Mental causation in a physical world

It is generally accepted that the most serious threat to the possibility of mental causation is posed by the causal self-sufficiency of physical causal processes. I argue, however, that this feature of the world, which I articulate in principle I call Completeness, in fact poses no genuine threat to mental causation. Some find Completeness threatening to mental causation because they confuse it with a stronger principle, which I call Closure. Others do not simply conflate Completeness and Closure, but hold that Completeness, together with certain plausible assumptions, entails Closure. I refute the most fully worked-out version of such an argument. Finally, some find Completeness all by itself threatening to mental causation. I argue that one will only find Completeness threatening if one operates with a philosophically distorted conception of mental causation. I thereby defend what I call naïve realism about mental causation.