Qualia [kwah-lee-uh], singular ‘quale’ [kwah-lee], from a Latin word meaning for ‘what sort’ or ‘what kind,’ is a term used in philosophy to refer to subjective conscious experiences as ‘raw feels.’ Examples of qualia are the pain of a headache, the taste of wine, the experience of taking a recreational drug, or the perceived redness of an evening sky.

American philosopher Daniel Dennett writes that qualia is ‘an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us.’ Erwin Schrödinger, the famous physicist, had this counter-materialist take: ‘The sensation of color cannot be accounted for by the physicist’s objective picture of light-waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so.’

The importance of qualia in philosophy of mind comes largely from the fact that they are seen as posing a fundamental problem for materialist explanations of the mind-body problem. Much of the debate over their importance hinges on the definition of the term that is used, as various philosophers emphasize or deny the existence of certain features of qualia.

Daniel Dennett identifies four properties that are commonly ascribed to qualia. According to these, 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 things. Private; that is, all interpersonal comparisons of qualia are systematically impossible. And 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.

If qualia of this sort exist, then a normally sighted person who sees red would be unable to describe the experience of this 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 700-nm wavelength is directed at you,’ supporters of this kind of qualia contend that such a description is incapable of providing a complete description of the experience.

Another way of defining qualia is as ‘raw feels.’ A raw feel is a perception in and of itself, considered entirely in isolation from any effect it might have on behavior and behavioral disposition.

Since it is by definition difficult or impossible to convey qualia verbally, it is difficult to demonstrate them directly in an argument; a more tangential approach is needed. Arguments for qualia generally come in the form of thought experiments designed to lead one to the conclusion that qualia exist.

Although it does not actually mention the word ‘qualia,’ Thomas Nagel’s paper ‘What Is it Like to Be a Bat?’ is often cited in debates over qualia. Nagel argues that consciousness has an essentially subjective character, a what-it-is-like aspect. He states that ‘an organism has conscious mental states if and only if there is something that it is like to be that organism — something it is like for the organism.’ Nagel also suggests that the subjective aspect of the mind may not ever be sufficiently accounted for by the objective methods of reductionistic science. He claims that ‘[i]f we acknowledge that a physical theory of mind must account for the subjective character of experience, we must admit that no presently available conception gives us a clue how this could be done.’ Furthermore, he states that ‘it seems unlikely that any physical theory of mind can be contemplated until more thought has been given to the general problem of subjective and objective.’

The inverted spectrum thought experiment, originally developed by John Locke, 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 inverted. Furthermore, we discover that no physical changes have occurred in our brains or bodies that would explain this phenomenon. Supporters of the existence of qualia argue that since we can imagine this happening without contradiction, it follows that we are imagining a change in a property that determines the way things look to us, but that has no physical basis.

The argument thus claims that if we find the inverted spectrum plausible, we must admit that qualia exist (and are non-physical). Some philosophers find it absurd that an armchair argument can prove something to exist, and the detailed argument does involve a lot of assumptions about conceivability and possibility, which are open to criticism. Perhaps it is not possible for a given brain state to produce anything other than a given quale in our universe, and that is all that matters.

A similar argument holds that it is conceivable that there could be physical duplicates of people, called ‘zombies,’ without any qualia at all. These ‘zombies’ would demonstrate outward behavior precisely similar to that of a normal human, but would not have a subjective phenomenology. It is worth noting that a necessary condition for the possibility of philosophical zombies is that there be no specific part or parts of the brain that directly give rise to qualia—the zombie can only exist if subjective consciousness is causally separate from the physical brain.

Joseph Levine’s paper ‘Conceivability, Identity, and the Explanatory Gap’ takes up where the criticisms of conceivability arguments, such as the inverted spectrum argument and the zombie argument, leave off. Levine agrees that conceivability is flawed as a means of establishing metaphysical realities, but points out that even if we come to the metaphysical conclusion that qualia are physical, there is still an explanatory problem. ‘Even if conceivability considerations do not establish that the mind is in fact distinct from the body, or that mental properties are metaphysically irreducible to physical properties, still they do demonstrate that we lack an explanation of the mental in terms of the physical.’ ‘In the end, we are right back where we started. The explanatory gap argument doesn’t demonstrate a gap in nature, but a gap in our understanding of nature. Of course a plausible explanation for there being a gap in our understanding of nature is that there is a genuine gap in nature. But so long as we have countervailing reasons for doubting the latter, we have to look elsewhere for an explanation of the former.’

