Functionalism is the theory that the mental state is more like a mouse trap than a diamond. That is, what makes a mental state more of a problem than what it does, not from what it is created. This distinguishes functionalism from the traditional mind-body dualism, such as René Descartes, which he thinks the mind is made of a special kind of substance, res cogitans (the substance of thought.) It also distinguishes functionalism from contemporary monism like JJC Smart’s mind-brain identity theory. The theory of identity says that the mental state is a special kind of biological state – that is, the state of the brain – and may have to be made of certain types, namely the brain. Mental state, according to identity theory, is more like a diamond than a mousetrap. Functionalism is also distinguished from the behaviorism of B. F. Skinner because it accepts the reality of the internal mental state, rather than simply connecting the psychological state with the whole organism. According to behaviorism, the mental states of a creature depend only on how he behaves (or tends to behave) in response to stimuli. Conversely, functionalists usually believe that internal and psychological states can be distinguished from “fine grains” rather than behavior – that is, different internal or psychological states can produce the same behavior. So functionalists think that’s what internal circumstances do to make them into mental states, not just what the creatures do.