Functionalism is currently the most popular and well-known theory of mind. This is mostly due to the influence of computers on modern society - both in scientific terms and in the popular imagination through films, books, etc. As a result, most people presented with the functionalist perspective - though they would probably not know it by that term - would find it common sense.

But what exactly is the functionalist perspective? Functionalism tries to move beyond both Behaviourism and Identity Theory by taking elements from both. Like those two theories, Functionalism is generally taken to be a materialist theory. However, it differs from the other two theories in the following ways:

1. Brain states are not mental states. Identity Theory supposes that brain states are identical to mental states. However, there are problems with this. If I say, "I am in pain" it is not the same as saying, "The C-fibres in my brain are firing". But, if mental states and brain states are identical, shouldn't these two statements mean the same thing? If not, and certain types of neurological process cannot be matched up with certain types of mental state, then something over and above simple physical processes must be taking place.

2. Behaviourism cannot account for mental states. Behaviourism attempts to account for the mind in terms of actual or possibly observable behaviour. However, the problem with this view is that:

a) Different behaviours can result from the same stimulus. Imagine that you hear the doorbell - how do you react? Perhaps you run to answer it because you are expecting an important visitor; perhaps you ignore it; etc. In other words, there is no one response that can be linked to the same stimulus. So, if this is the case, what causes us to behave differently? The non-behaviourist would answer that it is our beliefs. However, this is a problem for the behaviourist in that it presupposes something that cannot be explained simply in terms of actual or possible behaviour.

b) Different stimuli can produce the same response. As with the previous example, it is also difficult to say that there is a definite relationship between a certain type of stimulus and a certain response. For example, someone might laugh at someone falling over, seeing a photograph or from hearing a story - whilst someone else might not laugh at any of those things. In other words, there is no certain, one-to-one relationship between a stimulus and a response. If this is so, must we again say that beliefs are responsible for this?