I want to compare two explanations of autism. Both these explanations are suggested by the apparent fact that people with autism have difficulty in understanding the mental states of others, though both seek to explain a great deal more about autism than this. Each derives from a hypothesis about what it is that enables normally developing children to understand those mental states. So I shall begin by explaining, very briefly, what those two hypotheses are and what is at stake between them.

Knowing that and knowing how

According to one view, I understand the minds of others – and, incidentally, my own mind as well – by virtue of possessing a theory of mind: a theory either acquired by observation and hypothesis formation, or a theory innately given (see, respectively, the contributions by Alison Gopnik and Gabriel Segal to this volume). This view is generally known as the ‘theory-theory’. The other view says that I understand the minds of others by imaginatively projecting myself into their situations and using my own mind as a model of theirs. Running my own mental states ‘off-line’, I am able to simulate the mental processes of another, and thereby to learn, for example, what decision he will make. This is the simulation-theory; it is a version of the idea that our access to the minds of others is partly through empathetic contact with them (Heal, 1986 and Gordon, 1986).