The questions of how to understand free will and mental causation are clearly connected, for events of seemingly free choosing are mental events that appear to be efficacious vis-à-vis other events. Nonetheless, the free will and mental causation debates have proceeded largely independently of each other. Here we aim to make progress in determining the mutual bearing of these debates. We first argue that the problems of free will and of mental causation can be seen as special cases of a more general problem of mental ‘quausation’, concerning whether and how mental events of a given type can be efficacious qua the types they are—qualitative, intentional, freely deliberative—given reasons to think such events are causally irrelevant. We go on to identify parallels between hard determinism and eliminativist physicalism and between soft determinism and nonreductive physicalism, and we use these parallels to identify a new argument against hard determinism and to reveal and motivate a common strategy underlying apparently diverse soft determinist accounts.