Qualia

Qualia are the subjective or qualitative properties of experiences.
What it feels like, experientially, to see a red rose is different
from what it feels like to see a yellow rose. Likewise for hearing a
musical note played by a piano and hearing the same musical note
played by a tuba. The qualia of these experiences are what give each
of them its characteristic "feel" and also what distinguish them from
one another. Qualia have traditionally been thought to be intrinsic
qualities of experience that are directly available to introspection.
However, some philosophers offer theories of qualia that deny one or
both of those features.

The term "qualia" (singular: quale and pronounced "kwol-ay") was
introduced into the philosophical literature in its contemporary sense
in 1929 by C. I. Lewis in a discussion of sense-data theory. As Lewis
used the term, qualia were properties of sense-data themselves. In
contemporary usage, the term has been broadened to refer more
generally to properties of experience. Paradigm examples of
experiences with qualia are perceptual experiences (including
nonveridical perceptual experiences like hallucinations) and bodily
sensations (such as pain, hunger, and itching). Emotions (like anger,
envy, or fear) and moods (like euphoria, ennui, or anxiety) are also
usually taken to have qualitative aspects.

Qualia are often referred to as the phenomenal properties of
experience, and experiences that have qualia are referred to as being
phenomenally conscious. Phenomenal consciousness is often contrasted
with intentionality (that is, the representational aspects of mental
states). Some mental states—for example, perceptual
experiences—clearly have both phenomenal and intentional aspects. My
visual experience of a peach on the kitchen counter represents the
peach and also has an experiential feel. Less clear is whether all
phenomenal states also have intentional aspects and whether all
intentional states also have phenomenal aspects. Is there really
something that it is like to have the belief—even the occurrent
belief—that there is a peach on the counter? What could be the
representational content of the experience of an orgasm? Along these
lines, the nature of the relationship between phenomenal consciousness
and intentionality has recently generated considerable philosophical
discussion. Some philosophers think that phenomenal consciousness
reduces to intentional content, while others think that the reductive
relationship goes in the other direction. Still other philosophers
deny both claims.

From the standpoint of introspection, the existence of qualia seems
indisputable. It has, however, proved remarkably difficult to
accommodate qualia within a physicalist account of the mind. Many
philosophers have argued that qualia cannot be identified with or
reduced to anything physical, and that any attempted explanation of
the world in solely physicalist terms would leave qualia out. Thus,
over the last several decades, qualia have been the source of
considerable controversy in philosophy of mind.

1. The Hard Problem of Consciousness

One of the most fundamental questions about the mind concerns its
relationship to the body (and, more specifically, its relationship to
the brain). This has become known as the mind-body problem. Although
it dates back at least to Plato's Phaedo, the problem was thrust into
philosophical prominence by René Descartes. In taking up these issues
in his Meditations on First Philosophy, Descartes argued for a dualist
view according to which the mind and the body are fundamentally
different kinds of things: While the body is a material thing existing
in space, the mind is an immaterial thing, one that altogether lacks
spatial extension. In contrast to dualists, the materialists claim
that everything that exists must be made of matter. Historically,
materialism was associated with Thomas Hobbes. Starting in the
twentieth century, this position has become known as physicalism, the
claim that everything that exists—all things and all properties of
things—must fundamentally be physical. Most philosophers today endorse
some form of physicalism.

For some aspects of consciousness, it is relatively straightforward to
see how they can be accommodated within a physicalist picture.
Consider, for example, our abilities to access, report on, and attend
to our own mental states. It seems reasonable to assume that as
neuroscience progresses and we learn more and more about the brain, we
will be able to explain these abilities in terms of neural mechanisms.
Aspects of consciousness that can be explained in this way constitute
what David Chalmers has referred to as the easy problems of
consciousness. The assertion that these problems are easy does not
mean that they have already been solved or even that we are close to
finding solutions. As Chalmers explicitly notes, we should think of
"easy" as a relative term. In most cases, we are still nowhere near
having a complete explanation of the relevant phenomena. Rather, what
makes the problems easy is that, even though the solutions to these
problems probably still require decades or even centuries of difficult
empirical investigation, we nonetheless have every reason to believe
that we can reach them using the standard methods of cognitive science
and neuroscience. (Chalmers 1995, 1996) Solving the problem of
attention, for example, simply awaits the empirical identification of
a relevant neural mechanism. But what kind of mechanism could account
for qualia? Though we strongly suspect that the physical system of the
brain gives rise to qualia, we do not have any understanding of how it
does so. The problem of accounting for qualia has thus become known,
following Chalmers, as the hard problem of consciousness.

The hard problem of consciousness relates quite closely to what Joseph
Levine had previously referred to as the explanatory gap. Given the
scientific identification of heat with the motion of molecules, there
is no further explanation that needs to be given: "our knowledge of
chemistry and physics makes intelligible how it is that something like
the motion of molecules could play the causal role we associate with
heat…. Once we understand how this causal role is carried out there is
nothing more we need to understand." (Levine 1983) In contrast, when
we are told that pain is to be identified with some neural or
functional state, while we have learned quite a bit, there is still
something left unexplained. Suppose, for example, that we precisely
identify the neural mechanism that accounts for pain—C-fiber firing,
let's say. Still, a further question would remain: Why does our
experience of pain feel the way that it does? Why does C-fiber firing
feel like this, rather than like that, or rather than nothing at all?
Identifying pain with C-fiber firing fails to provide us with a
complete explanation along the lines of the identification of heat
with the motion of molecules.

