 There are many ways to understand mental natural kinds, and theories have been proposed by eliminativists, identity theorists, functionalists and many others. We will treat each of these in turn. Physicalists hold that the differences in mental kinds relate somehow to differences in states of the subject’s brain, or, more generally, the subject’s body. At one extreme, the (type) identity theory of mind holds that types of mental state are identical with types of brain state. If so, we may expect the kinds of psychology to be identical with the kinds of neuroscience.