Non-reductive physicalism and the problem of strong closure.

Closure is the central premise in one of the best arguments for physicalism—the argument from causal overdetermination. According to Closure, at every time at which a physical event has a sufficient cause, it has a sufficient physical cause. This principle is standardly defended by appealing to the fact that it enjoys empirical support from numerous confirming cases (and no disconfirming cases) in physics. However, in recent literature on mental causation, attempts have been made to provide a stronger argument for it. This essay argues that, insofar as these attempts are successful, they actually establish a far stronger closure principle. Worryingly, the acceptance of this stronger principle presents a new problem for the most popular form of physicalism, that of nonreductive physicalism. The problem shall be referred to as the 'Problem of Strong Closure.