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COMMON SENSE ABOUT QUALITIESAND SENSES

Peter W. RossDepartment of PhilosophyCSU, Pomona3801 W. Temple Ave.Pomona, CA 91768Internet: [email protected]

mailto:[email protected]

COMMON SENSE ABOUT QUALITIESAND SENSES

What are the limits on scientific understanding of

perceptual states? One common way of addressing this question is

to consider the problem of the explanatory gap. Setting aside

the issue of the metaphysics of perceptual states, the problem is

whether there can be an explanation of the qualitative properties

of perceptual states in scientific terms. Some theorists, for

example, Ned Block (1995, pp. 380-382) claim that we should

characterize the qualitative properties of perceptual states as

qualia, that is, as mental properties of perceptual states which

are what it is like to be conscious of qualitative properties.

These theorists claim that qualia at least resist explanation in

scientific terms, and allow that the problem of the explanatory

gap might always be a serious epistemological problem.

Consequently, qualia mark at least a potential limit on

scientific understanding of perceptual states.

Much ingenuity has been devoted to arguments attempting to

show that perceptual states do or don't have qualia. Recently,

attempts along these lines take up the question of how we

distinguish sensory modalities.i For example, Block (1996, p.

28) has suggested that distinguishing sensory modalities requires

that perceptual states have qualia. Thus the issue of

2COMMON SENSE ABOUT QUALITIES AND SENSES

distinguishing the senses might offer the basis for a new

argument for qualia.

However, at another extreme, Brian Keeley (2002) argues that

our common-sense way of distinguishing the senses in terms of

qualitative properties is misguided, and offers a scientific

eliminativism about common-sense sensory modalities which avoids

appeal to qualitative properties altogether. This eliminativism

about the senses could make way for a non-qualitative

characterization of perceptual states which avoids the potential

limit imposed by qualia.ii Considering these opposing claims, we

can use the issue of how we distinguish the senses as a vantage

point from which to consider what limits, if any, circumscribe

scientific understanding of perceptual states.

I'll argue, contrary to Keeley, that common sense is correct

that qualitative properties are necessary for distinguishing

senses. But, contrary to Block, I'll argue that our common-sense

distinction doesn't show that perceptual states have qualia.

Thus, a non-qualitative characterization of perceptual states

isn't needed to avoid the potential limit on scientific

understanding imposed by qualia. For, as far as the issue of

distinguishing senses indicates, we need not characterize these

ii Keeley (2002, p. 27) allows that perceptual states might have qualia. Thus Keeley's view isn't presented as an attempt to avoid qualia as such. Instead it presented an attempt to avoid qualia in the provision of individuation conditions for senses, which, according to Keeley, is necessary for the concept of sense to be scientifically useful.


qualitative properties as being qualia.

In section I, I'll describe two general strategies for

distinguishing senses: a common-sense strategy which relies on

qualitative properties and an eliminativist one which denies that

qualitative properties are necessary for distinguishing senses.

Keeley's (2002) attempt to provide individually necessary and

jointly sufficient conditions stated in non-qualitative terms

provides an example of the eliminativist option which requires

serious consideration. In section II, however, I'll show Keeley

fails to demonstrate that qualitative properties are dispensible

in distinguishing senses. In section III, I'll offer a

minimalist account for distinguishing senses. According to this

account, qualitative properties are necessary for distinguishing

senses, but the prospects are poor for building on this single

necessary condition to establish independently necessary and

jointly sufficient conditions. However, I'll point out that we

can address the issue of the limits on a scientific understanding

of perceptual states while avoiding the problem of providing

full-fledged individuation conditions for senses. I'll then show

in section IV that we need not characterize the qualitative

properties that are necessary for distinguishing senses as being

qualia. Consequently, the necessity of qualitative properties in

distinguishing senses does not found a new argument for a

potential limit on scientific understanding of perceptual states.


I. Strategies for distinguishing senses

I'll first set the stage by describing what I take to be the

default view about distinguishing senses; I'll call this the core

common-sense view.

Core common-sense view: if a sense is distinct, it produces

perceptual states characterizable by a distinctive

qualitative property (such as color for vision).iii

This view doesn't attempt to give a full account of the

distinction among the senses. In its provision of a single

necessary condition, the core common-sense view says nothing

about whether there are additional necessary conditions and it

says nothing at all about sufficient conditions for

distinguishing senses. In section III, I'll argue that this

single necessary condition is in fact the only plausible

necessary or sufficient condition.

Furthermore, the core common-sense view abstracts from the

metaphysics of qualitative properties, holding that common sense

distinguishes among senses by way of distinctive qualitative

properties, whatever the metaphysics of these properties might be

(that is, whether they are, for example, properties of physical

objects or properties of mental states). This abstraction from

the metaphysics of qualitative properties reflects the fact that

common sense doesn't offer a claim about this metaphysics.

For example, common sense doesn't claim simply that colors


are mind-independent properties of objects. While it might be a

bit of common sense that the red of a fire engine is a mind-

independent property of the fire engine (although even this

doesn't offer a claim about metaphysics since it's not clear what

common sense makes of the concept of mind-independent property),

it's not clear at all what common sense has to say about the red

of an afterimage of the sun. Michael Tye's contention (2000, p.

147) that common sense claims that colors are mind-independent

properties is plausible largely because he focuses on the colors

of ordinary physical objects. However, if we consider a broader

range of colors--including afterimage colors, for example--common

sense offers no decision. Thus common sense offers no claim

about the metaphysics of colors tout court (which is not to say

there aren't theoretical claims about the metaphysics of colors

tout court, or that there isn't a theoretical justification for

the claim that colors tout court are in fact mind-independent

properties of objects).

Thus, the core common-sense view is incomplete in various

ways. Nevertheless, it is useful in that it serves to clarify

the crucial difference between a common-sense strategy for

distinguishing senses which relies on qualitative properties, and

an eliminativist strategy which claims that qualitative

properties are not necessary. Indeed, the core common-sense view

is precisely what eliminativism rejects.


Keeley (2002) proposes eliminativism about common-sense

sensory modalities in the spirit of Paul Churchland's

eliminativism about propositional attitudes. I take this spirit

to be, basically, that a common-sense classificatory scheme for

some aspect of mentality should be replaced by a significantly

different scientific classificatory scheme. Thus, Churchland,

allowing that there's mental representation, rejects the common-

sense division of mental representations into sentence-like

structures in favor of a scientific classificatory scheme.

Similarly, Keeley's target is a common-sense classificatory

scheme. Allowing that there are sensory modalities, Keeley

rejects the common-sense distinction among senses in terms of

qualitative properties and offers a significantly different

scientific classificatory scheme.iv

Keeley (2002, pp. 6-8) claims that we must make a move to

eliminativism in order to specify a scientifically useful concept

of sensory modality which neuroethologists and other perceptual

scientists can apply to non-human animals. To this end, he

proposes four criteria--which are intended to shun qualitative

properties--as being independently necessary and jointly

sufficient for distinguishing modalities:

(1) distinctive external physical conditions, particularly

distinctive stimuli--for example, electromagnetic radiation

for vision and pressure waves for hearing (a criterion which


Keeley labels physics);

(2) distinctive sense organs, including their connection

with the brain (labeled neurobiology);

(3) distinctive abilities "to discriminate behaviorally

between stimuli" (labeled behavior); and

(4) distinctive evolutionary or developmental importance of

a putative modality (labeled dedication).

