallible of course. We might fail to
imagine a particular experience that would falsify our hypothesis about our own application
criterion associated with a given phenomenal concept, but still the imagination test is a
legitimate test of a given hypothesis about our own phenomenal application criterion.
Contrary to this, imagination is not used to test phenomenal application criteria in the
argument for the modal claim about reddish green. In this case we try to imagine an
experience that fulfils a particular phenomenological description (the description of being the
experience of a hue that is phenomenally composed of red and green). If we find ourselves
incapable to fulfil this imaginative act, then we take this to be an argument for the
impossibility of an experience that fulfils the description. So the role of imagination in the two
cases is radically different in two ways:
(a) In the first case we try to imagine a color that fulfills a certain phenomenological
description concerning phenomenal composition and if we succeed we go on to test whether
this would count as falling under the phenomenal concept at issue. We can test our
hypothesis about the phenomenal criterion of application only if we succeed in imagining an
experience that fulfils the relevant phenomenological description. Contrary to this, in the
second case, we try to imagine an experience that fulfils a particular phenomenal description
concerning its phenomenal composition and take our failure to do so as support for the
modal claim.
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(b) In the first case, the imagined experience is used to test our phenomenal application
criteria of a given phenomenal concept. This is clearly a legitimate test that is not in need of
any special additional argument. In the second case, the incapacity to imagine an experience
that fulfils a particular phenomenal description is taken to be an argument for the
impossibility of an experience of this kind. This is clearly a step that does need an additional
argument. While it is unproblematic to use imagined experiences to test one's own
application criteria it is highly problematic to take one's incapacity to imagine something as
an argument for its impossibility. No such step from our incapacity to imagine to a claim
about metaphysical impossibility is in the first argument concerning violet. We conclude that
imagination does play a role in both arguments but that the role is so different that the
possibility of experiences of reddish greens would not undermine the modal claim about
violet.
Third objection
The argument for the modal claim about violet is correct but the consequence depends on a
terminological (or conceptual) decision. We decide to call an experience a violet experience
just in case it is an experience of a color that is phenomenally composed of red and blue
(where none of the two components prevails too much). An experience has to fulfil this
condition in order to fall under the concept by stipulation. We could however just as well
stipulate that nothing falls under the concept of being an experience of green unless it is
either an experience of pure green or an experience of green with a slightly yellowish or
slightly bluish component. Given this stipulation, an experience with a reddish component
does not count as an experience of green. In this way we exclude the possibility of
experiencing reddish greens by stipulation. We could do the same for the concept of a red
experience. An experience with a greenish component would not count as a red experience
and so again - by stipulation - experiences of greenish red are excluded. We thus arrive at
the modal claim that it is impossible to have experiences of reddish green or greenish red but
we arrive at this conclusion by mere stipulation. It is clear that we cannot decide any
interesting substantial issue about what is essential for certain kinds of experiences merely
by stipulation. So the modal claim at issue really turns out to be quite uninteresting and it is
not open to any empirical rejection. If someone claims - like the subjects in the experiences
at issue - to have been able to see a reddish green or a greenish red, then we simply can
reply that he or she is misusing language and we can reply in this way simply because we
decided to use the concepts involved in that particular way. This reasoning about the reddish
green case has consequences for the modal claim about violet as well. What seems to be a
substantial claim about metaphysical necessity really is nothing but a trivial consequence of
our decision to use the concept violet experience in a particular way.
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Answer to the third objection
According to this objection both modal claims are the trivial result of our decision to use the
concepts involved in a particular way. Let us call this view the stipulative view (about the
modal claim under consideration). The stipulative view is however false for both cases. We
will first discuss the stipulative view about the impossibility claim concerning reddish greens.