Some philosophers have claimed that closing the explanatory gap and
fully accounting for qualia is not merely hard but rather impossible.
This position, often referred to as new mysterianism, is most closely
associated with Colin McGinn. According to McGinn, we will in
principle never be able to resolve the mystery of what it is about the
brain that accounts for qualia. (McGinn 1989) A similar, though
slightly weaker, view is held by Thomas Nagel. According to Nagel, we
currently do not have the conceptual apparatus necessary to even begin
to understand how physicalism might be true. In order to solve the
hard problem of consciousness, we would have to undergo a complete
overhaul of our entire conceptual apparatus—a conceptual revolution so
radical that we cannot even begin to conceive what the resulting
concepts would be like. (Nagel 1998) But other philosophers reject the
pessimism of the new mysterians as unwarranted or premature. Chalmers,
for example, suggests that an explanation of how consciousness relates
to the physical, even if it does not reduce to it, may well be
enlightening. (See Chalmers 1996, 379)

It is perhaps easiest to see why the hard problem of consciousness is
so hard by looking at particular attempts to account for qualia. The
following three sections review three different theories of mental
states—functionalism, physicalism, and representationalism—and the
problems they face in accounting for qualia.
2. Qualia and Functionalism

The contemporary debate about qualia was framed in large part by
discussions of functionalism in the late 1960s and early 1970s. Some
attention had earlier been paid to qualia in connection with type
identity theory, the view that mental state types could be identified
with physical state types (for example, the mental state type pain
might be identified to the neural state type C-fiber firing). But it
was with the emergence of functionalism as a theory of mind that the
debate about qualia began to heat up.

The intuition underlying the functionalist view is that the function
of a mental state is its defining feature. Mental states are defined
in terms of the causal role that they play in the entire system of the
mind—that is, in terms of their causal relations to sensory stimuli,
behavioral outputs, and other mental states. By defining mental states
in this way, functionalism avoids many of the objections aimed at
philosophical behaviorism, an early 20th century theory of mental
states that defines them simply in terms of their input-output
relations. Moreover, because a causal role can be defined
independently of its physical realization (that is, because functional
states are multiply realizable), functionalism avoids many of the
objections aimed at the type identity theory. Rather than define pain
in terms of C-fiber firing, functionalism defines pain in terms of the
causal role it plays in our mental life: causing avoidance behavior,
warning us of danger, etc., in response to certain environmental
stimuli.

As plausible as functionalism may seem, however, it has long faced the
charge that it is unable to account adequately for qualia. The causal
role of a state seems to come apart from its qualitative aspects. To
show this, opponents of functionalism have mounted two different kinds
of arguments: (1) those aiming to show that two systems might be
functionally identical even though only one of them has any qualia at
all, and (2) those aiming to show that two systems might be
functionally identical even though they have vastly different qualia
from one another.

Falling in the first of these two categories, the absent qualia
argument tries to establish that a system could instantiate the
functional state of, say, pain without having any pain qualia. Ned
Block originated this objection to functionalism with the thought
experiment of the homunculi-headed robot (Block 1978). Suppose a
billion people were recruited to take part in a giant experiment. Each
individual is given a very small task to perform—for example, to press
a certain button when a certain light comes on. In doing so, each of
them plays the causal role of an individual neuron, with the
communications between them mirroring the synaptic connections among
the neurons. Now suppose that signals from this network of people are
appropriately connected to a robot body, so that the signals from the
network cause the robot to move, talk, etc. If the network were set up
in the right way, then it seems in principle possible that it could be
functionally equivalent to a human brain. However, intuitively
speaking, it seems very odd to attribute qualia to the robot. Though
it might be in a state functionally equivalent to the state you are in
when you have a pain in your right toe, it seems implausible to
suppose that the robot is feeling pain. In fact, it seems implausible
to suppose that the robot could have any phenomenal experience
whatsoever. Thus, if the absent qualia objection is right, we can have
functional equivalence without qualitative equivalence, so qualia
escape functional explanation.

A related objection, falling into the second category, is the inverted
qualia argument against functionalism, which arises from considering a
possibility originally suggested by John Locke. Suppose that two
people, Norma and Abby, are qualitatively inverted with respect to one
another. Both of them refer to stop signs, Coke cans, and Elmo as
"red," and both refer to sugar snap peas, Heineken bottles, and Kermit
the Frog as "green." But Abby's phenomenal experience when she sees a
Coke can is like Norma's phenomenal experience when she sees a
Heineken bottle. When Norma sees the Coke can, she has a reddish
experience; when Abby sees the Coke can, she has a greenish
experience. Likewise, when Norma sees the Heineken bottle, she has a
greenish experience; but when Abby sees the Heineken bottle, she has a
reddish experience. Qualitatively, the two are inverted relative to
each other.

Though most people find this scenario conceptually coherent, the
functionalist can make no sense of this inversion. Abby and Norma both
refer to the Coke can as "red." They both indicate that it is the same
color as stop signs and ripe tomatoes. Functionally speaking, there is
nothing to differentiate the states that Abby and Norma are in when
they see the Coke can. But, by hypothesis, they have different
qualitative experiences when they see the Coke can. Thus, it looks as
if functional definitions of mental states leave out the qualitative
aspects of mental states.

In response to these qualia-related objections, the functionalist
might try to argue that we have not really imagined the scenarios that
we think we have imagined. For example, can we really imagine what
would happen if we had a billion people participating in a network to
operate the robot? (In fact, even a billion people would not be enough
to simulate the human brain, which is estimated to have 100 billion
neurons.) Along these lines, William Lycan (1995, 50-52) argues that
our intuition that the robot does not have qualia stems from a
misguided focus on each microscopic part of the system rather than on
the macroscopic system as a whole. Likewise, the functionalist might
offer considerations to show that, contrary to how it first seems, the
notion of behaviorally undetectable qualia inversion is not
conceptually coherent after all. For example, because saturated yellow
is brighter than saturated blue, the inversion between Norma and Abby
would be detectable if they were both shown patches of saturated blue
and saturated yellow and asked which was brighter. (See Tye 1995,
203-4)

Alternatively, if the functionalist cannot convince us that the absent
qualia and inverted qualia scenarios are incoherent, he might instead
narrow the scope of the theory, restricting it to mental states that
are not qualitative. As John Haugeland argues, we can "segregate" the
states that can be functionalized from the states that cannot: "if
felt qualities are fundamentally different, so be it; explaining them
is somebody else's business." (Haugeland 1978, 222) However, while
this kind of segregation might save functionalism as a theory of
cognition, it does so only by ignoring the hard problem of
consciousness.
3. Qualia and Physicalism

As described above, the absent qualia objection and the inverted
qualia objection specifically target functionalism, but they can be
generalized to apply to physicalism more broadly. For the inverted
qualia argument, the generalization is straightforward. Just as we can
conceive of Abby and Norma being in functionally identical states, it
does not seem implausible to suppose that their brains might be
physically identical to one another. If so, then just as qualia escape
functional explanation, they also escape physical explanation.