To further support his eliminativism, Keeley also denies that the

following common-sense criteria are necessary:

(5) distinctive qualitative properties of objects (for

example, color for vision, flavor for taste, and so on), the

proper sensible criterion,v and

(6) distinctive introspectible mental qualitative properties

of perceptual states, the distinctive quale criterion.vi

I'll argue, however, that Keeley's attempt to avoid an

appeal to qualitative properties fails. I'll show that Keeley's

behavior criterion makes tacit appeal to qualitative properties

and that an appeal to qualitative properties need not be at odds

with science in any event, despite Keeley's claim that a

scientifically useful concept of modality must be shorn of

qualitative specification. To the contrary, Keeley

underestimates how effectively science, in particular

psychophysics, can shore up the core common-sense view.

II. A defense of the indispensibility of qualitative properties


A. The use of MDS in distinguishing senses

Indeed, psychophysics is the first place that a

scientifically informed supporter of the common-sense distinction

will look. As Austen Clark (1993, Ch. 5) points out,

psychophysicists employ the techniques of multidimensional

scaling (MDS) for scientific investigation of the sensory

modalities of non-human animals well as human beings.

MDS is a set of statistical techniques which can generate a

spatial representation of the relative qualitative similarities

among a range of qualitative properties such as colors, where

relative qualitative similarities are gauged in non-human animals

by techniques such as stimulus generalization tests. (Stimulus

generalization refers to a psychophysical effect in which the

strength of a conditioned response grades off as the stimulus

increasingly differs from the original conditioned stimulus.)

And in particular, given data for the relative qualitative

similarities among a range of properties, MDS generates

dimensions along which qualitative properties are ordered. Thus,

using MDS we can map out what is called a psychological quality

space for that range of qualitative properties.vii

The psychological quality space that's most commonly

discussed is the psychological color space with dimensions of

hue, saturation, and lightness. This quality space orders colors

with respect to relative qualitative similarity along these three

dimensions; for example, it represents that: orange is more

similar in hue to red than it is to green; that fire engine red

and pink are determinates of red which differ with respect to


saturation; and that pink and maroon are determinates of red

which differ with respect to lightness.

MDS allows us to use behavioral data from human beings or

non-human animals to address whether a candidate modality

perceives qualitative properties at all, and, if so, whether it

has a distinctive qualitative property. In particular, MDS

provides the following characterization of qualitative

properties: a determinable property D is a qualitative property

of perception (thus setting aside properties of states such as

pain) if and only if its determinates D1, D2,…Dn can be ordered

into a psychological quality space (that is, an N-dimensional

order in which the ordering is determined by relative

similarity--which can be tested in terms of stimulus

generalization) (Clark, 1993, p. 79, pp. 91-94, pp. 117-119).

Furthermore, MDS can help us tell whether a candidate modality

alone perceives a qualitative property by investigating whether

the qualitative property has a distinctive psychological quality

space.

Again color provides a useful example. MDS can help us find

out whether an animal uses a candidate modality to perceive a

range of colors, and whether the modality is distinctive in this

respect. First, MDS can help us determine whether an animal

perceives a qualitative property with a psychological space akin

to the human color space (where by "akin" I mean to include

psychological spaces with greater or fewer dimensions than the

human color space, but which nevertheless overlap it--such as a

one-dimensional grey-scale space).


Then, if this psychophysical investigation indicates that

the candidate modality perceives a qualitative property with a

kindred psychological space, and this indication is supported by

findings from other sciences such as physiology and genetics, we

can consider whether the animal perceives a range of colors.

(For the relevance of evidence from physiology and genetics, see

C. L. Hardin's 1993, pp. 145-154; Evan Thompson's 1995, Ch. 4;

and Peter Bradley and Michael Tye's 2001, pp. 471-475. These

authors also stress the challenge of attributing color vision to

other species, considering our incomplete evidence in these

sciences. Even so, they all claim that such attributions are

empirically testable given more evidence.)

If this further investigation finds that the animal

perceives a range of colors, MDS--along with simpler

psychophysical techniques--can help us find out whether the

candidate modality alone perceives color.

Furthermore, MDS makes precise what is meant by "a range of

colors" so that we can use this concept to support the claim that

color is necessary to distinguish vision from other modalities.

A range of colors is a range of properties such that: a property

is a member of the range if and only if there is a qualitative

resemblance route through a color space from it to any other

property in the range; a qualitative resemblance route is a span

of qualitative properties which is continuous in that points

along the span which are sufficiently close are indiscriminable,

even though points farther apart are discriminable. So, for

example, there is a qualitative resemblance route from red (or


magenta) to any other color (determinable or determinate), but

there is no such route from red to C-sharp.

The first clue to difficulties with Keeley's eliminativism

is provided by his misleading label for criterion (5), the so-

called behavior criterion. He discusses this criterion in terms

of the use of MDS by psychophysicists. But in this case, this

criterion involves not simply behavior but instead the

dispositional relation between stimuli, sensory response, and

behavior which is the focus of psychophysics. (In fact,

considering his labels for the first two criteria, Keeley should

have called the third psychophysics.)

By labeling this criterion "behavior," though, Keeley

misleadingly suggests that qualitative properties have not

entered the picture. But they have, since psychophysics in

general, and the use of MDS to generate psychological quality

spaces in particular, does not merely study behavior, but rather

uses behavioral evidence to study qualitatively characterized

sensory responses to stimuli.

1. A methodological worry

Keeley's motivation for subsuming psychophysics under

behavior is methodological.viii He's interested in a concept of

sensory modality which applies to non-human animals. Since it's

a tricky question what qualitative properties other animals

experience, it might seem methodologically best to simply appeal

to behavior.

This methodological worry isn't compelling, however. The

best explanation of other people's qualitative similarity


classifications is that they have sensory modalities which can be

characterized in terms of qualitative properties (either

qualitative properties of physical objects, or of mental states,

or of both). It's not clear why this consideration shouldn't

apply to at least many kinds of animals as well (where relative

qualitative similarity classifications are gauged by such methods

as stimulus generalization tests)--and particularly if the

inference is also supported by findings from other sciences such

as physiology and genetics.

The deepest problem with Keeley's eliminativist proposal is

that by subsuming psychophysics under behavior, he artificially

separates the behavior criterion from the proper sensible and

distinctive quale criteria, that is, from the criteria that

involve qualitative properties. For if psychophysics can be used

to support the claim that qualitative properties are necessary

for distinguishing senses, then psychophysics shows that it's

false that a scientifically useful concept of sensory modality

must be eliminativist.

