Abstract

For the physicalist, the mind-body problem is the problem of finding a place for the mind in a world that is fundamentally physical. What does “fundamentally physical” mean? I think any physicalist will accept at least the following two claims. First, the world contains nothing but bits of matter and aggregates of bits of matter. There are no Cartesian souls, or Hegelian spirits, or neo-vitalist entelechies—as the emergentist C. Lloyd Morgan put it, no “alien influx” into the natural order. This ontological thesis is sometimes called “ontological physicalism”. Second, we have the supervenience thesis: physical facts determine all the facts, and the physical properties of a thing determine all its properties. At this point, then, the world looks like this: all the things that exist are physical things—either basic bits of matter or wholly made up of bits of matter. These physical things have properties. What properties? First, there are basic physical properties, like mass, size, shape, electric charge, and so on—properties and magnitudes in terms of which laws of physics are formulated. But some properties of complex physical systems, like biological organisms, seem prima facie nonphysical—at least, they are not among the properties investigated in physics or the physical sciences. Prominent among them are mental properties—beliefs, desires, sensations, emotions, and the rest. The supervenience thesis says that such properties are fixed by the physical properties of the systems that have them; once the physical properties of a system are fixed, that fixes all of its properties. And yet property dualists, or nonreductive physicalists, maintain that although certain non-physical properties are determined by physical properties, they are irreducible to, and remain distinct from, physical properties. Although thoughts and pains are determined by the biology, and ultimately physicochemistry, of an organism, they are not biological/physical properties themselves, and there exists a special autonomous science of psychology, or cognitive science, that is responsible for investigating them.