For at least some of them, this would seem to include sensory qualities like color, odor, taste, sound, and the like as common sense understands them. For the mechanistic revolution Chomsky alludes to was not merely, and indeed not even essentially, committed to the idea that material causation involves literal contact. It was also and more lastingly committed to some variant or other of a “primary/secondary” quality distinction on which there is nothing in the material world that “resembles” our “ideas” of the sensory qualities mentioned (as Locke would put it). If we want to redefine the “red” of a fire engine in terms of how its surface reflects photons at certain wavelengths, we can say that the fire engine is red. But if by “red” we mean the way red “looks” to us when we perceive it, then nothing like that exists in the fire engine, which is (if we think of color in these commonsense terms) intrinsically “colorless.” And so on for sounds, tastes, and all the rest. Color, odor, taste, sound, and the like – again, as common sense understands them (rather than as redefined for purposes of physics) – are reinterpreted by mechanism as projections of the mind, existing only in consciousness. This is the origin of the “qualia problem,” and the puzzle now becomes how to relate these “qualia” or “phenomenal properties” to the intrinsically colorless, odorless, tasteless particles that make up the brain just as much as they do external material objects.
The dialectical situation in which the knowledge argument is usually taken to be located is the following: it is accepted that physicalism gives an adequate account of non-conscious reality, which constitutes almost 100 percent of the universe, but struggles to accommodate certain features of mental life, namely the “what it’s like” or qualia of certain conscious states. These latter constitute “the hard problem” for physicalism. The fact that they also constitute such a tiny part of the world is presented as a reason for thinking that they cannot plausibly be held to refute a unified physicalist account.