Epicurus' On Nature 25 is the key text for anti-reductionist interpretations of Epicurus' philosophy of mind. In it, Epicurus is trying to argue against those, like Democritus, who say that everything occurs 'of necessity,' and in the course of this argument, he says many things that appear to conflict with an Identity Theory of Mind and with causal determinism. In this paper, I engage in a close reading of this text in order to show that it does not contain any clear statement of either a doctrine of radically emergent properties and "downwards causation" (contra David Sedley) or of the non-reducibility of the mental to the atomic (contra Julia Annas). I argue that Epicurus' main thesis is that we cannot consistently argue against our conception of ourselves as rational agents, and that it is our reason that allows us to reform our characters, control our actions, and blame and praise one another appropriately. The way that Epicurus describes the development and causal efficacy of reason in On Nature book 25 is consistent both with reductionism and (more surprisingly) with causal determinism.