This paper explores the use of supervenience in clarifying and elucidating debates about empirical arguments surrounding the mind-body problem and mental causation. In particular, it examines William James’s famous evolutionary argument against epiphenomenalism, and shows that concepts associated with supervenience—in combination with Bayesianism—can transform our understanding of how the evidence the argument adduces should be handled. After providing a thorough critique and updating of the traditional argument using the tools provided by supervenience, objections to the general approach are also addressed.