2. A mismatch between psychophysics and common sense?

In response, Keeley argues that, as it turns out,

psychophysics can't be used to support the necessity of

qualitative properties in distinguishing senses. Keeley contends

that MDS's differentiation of modalities, by differentiating too

many, would badly mismatch our common-sense differentiation:

…not only can you not get from red to C-sharp…you also

cannot get from red to 'moving left to right across the

visual field' (or however motion sensations ought to be


described), nor from C-sharp to 'darn that's as loud as a

747 engine from ten feet away' (or however auditory

intensity sensations ought to be described). Lacking the

appropriate matching relationships, there is no reason to

class the "color" and "motion" submodalities of vision as

both being submodalities of vision.…Such an account fails to

provide the resources for grouping together as "the same

modality" sensory qualities that we would intuitively group

together. (2002, p. 16; emphasis in original).

Keeley's aim is to show that if psychophysics meshes badly with

common sense, there's little that psychophysics can do to support

our common-sense distinction. Thus, a scientific concept of

sense replaces rather than supports the common-sense concept.

And, according to Keeley, since the lack of a qualitative

resemblance route cannot plausibly be necessary and sufficient

for distinguishing sensory modalities, psychophysics does in fact

mesh badly with common sense.

Yet, while Keeley is right that the lack of a qualitative

resemblance route cannot plausibly be necessary and sufficient

for distinguishing senses, this isn't how we should try to mesh

psychophysics and common sense. The core common-sense view is

that a qualitative property distinctive of a modality is merely

necessary for distinguishing modalities. Accordingly, so long as

psychophysics can be used to characterize such distinctive

qualitative properties, science supports rather than replaces

common sense.

Keeley's first example--that we cannot get from red to


'moving left to right across the visual field'--overlooks the

fact that we need not think that every distinction that MDS

allows us to draw is sufficient for differentiating modalities.

Instead, a qualitative property distinctive of a modality is

necessary. In this case, the relevance of MDS is in

characterizing qualitative properties such as color which are

distinctive to a modality, as opposed to spatial properties which

are not.ix

The second example--we cannot get from C-sharp to 'darn

that's as loud as a 747 engine from ten feet away'--does not take

seriously how MDS maps a quality space for sound. The dimensions

of this space include pitch and loudness; as well, since

different pitch-loudness pairs can combine into chords, auditory

quality space can include a number of pitch-loudness pairs up to

a maximum complexity beyond which the addition of pitch-loudness

pairs produces no discriminable difference (Clark, 1993, pp. 134-

138). So, the quality space for sound in fact would provide a

qualitative similarity route from (some particular loudness) of

C-sharp to the pitch-loudness pairs characterizing some

particular complex sound produced by a 747 engine.

Against Clark's general strategy of using psychophysics to

distinguish modalities, Keeley claims it "…attributes the wrong

modalities to the wrong organisms.…[H]umans are easily capable of

discriminating fully charged nine-volt batteries from 'dead'

ones, simply by sticking them to the tongue" (2002, p. 16).

Here, Keeley's claim is that if the ability to discriminate

electrical potency were necessary and sufficient for having an


electrical modality, then the mistaken conclusion drawn from

psychophysical data would be that "…humans would have an

electrical modality!" (2002, p. 16).

But, again, Keeley doesn't consider that the relevance of

psychophysics is with regard to characterizing a qualitative

property which is distinctive of a modality. It might be that we

identify battery potency with our tongues on the basis of a

qualitative property (or a combination of qualitative properties)

distinctive of familiar senses (such as touch, or a combination

of taste and touch); if so, the conclusion that we have an

electrical modality would not be plausible. If, however, MDS

were to indicate that we identify battery potency on the basis of

a qualitative property not perceived by familiar senses and which

thus has its own psychological quality space, then the claim that

we have an electrical modality would at least become worthy of

further investigation. While the indication of a distinctive

qualitative property might not provide sufficient evidence for

attributing an electrical modality (for it could be an additional

distinctive qualitative property perceived by touch, for example)

nevertheless this indication is quite plausibly necessary

evidence.

Thus, when considered in the right way, the psychophysical

evidence does support common sense, despite Keeley's claims to

the contrary. He claims that qualitative properties of objects

play no role in a useful scientific concept of sensory modality.

At the same time, he claims that the behavior criterion is

necessary for distinguishing senses. My argument has been that


we can strike down the artificial separation of the behavior

criterion from the criteria that involve qualitative properties,

and use MDS to support a necessary role for distinctive

qualitative properties.

It is true that scientists and philosophers are hesitant to

attribute conscious qualitative states to other species, but this

is typically in recognition of the inadequacies of our current

grasp of consciousness. It may seem that these inadequacies

enforce a de facto eliminativism. However, a de facto

eliminativism doesn't provide reason enough for Keeley's in-

principle eliminativism. And in section IV, I'll argue that

there's no reason to accept even de facto eliminativism.

However, Keeley follows up these considerations regarding

psychophysics with independent arguments against the necessity of

each of the proper sensible and distinctive quale criteria.

B. Proper sensibles

The argument against the necessity of the proper sensible

criterion is borrowed from Paul Grice's "Some Remarks about the

Senses" (1962) and as Keeley deploys it, the argument amounts to

the point that proper sensibles help distinguish sensory

modalities only because qualia distinguish proper sensibles.

Consequently, Keeley claims, "…the cogency of [the proper

sensible criterion] rests on the foundation provided by [the

distinctive quale criterion]" (2002, p. 22).

This reliance on Grice's argument is odd, however, because

Keeley does not even consider what is by now an obvious response,

namely that provided by intentionalism about the qualitative


aspect of sensory experience.x According to intentionalism, this

qualitative aspect is characterized in terms of its

representation of physical qualitative properties of objects.

Thus, the proponent of intentionalism claims, contrary to Grice,

that the introspectible qualitative properties of the distinctive

quale criterion just are represented physical properties of

objects of the sort referred to in the proper sensible

criterion.xi In this case, the proper sensible criterion

provides the foundation, and we can dispense with the distinctive

quale criterion.

C. Modalities without qualities?

In section IV, I'll show that Grice's argument for qualia

can be countered.xii However, in his final attempt to finish off

the need for qualitative properties in distinguishing senses,

Keeley presents an additional objection, which, although it

targets the necessity of the distinctive quale criterion, could

easily be modified to target the necessity of the proper sensible

criterion as well; indeed, its target is best thought of as the

core common-sense view.

There could be, Keeley contends, sensory modalities which

produce states that can't be characterized in terms of

qualitative properties at all,xiii taking as an example the

xii

? See [author's paper] for an intentionalist response to Grice's argument. In section IV, my response appeals to mental qualitative properties, and so is not intentionalist; however, I do not characterize mental qualitative properties as qualia, and so still side with intentionalism against qualia.


possibility that human beings have a vomeronasal system which

perceives pheromones. The upshot is that qualitative properties

are not necessary for distinguishing sensory modalities, and the

common-sense concept of sensory modality goes by the wayside.

