Identity theory is one view of modern materialism that asserts that mind and matter, however capable of being logically distinguished are only different expressions of a single reality that is material; that every mental property is identical with some physical property. Identity theory is the position in the philosophy of mind which maintains that mental states and brain activities are identical, though viewed from two perspectives.
It is a form of monistic materialism in that it maintains that the mind is essentially material in nature and if it is such, it is an alternative to classical dualism which holds that minds and mental events are made of a spiritual substance which is distinct from one's material body. Identity theory adresses the problem of distinguishing sameness from change, or unity from diversity; primarily examined in connection with personal identity, universals, and the law of identity in logic. In personal identity the concern has been to determine whether anything in the body or mind remains constant; philosophers have reached no general agreement on this point. The term identity has also become increasingly important in modern psychology. It has bee used to designate a sense of self that develops in the course of a man's life and that both relates him to and sets him apart from his social milieu. Identity theory addresses the short comings of behaviorism, which maintains that mental terms designate dispositions to behave in certain ways. The key difference is that behaviorism denies mental states and focuses instead on only observable behavior. Furthermore, whereas behaviorism is usually seen as a semantic theory about the meaning of terms, identity theory is a scientific claim about mental states and brain activities themselves.