The qualia-based objections are supposed to pose a 'hard' problem for defenders of physicalism. The implication is that the problems posed by intentionality are, if not exactly 'easy,' then at least tractable. An earlier post discussed a version of the knowledge argument, which is one of the qualia-based objections. (Two others are the absent qualia argument and the zombie argument.) It seems to me, though, that intentionality is also a damned hard problem for physicalists to solve, so hard in fact as to be insoluble within physicalist constraints and another excellent reason to reject physicalism.
Before proceeding I want to make two preliminary points.
The first is that the untenability of physicalism does not entail the acceptability of substance dualism. Contrapositively, the unacceptability of substance dualism does not entail the tenability of physicalism. So if a physicalist wishes to point out the problems with substance dualism, he is free to do so. But he ought not think that such problems supply compelling reasons to be a physicalist. For it is obvious that the positions stand to each other as logical contraries; hence both could be be false.
My second point is that considerations of parsimony do favor physicalism over dualistic schemes -- but only on condition that the relevant data can be adequately accounted for. And that is one big 'only if.' (See The Use and Abuse of Occam's Razor: On Multiplying Entities Beyond Necessity.)
An Argument Sketched. Mary, Meet Marty.
We were talking about Frank Jackson's Mary. Now I introduce Marty, a Martian scientist who like Mary knows everything there is to know about human brains and their supporting systems. So he knows all about what goes in the human brain and CNS when we humans suffer and enjoy twinges and tingles, smells and stinks, sights and sounds, etc. We will suppose that Marty's sensorium is very different, perhaps totally different than ours. He may have infrared color qualia but no color qualia corresponding to the portion of the EM spectrum for which we have color qualia. Marty also knows everything there is to know about what goes on in my head when I think about various things. We may even suppose that Marty is studying me right now with his super-sophisticated instruments and knows exactly what is going on in my head right now when I am in various intentional states.
Suppose I am now thinking about dogs. I needn't be thinking about any particular dog; I might just be thinking about getting a dog, which of course does not entail that there is some particular dog, Kramer say, that I am thinking about getting. Indeed, one can think about getting a dog that is distinct from every dog presently in existence! How? By thinking about having a dog breeder do his thing. If a woman tells her husband that she wants a baby, more likely than not, she is not telling him that she wants to kidnap or adopt some existing baby, but that she wants the two of them to engage in the sorts of conjugal activities that can be expected to cause a baby to exist. Same with me. I can want a dog or a cat or a sloop or a matter transmitter even if the object of my wanting does not presently exist.
So right now I am thinking about a dog, but no presently existing dog. My thinking has intentional content. It is an instance of what philosophers call intentionality. My act of thinking takes an object, or has an accusative. It exhibits aboutness or of-ness in the way a pain quale does not exhibit aboutness of of-ness. It is important to realize that my thinking is intrinsically such as to be about a dog: the aboutness is not parasitic upon an external relation to an actual dog. That is why I rigged the example the way I did. My thinking is object-directed despite there being no object in existence to which I am externally related. This blocks attempts to explain intentionality in terms of causation. Such attempts fail in any case. See my post on Representation and Causation.
The question is whether the Martian scientist can determine what that intentional content is by monitoring my neural states during the period of time I am thinking about a dog. The content before my mind has various subcontents: hairy critter, mammal, barking animal, man's best friend . . . . But none of this content will be discernible to the Martian neuroscientist on the basis of complete knowledge of my neural states, their relations to each other and to sensory input and behavioral output. To strengthen the argument we may stipulate that Marty lacks the very concept dog. Therefore, there is more to the mind than what can be known by even a completed neuroscience. Physicalism (materialism) is false.
The argument is this:
1. Marty knows all the physical and functional facts about my body and brain during the time I am thinking about a dog.
2. That I am thinking about a dog is a fact.
3. Marty does not know that I am thinking about a dog.
4. Marty does not know all the facts about me and my mental activity.
5. There are mental facts that are not physical or functional facts, and physicalism is false.
Credit where credit is due: The above is my take on a more detailed and careful argument presented here by Laurence BonJour. Good day!