Qualia is the term to used describe actual subjective experience and sensation, as opposed to mere knowledge and information.

The concept is best described by Frank Jackson's color blind scientist thought experiment: A scientist knows everything there is to know about the color red from physics, optics and neuroscience, but is color blind, and so she doesn't know what it's actually like to see the color red. If we then somehow repaired her vision so that she can now see colors, and let her see the color red, she would learn something new about red that she didn't know before, despite all of her previous knowledge about the physics and biology involved. This additional knowledge she gains is the qualia of seeing red.

What I don't understand about qualia is that they are consistently presented in every philosophy of mind source I've come across as an argument for dualism and against materialism/physicalism. Somehow, the existence of qualia is seen as proof that there is a non physical dimension to the mind (i.e. dualism), since if the mind where purely physical, there would be no difference between knowing about the color red and seeing the color red. Frank Jackson, Thomas Nagel and many others argued that qualia is definite proof in favor of dualism. David Chalmers called this the "hard problem of consciousness", the fact that philosophers have not been able to explain qualia in terms of physical brain processes.

I can see why the existence of qualia is an argument against functionalism or against the computational theory of mind: if the mind was just a fancy computer with functional states, it wouldn't matter whether knowledge of red came from other systems (learning about red through science) or direct sensation (seeing it with one's own eyes), the mental state "knowledge of red" would correspond to the same functional/computational state. The existence of qualia proves that the two states are different, and hence disproves functionalism.

But I don't see why it is an argument against physicalism in general. If anything it seems to me like the existence of qualia is a solid argument for the type identity theory of mind, (which is a more radically physicalist position than functionalism since it denies mental states any independent existence at all): knowledge about red is different from actually seeing red not because of any dualist mental substance, but because they correspond to different neurons firing in different parts of the brain. This would confirm type identity theory exactly: knowledge of red corresponds to one brain state and the sensation of red corresponds to another brain state. The sensation of seeing red, the actual qualia, is not multiply relizable, hence qualia are an argument for type-identity, and against functionalism, not in support of dualism.

My questions:

  1. Can qualia be an argument for the type identity theory of mind?
  2. Why does the existence of qualia imply the existence of a seprate non physical mental substance?

5 Answers 5


One of the basic arguments is the argument from knowledge, it is similar in spirit to Frege's argument for distinguishing sense and reference. "Hesperus is Hesperus" tells us nothing interesting, "Hesperus is Phosphorus" conveys something non-trivial, a new knowledge. Therefore, there is something to the word over and above its referent, the sense, because Hesperus and Phosphorus co-refer. Similarly, when Mary the color scientist, who knows everything physical there is to know about color, steps out of her black and white room and sees red for the first time, she seems to gain new knowledge. Therefore, there is something to the red over and above its physical correlates, the residual quale of red, which is by definition non-physical.

This being said, the argument is more of an intuition pump than logic. Indeed, Burge and Searle are dissatisfied with available materialistic accounts of qualia, but Searle is a materialist, and Burge is agnostic on the issue. Even Crick, the Nobel prize winning biologist turned neuroscientist, who is even a (programmatically) reductive materialist, calls Dennett "unhelpful on qualia" and suggests that the issue is not ripe for resolution. Type identity theory is considered non-viable for other reasons, and so is a non-starter. The idea that qualia have similar physical correlates in organisms with vastly different constitutions strains credulity, and has few supporters since Putnam's critique. Even the idea that qualia have the same physical correlates at all times within the same brain is questionable given well known plasticity of the brain.

  • 1
    Might a materialist not say that when Mary sees red for the first time, her brain moves into a state that was possible, but not yet visited, before? Is there any contradiction here, unless 'knows everything physical that there is to know about color' requires all possible color-related states to have been visited, in which case the argument becomes self-contradictory?
    – sdenham
    Commented Apr 6, 2018 at 21:03
  • @sdenham I think the argument is trying to draw a contrast between knowledge of physical properties and phenomenal experience (of color) rather than between brain and mental states. So what Mary's brain does is moot. Responses by materialists are described under the link in the post.
    – Conifold
    Commented Apr 6, 2018 at 22:21
  • The argument may be trying to draw a contrast between knowledge of physical properties and phenomenal experience, but the responses of materialists that you refer to show that they do not (all) concur. If the thought experiment has a place in an answer to the original question, then presumably objections to the argument (especially materialists' objections, given the topic of the question) are equally relevant.
    – sdenham
    Commented Apr 6, 2018 at 23:36
  • @sdenham This is an argument attached to an intuition pump, one does not need to concur with the premises it derives from intuition. The intended targets are those who do, others need not object, they can simply disregard it.
    – Conifold
    Commented Apr 6, 2018 at 23:42
  • Ah, yes - I never have fully understood the rules by which intuition may be introduced into an argument, without apparently making that argument conditional on the intuition. Maybe I should take up Amazon's offer to sell me an intuition pump.
    – sdenham
    Commented Apr 7, 2018 at 0:05

The definition of qualia is strong, but there have been questions as to whether it is strong enough to draw a line between functionalists and dualists or not.