This argument, more than Keeley's other arguments, vividly

captures the difference between the common-sense and

eliminativist strategies. Since Keeley's necessary and

sufficient conditions don't seem to eliminate the human senses

of, for example, vision and hearing (and don't seem to be

intended to do so), his eliminativism might appear to be an idle

view--an eliminativism about common-sense modalities without

elimination. Yet with the argument for modalities without

qualities, it becomes clear that the main result of rejecting

qualitative properties would be to expand the number of

modalities, even while recognizing at least some familiar ones in

somewhat unfamiliar terms. In addition, it might seem that this

argument, as straightforward as it is, avoids tendentious

assumptions about the proper use of psychophysics in supporting

common sense.

Nevertheless, I'll show that this appearance is misleading.

Take the possibility of a human vomeronasal system. If human

beings have such a system, then either it produces states that

can be ordered into a psychological quality space or it doesn't.

It's common ground that for something to be a sensory modality,

it must produce perceptual states. Furthermore, it's

uncontroversial that perceptual states are a species of mental

state. But if states of the vomeronasal system can't be ordered


into a psychological quality space, Keeley's contention is

vulnerable to the objection that they are not mental states at

all but rather non-mental physiological states, and consequently

the vomeronasal system isn't a sensory modality. Keeley notes "…

the vomeronasal sense seems akin to an olfactory version of

blindsight" (2002, p. 25). (Blindsight patients have a scotoma--

and so a lack of consciousness--in a portion of the visual field,

but nevertheless can make guesses about what's contained in that

portion of the visual field with an accuracy above chance.)

Although the comparison with blindsight suggests that these

states are mental, this comparison is misleading. Though it is

uncontroversial that visual states are mental, the worry remains

that, if states of the vomeronasal system have no quality space,

they are not mental but rather are merely physiological.

However, if there is a psychological quality space for

pheromones (involving a qualitative resemblance route along at

least one dimension), then the vomeronasal system produces

qualitative states.

The point of contention is the first horn of this dilemma,

since the interesting question is whether a human vomeronasal

system could be a modality without qualities. Considering

Keeley's view, an obvious objection to the first horn of this

dilemma is that it rests on question begging assumptions. In

particular it assumes that perceptual states are a species of

mental state, and that what distinguishes perceptual states from

non-mental states are qualitative properties.

Again, it is uncontroversial that perceptual states are


mental. There are robotic sensing systems, but to the degree

that robotic systems perceive, they have mental faculties.

Indeed, such robotic systems have a form of non-biological

mentality. Moreover, Keeley doesn't dispute this assumption.

The controversial assumption is that what distinguishes

perceptual states from non-mental states are qualitative

properties. But, presumably, there is some way of distinguishing

perceptual states from non-mental physiological states.

Drawing the distinction between perceptual states and non-

mental states in terms of qualitative properties is defensible on

the following grounds. First, if the states of a physiological

system can be ordered into a psychological quality space, they

are mental. David Hilbert (1992, p. 357) notes that some

invertebrates' abilities to discriminate behaviorally among

different color stimuli amount to color tropisms, and do not

indicate that these creatures have perceptual states. Hilbert

offers the following example: consider an invertebrate with

separate response mechanisms which are sensitive to wavelength,

so that due to one mechanism it would move toward red light

(predominantly long wavelength light) but due to the other it

would move away from blue light (predominantly short wavelength

light). The creature would discriminate behaviorally among

different color stimuli, but this wouldn't show that it has

perceptual states of (chromatic) color. Rather, in order to

perceive color, "[t]he information acquired through the different

photo-receptor mechanisms must interact somehow" (p. 357).

Hilbert continues that one indicator of having met this


additional necessary condition "…would be the ability to classify

stimuli as more or less similar on a dimension different from

brightness" (p. 357).

Furthermore, if we describe the biological function of

(chromatic) color vision in ecological terms--for example, to

promote object detection against a background (see J. D. Mollon,

1989 for a description of this sort)--then the ability to

classify stimuli in terms of relative qualitative similarity is

plausibly sufficient. For considered from the standpoint of

ecology, the function of color vision is fundamentally to

identify objects (or creatures) and their states (of ripeness or

emotion) (see Thompson, 1995, chs. 4-5, and Gary Hatfield, 1992

for arguments for the ecological approach to the function of

color vision). From this standpoint, this function is so

directly served by the ability to make qualitative similarity

classifications--for example, the ability to easily differentiate

contrasting pairs, for instance, red and green, and yellow and

blue--that this ability is plausibly sufficient for having

(chromatic) color vision. So it's plausible that a state's being

characterizable in terms of qualitative properties is sufficient

for its being mental; no non-mental states are characterizable in

terms of qualitative properties.

Second, if the states of a physiological system are

perceptual, they can be ordered into a psychological quality

space. Perceptual states are typically characterized in terms of

their causal roles as well as in terms of qualitative properties.

So, for example, perceptual states are characterized in terms of


leading to the production of perceptual beliefs, and other

beliefs and other intentional states. Yet, if a state not

characterizable in terms of qualitative properties leads to the

production of, for example, perceptual beliefs, we are hesitant

to call it a perceptual state. And this is reasonable given that

it would seem to amount to a power of divination (for a similar

claim, see Grice 1962, p. 248).

However, blindsight patients, who are not conscious of

qualitative properties within blind regions of their visual

fields, give no credence to their guesses about what's contained

within these regions. Yet we do attribute a form of sight to

these patients with respect to their unconscious regions, despite

the lack of credence. But it's plausible that they have sight in

these regions only because they can accurately discriminate, for

example, shapes, patterns, and locations, which (in vision)

require discrimination of (chromatic or non-chromatic) color

(Holt, 2002, pp. 20). In other words, if patients were not able

to accurately discriminate the qualitative properties of stimuli,

and thus were not able to accurately discriminate shapes and so

on, there would be no question of attributing sight at all. So a

state's being characterizable in terms of qualitative properties

is necessary for its being perceptual; no perceptual states are

not characterizable in terms of qualitative properties. Taking

this point together with the point that no non-mental states are

characterizable in terms of qualitative properties, qualitative

properties distinguish perceptual states and non-mental states.

Furthermore, in the context of considering our vomeronasal


states, Keeley merely asserts that they could be perceptual

states not characterizable by qualitative properties. But for

this assertion to be plausible, he must address how we

distinguish perceptual states from non-mental physiological

states in a way that counts vomeronasal states as perceptual, and

offer an alternative which is at least as defensible.

Taking a broader perspective, Keeley's contention that a

scientifically useful concept of modality avoids qualitative

properties has the effect of drawing too sharp of a distinction

between common-sense and scientific concepts. These concepts

might diverge at points, and where they diverge it can be that

common sense goes wrong in ways that science can identify and

correct. For example, perhaps there is a human vomeronasal

modality. If it is a common-sense assumption that there isn't

one, then psychophysics can provide reasons to think that this

assumption is false.xiv Nevertheless, science supports the common

sense view that qualitative properties are necessary for

distinguishing senses. So there are some points of agreement as

well, and the distinction between scientific and common-sense

concepts of sensory modality is much blurrier than Keeley

suggests. Agreement with Keeley's optimism about having a

scientifically useful concept of sensory modality needn't bring

eliminativism.