The generalization is less straightforward with the absent qualia
argument. The homunculi-headed robot, though functionally identical to
a human being, is not physically identical to a human being. However,
in recent work, Chalmers has argued that we can conceive of what he
terms "zombies"—beings who are molecule-for-molecule identical with
phenomenally conscious beings but who are not themselves phenomenally
conscious. In appearance and action, a conscious being and his zombie
replica would be indistinguishable, but for the zombie, as Chalmers
says, "all is dark inside." (Chalmers 1996, 96) When Zack and Zombie
Zack each take a bite of chocolate cake, they each have the same
reaction—they smile, exclaim how good it is, lick their lips, and
reach for another forkful. But whereas Zack, a phenomenally conscious
being, is having a distinctive (and delightful) qualitative experience
while tasting the chocolate cake, Zombie Zack is experiencing nothing
at all. This suggests that Zack's consciousness is a further fact
about him, over and above all the physical facts about him (since all
those physical facts are true of Zombie Zack as well). Consciousness,
that is, must be nonphysical.

Chalmers' argument has the standard form of a conceivability argument,
moving from a claim about conceivability to a claim about metaphysical
possibility. Though zombies are probably not physically possible—not
possible in a world that has laws of nature like our world—the fact
that they are conceivable is taken to show that there is a
metaphysically possible world in which they could exist. This form of
argument is not entirely uncontroversial (see, for example, Hill and
McLaughlin 1999), and there is also considerable debate about whether
Chalmers is right that zombies are conceivable (see, for example,
Searle 1997). But if Chalmers is right about the conceivability of
zombies, and if this conceivability implies their metaphysical
possibility, then it would follow that physicalism is false.

An early and influential discussion of the general problem that qualia
pose for physicalism can be found in Thomas Nagel's seminal paper,
"What is it like to be a Bat?" (Nagel 1974). Although it might be that
not all living creatures have phenomenal experiences, we can be pretty
confident that bats do—after all, they are mammals who engage in
fairly sophisticated behavior. In Nagel's words, there is something
that it is like to be a bat. But the physiology of bats is radically
different from the physiology of human beings, and the way they
interact with the world is radically different from the way that we
interact with the world. What we do via vision, they do via
echolocation (sonar). We detect objects by sight; bats detect objects
by sending out high-frequency signals and detecting the reflections
from nearby objects. Because this way of perceiving the world is so
different from our own, it seems that their perceptual experiences
must be vastly different from our own—so different, in fact, that
Nagel argues that it is unimaginable from our perspective. We, who are
not bats, cannot know what it is like to be a bat. Qualia are
inherently subjective, and as such, Nagel argues that they cannot be
accommodated by physicalism: "Every subjective phenomenon is
essentially connected with a single point of view, and it seems
inevitable that an objective, physical theory will abandon that point
of view." (Nagel 1974, 520)

Related worries about physicalism and qualia have been forcefully
developed by Frank Jackson in his well-known thought experiment
involving Mary, a brilliant color scientist who has spent her entire
life in a black-and-white room. (Jackson 1982) Although she has normal
color vision, her confinement has prevented her from ever having any
color sensations. While in the room, Mary has studied color science
through black and white textbooks, television, etc. And in that way
she has learned the complete physical story about color experience,
including all the physical facts about the brain and its visual
system. She knows all the physical facts about color. But she has
never seen anything in color. Now suppose that Mary is one day
released from her room and presented with a ripe tomato. What should
we imagine happens? Most people have the very strong intuition that
Mary learns something from this perceptual experience. "Aha!" she
might say. "Now I finally know what the color red is like."

The Mary case is the centerpiece of Jackson's knowledge argument
against physicalism. While in the room, Mary knew all the physical
facts about color, including the color red. When she is released from
the room, Mary learns something about the color red, namely, what
seeing red is like. What Mary learns consists of new, factual
information. So there are facts about color in addition to all the
physical facts about color (since Mary already knew all the physical
facts about color). Thus, the argument goes, physicalism is false.

In the quarter century since Jackson's development of the knowledge
argument, a vast literature has developed in response to it.
Attempting to save physicalism, some philosophers deny that Mary
learns anything at all when she leaves the room. If we really imagine
that Mary has learned all the physical facts about color while in the
room, then there would be no "Aha!" moment when she is shown a ripe
tomato. We are led to think otherwise only because we typically fall
short of imagining what we've been asked to imagine—we imagine only
that Mary knows an immense amount about colors, that she has mastered
all the information contained in our present science of color, which
still remains incomplete. As Patricia Churchland has argued, "How can
I assess what Mary will know and understand if she knows everything
there is to know about the brain? Everything is a lot, and it means,
in all likelihood, that Mary has a radically different and deeper
understanding of the brain than anything barely conceivable in our
wildest flights of fancy." (P.S. Churchland 1986, 332; see also
Dennett 1991, 399-400)

Despite these reservations about what happens when Mary leaves the
room, most philosophers—even most physicalists—accept Jackson's
assessment that Mary learns something from her experience with the
ripe tomato. Physicalists who grant this point have typically
attempted two different strategies to respond to the knowledge
argument: (1) They might accept that Mary gains new knowledge that
isn't understood in terms of facts; or (2) they might accept that
Mary's knowledge is factual but deny that she's learned anything new;
rather, facts that she already knew are presented to her in a new way.

