Aristotle seems to argue in several places that not everything happens “of necessity,” and that some aspects of the future are genuinely open. But he also seems to hold that everything that happens has a cause, and that causes necessarily produce their effects. Two features of Aristotle’s theory of causation explain how he can consider these commitments to be consistent: (1) the distinction between accidental and intrinsic (or per se) causation, and (2) the fact that there are multi-stage causal sequences that are not reducible to the sum of their stages. In this talk I argue for an interpretation of Aristotle’s position and give an account of the sense in which some future events count as not necessary.