Functionalism

1. Origins of functionalism

Originally functionalism was a response to philosophical behaviourism. The behaviourists rejected the traditional Cartesian picture of the mind as an essentially private realm accessible only to the conscious subject (Descartes 1641). Instead they argued that mental states are dispositions to behaviour, and so are publicly accessible. To desire an ice cream, said the behaviourists, is to be disposed to eat one when the opportunity presents itself (see Behaviourism, analytic; Private states and language).

The functionalists argued that behaviourism fails to distinguish sufficiently between mental cause and behavioural effect. They argued that there is no simple pairing of mental states with pieces of behaviour, since which behaviour issues from any given mental state will depend on the agent’s other mental states. My desire for an ice cream will make me walk to the fridge if I believe it contains an ice cream, but it will make me walk down the street to the shop if I believe I can buy an ice cream there.

Because of this, functionalists argued that mental states are inner causes distinct from their behavioural effects. In saying this, however, they did not want to return to the Cartesian conception of mental events as essentially private states. In their view, mental states are part of the public world of causes and effects studied by science. They are ‘inner’ only in the sense that they are unobservable causes of overt behaviour, in the same way as atomic structures are unobservable causes of chemical reactions.

Because they take mental states to be unobservable, functionalists think that we only have an indirect grasp of their nature, as playing a certain causal, or ‘functional’, role in a cognitive system. One important consequence of this is that different physical states might play the relevant role in different beings, or even in the same being at different times. (Indeed functionalism as such leaves it open that this role could be played by some special non-physical state. In this sense functionalism is compatible with dualism (see Dualism). However, most functionalists also hold, for independent reasons, that mental roles are in fact filled by physical states. I shall simplify the following discussion by adopting this assumption.)

Some early functionalists, most notably Hilary Putnam (see Block 1980), appealed to an analogy with computers to add precision to the idea of a causal role. Putnam pointed out that any programmed computer can be abstractly characterized as a Turing machine, independently of its ‘hardware’ or physical make-up; he then argued that any two systems will share mental states as long as they have the same Turing machine description (see Putnam, H. §6; Turing machines). Today, however, it is more common to elaborate functionalism in terms of the analogy with scientific unobservables.

Unobservable entities of any kind pose a prima facie problem which has been much discussed in the philosophy of science. How should we understand terms like ‘ionized’, ‘radioactive’, ‘diatomic’, and so on, given that we have no direct access to their referents? Frank Ramsey argued that our grasp of such terms derives from our theories about the relevant unobservables. If we have a theory T(P₁…P_n, O), about how various unobservable properties, P₁…P_n, relate to each other and to observables O, then we can read claims involving these properties as claims about whichever properties happen to play the relevant theoretical roles. More precisely, a claim attributing property Π, to individual $\underset{¯}{a}$ , say, can be read as the claim $( F_1\dots F_n)(T(F_1\dots F_n,O)\&F_i\underset{¯}{a})$ . (In words: ‘There exist properties F₁…F_n, which are related to each other and to observables as T says, and $\underset{¯}{a}$ has the ith one.’) Note that this way of understanding claims about the Ps does not credit us with any prior understanding of these terms, but only with an understanding of existential quantification and of the observable terms O (see Ramsey, F.P. §5).

Functionalists take an analogous attitude to terms for mental states, like ‘belief’, ‘desire’, ‘jealousy’, ‘pain’, and so on. Suppose that our psychological theory contains such assumptions as that: anybody faced with an ice cream will believe there is an ice cream in front of them; anybody who is hungry and hot will desire an ice cream; anybody who desires an ice cream and believes one is in front of them will reach out for it; and so on. Then we can understand ascriptions of desires and beliefs to particular people as claims that there are states which behave as this theory claims, and that the people in question have them.