Functionalism was seen in a broad form in Aristotle's De Anima - the mind is best conceived not as a material/ immaterial organ but as a set of capacities and functions which are in turn related to our internal organization.
David Armstrong, identity theorist, in 1970 Nature of Mind introduced functionalism to cognitive science. It was developed by Hilary Putnam.
According to Putnam (1973) the invention of the computer was an important event in contemporary philosophy of mind because it led to the idea of functional organisation. The functionalist idea challenges the assertion that thinking and other ``intelligent functions'' need to be carried out by the same specified machinery in order to reflect the same kind of process. Computers demonstrated that the processes we would once have termed ``thinking'', and assumed to be possible only by humans or others with brains like ours, could be carried out by mechanisms consisting of vaccuum tubes or transistors.
If there was an identity between two intelligent systems, it could not reside in the hardware: it had to occur in the software. Human beings and machines and perhaps other kinds of intelligent entities, could be capable of realising the same kinds of program.
Putnam later modified his position considerably: see Putnam, H. (1994) To Functionalism and Back Again in The Oxford Companion to the Philosophy of Mind, Ed. Guttenplan and Putnam, Basil Blackwell.
Cognitivism (Jerry Fodor, 1975, 1981): Mentalism which steers clear of Cartesian dualism: is a variant of functionalism, also accepts intentionality. Accepts the general information processing approach that cognitive activities consist of the manipulation of symbols. Believes that symbols of the mind are abstract entities that need bear no configurational relationship to the real-world entities that they denote.
But further Fodor, a former student of Chomsky, believes that these symbol-like representations must exist somewhere and be manipulated in some way. He believes in a medium, or a ``language of thought'' that, like natural language, is innate. For Functionalism and LOT see pp. 62-65 in Bechtel et. al., 1999.
Tutorial sec. will consider the arguments for functionalism.