Mind, identity theory of

4. Functionalism and the identity theory

When identity theorists first discussed the qualia objection they urged that when we itch, smell a rose, and quite generally when we are in a mental state, we are not introspectively aware of the intrinsic nature of the mental state. For they granted, as we noted earlier, that mental states do not present themselves to us as states of the brain. The identity theorists held that what happens when we introspect is that we are aware of highly relational properties of our mental states, properties like being like what goes on in me when a pin is stuck in me (in the case of pain), being like what goes on in me when I see blood and geranium petals (in the case of sensing red), and being of a kind apt for the production of scratching behaviour (in the case of itches). In bringing relational properties into the picture, the early identity theorists can be seen as precursors of functionalist theories of mind. For functionalism is a theory according to which what makes something the mental state it is is a highly relational feature of it, that feature known as its functional role.

According to functionalism, we can think of mental states as causal intermediaries between inputs from the environment, outputs in the form of behavioural responses, and other mental states. Pain, for instance, is an internal state that is typically caused by bodily damage, and typically causes the desire that it itself cease along with behavioural responses that tend to minimize the damage. The perception that there is coffee in front of me is an internal state typically caused by coffee in front of me, which in turn causes belief that there is coffee in front of me, and this belief, when combined with desire for coffee, typically causes movement towards the coffee. Mental states are, that is, specified in terms of their place in a huge network of interlocking states (of which we have just described a tiny fragment) (see Functionalism). Our concern here is with the implications of this general approach for the identity theory.

Functionalism can be, and often is, regarded as entirely consonant with the identity theory, being indeed a good way of arguing for it; or functionalism can be, and often is, regarded as a major objection to the identity theory. It all depends on the kind of identity theory.

If mental states are defined by their place in a network, then the question of what some given mental state is comes down to the question of what state occupies the relevant place in the network. An analogy: money can be defined in terms of a characteristic functional role, a role we are all only too familiar with through our knowledge of what you can do if you have money, and cannot do if you do not have money. In consequence, the question of what money is is the question of what plays, or occupies, the money-functional role, be it paper notes, coins, cowrie shells, or whatever. But, identity theorists observe, by far the most plausible candidates for what play the functional roles associated with mental states are various states of the brain. Thus, functionalism gives us a simple argument for the identity theory of the following structure: pain = what plays the pain-role; what plays the pain-role = a state of the brain (say, C-fibres firing); therefore, pain = C-fibres firing. And likewise for all the mental states. Identity theorists who see the identity theory as a natural offshoot of functionalism, often refer to the identity theory as ‘central state materialism’.

Approaching the identity theory through functionalism commits identity theorists to an anti-essentialist theory of mind. For the brain state that occupies the pain-role and so is, according to them, pain, might not have done so, and so might not have been pain. And the same goes for all mental states. Early expositions of the identity theory made this point by insisting that the identity of pain with, say, C-fibres firing was a contingent identity, and drew an analogy in this regard with the scientific identities we mentioned before. However, at least some of these identities are arguably necessarily true. It is arguable that water is necessarily H₂O. Certainly, we had to discover the identity of water and H₂O by empirical investigation, which makes it an a posteriori matter, but what we discovered was an essential feature of water. However, the identity theory must hold that the identities it posits are contingent. They are like the identity of the President of the United States in 1997 with Bill Clinton, which is contingent because that which occupies the role definitive of being President in 1997 is a contingent matter. (Dole was swimming against an economic tide, not a logical one.)

Although functionalism is a good way of arguing for the identity theory, it is a major objection to one kind of identity theory. We noted that identity theorists appeal to scientific identities in explaining and introducing their theory. These identities concern kinds or types. When scientists tell us that lightning is an electrical discharge, they are not merely telling us that the instance or token of lightning we saw last night is an instance or token of an electrical discharge; they are telling us, in addition, about what kind of happening lightning in general is. Again, the claim that temperature is mean molecular kinetic energy is a claim about kinds or types; it tells us what the property of temperature (in gases, anyway) is – namely, mean molecular kinetic energy. This suggests that we should think of the (mind-brain) identity theory as a type-type identity theory. Moreover, the theorists’ favourite illustration – ‘Pain = C-fibres firing’ – is a type-type identity statement.

The problem is that different types of state might occupy the pain-role in different creatures. Perhaps it is C-fibres firing in humans but D-fibres firing in dolphins. But dolphins with their D-fibres firing would then be just as much in pain as we are when our C-fibres are firing. It is the role occupied, not the occupier, that matters for being in pain according to functionalism. And the point is independently plausible. We feel sorry for dolphins that exhibit all the signs of pain despite not knowing in any detail how intrinsically alike our and their brains are. But the identity theorist cannot allow both that pain = C-fibres firing, and that pain = D-fibres firing. That would, by the transitivity of identity, lead to the false contention that C-fibres firing = D-fibres firing.

Two responses are possible. Identity theorists can retreat to a token-token identity theory. Each and every token or instance of mental state M is some token brain state, but mental types are not brain types, being instead functional types. Alternatively, they can allow that the identities between mental types and brain types may need to be restricted. Think again of the example of money. Although different types of things are money in different societies, we can make true identity claims about the types of things that are money in the different societies. For instance, money in our society = notes and coins produced by the mint, whereas money in early Polynesian society = cowrie shells (or whatever). Similarly, although temperature in gases = mean molecular kinetic energy, in substances of which the molecules do not move freely it is something else. In the same way, if indeed it is C-fibres in us but D-fibres in dolphins that play the pain-role, then identity theorists must restrict themselves to ‘Pain in humans = C-fibres firing’ and ‘Pain in dolphins = D-fibres firing’. The question of what humans in pain and dolphins in pain have in common would remain, of course, for they would not ex hypothesi share the same kind of brain state. And the identity theorists’ answer must be that what they would have in common would be that each has a state inside them playing the pain-role, although not the same state.