Philosopher Frank Jackson posed a thought question in 1982 that clarifies the problem that qualia poses for the strict materialist approach to the mind-brain question. It is framed as an epistemological problem. Materialism claims that the physical facts about mental states are all the facts there are. We may not understand all the material facts now (we certainly don’t ), but there are no facts about mental states that are not, in the final analysis, reducible to material facts, such as neurotransmitters, neurons, axonal electrochemical gradients, etc. Can materialism really provide all that can be known about color?
Jackson called his thought question "Mary’s Room" (1), and it has since come to be known more generally as the ‘Knowledge Argument’:
Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence ‘The sky is blue’. (…) What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not?
Jackson believed that Mary did learn something new: she learned what it was like to experience color.
It seems just obvious that she will learn something about the world and our visual experience of it. But then is it inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism [materialism] is false.[my brackets]
Many philosophers have ventured materialistic hypotheses to explain qualia in an effort to salvage the materialist paradigm, and Jackson himself later in life came to accommodate materialism (grist for future posts). But in the view of most philosophers of the mind, the Knowledge Argument represents a profound problem for any strict materialist solution to the mind-body problem. When we experience qualia, we know something that is not material knowledge. Therefore, the mind cannot be explained completely by materialism. The fact that we experience qualia is difficult to elide, and there is nothing in materialistic explanations, and nothing in neuroscience, that invokes subjective experience.
Yup. If somehow we didn't already know we were conscious, none of the facts of neuroscience would give us the hint that we were, since these facts would be the same regardless of the existence of consciousness (which they must be on the materialist assumption that consciousness cannot act as a cause separate and independent from the merely physical). All of the facts of materialist neuroscience are just as consistent with the non-existence of consciousness, and hence cannot imply or explain consciousness. So we have a brute and obvious fact of reality that materialist science is wholly incapable of explaining.
To the foolish, this is a cause for complaint.