In this paper I shall define a thesis I shall call ' determinism ', and argue that it is incompatible with the thesis that we are able to act otherwise than we do. Other theses, some of them very different from what I shall call ' determinism ', have at least an equal right to this name, and, therefore, I do not claim to show that every thesis that could be called ' determinism ' without historical impropriety is incompatible with (...) free will. I shall, however, assume without argument that what I call ' determinism ' is legitimately so called. In Part I, I shall explain what I mean by ' determinism '. In Part II, I shall make some remarks about 'can'. In Part III, I shall argue that free will and determinism are incompatible. In Part IV, I shall examine some possible objections to the argument of Part III. I shall not attempt to establish the truth or falsity of determinism, or the existence or nonexistence of free will. (shrink)