Causal powers are ubiquitous. Electrons are negatively charged; they have the power to repel other electrons. Water is a solvent; it has the power to dissolve salt. We use concepts of causal powers and their relatives-dispositions, capacities, abilities, and so on-to describe the world around us, both in everyday life and in scientific practice. But what is it about the world that makes such descriptions apt?

On one view, the neo-Humean view, there is nothing intrinsic about, say, negative charge, that makes its bearers have the power to repel other negatively charged particles. Rather,...