III. A minimalist account

My positive account of sensory modalities ventures only as

far as the core common-sense view, that is: if a sense is


distinct, it produces perceptual states characterizable by a

distinctive qualitative property. I'll argue that the core

common-sense view is correct, but that the prospects are poor for

building on it to establish independently necessary and jointly

sufficient conditions for distinguishing senses. Yet all is not

lost; I'll point out that a full account of individuation

conditions is unnecessary for addressing the problem of the

limits on a scientific understanding of perceptual states.

My response to Keeley's modalities without qualities

argument provides some support to think that the core common-

sense view is correct. For according to that response, senses

must produce states characterizable in qualitative terms (to be

distinguishable from non-mental physiological capacities). But

the core common-sense view claims more than this: it claims that

distinct senses must produce states characterizable by

distinctive qualitative properties.

Necessary conditions for distinguishing senses are

conditions where it's not possible for distinct senses to violate

the condition. For example: if having distinct physical stimuli

is a necessary condition, then it's not possible for distinct

senses to violate that condition (and have the same stimulus).

Another example: the core common-sense view claims that it's not

possible for distinct senses to perceive the same ranges of

qualitative properties (that is, the same qualitative

determinables).

The core common-sense view presents a plausible necessary

condition. Consider a modification of a thought experiment from


Grice's (1962).xv Martians land on Earth. Oddly, they have two

sets of what look like human eyes. These sets of eyes are

identical in various respects: they are sensitive to the same

physical stimulus, and perceive the same set of properties of

objects (and, in fact, they function just like human eyes in

these ways as well). Let's assume that the sensory capacities

conveyed by these sets of eyes have the same evolutionary or

developmental importance as well. It seems that the two sets of

eyes are organs of the same sense.

Now let's consider another scenario where we hold constant

that two Martian sense organs perceive the same set of

qualitative properties, but allow that these sense organs differ,

as do the physical stimuli that these organs sense and the

evolutionary importance of the sensory capacities of these

different organs. Does it makes sense to distinguish these

senses on the basis of a combination of distinctive physical

stimulus, distinctive sensory organ, and distinctive evolutionary

importance, even while they perceive the same ranges of

qualitative properties? Or is perceiving the same ranges of

qualitative properties sufficient for being the same sense (the

contrapositive of the claim that perceiving different ranges of

qualitative properties is necessary for distinguishing senses)?

Richard Gray (in press) offers an example relevant to this

question: imagine a creature that perceives radiant heat by way

of two infra-red sensitive pits located between its nose and

eyes, and kinetic heat by contact with its body (excluding the

infra-red sensitive pits). Furthermore, its capacities to sense


radiant and kinetic heat (different kinds of energy from the

standpoint of physics and so different physical stimuli) have

different evolutionary importance (since the pits have evolved to

detect prey). Nevertheless, if psychophysicists were to show

that the creature's infra-red detecting states could be ordered

in a way that best fit the psychological quality space for

temperture, it would be plausible that in the cases of both

radiant and kinetic heat the creature uses differently evolved

organs of a single sense, touch, to perceive temperature.

However, if, instead, psychophysicists were to show that the

creature's infra-red detecting states could be ordered in a way

that best fit the psychological quality space for (perhaps the

black-white dimension of) color, it would be plausible that the

creature uses differently evolved organs of a single sense,

vision, to perceive different parts of the electromagnetic

spectrum. Either way, what's sufficient for being the same sense

is the range of qualitative properties perceived--temperature or

color. Thus it's plausible that perceiving the same ranges of

qualitative properties is sufficient for being the same sense;

consequently, it's plausible that perceiving different ranges of

qualitative properties is necessary for distinguishing senses.

The creature that Gray describes is in fact the pit viper.

As Gray points out, neuroethologists, distinguish the pit viper's

pits and eyes as organs of different senses, and he conjectures

that this is largely because these organs are used independently

and have different evolutionary importance. However, the

hypothesized psychophysical evidence is not available. My claim


is that if the hypothesized psychophysical evidence we to become

available, neuroethologists would, or at least would have good

reason to, reclassify the pit viper's senses.

Moreover, this claim is bourne out by considerations that

show that classifications of sense organs are derivative of

qualitative properties that they are used to sense. In fact,

while the core common-sense view presents a plausible necessary

condition, there is no other; as it turns out, proposals of

additional independently necessary conditions are unpromising.

Take physical stimulus. It seems we should characterize

physical stimulus in terms of physics. But in that case, sound

waves are a kind of pressure wave that is on the same spectrum as

vibrations that can be felt. But then if physical stimulus is

independently necessary, hearing and touch are not distinct

senses because they have the same physical stimulus. But, I take

it, that's not plausible.

A way of getting around this problem is to characterize

physical stimuli in terms of qualitative properties--for example,

to distinguish a physical stimulus as sound waves because it is

in a portion of a spectrum of pressure waves that can be heard.

But then qualitative properties are doing all the work, and

adding the stimulus condition as independently necessary is

superfluous.

The addition of either sense organ or evolutionary

importance as an independently necessary condition is similarly

vulnerable to the charge of being derivative of qualitative

properties. For example, if the core common-sense view is right,


we can characterize sense organs in terms of the distinctive

qualitative properties of the states they produce. But then

distinguishing sensory organs according to modality becomes

derivative of qualitative properties. For example, if antennae

are used to sense texture, they are tactual organs; if they are

used to sense sounds, they are auditory organs. Again,

distinctive qualitative properties are doing all the work, and

adding the sense organ condition is superfluous.

So it seems that it's at least difficult to get a proposal

of multiple independently necessary conditions off the ground.xvi

And sufficient conditions are even more obviously difficult

to come by. Distinctive qualitative properties aren't sufficient

for distinguishing senses: touch is associated with multiple

distinctive qualitative properties, for example, temperature,

i In the last few years there has been growing interest in this issue; recent papers largely or exclusively devoted to it include Dominic M. McIver Lopes (2000), (author's paper [2001]), Brian Keeley (2002), Alva Noë (2002), Matthew Nudds (2004), and Richard Gray (in press).

iii

? It might seem that synaesthesia shows that there are no such distinctive qualitative properties. Synaesthesia is a rare condition where a property distinctive of one modality supposedly is perceived through another modality; for example, in one manifestation, colors supposedly are heard. If colors really can be heard (and sounds can be perceived by a modality other than hearing, and so on), then it seems that the core common-sense view is false.

It's difficult to tell, though, if synaesthesia really does indicate that color is not distinctive of vision, or if, instead, certain colors are merely associated with certain sounds. A suggestion in favor of mere association is that particular color-sound pairings are idiosyncratic. Richard E. Cytowic points out, "Scriabin and Rimsky-Korsakov, for example, disagreed on the color of given notes and musical keys" (1997, p. 26). Admittedly, this point is not decisive. But, as well, our


texture, and hardness. But is this sufficient to claim that

touch should be divided into multiple modalities? We can

stipulate an answer, of course, but it's difficult to know how to

do better.

