Once we agree on a definition of physicalism or physical causes, we have to understand what mental states are. This description by William Hasker makes sense to me:Let us begin with a modest proposal: there are intentional conscious experiences. There are, that is to say, such episodes as a person wondering whether it is going to rain, or believing that this has been an unusually cold winter, or deciding to let the credit card balance ride for another month. In typical cases such as these the intentional content of the experience, what the experience is about, is something distinct from the experience itself, something that could exist or obtain (or fail to exist or obtain) regardless of whether or not the experience occurred. These episodes are consciously experiened; when we have them we are aware of having them, and there is "something it is like" to be having them.
This is an important concept. The idea that there is "something it is like" to, say, find a winning combination against Reppert in chess, is critical. When I play against a computer, and the computer finds a winning combination against me, the thing "functions as if" it has found the winning line against me, but there is nothing it is like to find that combination. Fritz wins all the time but never experiences the thrill of victory or the agony of defeat.
My conviction is that the intentionality Fritz possesses is a second-rate, derived, kind of intentionality, which is not to be confused with the intentionality that comes from my conscious perception of what is going on on the chessboard. Therefore, in my view, the problem of propostional attitudes "inherits" all the "hard" problems related to consciousness. When I am talking about intentionality, this is first and foremost what I have in mind, and acccounts of intentionality that leave this out are drastically incomplete.
This, to my mind is a "great divide" between myself and many naturalists.