I. Definition

Qualia are the phenomenal qualities of experiences—the raw felt qualities of sensations, emotions, thoughts, or anything else.  They are experienced privately, subjectively, and directly; all the content of consciousness states is made of them.

How do you know that you’re conscious?

You probably answer, because you’re experiencing something—thoughts, feelings, sensations, sights, or sounds.  But a camera can also have images.  Does a photograph or computer screen experience the image? What’s the difference between your experience of an image and an image as an artifact?  One answer is, there is something it is like to see an image.  There is nothing it is like to be a photograph (as far as we can tell).

There is “something it is like” to hear a guitar, see a sunset, or feel someone’s arm brush against yours.  There is something it is like to have a thought or feel an emotion.  And this is what a computer doesn’t have. It may record a guitar, even identify the rhythm, timber, and pitches.  It can know the shape of the sound-waves.  But there is nothing it is like to be the computer experiencing those things (probably).

The qualities of experiences are called qualia – sometimes referred to as “raw feels”— such as the raw sensation of C-sharp, a flash of lightning, or someone’s skin against yours.  Or what happiness feels like.

Qualia are central to the questions “what is consciousness” and “how does the brain generate consciousness”?  And qualia can be difficult to talk or even think about clearly; some people argue very seriously that they don’t exist.  While others have argued that only qualia exist!

Here are some often recognized properties of qualia (all debatable):

  • That they are ineffable (indescribable)
  • They are non-physical
  • They are irreducible (cannot be taken apart into simpler pieces that are not qualia)
  • They are private; you can never experience someone else’s qualia.
  • They are experienced directly; you don’t need anything to tell you whether you’re experiencing qualia – if you seem to be, you are!
  • They are not identical to the physical processes that cause them.

Some of these properties present major questions for philosophy and science:

  • How can physical brain processes have non-physical properties? This is called “the hard problem” of consciousness.
  • If they’re not identical to the physical processes, what is the extra something? This is the “knowledge problem” and the “explanatory gap.”
  • Are they functional? If not, why do we have them?
  • Are they representational? Conceptual? Intentional? (see section four)

So, qualia take us right to the heart of the most difficult topic in philosophy – consciousness; hang on to your hat!


II. The History of Qualia

The word “qualia” is plural.  The singular is “quale” (pronounced ‘KWA-lay’).  These are forms of the Latin word for “what sort” or “what kind.”

The first person to use “qualia” in its modern sense was Clarence Irving Lewis, in 1929. And the discussion about qualia really got rolling in the 60s and 70s, especially following Thomas Nagel’s 1974 article “What it is like to be a bat” where he defined consciousness as having a “what it is like” to be something.

The first debates about qualia revolved around the philosophy of functionalism, historically associated with behaviorism in psychology.  Functionalism defines cognitive processes in terms of what they do.  It is associated with “identity theory,” an assumption of physicalism, which says that mental processes are identical to the neurological events which correspond to them.

Qualia challenge both functionalism and physicalism; historically, this challenge is represented by Frank Jackson’s 1982 “thought experiment” about Mary the neuroscientist (here in my simplified version):  Mary is a neuroscientist who has never seen color; she was born that way.  Suppose that Mary has the scientific instruments and reference materials necessary to learn everything that can possibly be known about the experience of color in the brain, down to the last detail. Then one day, someone develops a cure for Mary’s color-blindness, and it works.  The question is, when Mary sees color for the first time, does she learn anything she didn’t already know? Most people say “yes.” This is known as the “knowledge argument” against physicalism; it supposedly proves that there is something more to qualia than the physical brain processes we can objectively observe.

At the same time, Mary is an argument against functionalism as well, and an argument for what philosophers call “epiphenomenalism” – the idea that qualia have no function—that they cause nothing.

In order to understand why Mary’s experience might imply epiphenomenalism, we can proceed to the next historic thought experiment connected with qualia—David Chalmers’ 1996 “zombies” thought experiment. Which takes us right into “controversies about qualia.”


