In this example, which is contrary to epiphenomenalism, mental states do cause behavior. Epiphenomenalism, just as idealism, precludes the possibility of free will. If the environment causes brain activity and brain processes dictate our behavior, then humans simply exist passively and in a state of powerlessness. Thus, according to this theory, humans have no free will. Materialism, a subcategory of monism, contains three additional mind-body theories.
Materialism defines reality as consisting of only matter.
This excludes the mind from contributing to one's reality. The materialist theories are identity theory, behaviorism, and functionalism. Identity theory states that the mind is created from the interaction of the brain and the central nervous system. That is, the mind is equivalent to both the brain and the central nervous system. The mind, according to the identity theory, is a by-product of biochemical processes conducted by the brain.