The question I shall consider is whether there are any mental causes, that is, whether there is anything which is both a state of mind and a cause of other mental or physical happenings. The obvious common-sense answer to this question is Yes. In ordinary discourse (that is, outside philosophy and psychology) we constantly refer to human actions and experiences in what appears to be causal language; we seem to be saying that some states of mind are causes of other states of mind, and of some bodily activities. Sometimes we do this by using the word ‘cause’ itself— ‘His driving into the ditch was caused by his seeing a child run into the road’, ‘The cause of his silence was his wish to protect his friend’. More often we use expressions which in physical contexts are admittedly causal— ‘A glimpse of the look on her face made him hesitate’, ‘Ambition was the driving force of his career’. Most philosophers have taken for granted the genuineness of these causal attributions. But recently it has been frequently denied that any state of mind can be properly described as the cause either of other states of mind or of physical occurrences, at any rate if by a state of mind one means a state of consciousness. Some philosophers who deny this are materialists, advocates of the Unity of Science. They believe that everything that happens in the universe can be causally accounted for by reference to a single set of fundamental laws, the laws of physics, and since a state of consciousness is not, as such, a physical state of any kind, it cannot have a place in the causal explanation of any event, and must be an epiphenomenon. Others are believers in an indeterminist interpretation of human freedom, and hold that o t introduce the category of cause and effect into the explanation of human actions is to deny that there is any genuine free will. I shall not be concerned with either of these general metaphysical objections, neither of which convinces me; but I shall consider some more specific objections to the admission of particular sorts of mental causes.