Free will, if such there be, involves free choosing: the ability to mentally choose an outcome, where the outcome is 'free' in being, in some substantive sense, up to the agent of the choice. As such, it is clear that the questions of how to understand free will and mental causation are connected, for events of seemingly free choosing are mental events that appear to be efficacious vis-a-vis other mental events as well as physical events. Nonetheless, the free will and (...) mental causation debates have proceeded largely independently of each other. Here we aim to make progress in determining how the free will and mental causation debates bear on one another. We first argue that the problems of free will and of mental causation can be seen as special cases of a more general problem, concerning whether and how mental events of a given type may be efficacious, qua the types of event they are---qualitative, intentional, freely deliberative---given their apparent causal irrelevancy for effects of the type in question; here we generalize what Horgan 1989 identifies as "the problem of mental quausation" (S1). We then build on this result to identify fruitful parallels between hard determinism and eliminative physicalism (S2) and soft determinism and non-reductive physicalism (S3). (shrink)