Qualia (singular: "quale", pronounced KWAHL-ay) are most
simply defined as the properties of sensory experiences by virtue
of which there is something it is like to have them. These properties
are, by definition, epistemically unknowable in the absence of direct
experience of them; as a result, they are also incommunicable. The
existence or lack of these properties is a hotly debated topic in
contemporary philosophy of mind.
Qualia have played a major role in contemporary philosophy of mind,
largely because they are often seen as being a de facto refutation
of physicalism. There is some debate over the precise definition
of qualia, as various philosophers emphasize or deny the existence
of certain properties.
Definition of qualia
Daniel Dennett identifies four properties which are commonly ascribed
to qualia; that is, qualia are:
- ineffable; that is, they cannot be communicated, or apprehended
by any other means than direct experience.
- intrinsic; that is, they are non-relational properties, which
do not change depending on the experience's relation to other
- private; that is, all interpersonal comparisons of qualia are
- directly or immediately apprehensible in consciousness; that
is, to experience a quale is to know one experiences a quale,
and to know all there is to know about that quale.
It is important to note that qualia do not have the status of
observed properties, which we are sure exist but might be wrong
about; rather, the concept of qualia is first and foremost dependent
on its definition, and the existence of qualia is predicated on
the existence of properties which fit that definition. Thus if we
were to discover that there is such a property as "what it
is like to have a certain experience", but that this property
was in fact knowable to others, it would not be a quale. Thus the
contemporary debate over whether or not qualia exist is largely
centered on whether or not experiences do in fact have properties
that fit this definition. At the present time, there is little consensus
over whether or not this is indeed the case.
If qualia exist, a normally-sighted person who is able to see red
is unable to describe the experience of such a perception in such
a way that a listener who has never experienced color will be able
to know everything there is to know about that experience. Though
it is possible to make an analogy, such as "red looks hot",
or to provide a description of the conditions under which the experience
occurs, such as "it's the color you see when light of such-and-such
wavelength is directed at you," supporters of qualia contend
that such a description is incapable of providing a complete description
of the experience.
C. I. Lewis, in his book Mind and the World Order published in
1929, was the first to use the term "qualia" in its generally
agreed modern sense. (His original definition was that qualia are
the "recognizable qualitative characters of the given.")
There is an ancient Sufi parable about coffee which nicely expresses
the concept: "He who tastes, knows; he who tastes not, knows
Arguments for qualia
Arguments for qualia generally come in the form of thought experiments
which are designed to lead one to the conclusion that qualia exist.
For example, the inverted spectrum thought experiment invites us
to imagine that we wake up one morning, and find that for some unknown
reason all the colors in the world have been reversed. Furthermore,
we discover that no physical changes have occurred in our brains
or bodies that would explain this phenomenon. Supporters of qualia
argue that since we can imagine this happening without contradiction,
it follows that we are imagining a change in a property which determines
the way things look to us, but which has no physical basis. The
argument thus claims that if we find the inverted spectrum plausible,
we must admit that qualia exist.
The knowledge argument
In Frank Jackson's "Epiphenomenal Qualia" (Jackson 1982),
Jackson offers what he calls the "Knowledge Argument"
for qualia. The clearest example of this argument runs as follows:
Mary the color scientist knows all the physical facts about color,
including every physical fact about the experience of color in other
people, from the behavior a particular color is likely to elicit
to the specific sequence of neurological firings that register that
a color has been seen. However, she has been confined from birth
to a room that is black and white, and is only allowed to observe
the outside world through a black and white monitor. When she is
allowed to leave the room, it must be admitted that she learns something
about the color red the first time she sees it—specifically,
she learns what it is like to see that color.
