Throughout the 1990s, Jaegwon Kim developed a line of argument that what purport to be nonreductive forms of physicalism are ultimately untenable, since they cannot accommodate the causal efficacy of mental states. His argument has received a great deal of discussion, much of it critical. We believe that, while the argument needs some tweaking, its basic thrust is sound. In what follows, we will lay out our preferred version of the argument and highlight its essential dependence on a causal-powers metaphysic, (...) a dependence that Kim does not acknowledge in his official presentations of the argument.i We then discuss two recent physicalist strategies for preserving the causal efficacy of the mental in the face of this sort of challenge, strategies that (ostensibly) endorse a causal powers metaphysics of properties while offering distinctive accounts of the physical realization of mental properties. We argue that neither picture can be satisfactorily worked out, and that seeing why they fail strongly suggests that nonreductive physicalism and a causal powers metaphysic are not compatible, as our original argument contends. Since we also believe that robust realism concerning mental causation should not be abandoned, we take the argument of this paper to strongly motivate an account on which the mental is unrealized by and ontologically emergent from the physical. In a final section, we sketch what an ontologically emergentist account of the mental might look like. (shrink)