Thus, having a belief is being in a computational relation to a representation, as is having a desire. Every primitive concept in thought has a neural symbol in the brain. The end result of this in behavior is that the representation that is a belief causes an individual to behave as if it were true, whereas the representation that is a desire causes the individual to behave to make it true.

Wilfred Sellars (1912–1989) introduced the concept in his 1956 paper, “Empiricism and Philosophy of Mind.” According to Sellars, there can be no mental foundations of knowledge such as sense data, and he also rejected the pragmatists’ “myth of the given.” (By “the given,” the pragmatists referred to that part of experience that is not influenced by the perceiver or thinker.) Functionalism, as developed by Sellars, as well as Hilary Putnam (1926-) in his early writings, is the thesis that mental states can be defined by three things: what causes them, their effects on other mental states, and their effects on behavior. That is, mental states can be understood in terms of their functions, which operate like the software of a computer.