I'm not claiming to have decisively put to rest the idea of

formulating necessary and sufficient conditions for

current understanding of synaesthesia is too murky to decisively reject the core common-sense view.iv

? Although Churchland assumes that common sense models mental representation on linguistic representation, this assumption is controversial. By contrast, Keeley's assumption that common sense divides sensory modalities according to qualitative properties is not controversial.v

? Keeley calls this the proper object criterion; I'll use the label "proper sensibles" to underscore that they are properties not objects. As Keeley notes, the idea of distinguishing modalities on the basis of distinctive qualitative properties of objects goes back to Aristotle. For historical background, see Richard Sorabji (1971).vi

? Keeley calls this the sensation criterion.vii

? For an extremely clear and detailed description of MDS, see Austen Clark (1993) pp. 76-101 and pp. 210-221.viii

? Keeley's (2002) suggests this, and he's confirmed this in conversation.ix

? Of course, that spatial properties are not distinctive is determined by the fact that they can be perceived by more than one modality, each of which perceives a distinctive qualitative property. Since qualitative properties can be characterized in terms of psychological quality spaces, but this characterization doesn't require reference to any particular sense, there is no danger of circularity.x

? This reliance is also odd because Grice's aim is just the opposite of Keeley's--Grice wants to show that qualia are indispensable in distinguishing modalities. But it turns out that the discussion of Grice is superfluous since, as I'll discuss next, Keeley offers another argument, and this further


distinguishing senses. But the prospects are poor (and, I

suspect will get poorer with the bringing of messy pit-viper-type

cases to bear on the issue). Thus it's best to avoid--as the

core common-sense view does--the problem of offering

independently necessary and jointly sufficient conditions.

argument can be used to reject the necessity of either the distinctive quale criterion or the proper sensible criterion.xi

? A possible reason that Keeley doesn't consider intentionalism is that he might consider physical properties in general as being physical stimuli; also he might consider qualitative properties in general to be qualia. If so, we can see why Grice's idea that physical properties are qualitative only in virtue of (perhaps dispositional relations with) qualia would be appealing. Furthermore, we can see why the issue of physical properties being qualitative independently of qualia--the intentionalist view--would never come up.xiii

? In this argument Keeley's target is qualia, which, following the typical characterization, he understands to be necessarily conscious. I'll take up the question of whether mental qualitative properties are necessarily conscious in section IV. In the meanwhile I'll respond to Keeley's argument in a way that doesn't assume that mental qualitative properties are necessarily conscious.xiv

? So science could correct common sense with respect to what Nudds calls the counting question, "that is, why do we have five senses?" (2004, p. 31). In the case of a vomeronasal system, science could help to show that the underlying assumption of the counting question--that human beings have five senses--is false.xv

? I've modified the set up of the thought experiment: Grice's thought experiment assumes a difference in senses for which a difference in qualitative properties is necessary. By contrast, I'll argue for the contrapositive: a sameness in senses for which sameness in qualitative properties is sufficient.

More importantly, I'll modify how the thought experiment is used: in arguing for the core common-sense view, I'm making no assumption as to whether qualitative properties are properties of physical objects or of mental states. By contrast, Grice uses the thought experiment to argue for the necessity of qualia in


Furthermore, even while avoiding the problem of full-fledged

individuation conditions we can do substantial work by focusing

on the issue of the necessity of qualitative properties in

distinguishing senses. After all, the basic questions relevant

to the problem of the limits on a scientific understanding of

perceptual states are these: are qualitative properties

necessary for distinguishing senses? If so, are qualia

necessary?

So far, I've addressed the first of these two questions:

I've argued that qualitative properties are necessary for

distinguishing senses, and so Keeley's eliminativism fails. I'll

now argue that qualia aren't necessary.

IV. The dispensability of qualia

A. Qualitative properties and consciousness

Because my aim so far has been a defense of the core common-

sense view, and this view abstracts from the metaphysics of

qualitative properties, the discussion has been neutral on the

question of whether qualitative properties are physical

qualitative properties of physical objects or mental qualitative

properties of mental states. However, I'll now argue that, as

far as the issue of distinguishing the senses shows, the

qualitative properties necessary for distinguishing senses need

not be qualia, that is, they need not be mental qualitative

properties that are characterized in a certain way: as what it's

like to be conscious of qualitative properties. I'll offer an

distinguishing senses.


alternative way of characterizing mental qualitative properties

which avoids marking a potential limit on scientific

understanding of perceptual states.

The standard way to characterize qualia is as what it's like

to be conscious of colors or smells or sounds (or any other

qualitative property). This characterization has it that these

mental qualitative properties are necessarily conscious--there

must be something it's like to have them, where there being

something that it's like requires consciousness.

According to the alternative I'm suggesting,xvii qualitative

properties can be characterized in terms of psychological quality

spaces. In this case, a non-human animal has a determinable

mental qualitative property just in case MDS tells us that it

makes qualitative similarity classifications (as indicated by

stimulus generalization tests) which can be ordered into a

psychological quality space.

This way of characterizing mental qualitative properties

avoids the issue of consciousness. For the mental qualitative

properties which we infer on the basis of behavioral evidence are

neural properties which need not be conscious. In the right

neurophysiological context (so, for example, barring damage

resulting in blindsight) these mental qualitative properties are

conscious. But with regard to blindsight, we can infer that

blindsight patients have mental qualitative properties which

process information contained in the blind spots of their visual

fields on the basis of behavioral evidence--and in this case,

these qualitative properties are not conscious.


An unconscious qualitative property may sound like an

oxymoron. After all, proponents of qualia define these mental

qualitative properties as being necessarily conscious. However,

in providing an alternative, the proposal is to characterize

mental qualitative properties in terms of psychological quality

spaces rather than in terms of consciousness. As David Rosenthal

(1991 and 2005) argues, the idea the mental qualitative

properties are necessarily conscious is unmotivated. Even common

sense allows that mental qualitative properties need not be

conscious (for example, common sense allows that a headache that

dips out of consciousness doesn't thereby cease to exist).

Moreover, this alternative offers important benefits. It

allows us to set aside the question of conscious perception while

distinguishing senses in non-human animals. Nevertheless, it

retains the common-sense characterization of perceptual states in

terms of qualitative properties. Consequently, unlike

eliminativism, it doesn't leave us at sea with respect to the

issue of how to distinguish perceptual states from non-mental

physiological states.

In section II, I noted that, due to the inadequacies of our

current grasp of consciousness, scientists and philosophers are

hesitant to attribute conscious qualitative states to other

species. This hesitancy may seem to amount to a de facto

eliminativism. However, if we can distinguish between

consciousness and qualitativeness as independent properties of

perceptual states, there's no reason to accept eliminativism de

facto or otherwise. For by drawing this distinction, we allow


that perceptual states can be characterized in terms of

qualitative properties--on the basis of behavioral evidence which

is best explained by perceptual states which can be ordered into

a psychological quality space--independently of consciousness.

