The term ‘functionalism’ means different things in many different disciplines from architectural theory to zoology. In contemporary philosophy of mind, however, it is uniformly understood to stand for the view that mental states should be explained in terms of causal roles. So, to take a simple example, a functionalist in the philosophy of mind would argue that pains are states which are normally caused by bodily damage, and tend in turn to cause avoidance behaviour.
Functionalism is often introduced by an analogy between mental states and mechanical devices. Consider the notion of a carburettor, say. For something to be a carburettor it need not have any particular physical make-up. Carburettors can come in many different materials and shapes. What makes it a carburettor is simply that it plays the right causal role, namely that it mixes air with petrol in response to movements of the accelerator and choke. Similarly, argue functionalists, with the mind. The possession of mental states does not depend on the physical make-up of the brain; it depends only on its displaying the right causal structure. Since organisms with very different sorts of biological make-up, like octopuses and humans, can have states with the causal role of pain, say, it follows from functionalism that octopuses and humans can both be in pain.
There exists a number of different subspecies of functionalism. One important division depends on how the relevant causal roles are determined. ‘Common-sense’ functionalists take them to be fixed by common-sense psychology; ‘scientific’ functionalists take them to be fixed by the discoveries of scientific psychology. So, for example, common-sense functionalists will hold that emotions play the causal role that common-sense psychology ascribes to emotions, while scientific psychologists will argue that scientific psychology identifies this causal role.
Functionalism, of whatever subspecies, is open to a number of well-known criticisms. One central objection is that it cannot accommodate the conscious, qualitative aspect of mental life. Could not a machine share the causal structure of someone who was in pain, and thereby satisfy the functionalist qualification for pain, and yet have no conscious feelings?
It might seem that functionalists can respond to this difficulty by being more stringent about the requirements involved in the causal role of a given human sensation. But there is a danger that functionalism will then lose much of its appeal. The original attraction of functionalism was that its ‘liberal’ specification of causal roles allowed that humans could share mental states with non-humans. This feature is likely to be lost if we switch to more ‘chauvinist’ specifications designed to explain why non-humans do not share our conscious life.
Another objection to functionalism is that it cannot account for mental representation. Functionalism focuses on the way mental states enter into causal structure. But it is doubtful that mental representation can be explained in purely causal terms.
Some philosophers argue that the issue of mental representation can be dealt with by adding some teleology to functionalism, that is by considering the biological purposes for which mental states have been designed, as well as their actual structure of causes and effects. However, once we do appeal to teleology in this way, it is not clear that we still need a functionalist account of representational states, for we can now simply identify such states in terms of their biological purposes, rather than their causal roles.
Common-Sense Psychology and Scientific Psychology