III. Quotes about Qualia

Quotation #1:

“The subject matter is perhaps best characterized as “the subjective quality of experience.” When we perceive, think, and act, there is a whir of causation and information processing, but this processing does not usually go on in the dark. There is also an internal aspect; there is something it feels like to be a cognitive agent. This internal aspect is conscious experience. Conscious experiences range from vivid color sensations to experiences of the faintest background aromas; from hard-edged pains to the elusive experience of thoughts on the tip of one’s tongue; from mundane sounds and smells to the encompassing grandeur of musical experience; from the triviality of a nagging itch to the weight of a deep existential angst; from the specificity of the taste of peppermint to the generality of one’s experience of selfhood. All these have a distinct experienced quality. All are prominent parts of the inner life of the mind. We can say that a being is conscious if there is something it is like to be that being, to use a phrase made famous by Thomas Nagel.” ― David J. Chalmers, The Conscious Mind: In Search of a Fundamental Theory

This quotation from David Chalmers nicely summarizes the mystery of qualia and how it’s framed by contemporary philosophers.

Quotation #2:

Esse est percipi, to be is to be perceived, said good old Berkeley; but, according to most philosophers, he was wrong. Yet, obviously, there are things for which the adage holds. Perception, trivially, to begin with. If elements of conscious awareness–pains, tickles, feelings of heat and cold, sensory qualia of colors, sounds, and the like–have any existence, it must consist in their being perceived by a subject…. This shows, of course, that such experiences are epiphenomenal, at least with respect to the physical world.” – Zeno Vendler

Vendler refers to Berkeley’s idealism—the idea that all existence gets its “being” from consciousness—is just that which is perceived–never a popular philosophy in the western world.  But, Vendler notes, it is true of one thing—qualia.  Like many philosophers, Vendler is certain that this means qualia must do nothing, physically.  Others disagree; Chalmers’ ‘natural dualism’ and other metaphysical proposals, such as ‘pan-psychism’ might imply otherwise.


IV. Types of Qualia

We could classify qualia according to the senses – visual, auditory, tactile, etc.  But in practice, this is not very relevant to the philosophy of qualia.  Instead, we will consider the most well-known proposals about what qualia are.

Epiphenomenal Qualia:  Qualia that have no physical effect on anything (therefore no evolutionary function); this proposal assumes that not having qualia wouldn’t make a functional difference to anyone.

Phenomenal information: This idea of qualia, associated with philosopher David Lewis, says that qualia are not epiphenomenal, not a needless experience thrown on top of the brain’s sensory information – they are that information.  So, this could be regarded as a physicalist, functionalist conception of qualia.

Neural oscillations: this is one of the best known neurobiological hypotheses about qualia, this one associated with philosopher Rodolpho Llinas.  Llinas uses evidence from experiments with anesthesia to prove that qualia correspond to a certain kind of electrical oscillation occurring in neural circuits; anesthesia shows that turning off these oscillations corresponds to turning off qualia.

Representational Qualia: Also, known as “non-conceptional intentional content.”  This conception claims that qualia are about something; this is what philosophers mean by intentional and that would make qualia representational. Philosophers disagree about whether they represent the objects they are caused by (so the redness of an apple would represent the apple) or whether they represent an abstract quality (so the redness of an apple merely represent that color of red).


V. Qualia versus Propositional Attitudes

Most philosophers would contrast qualia with propositional attitudes, another definitive feature of consciousness.  Propositional attitudes refer to states of mind such as doubt, belief, and desire.  They are attitudes that your mind can have to objects of thought or awareness.  To understand why we contrast these with qualia consider the difference between hearing a person at your door (qualia), and hearing that a person is at your door (propositional attitude).  One is a direct ineffable experience of sound.  The other one does not refer to any experience of the person coming through the door; your room-mate might have sent you a text message telling you that someone was at your door!  The first is a quale; the second is a concept.  It’s confusing because concepts have their own qualia too – but not the qualia of the things the concepts are about.  These are two very different forms of awareness—perceiving something versus perceiving that something.


VI. Controversies about Qualia

Do Qualia Refute Physicalism?

Chalmers’ zombie “thought experiment” reinforces Jackson’s knowledge argument about Mary in another attempt to refute physicalism.