B. Grice's visiting Martians

However, there has been recent interest, largely the result

of a reconsideration of Grice's "Some Remarks," in whether the

problem of distinguishing senses shows that perceptual states

have qualia--that is, mental qualitative properties which are

what it's like to be conscious of qualitative properties.

Grice argues in "Some Remarks" that qualia are necessary for

distinguishing senses.xviii I'll counter that the qualitative

properties needed to distinguish senses are--so far as Grice

shows--physical qualitative properties of physical objects and

mental qualitative properties that are not necessarily conscious.

Unlike qualia, neither of these properties mark a potential limit

on scientific understanding of perceptual states, since when not

conscious neither property presents a special difficulty for

scientific understanding.

There are, of course, other arguments for the existence of

qualia. However, Grice's argument would provide a new and

interesting way to make this case. My main objective here is to

show that Grice's argument doesn't succeed.

(Although Grice doesn't use the term 'qualia', instead

favoring the term 'introspectible character' throughout "Some

Remarks", and the using the terms 'phenomenal character', and


'experiential flavor or quality of experience' in his

"Retrospective Epilogue," he describes how perceiving with the

two sets of eyes are different for the Martians in terms of

considering "…whether [perceiving] something to be round [with

one set of eyes] was like [perceiving] it to be round [with the

other set], or whether when something [appeared] blue to them

[with one set] this was like or unlike its [appearing] blue to

them [with the other set]" (1962, p. 261). Following the current

convention, I'll refer to such mental qualitative properties that

are 'what it's like' to be conscious of color as qualia.)

Grice argues for the necessity of qualia on the basis of the

Martian thought experiment: Martians have two sets of eyes which

are sensitive to the same physical properties, and perceive the

same ranges of properties (colors and shapes for example). Due

to these similarities, it seems that the two sets of eyes are

organs of the same sense. But, Grice continues, if we ask a

Martian whether perceiving blue with one set of eyes is like

perceiving blue with the other set, the Martian says "There is

all the difference in the world" between these perceptual

experiences, pointing out a qualitative difference.

Grice claims that we would conclude that the two sets of

eyes are of different senses. Since physical stimulus, sense

organ, and perceived properties of objects aren't sufficient for

distinguishing these different senses, then, Grice argues,

another condition--in particular, the distinctive qualia

condition--is necessary. In "Some Remarks," Grice's main focus

is the relationship between perceived properties of objects and


qualia, and in particular to consider whether qualia are

dispensable with regard to distinguishing senses; the point of

the Martian thought experiment is to demonstrate that they

aren't.xix

I'll show, however, that, Grice's argument is unsuccessful.

Perhaps the Martians distinguish their two sets of eyes because

each set perceives a proper sensible (a distinctive qualitative

property of physical objects). If so, we can account for "all

the difference in the world" in terms of proper sensibles, and

qualia aren't needed to distinguish senses. Grice seems to rule

this possibility out in the set up for the thought experiment--

because supposedly the two sets of eyes perceive the same ranges

of properties of objects. But without an independent reason for

thinking that the two sets of eyes perceived the same ranges of

properties, this claim is question begging.

So Grice needs to provide an independent reason for thinking

that we must account for qualitative differences in terms of

qualia. But he suggests an independent reason in his comments

about the generic resemblance among perceptual states of the same

sense.

C. Generic resemblance

Grice claims:

…the way to describe our visual experiences is in terms of

how things look to us, and such a description obviously

involves the employment of property-words. But in addition

to the specific differences between visual experiences,


signalized by the various property-words employed, there is

a generic resemblance signalized by the use of the word

'look', which differentiates visual from non-visual sense-

experience. This resemblance can be noticed and labeled,

but perhaps not further described (1962, p. 267).

Thus visual experiences share a generic resemblance; auditory

experiences share a generic resemblance; and so on. Grice

intends for this point about generic resemblance to support his

case for the claim that qualia are necessary for distinguishing

senses. I'll offer an interpretation of what Grice has in mind,

and state why this consideration doesn't indicate that qualia are

necessary.

Visual experiences are distinctive in that they involve

color. Consequently a generic resemblance among visual

experiences derives from a generic resemblance among colors;

broadly speaking, a generic resemblance among the perceptual

states of a modality derives from a generic resemblance among

determinable (or generic) qualitative properties that are

distinctive of that modality. What Grice might have in mind is

that each determinable qualitative property distinctive of a

sense is a dispositional relation between a range of physical

properties of physical objects and a determinable quale.

This proposal is a common version of dispositionalism about

qualitative properties, according to which a color, for example,

is a disposition of a certain range of physical properties of

physical objects to produce color qualia. According to this kind

of dispositionalism, we don't attribute qualia to physical


objects. Nevertheless, we are aware of them in perception in an

indirect way since they determine the qualitative character of

properties (such as dispositional colors) which we do attribute

to physical objects. Thus, they can make "all the difference in

the world" in the perception of the properties of physical

objects. Furthermore, qualia are, as Grice says, introspectible.

In the case of the visiting Martians, the idea would be that, in

addition to a blue quale which the two sets of eyes have in

common, there is also a quale distinctive of each set.

Supporting this interpretation, Grice suggests that he favors

this kind of dispositionalism in his "Retrospective Epilogue,"

(p. 343).

And perhaps the idea that different senses are distinguished

by different determinable qualia is what Block has in mind when

he remarks (1996, p. 28) that considerations about distinctions

among the senses provide a basis for accepting qualia.

Yet this line of reasoning for qualia is unconvincing.

Psychophysics' use of MDS again provides a useful way of looking

at the issue. If we can understand a generic resemblance among

perceptual states in terms of a determinable qualitative

property, we can, in turn, understand this determinable

qualitative property in terms of a psychological quality space.

Viewed this way, generic resemblance among visual states amounts

to our recognition that there is a qualitative resemblance route

through the psychological color space from any color determinate

to any other color, but not to a sound. Furthermore, understood

this way, generic resemblance "can be noticed and labeled, but


perhaps not further described" in the sense that our recognition

that we can place a determinate color in the psychological color

space is a non-inferential recognition that we can't redescribe

in other terms (at least not in other non-scientific terms).

But, if this interpretation of Grice is along the right

lines, generic resemblance provides no reason to think that

perceptual states have qualia. We do think of psychological

color spaces in terms of qualitative properties of which we are

conscious. But this by itself doesn't demonstrate that mental

qualitative properties must be conscious. Instead, it could be

that a better way of characterizing mental qualitative properties

is as properties are inferred as the best explanation of

behavioral evidence, whether they are conscious or not. So an

understanding of generic resemblance in terms of a psychological

quality space offers an opportunity to avoid qualia, rather than

forcing us to accept them.