Personally, I believe the only reason why functionalists have any problem with qualia is the cases where they overstep and state something like "I can explain what you think 'red' is." Functionalism does not always claim that they have a mapping of brain states to qualia, just that one exists. If one accidentally claims they know the mapping, they have been wrong (so far, at least). I don't think this is a problem for functionalism in general, but it does mean complications in interaction with dualists.

One particular issue is that, if I create a perfect clone of you, its qualia should correspond to the same brain states as your qualia, violating the theory that qualia is personal. This becomes an issue for these perfect-world thought experiments -- the idea of creating a perfect clone is so extraordinarily far from anything we know how to do in this world (and may potentially be actually impossible), that this debate becomes a bit of a scuffle from time to time. You could argue it is similar in nature to the "can God create a rock so heavy that even he cannot lift it" arguments, which remain a paradox until you start to dig at the meaning of language and so forth.

  • You say the definition of qualia is strong. I am not familiar with the issue or terminology, but isn't inescapable "self-reporting" simply an obstacle to many "physicalist" accounts? Commented Oct 24, 2015 at 22:48
  • @NelsonAlexander Its only an obstacle if one wishes to make it an obstacle. As of yet, from talking with physicalists, I have not found a case where qualia is a problem and yet basic chaos theory is not a problem, because the things which can cause problems for qualia also cause problems when your measurement devices must invariably change the state of the system in a way that matters to you. (These sorts of issues DO arise in 'provability' scenarios, where you have to prove that the world is physical. However, it does seem that proofs for physicalism, dualism, or idealism tend not...
    – Cort Ammon
    Commented Oct 24, 2015 at 23:55
  • ... to qualify as proofs to the other two approaches.
    – Cort Ammon
    Commented Oct 24, 2015 at 23:57
  • @jobermark I am reading my answer, over and over, and for the life of me, I can see nothing to support your genetic clone analogy. I never once mentioned genetics. I did mention the concept of a hypothetical "perfect clone," along with statements both a) we don't know how to do it and b) it may actually be impossible by the laws of physics. The entire point of the perfect clone phrasing was to avoid the exact misinterpretation you have elected to undertake today.
    – Cort Ammon
    Commented Oct 26, 2015 at 0:22
  • A concept is unlikey to cause the same activation in the same body twice. So why would it cause the same activation in a copy of it, however exact? I can remove the decoration and we can just stop there.
    – user9166
    Commented Oct 26, 2015 at 0:30
  1. Why does the existence of qualia imply the existence of a seperate non-physical mental substance.

I refer you to your earlier sentence: "knowledge of red corresponds to one brain state, and the sensation of red to another".

This misses the existence of inner life for want of a better word; one could say that knowledge of red is a kind of qualia of a certain subtle kind ie invisible to any of our outer senses; this is why it's easier to focus on a qualia that is the least subtle, which means out of all our outer senses it's easiest to focus on sight: the sensation of red.


I'm not familiar with the arguments here, but it seems there would be an issue with measurement.

To carry out any sort of "materialist-physicalist" interpretation entails, by definition, some way of defining and measuring "things." At least the possibility. What would this "atomic" level of qualia be? We can label color swatches and match them to spectra. But this does not capture the "sensation" of red, which must finally rely on self-reporting.

So if qualia are admitted, it may just be that they can never fit into the models that define some sort of "physicalist" interpretation. It's self-reporters all the way down. Not an ontological but a methodological dualism, which one might argue amounts to the same.


1) It seems premature, since we have no good evidence that 'red' has any neuronal processes in common at all once it leaves the optic nerve, to suppose that we know anything about how it might be multiply represented in the brain. (So why hold a theory so far from any data?)

2) It is more likely that red has no direct representation in the brain at all, but that it is a commonality by reference that we project onto things. Fear, or negativity, or resistance, or the notion of a person's presence, or the idea that there is a confusing contrast between tasks, or even the idea that color should or should not matter at the moment to the task at hand, do seem to have fMRI representations, but we have found real brain patterns for nothing as direct as red.

That being the case, a color is more likely to be a concept, like that of a variable, or of a personality, and we would never believe that the concept of a variable has a locus in the brain, or some simple cohesive brain-state map. Apparently simple concepts do not appear to be physiologically simpler than their less simple relatives.

What part of the processing that we do takes this very non-simple thing and makes it seem simple to us? We find it hard to accept that red really is in no way simple. It bends our notions of perception to imagine that red might be irreducibly complex.

The obvious answer is that this concept, although not simple to the brain, is simple to something else, the mind. And that suggests that the mind and the brain, even as representations of the same process, might be more productively looked at as very different things. Even if the mind is a "virtual machine" running on the brain, the virtualization may be so complete that linking the two kinds of "instruction sets" is not productive.

In that way, for emergentists, qualia suggest dualism may be a better framing than any kind of representationalistic monism that destroys our ability to consider simple concepts simple.

  • " Fear, or negativity, or resistance, or the notion of a person's presence, or the idea that there is a confusing contrast between tasks, or even the idea that color should or should not matter at the moment to the task at hand, do seem to have fMRI representations, but we have found real brain patterns for nothing as direct as red." Can you point me to some resource on that statement? It is very intriguing. Commented Oct 28, 2015 at 19:04

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