Determinism is often defined as the view that every event has a cause. Neither event nor cause is as simple a notion as it looks. It is not easy to give a definition of ‘event’ which enables one to decide, for instance, how many events take place in a given region during a given period of time. The difficulty of giving such a definition places an obstacle to the coherent formulation of determinism; for present purposes I shall assume, without prejudice, that such difficulties can be overcome, and that among ‘events’, however the term is defined, will be included the movements of human bodies and the thoughts that pass through human minds. By ‘cause’ I will mean sufficient antecedent condition: that is to say, a state or event preceding in time the event to be explained, such that it is a sufficient condition for the occurrence of such an event. This means that there is a covering law to the effect that whenever such a causal condition obtains, it is followed by an event of the appropriate kind. So if determinism is true, it will be the case for any event E that there was an antecedent event or state C such that there is a true covering law to the effect that whenever a situation such as C obtains there will follow an event such as E. Every event will fall under a description such that there exists a law from which, in conjunction with a description of the antecedent conditions, it can be deduced that an event of that description will occur.