According to the third objection we could take the following decision: If a person had an
experience of a color that is phenomenally composed for her then of red and green, then we
will neither count this experience as being an experience of a reddish green nor count this
experience as being an experience of greenish red. We simply decide that color experiences
do not count as experiences of red if they contain a greenish component and do not count as
green if they contain a reddish component. We thus arrive at the modal claim at issue in a
trivial way. There are two points to be made about this proposal (A) The question was
whether it is possible to have an experience that has both a red and a green component. We
cannot exclude this possibility by deciding that we would not call an experience of this
particular kind an experience of reddish green of greenish red. In formulating his stipulation
the proponent of the present objection uses the term “red” and the term “green” to refer to a
specific potential phenomenal component of a color as it is perceived by a subject. But once
the reference to these components is assumed as fixed we can ask whether or not it is
possible to have an experience of a color that contains for the person at the relevant moment
both a reddish and a greenish component. According to the modal claim the answer to this
question is “no”. The proposed stipulation however is silent about the answer to this
question. The proposed stipulation excludes that we call an experience of a color an
experience of reddish green or greenish red but it does not exclude that a perceived color
might be phenomenally composed of red and green. So, contrary to the above objection the
modal claim we are interested in no trivial consequence of the proposed stipulation. (b) A
second point to stress is that the proposed stipulation is unacceptable given the use of the
rest of our phenomenal terms. We call an experience an experience of a reddish blue just in
case it is an experience of a color that is phenomenally composed of red and blue (where the
blue component prevails). To decide that an experience that is in fact an experience of a
color that is for the subject on that occasion phenomenally composed of red and green (with
e.g. a prevailing green component) should not be called an experience of reddish green
would be a highly misleading deviation. – From a more abstract point of view we may say
that a person who finds the proposal plausible might not have seen that there are two
different uses of the term “red” in descriptions of experiences. We use the term “red” in “has
a red experience” to express the property of having an experience of a color that comprises
many different shades (from almost orange to almost violet). To have a red experience is to
have an experience of a color that has a sufficiently prevailing red component where a blue
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or a yellow component can be present as well. The second use of “red” in the context of the
description of experiences is its use to refer to a particular phenomenal component in a color
as it is perceived by a subject. Once the meaning of our color component talk is fixed (once
we know what specific potential components we refer to using the words “red” and “green”)
the modal question at issue can be formulated and its answer cannot be found by any
decision about how to use the broad concept of having an experience of red in the sense that
comprises a great range of color shade experiences. – We conclude that the stipulative view
about the impossibility claim concerning reddish greens is false.
The reconstruction we have proposed for the best justification of the necessity claim
concerning violet might invite the stipulative view about this modal thesis. After all the
argument uses assumptions about the use of the phenomenal concept of violet in two
places: in premises 1, where a claim about the phenomenal criterion of application is at issue
and in premise 3 where it is assumed that in the case of phenomenal concepts there is no
difference between the criterion of application to actual or to counterfactual cases. However,
the stipulative view misinterprets the status of premise 1. Premise 1 is not the result of an
arbitrary decision. It is not open to us to decide about the phenomenal criterion associated
with the use of the phenomenal concept of violet experiences. Rather, we already have the
phenomenal concept of violet experiences and then try to find a description of the
phenomenal criterion we actually apply by trying to become aware of and to conceptualize
the phenomenal aspect shared by those and only those experiences that we are (or would
be) ready to subsume under the concept. Also, the stipulative view misinterprets the way we
arrive at the phenomenal criterion for the application of the concept to counterfactual cases.
Here again we do not simply decide that we would not count an experience as being an
experience of violet unless it is an experience of a color that is phenomenally composed for
the subject at issue on the relevant occasion of red and blue. Rather, we are forced to accept
this constraint on the application of the concept to counterfactual cases if our
phenomenological hypothesis in premise 1 is correct. But premises 1 is a phenomenological
hypothesis that might be wrong. So we are not free to decide about how we apply the
concept to counterfactual cases. How we have to apply it to counterfactual cases depends
on how we do apply it to actual cases and the latter is already fixed. This dependence is of
course based on the conceptual insight expressed in premise 3. Here again, somebody
might see room for an arbitrary decision. Couldn’t we decide to use our phenomenal
concepts in a way that makes – contrary to premise 3 – other aspects of the experience
essential for having an experience of the relevant kind?
