I began to think seriously about physicalism in the sense of this book in 1987, when I started work on my doctoral dissertation at Oxford. But by the time the dissertation had been accepted, in 1990, I had entirely lost confidence in the radically eliminativist version of physicalism that it defended. The result of my subsequent efforts to determine what was reasonable and what was not in my earlier views was a series of journal articles on physicalism; and when I began work on the present book, in the fall of 1998, I conceived my task as little more than that of revising those earlier papers, linking them up, and supplementing them here and there.

I conceived wrong. When I reviewed my earlier papers, they somehow seemed to say a lot less than I had remembered; and what they did say was often not quite right. So I decided essentially to start again. I also decided that I had to make an empirical case for physicalism, and in some detail, partly because I was irritated by the charge that adherence to physicalism is entirely unwarranted, but partly also because I had in the meantime grown skeptical about the possibility of a priori philosophical knowledge, and it seemed ludicrous to leave off the project of defending physicalism at exactly the point where, by my own account, it just starts to get interesting.