To pursue strategy (1), the physicalist might argue that the knowledge
Mary gains when she leaves the room consists in nonfactual knowledge.
Along these lines, David Lewis (1988) offers the ability hypothesis:
When Mary leaves the room, all that happens is that she gains some new
abilities regarding color that she didn't have before. Unlike before,
Mary is now able to imagine, recognize, and remember the color red. So
she gains know-how, but she doesn't learn any facts. Pursuing strategy
(1) in a different way, Earl Conee (1994) offers the acquaintance
hypothesis: When Mary leaves the room, all that happens is that she
becomes acquainted with the color red. When you meet someone for the
first time that you've previously heard or read a lot about, you don't
necessarily learn any facts about them; rather, you just become
acquainted with them. Conee thus argues that acquaintance knowledge
(like ability knowledge) should not be understood in terms of facts.
If either the ability hypothesis or the acquaintance hypothesis is
right, and Mary does not learn any facts when she leaves the room,
then the knowledge argument does not show that the physical facts are
incomplete.

To pursue strategy (2), the physicalist might argue that Mary doesn't
gain any new knowledge when she leaves the room; rather, she simply
comes to apprehend an old fact under a new guise. While in the room,
she did not have the conceptual apparatus she needed in order to
apprehend certain color facts in a phenomenal way. Having seen color,
she has now gained new concepts—phenomenal concepts—and thus is able
to re-apprehend the same facts she already knew in a different way.
(Loar 1990) Whether there are genuinely phenomenal concepts, and if
so, whether they do the work in answering the knowledge argument that
the physicalists want them to, has recently been generating a growing
literature of its own.
4. Qualia and Representationalism

While functionalism and physicalism are put forth as general theories
of mind, representationalism aims specifically to give an account of
qualia. According to this view, the qualitative character of our
phenomenal mental states depends on the intentional content of such
states. Representationalist views divide into two categories depending
on exactly how they characterize this dependence. Weak
representationalism makes a claim only about supervenience: The
qualitative character of our mental states supervenes on the
intentional content of those states (that is, if two experiences are
alike representationally, then they are alike phenomenally). Strong
(or pure) representationalism makes a further claim: The qualitative
character of our mental states consists in the intentional content of
such states. Strong representationalism thus offers a theory of
qualia—it attempts to explain what qualitative character is. This
section addresses the strong representationalist theory of qualia;
hereafter, the modifier "strong" will be omitted.

Recall the distinction above between the easy problems of
consciousness and the hard problem. Accounting for representational
content is supposed to be one of the easy problems. It may take us an
enormous amount of empirical work to get to the solution, but the
standard methods of cognitive science will be able to apply. Thus, if
qualia can be reduced to intentionality, then we have turned the hard
problem of consciousness into an easy problem. A full and satisfactory
account of qualia awaits only a solution to the easy problem of
intentionality.

Consider pain qualia. Traditionally, philosophers classified pain
experiences as non-intentional. However, the representationalist
claims that this is a mistake. When one has a pain in one's leg, the
experience represents damage in the leg. Moreover, its phenomenal
feel—its painfulness—consists in its doing so. As Michael Tye argues,
"[T]he phenomenal character of my pain intuitively is something that
is given to me via introspection of what I experience in having the
pain. But what I experience is what my experience represents. So,
phenomenal character is representational." (Tye 1990, 338)

Given that the representationalist typically does not want to claim
that all intentional content is qualitative, he must explain what is
special about the intentional content in which phenomenal character is
supposed to consist. My belief that Thomas the Tank Engine is blue and
my mental image of Thomas the Tank Engine have similar intentional
content; they both represent him as blue. So, what about the
intentional content of the latter gives it its distinctive
phenomenology? Here Tye has a particularly well-developed answer. He
suggests that phenomenal content is a species of nonconceptual
intentional content, in particular, nonconceptual intentional content
that is poised and abstract. (Tye 1995) Because we can experience many
things for which we lack concepts—for example, a proud parent might
visually experience his young child's drawing without having a concept
for the shape that the drawing is—it is important that phenomenal
content be restricted to nonconceptual content. The requirement that
the contents be poised means that they "stand ready and in position to
make a direct impact on the belief/desire system." (Tye 1995, 138) The
requirement that the contents be abstract means that no particular
concrete object is a part of them.

In support of their theory, representationalists often invoke what we
might call the transparency thesis. According to this thesis,
experience is alleged to be transparent in the sense that we "see"
right through it to the object of that experience, analogously to the
way that we see through a pane of glass to whatever is on the other
side of it. Gilbert Harman introduced such considerations into the
contemporary debate about qualia in a now-famous passage: "When Eloise
sees a tree before her, the colors she experiences are all experienced
as features of the tree and its surroundings. None of them are
experienced as intrinsic features of her experience. Nor does she
experience any features of anything as intrinsic features of her
experiences." (Harman 1990, 667) As Harman went on to argue, the same
is true for all of us: When we look at a tree and then introspect our
visual experience, all we can find to attend to are features of the
presented tree. Our experience is thus transparent; when we attend to
it, we can do so only by attending to what the experience represents.
Representationalists contend that their theory offers the best and
simplest possible explanation of this phenomenon. The best explanation
of the fact that we cannot introspectively find any intrinsic features
of our experience is that there are none to find; the phenomenal
character of experience is wholly constituted by the representational
content of the experience. (see especially Tye 1995, 2000)

Whether experience is really transparent in the way that the
representationalists suppose has lately been the subject of some
dispute, and there has also been considerable discussion about the
relationship between experiential transparency and representationalism
(See, for example, Kind 2003, Siewert 2004). Most problematic for the
representationalists, however, has been the fact that their view falls
victim to several persistent and compelling counterexamples. Many
phenomenal states simply do not seem to be doing any representing—or,
more cautiously, it seems that their phenomenal content far outruns
their representational content. Ned Block has argued this point using
the example of the orgasm: "Orgasm is phenomenally impressive and
there is nothing very impressive about the representational content
that there is an orgasm." (Block 2003, 543) He also discusses
phosphene experiences, the color sensations created by pressure on the
eyeball when one's eyelids are closed. Phosphene experiences do not
seem to be representing anything; we don't take the experience to
suggest that there are colored moving expanses out there somewhere.