The answer is again no. Our
phenomenal concept of having violet experiences is a phenomenal concept and this implies
that nothing but the particular phenomenal ‘feel’ is relevant to for the categorization we make
using the concept. It is not up to us to decide what we consider as essential. In introducing a
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concept of “having a violet experience” where it is not the phenomenal criterion that is
relevant for the application to counterfactual cases but something else (say the way the
experience is caused or the way it is realized in the brain) would be to introduce a different
concept and thereby to change the topic.
10. Concluding Remarks
We have argued that the modal claim about reddish greens has been challenged by the
empirical results at issue but that the modal claim about violet has not been challenged.
Could there be other empirical results that could give us reason to reject the claim that no
subject can have an experience of violet without thereby having an experience of red and
blue? Could it be that somebody constructs an experiment tomorrow where under unusual
circumstances people seriously and correctly claim to have seen a violet that did look neither
reddish nor bluish to them then but e.g. looked like a unique hue or looked like a color
phenomenally composed of red and yellow? According to the view we have proposed an
empirical rejection of the modal claim about violet is not a priori excluded. We might be
wrong in our assumption about the phenomenal criterion we actually apply when using the
phenomenal
concept
of
violet
experiences.
Premise
1
is
open
to
empirical
counterarguments. However, if we all associate the same phenomenal concept with the term
“has a violet experience” and if the phenomenal criterion for applications of that concept is
the one we mentioned then the possibility of empirical rejection of the modal claim is
excluded. An empirical argument against the modal claim would have to be an argument
against one of the preconditions just mentioned.
These reflections may raise the issue about the epistemic status of modal claims about
phenomenal structure of color experiences. In the case of reddish greens, can we arrive at
the modal claim a priori? If the rational intuition view is correct, then the answer seems to be
“yes”. According to that view to have the relevant concepts is sufficient to rationally intuit the
modal claim. But note that the modal claim is nonetheless open to an empirical rejection.
Also, acquiring the concepts involved requires phenomenological reflection on one’s own
color experiences. Something similar applies to the modal claim about violet. Who has the
relevant concepts is in principle able to see the truth of premises 1. Premise 1 therefore
seems to be a claim that we can know in a sense a priori. However, the claim involves an
empirical thesis about the actual criteria of application of one’s own phenomenal concept that
is open to empirical falsification. On a closer look it might well turn out that
phenomenologically justified modal claims about phenomenal composition (like the one
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about violet) do not fit well into the traditional distinction between a priori and a posteriori
knowledge. But we have to leave these related epistemological issues to another occasion.
Reference List
1. Bealer, G. (2000). A theory of the a priori. Pacific Philosophical Quarterly, 81(1), 1-30.
2. Billock, V. A., Gleason, G. A., & Tsou, B. H. (2001). Perception of forbidden colors in retinally
stabilized equiluminant images: an indication of softwired cortical color opponency? J
Opt Soc Am A Opt Image Sci Vis, 18(10), 2398-403.
3. Billock, V. A., & Tsou, B. H. (2004). What do catastrophic visual binding failures look like?
Trends Neurosci, 27(2), 84-9.
4. Boynton, R. M., & Olson, C. X. (1990). Salience of chromatic basic color terms confirmed by
three measures. Vision Res, 30(9), 1311-7.
5. Cavanagh, P. (1991). Vision at Equiluminance. J. Kulikowski, V. Walsh, & I. J. Murray (Eds),
Limits of Vision, Vol. 5 of Vision and Visual Dysfunction (pp. 234-250). Boca Raton:
CRC Press.
6. Chalmers, D. J. (1999). Materialism and the metaphysics of modality. Philosophy and
Phenomenological Research. 59(2), 473-496.
7. Crane, H. D., & Piantanida, T. P. (1983). On Seeing Reddish Green and Yellowish Blue.
Science, 221(4615), 1078-1080.
