Three Versions of Physical Closure

The Exclusion Argument has been regarded as the most powerful challenge to non-reductive physicalism. This argument presupposes a crucial thesis, Causal Closure of the Physical, which asserts that every physical effect has a sufficient physical cause. Although this thesis is widely accepted in contemporary philosophy of mind, philosophers say surprisingly little about what notion of physical entities should be adopted in the context. In this article, the author distinguishes between three versions of Closure that appeal to a narrow, a moderate, and a wide notion of the physical, respectively. The author then argues that none of the three versions can challenge non-reductive physicalism.