Consider also the experience of seeing something flying overhead and
hearing something flying overhead. While these two experiences have
quite different phenomenal characters, their representational contents
are plausibly the same: there's something flying overhead. (The most
obvious way of differentiating them—by talking of the "way" of
representing—brings in something nonrepresentational.) If this is
right, then phenomenal character does not supervene on
representational character. In response to objections of this sort,
intramodal representationalists restrict their view so that it applies
only within a given sensory modality. Unlike intermodal
representationalists, who claim that all phenomenal differences, even
differences between sensory modalities, can be explained in terms of
representational content, intramodal representationalists think that
we must offer some additional explanation to account for what makes a
phenomenal experience auditory rather than visual, or visual rather
than tactile. Typically, this additional explanation is provided in
functionalist terms. (See Lycan 1996, esp. 134-35)

Along with these sorts of counterexamples, representationalism also
falls victim to a version of the inverted qualia argument: the case of
Inverted Earth (Block 1990). On Inverted Earth, the colors of objects
are inverted relative to earth. Ripe tomatoes are green; unripe
tomatoes are red. Big Bird is blue; the Cookie Monster is yellow.
Other than this color inversion, everything else on Inverted Earth is
exactly like earth. Now imagine that, without your knowledge, you are
fitted with color-inverting lenses and transported to Inverted Earth.
Since the lens-inversion cancels out the inversion of colors of
Inverted Earth, you are unable to detect that you're in a different
environment. When you look at the sky on Inverted Earth, you have a
blue experience even though the sky there is yellow; when you look at
the green ripe tomatoes, you have a red experience. While originally
on earth, your red experience while looking at ripe tomatoes
represented red. But according to Block, after enough time passes and
you have become embedded in the linguistic and physical environment of
Inverted Earth, your reddish experience while looking at ripe tomatoes
represents green (since that is the color of the ripe tomatoes on
Inverted Earth). If Block's description of the Inverted Earth case is
correct, then two experiences having identical qualitative character
can differ in their intentional contents; thus, qualia do not
supervene on intentional content and representationalism must be
false.

In response to the Inverted Earth scenario, representationalists often
adopt a teleological account of intentionality according to which the
intentional contents of an individual's qualitative states are
determined by the evolutionary history of its species. This allows
them to reject Block's assertion that your intentional contents switch
to match the Inverted Earthlings intentional contents. Humans have
evolved such that red experiences represent red things. Thus, no
matter how long you spend on Inverted Earth, the intentional contents
of your reddish experiences will never switch to match the intentional
contents of the Inverted Earthlings.

A completely different source of worry about representationalism has
been raised by John Searle. Searle agrees with the representationalist
that there is a close connection between phenomenal consciousness and
intentionality, but he thinks that the representationalist gets the
explanatory connection backwards. Rather than explain consciousness in
terms of intentionality, Searle claims that we need to explain
intentionality in terms of consciousness: "There is a conceptual
connection between consciousness and intentionality that has the
consequence that a complete theory of intentionality requires an
account of consciousness." (Searle 1992, 132) Recent work by George
Graham, Terry Horgan, and John Tienson argues along similar lines. On
their view, "the most fundamental, nonderivative sort of
intentionality is fully constituted by phenomenology." (Graham and
Horgan 2008, 92; see also Horgan and Tienson 2002)
5. Eliminativism about Qualia

Rather than trying to find some way to fit qualia into a physicalist
theory of mind, some philosophers have taken an entirely different
attitude towards qualia. They deny that qualia exist. This position is
known as eliminativism about qualia, and it commonly constitutes a
part of a larger eliminativist project about mental states in general.
For example, Paul and Patricia Churchland have argued (both together
and individually) that as we gain more and more neuroscientific
understanding of our mental lives, we will come to see that our
current mental state concepts—belief, pain, sensation, qualia,
etc.—all need to be discarded.

The Churchlands offer numerous useful analogies to help make this
point. To consider just one of their examples: Ptolemaic theory placed
the Earth at the center of the universe, around which a giant
celestial sphere revolved. This created all sorts of difficult
problems in need of solutions, like determining the cause of the
sphere's rotation. When Newtonian theory displaced Ptolemaic theory,
the notion of the celestial sphere was completely discarded. It wasn't
that Ptolemaic theorists had an inadequate account of the celestial
sphere; rather, what was discovered was that there was no celestial
sphere. Thus, the problem of what causes the sphere's movement turned
out to be a pseudo-problem. Similarly, the Churchlands predict that as
our neuroscientific knowledge increases, we will come to see that the
problem of qualia is a pseudo-problem, because we will come to see
that there are no qualia—at least not as presently understood. Just as
the celestial sphere did not turn out to be identifiable with or
reducible to some element of Newtonian theory, qualia will not turn
out to be identifiable with or reducible to some element of future
neuroscientific theory. Rather, the concept will have to be eliminated
entirely. (P.S. Churchland 1986, 292-293; P.M. Churchland 1984, 43-45)