8. Crane, H. D., & Steele, C. M. (1985). Generation-V dual-Purkinje-image eyetracker. Applied
Optics, 24(4), 527-537.
9. Dacey, D. M., & Packer, O. S. (2003). Colour coding in the primate retina: diverse cell types and
cone-specific circuitry. Curr Opin Neurobiol, 13(4), 421-7.
10. Gordon, J., Abramov, I., & Chan, H. (1994). Describing color appearance: hue and saturation
scaling. Percept Psychophys, 56(1), 27-41.
11. Hardin, C. L. (1984). Are 'scientific' objects coloured? Mind, 93, 491-500.
12. Hardin, C. L. (1993). Color for Philosophers. Indianapolis: Hackett.
13. Lennie, P. (2000). Color vision: putting it together. Curr Biol, 10(16), R589-91.
14. Macpherson, F. (2003). Novel colours and the content of experience. Pacific-PhilosophicalQuarterly. 84(1), 43-66.
15. McLaughlin, B. P. (2003). Colour, Consciousness, and Colour Consciousness. Q. Smith, & A.
Jokic (eds), Consciousness: new philosophical perspectives . Oxford: Clarendon Press.
16. Mizrahi, V. (2005). A New Objectivist Approach to Color. V. Mizrahi, & M. Nida-Rümelin
(editors), Color and Color Ontology, Special Issue of Dialectica.
17. Nerger, J. L., Piantanida, T. P., & Larimer, J. (1993). Color appearance of filled-in backgrounds
affects hue cancellation, but not detection thresholds. Vision Res, 33(2), 165-72.
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31
18. Nida-Rümelin, M. (1999). Pseudonormal Vision and Color Qualia. S. Hameroff, A. Kaszniak, &
D. Chalmers (Editors), Toward a Science of Consciousness III . Cambridge: MIT Press.
19. Nida-Rümelin, M. (2006). "über das Rot im Lila" . J. Steinbrenner (editor), Farben in Philosophie
und Wissenschaft . Frankfurt: Suhrkamp Taschenbuch Wissenschaft.
20. Nida-Rümelin, M., & Schnetzer, A. (2004). Unique Hues, Binary Hues and Phenomenal
Composition, presented at the Joint Conference of the European Society for Philosophy
and Psychology and the Americal Society of Philosophy and Psychology, Barcelona,
July 2004.
21. Ramachandran, V. S. (2001). Synaesthesia--a window into perception, thought and language.
Journal-of-Consciousness-Studies. 8(12), 3-34.
22. Ramachandran, V. S., & Hubbard, E. M. (2001). Psychophysical investigations into the neural
basis of synaesthesia. Proc R Soc Lond B Biol Sci, 268(1470), 979-83.
23. Schnetzer, A. (2005). The Greenness of Green: Brentano on the Question Whether Green is
Unique or Binary .
24. Sternheim, C. E., & Boynton, R. M. (1966). Uniqueness of perceived hues investigated with a
continuous judgmental technique. J Exp Psychol, 72(5), 770-6.
25. Thompson, E. (1992). Novel colours. Philosophical-Studies, 68(3), 321-349.
1
See Nida-Rümelin, 2005a and Schnetzer & Nida-Rümelin, 2005.
See (Hardin, 1984) p.492-493.
3 For more about this point see M. Nida-Rümelin, 2005a
4 The status of green in this respect has actually been an issue among philosophers and among
scientists as well. See e.g.
5 Note that the fact that green and red when mixed on a piece of paper may appear grey or brownish
is no objection. These cases are not cases of phenomenal compositions in the sense at issue. (NidaRümelin & Schnetzer, 2004).
6 (Crane & Piantanida, 1983)
7(Billock et al., 2001).