Chalmers’ zombies would be beings physically identical to human beings in every detail—constructed that way perhaps—but without consciousness.  Chalmers’ point is that such zombies, which seem like a real possibility to many people—would have all the sort of knowledge about seeing colors that Mary has before her color-blindness is cured, or that any computer could have, and be able to behave exactly like human beings—but there would be nothing it is like to be zombie. They would have no qualia. This supposedly proves that qualia must be more than the physical aspect of brain activity.

Chalmers argues for “natural dualism”—that the non-physical private mind is something beyond what we can observe of the brain, but not in a supernatural sense; it’s still assumed to be an aspect of natural law, necessarily associated with those brain processes in some way.

One more argument with similar conclusions is “the inverted spectrum” thought experiment, first proposed by John Locke.  I describe a simplified version.  It’s an idea you may have thought about when you were a child.  What if your red is someone else’s green?  What if your entire color spectrum were inverted; how could you or anyone else ever know? According to argument, the mere fact that we can imagine this possibility proves that qualia are non-physical and non-causal, because they could be changed or be different in different people, without making any difference.

Together Mary and the Zombies (band name!) and the “inverted spectrum” argument suggest that qualia are real, non-physical, non-functional, and the essence of consciousness.

But, as you might guess, there are plenty of arguments against all these conclusions–entire careers spent refuting them!

Chalmers’ zombie argument is perhaps easiest to criticize.  It’s based on the assumption that Chalmersian zombies are possible—that there could be beings with the same physical structure as human beings, but no consciousness.  This is obviously questionable; it’s plausible to suppose that any being with a brain exactly like a human’s would also have to have consciousness.  Nevertheless, this argument will remain in competition until we can construct artificial beings with brains as powerful as humans’ and see what happens.  The only problem there is, how will we know whether they’re conscious or not? Take their word for it?

The inverted spectrum argument is also easy to attack, because it assumes that you would not be able to see the difference in the brain activity of a person with an inverted spectrum.  But this is probably not so, and some philosophers have even discussed the neuroscience necessary to undermine this argument.

One more argument against qualia, and for physicalism, comes from Daniel Dennett, one of the world’s most accomplished philosophers.  Dennett insists that qualia do not exist!  He says that if Mary truly knew everything about the seeing of color in the brain, she would in fact know everything to be known about the experience of seeing color; he says that our intuitions simply fail us in such thought experiments because we don’t think in sufficient detail about what it would mean for Mary to know “everything” about the perception of color in the brain.  In his book, “Consciousness Explained,” Dennett presents a lengthy argument, trying to prove, basically, that we only think we have experiences! It’s an illusion—a mistaken belief.  Many philosophers have joked that his book should have been called “Consciousness Explained Away.”  But Dennett is no fool, and his argument has yet to be conclusively disproven.


VII. Qualia in Pop Culture

Example #1: The Matrix: “tasty wheat” scene:

This scene from The Matrix presents a new version of the “inverted spectrum” argument discussed in section six above.  The philosophical argument begins with the realization that “tasty wheat” could taste like anything; and if there’s no way for the machines to know what it “really” tastes like, or for us to know what it tastes like to others, does that mean that qualia are non-physical and subjective, and physicalism is false?

Example #2: Steven Spielberg’s A.I.:

This scene from Spielberg’s film A.I presents a more realistic variant of Chalmer’s “zombie” argument—a situation which will almost surely become fact within 50 years—the existence of androids as intelligent as humans, but without the ability to experience qualia.  The main philosophical point of the “thought experiment” was that qualia exist as something more than the capacity to take in sensory information.  This robot “feels” pain in the sense of detecting damage to its skin, but it does not experience the qualia of pain–or love.  This future shows how questions about qualia may have far-reaching moral and social implications.  Are qualia the kind of things that can ever be engineered? Would the ability to experience qualia make androids deserving of “human rights”?


Which of the following are definitely qualia?





Which of the following is an undisputed quality of qualia?





The reality of qualia has often been thought to imply which of the following ideas?





Which of the following thought experiments is meant to refute physicalism?





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