Insofar as eliminative materialism merely makes a prediction about
what will happen once we increase our neuroscientific knowledge, it is
hard to evaluate. However, Daniel Dennett offers related arguments for
eliminativism designed to show there is such internal inconsistency in
our notion of qualia that we are hopelessly misguided in trying to
retain it. According to Dennett, there are no properties that meet the
standard conception of qualia (that is, properties of experience that
are intrinsic, ineffable, directly and/or immediately introspectible,
and private). He reaches this conclusion by consideration of numerous
thought experiments that are designed to tease out the alleged
confusions inherent in our concept of qualia. For example, consider
two coffee drinkers, Chase and Sanborn. Both discover one day that
they no longer like the Maxwell House coffee they've long enjoyed.
Chase claims: "Even though the coffee still tastes the same to me, I
now no longer like that taste." In contrast, Sanborn claims: "The
coffee now tastes different to me, and I don't like the new taste."
But, asks Dennett, how do they know this? Perhaps Chase's taste
receptors have changed so gradually that he hasn't noticed a change in
taste; that is, perhaps he's really in the situation that Sanborn
purports to be in. Or perhaps Sanborn's standards have changed so
gradually that he hasn't noticed that he now employs different
criteria in evaluating the coffee; that is, perhaps he's really in the
situation that Chase purports to be in. There seems no first-personal
way for Chase and Sanborn to settle the matter, calling into question
the idea that they have any kind of direct or special access to
private properties of their experience. We might try to devise some
behavioral tests to detect the difference, but if we could do so, that
would suggest that qualia could be defined relationally, in reference
to behavior, and this would call into question the idea that they are
intrinsic. Thus, concludes Dennett, our conception of qualia is so
confused that it would be "tactically obtuse" to try to salvage the
notion; rather, we should just admit that "there simply are no qualia
at all." (Dennett 1988)
6. Naturalistic Dualism

There is at least one further option available to philosophers when
confronting the hard problem of consciousness. Without denying the
reality of qualia, one might simply accept that they resist reduction
in physical, functional, or representational terms and embrace some
form of dualism. This is David Chalmers' own approach to the hard
problem. Because he believes that we can account for phenomenal
consciousness within a solely natural framework, he adopts what he
refers to as naturalistic dualism.

Descartes' dualism was a version of substance dualism. According to
Descartes, the mind is an immaterial substance existing independently
of the body. In contrast, Chalmers' dualism is a version of property
dualism. This view does not posit the existence of any nonphysical or
immaterial substances, but instead posits the existence of
properties—qualia—that are ontologically independent of any physical
properties. Though these properties are not entailed by physicalism
(that is, though they do not logically supervene on physical
properties) they may nonetheless somehow arise from them. As Chalmers
describes his view: "[C]onsciousness arises from a physical substrate
in virtue of certain contingent laws of nature, which are not
themselves implied by physical laws." (Chalmers 1996, 125)

Physics postulates a number of fundamental features of the world:
mass, spin, charge, etc. Naturalistic dualism adds nonphysical
phenomenal properties to this list. Correspondingly, it suggests we
must add fundamental laws governing the behavior of the fundamental
phenomenal features to the list of the fundamental laws governing the
behavior of the fundamental physical features of the world. We don't
presently understand exactly what these new laws and the completed
theory containing them will look like, and Chalmers admits that
developing such a theory will not be easy, but in principle it should
be possible to do so.

This commitment to lawfulness is what allows Chalmers to remain within
a naturalistic framework, even as he abandons the physicalistic
framework. On his view, "the world still consists in a network of
fundamental properties related by basic laws, and everything is to be
ultimately explained in those terms. All that has happened is that the
inventory of properties and laws has been expanded [beyond the
physical properties and laws]." (Chalmers 1996, 127-8) In a similar
spirit, Gregg Rosenberg has recently offered a view he calls liberal
naturalism.Though liberal naturalism holds that the fundamental
properties of the world "are mutually related in a coherent and
natural way by a single set of fundamental laws," it denies that these
properties and laws can all be completely captured in physical terms.
(Rosenberg 2004, 9)

In giving up physicalism, naturalists argue that we can retain almost
everything that's important about our current scientific worldview.
But the adoption of nonphysicalistic naturalism typically leads in two
directions that many have thought problematic. First, it seems to
imply panpsychism, the view that everything in the universe has
consciousness. Once you accept the existence of nonphysical features
of the world that are fundamental, it is hard to find a principled way
of limiting exactly where those fundamental features are found. As
Chalmers admits, "if experience is truly a fundamental property, it
seems natural for it to be widespread." (Chalmers 1996, 297; see also
Nagel 1979) Second, it seems to commit one to epiphenomenalism, the
view that qualia lack any causal power whatsoever. Intuitively, we
believe that the qualitative character of pain—the fact that it
hurts—causes us to react the way that we do when we feel pain. But if
qualia are epiphenomenal, then the painfulness of pain is causally
inert.

In addressing the first of these two worries, Chalmers denies that
naturalistic dualism entails panpyschism. Though he recognizes that it
provides a particularly elegant way of working out the details of the
view that experience supervenes naturally on the physical, he believes
that there remains the possibility that those details could be worked
out another way. Benjamin Libet, for example, offers a theory that
sees consciousness as fundamental without endorsing panpsychism (Libet
1996). In contrast to Chalmers and Libet, Rosenberg concedes that
nonreductive naturalism will most likely require us to adopt at least
a weak form of panpsychism, and he offers arguments to show why this
consequence should not be seen as threatening.

Even if naturalism leads only to a mild form of panpyschism, however,
most contemporary philosophers would find this extremely problematic.
How could blades of grass, or rocks, or atoms be conscious?
Panpsychism is almost universally regarded with skepticism, if not
outright scorn. Colin McGinn, for example, has claimed that
panpsychism is "metaphysically and scientifically outrageous." (McGinn
1996, 34) Similarly, in reaction to Chalmers' panpsychist musings,
John Searle calls panpsychism "absurd" and claims that there is "not
the slightest reason" to adopt it. (Searle 1997, 161)

The worries about epiphenomenalism are no less troublesome for the
naturalist than are the worries about panpsychism. Intuitively
speaking, qualia are important aspects of our mental lives. The
itchiness of an itch makes us scratch, the delicious taste of
chocolate leads us to reach for another piece, the wrenching feeling
of grief erupts in a flood of tears. But if qualia are physically
irreducible, then it seems they must be left out of the causal
explanations of our actions. We typically assume that the physical
world is causally closed; all physical events, including bodily
movements, can be given complete causal explanations in wholly
physical terms. Unless we reject causal closure, then assuming we do
not want to embrace the possibility of causal overdetermination,
qualia have no role to play in the causal story of our actions.