The perception of so-called ‘novel colors’ has also been reported by
synaesthetes. Color-blind subjects reported seeing synaesthetic ‘Martian colors’, normal subjects
have reported the perception of new colors. Fiona Macpherson (personal communication) has drawn
my attention to these reports. Cf. (Ramachandran & Hubbard, 2001); (Ramachandran, 2001)
8 Cf.(Thompson, 1992) and (Macpherson, 2003).
9 Cf. (Hardin, 1993)p.22.
10 For technical information cf. (Billock et al., 2001) p.2402. For the specific sort of eyetracker used in
the experiments cf.(Crane & Steele, 1985).
11 For interesting ‘do it yourself’ experiments involving the blind spot cf.
http://faculty.washington.edu/chudler/chvision.html
12 The complete story about the luminance pathway is of course more complicated. Cf. (Cavanagh,
1991) for a review on empirical work on the luminance pathway. Cf. (Billock & Tsou, 2004) for a
general account of the role of luminance in visual perception.
13 Cf. (Billock & Tsou, 2004) p.86.
14 In Crane and Piantanida’s study the only information available is that more than 12 subjects were
submitted to the stimulus.
15 For the subject reports see (Billock et al., 2001) pp. 2398-2399. We have put between parentheses
the number of subjects per percept. This information was available only for the study of Billock et al.
16 Cf. (Dacey & Packer, 2003) and (Lennie, 2000) for reviews on this subject.
17 As reported in (Billock et al., 2001) p.2398 and (Hardin, 1993) p.xxix.
18 In the second edition of Color for Philosophers p.xxix. Cf. also (McLaughlin, 2003) pp.113-114.
19 Apparently Crane and Piantanida knew also that the experiment worked better at equiluminance:
“By the way, when I called Hewitt Crane to tell him about our results, he told me that he and
Piantanida knew that the forbidden color effect worked better with equiluminant colors, but they never
2
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32
wrote a follow-up paper on the effect, so they had no venue to publish the fact in.” Vince Billock
(Private communication).
20 Private Communication.
21 This is a description of the experience made by one of the authors when using goggles of this
simple kind (MNR).
22 This claim is controversial. See (Sternheim & Boynton, 1966) ; (Boynton & Olson, 1990) for linguistic
studies showing that green is a primary hue and (Gordon, Abramov, & Chan, 1994) for a defence of
the methodology. For Brentano about this issue see (Nida-Rümelin & Schnetzer, 2004) (Schnetzer,
2005). For a non-realist position about phenomenal composition in general and about the issue of the
uniqueness of green see (Mizrahi, 2005).
23 I then misapply the term but do I also misapply the corresponding concept? The answer is a bit
tricky: I associate the wrong concept with the term but I do not misapply the phenomenal concept. For
the case of pseudonormality see (Nida-Rümelin, 1999), for the impossibility of misapplying
phenomenal concepts see (Nida-Rümelin, 2006).
24 These claims are closely related to the view about phenomenal concepts developed in (NidaRümelin, 2006).
25 The same intuitive idea is formulated by Kripke in his famous claim that the concept of pain fixes its
reference by way of a non-contingent reference fixer. According to one of the authors the idea is
however better captured in a framework that differs from Kripke's, see (Nida-Rümelin, 2006), last
section.
26 In this step we presuppose the following principle: Necessarily a being has property P1 if it has
property P2 iff in all counterfactual circumstances a being that has P2, also has P1.
27 The conceptual fact used here has been expressed in the two dimensional framework saying that
these concepts have identical primary and secondary intension see (Chalmers, 1999) for that they are
actuality-independent, see (Nida-Rümelin, 2006). Note that this is true only for the phenomenal
concepts and arguably false for the corresponding phenomenal terms see (Nida-Rümelin, 2006)
section *. This difference, however, does no harm to the above argument which is - for that reason formulated with respect to concept extension (and not with respect to extension of terms). The
argument would of course go through in a version that uses the extension of linguistic terms but it
would have to be formulated in a slightly different and a bit more complicated manner.
28 For a theory about rational intuition see e.g. (Bealer, 2000)
32