Brad Weslake

Consider the following causal exclusion principle: For all distinct properties F and F* such that F* supervenes on F, F and F* do not both cause a property G. Peter Menzies and Christian List have proven that it follows from a natural conception of causation as difference-making that this exclusion principle is not generally true. Rather, it turns out that whether the principle is true is a contingent matter. In addition, they have shown that in a wide range of empirically ordinary cases, it follows that F* causes G and F does not. These cases plausibly include instances where F* is a mental property and F and G are physical properties. If this is the right conception of causation, it therefore turns out that the physical world is not causally closed. In this paper I show that there is an alternative conception of causation as difference-making that does not have the same consequences. Whether the physical world is causally closed therefore turns out to depend, inter alia, on which conception of difference-making is correct. I give a number of arguments for the alternative conception of difference-making.

The non-reductive physicalist would like to believe that mental properties are not identical to physical properties; that there are complete causal explanations of all events in terms of physical properties; and that there are sometimes explanations of events in terms of mental properties. However, some have argued that these claims cannot all be true, since they are collectively inconsistent with a principle of causal exclusion. In this paper I argue that the best formulation of the interventionist theory of causation entails the falsity of the exclusion principle. However, I argue that it does so at the cost of revealing a weakness in the interventionist theory itself.