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Qualia are the experiences of sensory input (as opposed to the describable facts of such input). (The singular is the two-syllable word quale.) In the classic example, a sighted person can see red, but cannot describe the experience of such a perception; the best he can do is make an analogy (e.g., "red looks hot") or provide informational descriptions (e.g., "it's the color you see when light of such-and-such wavelength is directed at you."). Simpler still, consider the impossibility of ever describing the experience of seeing color to a person born blind.

C. I. Lewis, in his book Mind and the World Order published in 1929, introduced the term "qualia" for the first time in its generally agreed modern sense. To him it only meant "recognizable qualitative characters of the given", whereas among philosophers today, "qualia" is used to refer to parts of experiential knowledge, i.e., that which can only be known through experience. The ancient Sufis summed up this concept in their parable about coffee: "He who tastes, knows; he who tastes not, knows not."

Table of contents
1 Definitions / descriptions
2 The enigma of qualia
3 Theories
4 References

Definitions / descriptions

  1. Recognizable qualitative characters of the given. --C. I. Lewis (1929)
  2. Parts of experiential knowledge, i.e., that which can only be known through experience.
  3. The introspectively accessible, phenomenal aspects of our mental lives. --Stanford Internet Encyclopedia of Philosophy
  4. Simplest forms of experience.
  5. Outlets of the flow of experience (from consciousness).
  6. Finest levels of (mental) qualities.
  7. Finest levels of feeling.
  8. Junction points between being and experiencing.
  9. Starting points of becoming.
  10. Introspectible and seemingly monadic properties of sense datum, but universal, not particular.
  11. 'Quale' is to 'quality' as 'quantum' is to 'quantity'. (Etymologically)
  12. Subjective qualities of conscious experience.
  13. Subjective sensations. --Ramachandran & Blakeslee (1998)
  14. Orderly modes of consciousness.
  15. Remarkable special pluralities of consciousness, whereas pluralities can be qualities or point values or impulses or (even) aspects of consciousness.

The enigma of qualia

In past centuries, philosophers and scientists alike have pondered qualia for a long time without resolution. AI researchers wonder whether machines that pass the Turing Test would experience qualia, and whether they would even need to do so. It is also possible that a sentient AI would admit to experiencing qualia, but would fail to define qualia using only an unambiguous language like that of mathematics.

The lack of a concise definition of qualia also makes people wonder if color (and sounds, etc.) are experienced differently by each person. For example, it would be impossible to tell if some people see colors inverted, since they would still call roses red and grass green.

When philosophers start to use the term "qualia" in its broader sense such as "the introspectively accessible, phenomenal aspects of our mental lives", it is difficult to deny the existence of qualia. Philosophers typically disagree on which mental states have qualia, whether qualia are intrinsic qualities of their bearers, and how qualia relate to the physical world both inside and outside the head. The status of qualia is now hotly debated largely because it is critical for understanding the nature of consciousness. Qualia are at the very heart of the mind-body problem.

There is a chapter called "Qualia Disqualified" in the book Consciousness Explained by philosopher Daniel Dennett. In that chapter, Dennett argued that the philosophical topic of qualia has become too convoluted and bizarre to be of any further use. In contrast, the biologist Gerald Edelman was willing to accept qualia and incorporate them into his brain-based theory of mind.

A commonly held idea concerning qualia is that experience in and of itself is a fundamental feature of reality and is thus, similar to space and time, irreducible in terms of explanation. Materialists downplay such a concept as a tendency by dualists to place anything they cannot explain into the metaphysical domain. Not surprisingly, qualia are a key feature in the Explanatory Gap problem of AI research, which illustrates the difficulty in explaining human experience only by mechanical means.

Qualia have been so far only considered in terms of the present moment, at the temporal interface between future and past. You can remember the information about events, but not the actual feeling you had at the time. This helps us define a key differentiator between information and experience, and why knowledge exists in these two forms. For example, you could remember having been angry at receiving a parking ticket, but that fact is now informational in nature, since the police officer also remembers you being angry. If the memory makes you angry, then your present anger is a new experience altogether and not the original experience recurring. But this is good; otherwise, we could recall qualia such as pain and headaches might never end.

In Phantoms In The Brain (1998), Ramachandran and Blakeslee presented the problems of qualia by asking: How can the flux of ions and electrical currents in little specks of jelly the neurons in my brain generate the whole subjective world of sensations like red, warmth, cold or pain? By what magic is matter transmuted into the invisible fabric of feelings and sensations?

Qualia would also appear to be macroscopic phenomena. If one could live at a sufficiently high metabolic rate, for example, then external events would slow down and be able to be experienced in merely informational terms. For this reason, qualia have been hypothesized as a form of information compression or refactoring; it is the brain's way of analyzing data that it simply doesn't have time to analyze formally.


  1. The General Theory of Qualia (2003) by Pitkänen, M. of Department of Physical Sciences, High Energy Physics Division, University of Helsinki, Finland.
  2. The Three Laws of Qualia (1997) by Ramachandran, V. S. and Hirstein, W. of the Brain and Perception Laboratory, University of California at San Diego, USA.
  3. The Physicalist Theory of Qualia (1985) by Clark, Austen of the Department of Philosophy, University of Connecticut, USA.
  4. The Representational Theory of Qualia (?) by Lycan, William G. of University of North Carolina, USA.
  5. The Epiphenomenal Qualia (?) F. Jackson, F.
  6. The Homogeneity Theory (or Grainlessness Theory of Qualia).
  7. The "Inner Sense" Theory.
  8. The Theory of Special Phenomenal Knowledge (or of Funny Facts).
  9. The Ineffability of Qualia (or of "What It’s Like").