To decide whether perceptual states have qualia, we should

set aside the issue of how we distinguish sensory modalities, and

directly address the question of whether mental qualitative

properties are necessarily conscious. For, even if we assume

that the core common-sense view is correct, support for qualia

requires the additional claim that mental qualitative properties

are necessarily conscious. Thus, while a consideration of how we

distinguish the senses tells against eliminativism, it leaves us

where we started with respect to the question of qualia.

Instead, the issue of qualia requires that we directly address

the problem of the metaphysics and epistemology of qualitative


properties such as color. But this is a discussion, as Grice

(1962, p. 267) puts it, "for which at the moment I have neither

time nor heart."xx


NOTES

REFERENCES

Author's papers (2001), (manuscript)

Block, Ned (1995). "On a Confusion about a Function ofConsciousness," Behavioral and Brain Processes, Vol. 18, No. 2 ( 1995): 227-287. Reprinted in The Nature of Consciousness: Philosophical Debates, eds. Ned Block, Owen Flanagan, and Güven Güzeldere. Cambridge, Mass.: The MIT Press, 1997, 375-415. Page numbers refer to reprint.

Block, Ned (1996). "Mental Paint and Mental Latex," inPhilosophical Issues, 7: Perception, ed. Enrique Villanueva. Atascadero, Cal.: Ridgeview Publishing Company, 19-49.

Bradley, Peter and Michael Tye (2001). "Of Colors, Kestrals, Caterpillars, and Leaves," Journal of Philosophy, Vol. 98, No. 9 (September 2001): 469-487.

Clark, Austen (1993). Sensory Qualities. Oxford: Clarendon Press.

Cytowic, Richard E. (1995). "Synaesthesia: phenomenology and neuropsychology," Psyche, Vol. 2. Reprinted in Synaesthesia: Classic and Contemporary Papers, eds. Simon Baron-Cohen and John E. Harrison. Oxford: Blackwell Publishers Ltd., 1997, 17-39. Page numbers refer to reprint.

Gray, Richard (in press). "On the Concept of a Sense,"Synthese.

Grice, H. P. (1962). "Some Remarks about the Senses," in Analytical Philosophy, First Series, ed. R. J. Butler. Oxford: Blackwell, pp. 133-153. Reprinted in his Studies in the Way of Words, Cambridge, Mass.: Harvard University Press, pp. 248-268. Page numbers refer to reprint.

Grice, H. P. (1989a). "Retrospective Epilogue," in his (1989b), 339-385.

Grice, H. P. (1989b). Studies in the Way of Words. Cambridge, Mass.: Harvard University Press.

Hardin, C. L. (1993). Color for Philosophers: Unweaving the Rainbow, Expanded edition. Indianapolis: Hackett.


Hatfield, Gary (1992). "Color Perception and Neural Encoding:Does Metameric Matching Entail a Loss of Information?" in Proceedings of the 1992 Biennial Meeting of the Philosophy of Science Association, Vol. 1, Contributed Papers, eds. David Hull, Micky Forbes, and Kathleen Okruhlik, 492-504.

Hilbert, David R. (1992). "What Is Color Vision?" PhilosophicalStudies, Vol. 68, No. 3 (December 1992): 351-370.

Holt, Jason (2002). Blindsight and the Nature of Consciousness.Peterborough, Ontario: Broadview Press.

Keeley, Brian (2002). "Making Sense of the Senses: Individuating Modalities in Humans and Other Animals," Journal of Philosophy, Vol. 99, No. 1 (January 2002): 5-28.

Kind, Amy (2003). "What's So Transparent About Transparency?" Philosophical Studies, Vol. 115, No. ?, (?? 2003): 225-244.

McIver Lopes, Dominic M. (2000). "What Is It Like to See with Your Ears? The Representational Theory of Mind," Philosophy and Phenomenological Research, Vol. 60, No. 2 (March 2000): 439-453.

Mollon, J. D. (1989). "'Tho' She Kneel'd in That Place WhereThey Grew…': The Uses and Origins of Primate Colour Vision," Journal of Experimental Biology, Vol. 146 (September 1989): 21-38.

Noë, Alva (2002). "On What We See," Pacific PhilosophicalQuarterly, Vol. 83, No. 1 (March 2002): 57-80.

Nudds, Matthew (2004). "The Significance of the Senses," Proceedings of the Aristotelian Society, Vol. 104, Part 1: 31-51.

Sorabji, Richard (1971). "Aristotle on Demarcating the Five Senses," The Philosophical Review, Vol. 80, No. 1 (January 1971): 55-79.

Rosenthal, David M. (1991). "The Independence of Consciousness and Sensory Quality," in Philosophical Issues, 1: Consciousness, ed. Enrique Villanueva. Atascadero, Cal.: Ridgeview Publishing Company, 15-36.


Rosenthal, David M. (2005). "Sensory Qualities, Consciousness, and Perception," in his Consciousness and Mind. Oxford: Clarendon Press.

Thompson, Evan (1995). Colour Vision: A Study in Cognitive Science and the Philosophy of Perception. London: Routledge.

Tye, Michael (2000). Consciousness, Color, and Content. Cambridge, Mass.: The MIT Press.

xvi

? In [author's paper] my idea was to offer disjunctively necessary conditions (as I'll suggest that Grice's conditions can be interpreted as being). But I don't think that this will work either. Consider the proposal: if senses are distinct, then they have distinctive physical stimuli or distinctive sense organs or distinctive evolutionary history or distinctive qualitative properties. This proposal allows that senses are distinct even if they don't differ with respect to qualitative properties. Now I think that the core common-sense view is correct in claiming that a distinctive qualitative property is necessary for a distinct sense (not that a distinctive qualitative property is just a disjunct in disjunctively necessary conditions).xvii

? This alternative is described and defended at length by David Rosenthal (2005).xviii

? The fact that Grice (1962, p. 259) stresses the diaphanousness--what is currently called the transparency--of experience is consistent with his arguing for qualia. For an incisive discussion of the complexities of the relationship between transparency and qualia, see Amy Kind (2003).xix

? In fact, Grice doesn't intend to propose independently necessary and jointly sufficient conditions for distinguishing senses. At best, Grice might suggest that distinct physical stimuli, sense organs, perceived properties, and qualia are disjunctively necessary for distinct sensory modality. In that case, if a sense x-ing and a sense y-ing don't satisfy any of the disjuncts, then x-ing and y-ing are the same sense, and the Martian thought experiment is intended to show that the distinctive qualia condition is needed as an additional disjunct.xx


? But see (author's paper [manuscript]) for a development and defense of a proposal about the nature of color, in particular, a version of physicalism which avoids qualia. I owe many thanks to Brian Keeley for helpful comments on a draft of this paper. I also thank my colleagues in the Cal Poly philosophy department for their helpful responses; the audience of a CUNY Graduate School Cognitive Science colloquium, in particular David Rosenthal, Pete Mandik, Doug Meehan, Josh Weisberg, and Tony Dardis; and the Claremont Colleges Work in Progress group, in particular Dion Scott-Kakures, Amy Kind, Peter Graham, and Carrie Figdor. I also owe very many thanks to Richard Gray, with whom I've had many helpful discussions about the issues in this paper.

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