From Bill Lycan's preliminary description of his seminar on Dualism:
"First we shall examine the standard objections and consider some Dualist replies.
(I have come to think that the standard objections are actually pretty
feeble.)" Unless something has drastically changed, Bill is a staunch materialist in spite of this, so it's interesting that he'd trash the standard objections.
"April 4: Intentionality! (I think plain old intentionality is a much
worse problem for materialism than is anything in the area of subjectivity,
qualia, phenomenal character,....)"
I fairly well agree with that. In the fall of 2004, I wrote a paper for Bill on the Knowledge Argument. The argument runs as follows: you can know anything you want about the physical structure of the world, as well as neurology and psychology, the dynamics of color perception, etc, but if you have never seen red, then none of that information will tell you what it is like to see red. Therefore, there is some fact you do not know if you merely possess all the physical information. This is a problem for materialism (when you try to make this sentence precise, there be dragons in that forest...). The standard response is to say that you do gain information when you experience red which is not a consequence of physics, etc. This is just because you have a particular "introspective perspective" that is, your brain monitors the activities going on inside of your brain more or less directly, so that particular types of activity in your brain appear to you as seeing red.
My paper argued(*) that this response didn't get you squat, because the notion of a perspective was every bit as problematic for materialism as the explanatory gap between physics and color sensations. The problem is closely linked to how original intentionality arises: how is it that this particular lump of matter comes to have a viewpoint on the world, which is roughly similar to having any intentionality at all, since presumably any creature with intentionality has some sort of perspective.
(*) Actually, my paper did not argue anything. It flailed at various targets.