We can easily see why naturalism leads to epiphenomenalism by
reconsidering the zombie world. By hypothesis, your zombie twin is
behaviorally indistinguishable from you despite having no qualia. His
actions can be causally explained entirely by the physical workings of
his brain. But he's a molecule-for-molecule duplicate of you, so the
physical workings of your brain can provide a complete causal
explanation of your actions. Your qualia play no role in causing the
actions that you perform.

Chalmers addresses the threat of epiphenomenalism in two ways. First,
he suggests that our inadequate understanding of the nature of
causation may here be leading us astray: "it is possible that when
causation is better understood we will be in a position to understand
a subtle way in which consciousness may be relevant." (Chalmers 1996,
150) Second, he tries to show that epiphenomenalism may not be as
unpalatable as many have thought. In particular, he argues that we
don't have any reasons to reject epiphenomenalism except for its
seeming counterintuitive; there are no effective arguments against it.
(See also Jackson 1982.) Moreover, given the fatal flaws that threaten
the competing alternatives to naturalistic dualism, it may turn out
that accepting some degree of counterintuitiveness is the small price
we have to pay in order to develop a coherent and unmysterious view of
consciousness and its place in nature.
7. References and Further Reading

* Block, N. 2007. Consciousness, Function, and Representation.
Cambridge, Mass.: The MIT Press.
o A very useful collection bringing together Block's
impressive body of work in philosophy of mind on issues relating to
functionalism, qualia, and consciousness.
* Block, N. 2003. "Mental Paint." In Martin Hahn and Bjorn
Ramberg, eds., Reflections and Replies: Essays on the Philosophy of
Tyler Burge, 165-200. Cambridge, Mass.: The MIT Press, 2003. Reprinted
in Block 2007, 533-563; page references are to the reprinted version.
o A helpful characterization of the issues surrounding
representationalism (which Block calls representationism) and a
defense of a qualia realist view he calls phenomenism.
* Block, N. 1994. "Qualia." In Samuel Guttenplan, ed., A Companion
to the Philosophy of Mind, 514-520. Oxford: Blackwell Publishers.
Reprinted in Block 2007, 501-510.
* Block, N. 1990. "Inverted Earth." In James Tomberlin, ed.,
Philosophical Perspectives 4, Action Theory and Philosophy of Mind,
53-79. Atascadero, Calif.: Ridgeview. Reprinted in Block 2007,
511-532.
o A reply to Harman's "The Intrinsic Quality of Experience."
This paper introduces the much-discussed Inverted Earth thought
experiment, a version of the inverted qualia argument targeting
representationalism.
* Block, N. 1978. "Troubles with Functionalism." In C.W. Savage,
ed., Perception and Cognition: Issues in the Foundations of
Psychology, pp. 261-326. Reprinted with revision and abridgement in
Block 2007, 63-101.
o An influential work that develops in detail the absent
qualia objection to functionalism.
* Block, N., Flanagan, O., and Guzeldere, G., eds. 1997. The
Nature of Consciousness. Cambridge, Mass.: The MIT Press.
o An anthology collecting much of the classic work on consciousness.
* Byrne, A. 2001. "Intentionalism Defended." Philosophical Review
110: 199-240.
o A very useful overview of the issues surrounding
representationalism.
* Chalmers, D. 1996. The Conscious Mind: In Search of a
Fundamental Theory. Oxford: Oxford University Press.
o One of the most important books in philosophy of mind over
the last twenty years; introduces and discusses in detail the hard
problem of consciousness. Although the book is technical in parts, the
most technical sections are indicated by asterisk and can be skipped
without losing the overall argument.
* Chalmers, D. 1995. "Facing Up to the Problem of Consciousness."
Journal of Consciousness Studies 2: 200-219.
* Churchland, P.M. 1984. Matter and Consciousness: A Contemporary
Introduction to the Philosophy of Mind. Cambridge, Mass.: The MIT
Press.
o An accessible introductory text to the philosophy of mind,
though Churchland's own eliminativist leanings shade his treatment of
the issues discussed.
* Churchland, P.S. 1986. Neurophilosophy: Toward a Unified Science
of the Mind-Brain. Cambridge, Mass.: The MIT Press.
* Churchland, P.M. and Churchland, P.S. 1981. "Functionalism,
Qualia, and Intentionality." Philosophical Topics 12: 121-145.
* Conee, E. 1994. "Phenomenal Knowledge." Australasian Journal of
Philosophy 72: 136-150. Reprinted in Ludlow et al, 2004.
o A classic presentation of Conee's "acquaintance
hypothesis" in response to Jackson's knowledge argument.
* Dennett, D. 1991. Consciousness Explained. Boston: Little, Brown
and Company.
* Dennett, D. 1988. "Quining Qualia." In A. Marcel and E. Bisiach,
eds., Consciousness in Contemporary Science, 43-77. Oxford: Oxford
University Press.
o Argues, in Dennett's characteristically jocular style, for
eliminativism about qualia.
* Dretske, F. 1995. Naturalizing the Mind. Cambridge, Mass.: The MIT Press.
o A sustained argument for representationalism, with
sustained discussion of how representation works.
* Graham, G. and Horgan, T. "Qualia Realism's Contents and
Discontents." In Edmond Wright, ed., The Case for Qualia. Cambridge,
Mass.: The MIT Press (2008), 89-107.
* Harman, G. 1990. "The Intrinsic Quality of Experience." In James
