Metaphysics is out of fashion. There is, as department-store sales assistants say, not much call for it nowadays. The word “metaphysics” does not even occur in the index of the current bestseller about human nature, Steven Pinker’s The Blank Slate, nor does Professor Pinker’s text betray any interest in the topic. Most of us, if challenged to disclose our metaphysical beliefs, would probably offer a part-baked dualism. Yes, certainly there is an outer reality, “the universe,” made up of material objects whose behavior, thanks to four hundred years of diligent scientific inquiry, we can understand, or at any rate predict, in fine detail. And yes, there is an inner reality, “the self,” comprised of mental objects about which science has much less to say, and some irreducible core of which, we are inclined to think, exists independently of the material world. Those o ...