The mind seems to occupy a special place in the world. It is the seat of thought and feeling, of rationality and moral concern. Is it fundamentally different from the other things we find in the natural world? Is it possible for the mind to be investigated scientifically? Can one ever really know what is going on in the mind of someone else?

Such questions delineate the subject matter of the philosophy of mind. The central problem in this area is the mind-body problem: the project of finding an account of the mind that locates it in the broader physical world. While this problem does not exhaust the philosophy of mind, one's response to it imposes substantial constraints on what one may say about other questions in this area.

One of these questions concerns mental causation. It seems obvious that what happens in the...