Functionalism and the Computational Theory of Mind

Functionalism defines a mental state not by what it is intrinsically made of but by the causal or functional role it plays within a broader system: a mental state is characterized by its typical causes (such as sensory input or other mental states), its typical effects on other mental states, and its typical effects on behavior. Hilary Putnam's influential formulation, developed across papers including "Minds and Machines" (1960) and "Psychological Predicates" (1967), drew an explicit analogy to the Turing machine, an abstract mathematical model of computation introduced by Alan Turing in "On Computable Numbers, with an Application to the Entscheidungsproblem" (1936), arguing that a mental state could be understood as analogous to a "machine state" defined purely functionally, in terms of its role within a machine table specifying transitions among states given inputs, regardless of the particular physical hardware that happens to realize that abstract machine — an idea often summarized as the "functional-state identity theory" or, in a looser sense, machine functionalism.