The challenge is to provide a satisfying account of how a purely physical system can have mental states. Behind that stands the wider challenge of explaining what it is to be a subject of mental states. Behaviourism is a tremendously influential approach to meeting those challenges.

Behaviourism in psychology was a methodological project aimed at making psychology scientific. Attempts in the nineteenth and early twentieth centuries to do that by basing psychological laws on people's reports of their experiences had run into the sand, partly because of the difficulty of interpreting the reports. The new idea was that it ought to be possible to arrive at laws relating publicly observable facts about sensory inputs and behavioural outputs, without bothering about what experimental subjects had to say (although of course their reports themselves could be treated as just more behavioural outputs). This idea influenced philosophical thinking about psychology, resulting in philosophical behaviourism (I will usually omit “philosophical” from now on). In this chapter we shall examine some varieties of behaviourism, together with behaviouristically influenced ideas in general.

Behaviouristic reductionism

How do we know what other people are thinking or feeling? Often of course we don't know: people can be inscrutable or downright dishonest. But sometimes we do know. How? The obvious answer is that we can see what they do and hear what they say: we know on the basis of their behaviour.