Tomberlin, ed., Philosophical Perspectives 4, Action Theory and
Philosophy of Mind, 31-52. Atascadero, Calif.: Ridgeview. Reprinted in
Block et al, 1997, 663-675; page references to the reprinted version.
o Introduces considerations of the transparency of
experience into contemporary discussions of qualia.
* Haugeland, J. 1978. "The Nature and Plausibility of
Cognitivism." Behavioral and Brain Sciences 2: 215-260.
* Hill, C. and McLaughlin, B. 1999. "There are Fewer Things in
Reality than are Dreamt of in Chalmers' Philosophy." Journal of
Phenomenological Research 59: 445-454.
* Horgan, T. and Tienson, J. 2002. "The Intentionality of
Phenomenology and the Phenomenology of Intentionality." In David
Chalmers, ed., Philosophy of Mind: Classical and Contemporary
Readings. Oxford: Oxford University Press (2002), 520-533.
* Jackson, F. 1982. "Epiphenomenal Qualia." Philosophical
Quarterly 32: 127-136. Reprinted in Ludlow et al, 2004.
o Jackson's classic paper first laying out the Mary case and
the knowledge argument against physicalism.
* Keeley, B. 2009. "The Early History of the Quale and Its
Relation to the Senses." In John Symons and Paco Calvo, eds.,
Routledge Companion to the Philosophy of Psychology. New York:
Routledge Press.
o Reviews the history of the use of the term "qualia," both
before and after C.I. Lewis introduced it into the philosophical
literature in roughly its contemporary sense.
* Kind, A. 2003. "What's So Transparent About Transparency?"
Philosophical Studies 115: 225-244.
* Levine, J. 1983. "Materialism and Qualia: The Explanatory Gap."
Pacific Philosophical Quarterly 64: 354-361.
* Lewis, C.I. 1929. Mind and the World Order. New York: Charles
Scribner's Sons.
o Introduces the term "qualia" in its contemporary sense
(introspectible, monadic, subjective properties), though Lewis uses it
in the context of sense data.
* Lewis, D. 1988. "What Experience Teaches." In J.
Copley-Coltheart, ed., Proceedings of the Russellian Society 13:
29-57. Reprinted in Ludlow et al, 2004.
o An influential presentation of the "ability hypothesis" in
response to Jackson's knowledge argument.
* Libet, B. 1996. "Solutions to the Hard Problem of
Consciousness." Journal of Consciousness Studies 3: 33-35.
* Loar, B. 1990. "Phenomenal States." In James Tomberlin, ed.,
Philosophical Perspectives 4, Action Theory and Philosophy of Mind,
81-108. Atascadero, Calif.: Ridgeview. Revised version reprinted in
Ludlow et al, 2004.
* Ludlow, P., Nagasawa, Y., and Stoljar, D. 2004. There's
Something About Mary: Essays on Phenomenal Consciousness and Frank
Jackson's Knowledge Argument. Cambridge, Mass.: The MIT Press.
o An anthology that collects Jackson's original two papers
laying out the knowledge argument along with many important papers in
response. Also contains Jackson's recent surprising recantation of the
original argument, published here for the first time. Jackson now
believes that the representationalist view helps us to see how the
argument goes wrong.
* Lycan, W.G. 1996. Consciousness and Experience. Cambridge,
Mass.: The MIT Press.
o A development of Lycan's intramodal representationalism.
* Lycan, W. 1995. Consciousness. Cambridge, Mass.: The MIT Press.
* McGinn, C. 1989. "Can We Solve the Mind-Body Problem?" Mind 98:
349-366. Reprinted in Block et al, 1997, 529-542.
o Defends new mysterianism, that is, the view that the
problem of consciousness cannot in principle be solved.
* McGinn, C. 1996. The Character of Mind (Second Edition). Oxford:
Oxford University Press.
* Nagel, T. 1998. "Conceiving the Impossible and the Mind-Body
Problem", Philosophy 73: 337-352
* Nagel, T. 1979. "Panpsychism." In Mortal Questions. Cambridge
University Press.
* Nagel, T. 1974. "What is it Like to be a Bat?" Philosophical
Review 83: 435-450. Reprinted in Block et al, 1997, 519-527; page
references are to the reprinted version.
o A classic paper arguing that physicalism cannot
accommodate the subjective aspects of experience—much-cited and well
worth reading.
* Rosenberg, G. 2004. A Place for Consciousness. Oxford: Oxford
University Press.
* Searle, John. 1997. The Mystery of Consciousness. New York: New
York Review of Books.
o A collection of Searle's essays from The New York Review of Books.
* Searle, J. 1992. The Rediscovery of the Mind. Cambridge, Mass.:
The MIT Press.
o Argues for a conceptual connection between consciousness
and intentionality.
* Shoemaker, S. 1975. "Functionalism and Qualia." Philosophical
Studies 27, 291-315.
o An interesting argument attempting to show that
functionalism can handle inverted qualia. Shoemaker's own view about
qualia is somewhat idiosyncratic in that he denies they are directly
introspectible.
* Siewert, C. 2004. "Is Experience Transparent?" Philosophical
Studies, 117: 15-41.
* Tye, M. 2000. Consciousness, Color, and Content. Cambridge,
Mass.: The MIT Press.
o Further development of the representationalist view,
including responses to common criticisms of the view.
* Tye, M. 1995. Ten Problems of Consciousness. Cambridge, Mass.:
The MIT Press.
o Develops a strong representationalist view in an attempt
to unravel several puzzling aspects of consciousness (its
subjectivity, transparency, etc.).
* Tye, M. 1990. "A Representational Theory of Pains and their
Phenomenal Character." In James Tomberlin, ed., Philosophical
Perspectives 9. Atascadero, Calif.: Ridgeview.
o An early statement of representationalism, here limited
specifically to pain.