Frank Jackson offers what he calls the ‘knowledge argument’ for qualia. One example 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 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.

Later, however, Jackson rejected epiphenomenalism. This, he argues, is due to the fact that when Mary first sees red, she says ‘wow,’ so it must be Mary’s qualia that causes her to say ‘wow.’ This contradicts epiphenomenalism. Since the Mary’s room thought experiment seems to create this contradiction, there must be something wrong with it. This is often referred to as the ‘there must be a reply’ reply.

In ‘Consciousness Explained’ (1991) and ‘Quining Qualia’ (1988), Daniel Dennett offers an argument against qualia that attempts to show that the above definition breaks down when one tries 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 defined for qualia.

In Dennett’s updated version of the inverted spectrum thought experiment, ‘alternative neurosurgery,’ you again awake to find that your qualia have been inverted—grass appears red, the sky appears orange, etc. According to the original 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; or that 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 a response to the ‘Mary the color scientist’ thought experiment. 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 ‘quale’ of color. Mary would therefore already know exactly what to expect of seeing red, before ever leaving the room. Dennett argues that the misleading aspect of the story is that Mary is supposed to not merely be knowledgeable about color but to actually know all the physical facts about it, which would be a knowledge so deep that it exceeds what can be imagined, and twists our intuitions.

If Mary really does know everything physical there is to know about the experience of color, then this effectively grants her almost omniscient powers of knowledge. Using this, she will be able to deduce her own reaction, and figure out exactly what the experience of seeing red will feel like. Dennett finds that many people find it difficult to see this, so he uses the case of RoboMary to further illustrate what it would be like for Mary to possess such a vast knowledge of the physical workings of the human brain and color vision. RoboMary is an intelligent robot who, instead of the ordinary color camera-eyes, has a software lock such that she is only able to perceive black and white and shades in-between.

RoboMary can examine the computer brain of similar non-color-locked robots when they look at a red tomato, and see exactly how they react and what kinds of impulses occur. RoboMary can also construct a simulation of her own brain, unlock the simulation’s color-lock and, with reference to the other robots, simulate exactly how this simulation of herself reacts to seeing a red tomato. RoboMary naturally has control over all of her internal states except for the color-lock. With the knowledge of her simulation’s internal states upon seeing a red tomato, RoboMary can put her own internal states directly into the states they would be in upon seeing a red tomato. In this way, without ever seeing a red tomato through her cameras, she will know exactly what it is like to see a red tomato.

Dennett uses this example to show us that Mary’s all-encompassing physical knowledge makes her own internal states as transparent as those of a robot or computer, and it is almost straightforward for her to figure out exactly how it feels to see red.

Perhaps Mary’s failure to learn exactly what seeing red feels like is simply a failure of language, or a failure of our ability to describe experiences. An alien race with a different method of communication or description might be perfectly able to teach their version of Mary exactly how seeing the color red would feel. Perhaps it is simply a uniquely human failing to communicate first-person experiences from a third-person perspective. Dennett suggests that the description might even be possible using English. He uses a simpler version of the Mary thought experiment to show how this might work. What if Mary was in a room without triangles and was prevented from seeing or making any triangles? An English-language description of just a few words would be sufficient for her to imagine what it is like to see a triangle—she can simply and directly visualize a triangle in her mind. Similarly, Dennett proposes, it is perfectly, logically possible that the quale of what it is like to see red could eventually be described in an English-language description of millions or billions of words.

The veteran artificial intelligence researcher Marvin Minsky thinks the problems posed by qualia are essentially issues of complexity, or rather of mistaking complexity for simplicity: ‘Now, a philosophical dualist might then complain: ‘You’ve described how hurting affects your mind — but you still can’t express how hurting feels.’ This, I maintain, is a huge mistake — that attempt to reify ‘feeling’ as an independent entity, with an essence that’s indescribable. As I see it, feelings are not strange alien things. It is precisely those cognitive changes themselves that constitute what ‘hurting’ is — and this also includes all those clumsy attempts to represent and summarize those changes. The big mistake comes from looking for some single, simple, ‘essence’ of hurting, rather than recognizing that this is the word we use for complex rearrangement of our disposition of resources.’

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