Thanks for all the thoughtful replies.
I think I need to clarify what I'm trying to say a little bit further. When we talk about "mental states", I think we need to make a distinction between their informational content, their function and their structure on the one hand, and the feel
of them on the other. This is basically the distinction David Chalmers does when he talks about the 'hard' problem of consciousness.
Now I'm perfectly in agreement that as far as the informational content, the function and the structure of a mental state goes, this should pose no problem for the physicalist view. I can imagine how the brain could analyze these bits of 'data', as it were.
However, when it comes to the subjective feel
of mental states - the qualia or the consciousness of it all - then I think physicalism may run into some problems. What I don't see is how these subjective feels are supposed to, if you will, loop back into the system. Now of course you may argue that this is just because I see them as something "over and above" their functions and structures, and that I'm not willing to equate
them with these, which would make the problem go away.
I don't think you can
equate them, though. However hard you try to reduce the mental to the physical, saying that consciousness just is
its functions, it seems to me that you can't get away from the fact that there is also something it is like
to be these functions, to use Nagel's way of putting it. There's an objective/subjective split here that I think we need to acknowledge. No amount of mapping down the functions and structures of brain states will ever let us "see" the subjective states that accompany these. Indeed, we can't even prove that the brains we're investigating are, in fact, conscious. It is something we have to take for granted, "over and above" it's functions and structures, which we can
To return to the question of thinking about mental states, what puzzles me is that we can reflect upon, say, the sound
of a tree falling, rather than just the fact that soundwaves enter our ears, are translated into elecrical signals, sent to the brain where they are represented as some kind of informational structure (now of course we can't think about this without the knowledge of soundwaves etc., but my point should be clear: the qualitative feel
of sound doesn't seem to follow from these processes being performed alone).