It is worth observing that physicalists who advocate this kind of downwards special causation are in some danger of sawing off the branch they are sitting on, in that they now seem to be advocating counter-examples to the causal closure of the physical. If my arm’s waving is caused by my desire and not by my brain state, it would seem to have a mental cause and not a physical cause, and thus run counter to the closure thesis that every physical effect has some fully physical cause. Since the original rationale for embracing physicalism was supposed to be science’s discovery that the physical realm is causally closed, this may seem to leave physicalists in an awkward position.