This thought experiment has two purposes. First, it is intended
to show that qualia—the properties of experiences which determine
what it is like to have those experiences—exist. If we agree
with the thought experiment, we believe that Mary gains something
after she leaves the room—that she acquires knowledge of a
particular thing that she did not possess before. That knowledge,
Jackson argues, is knowledge of the quale that corresponds to the
experience of seeing red, and it must thus be conceded that qualia
are real properties, since there is a difference between a person
who has access to a particular quale and one who does not.
The second purpose of this argument is to refute the physicalist
account of the mind. Specifically, the Knowledge Argument is an
attack on the physicalist claim about the completeness of physical
truths. The challenge the Knowledge Argument poses to physicalism
runs as follows:
- Before her release, Mary was in possession of all the physical
information about color experiences of other people.
- After her release, Mary learns something about the color experiences
of other people.
- Therefore, Before her release, Mary was not in possession of
all the information about other people’s color experiences,
even though she was in possession of all the physical information.
- There are truths about other people’s color experience
which are not physical.
- Physicalism is false.
Finally, Jackson argues that qualia are epiphenomenal: that is,
that they are causally inefficacious with respect to the physical
world. Jackson does not give a positive justification for this claim—rather,
he seems to assert it simply because it defends qualia against the
classic problem of dualism. Our natural assumption would be that
qualia must be causally efficacious in the physical world—however,
if qualia are to be non-physical properties (which they must be
in order to constitute an argument against physicalism), it is almost
impossible to imagine how they could have a causal effect on the
physical world. By redefining qualia as epiphenomenal, Jackson is
thus able to protect them from the demand of playing a causal role.
Arguments against qualia
In his paper "Quining Qualia" and his book Consciousness
Explained, Daniel Dennett offers an argument against qualia which
attempts to show that the above definition breaks down when we try
to make a practical application of it. In a series of thought experiments
which he calls "intuition pumps", he brings qualia into
the world of neurosurgery, clinical psychology, and psychological
experimentation. His argument attempts to show that once the concept
of qualia is so imported, it turns out that we can either make no
use of it in the situation in question, or that the questions posed
by the introduction of qualia are unanswerable precisely because
of the special properties of qualia.
In Dennett's updated version of the "inverted spectrum"
thought experiment, "the neurosurgical prank", you again
awake to find that your qualia have been inverted—grass appears
blue, the sky appears green, etc. According to the classical account,
you should be immediately aware that something has gone horribly
wrong. Dennett argues, however, that it is impossible to know whether
the diabolical neurosurgeons have indeed inverted your qualia (by
tampering with your optic nerve, say), or have simply inverted your
connection to memories of past qualia. Since both operations would
produce the same result, you would have no means on your own to
tell which operation has actually been conducted, and you are thus
in the odd position of not knowing whether there has been a change
in your "immediately apprehensible" qualia.
Dennett's argument revolves around the central objection that,
for qualia to be taken seriously as a component of experience—for
them to even make sense as a discrete concept—it must be possible
to show that
a) it is possible to know that a change in qualia has occurred,
as opposed to a change in something else;
b) there is a difference between having a change in qualia and
not having one.
Dennett attempts to show that we cannot satisfy (a) either through
introspection or through observation, and that qualia's very definition
undermines its chances of satisfying (b).
Dennett also has his own response to the "Mary the color scientist"
He argues that Mary would not, in fact, learn something new if
she stepped out of her black and white room to see the color red.
Dennett asserts that if she already truly knew "everything
about color", that knowledge would include a deep understanding
of why and how human neurology causes us to sense the "qualia"
of color. Mary would therefore already know exactly what to expect
of seeing red, before ever leaving the room. Dennett argues that
although we cannot conceive of such a deep knowledge, if a premise
of the thought experiment is that Mary knows all there is to know
about color, we cannot assume that we can fathom or even describe
such knowledge -- or that such knowledge doesn't exist.
Hence, as a true physicalist, Dennett leaves open the possibility
that scientists may one day understand exactly how the brain creates
the illusion of qualia, a finding which would destroy the plausibility
of qualia as a real entity.