What does it mean to say that mind-body dualism is causally problematic in a way that other mind-body theories, such as the psychophysical type identity theory, are not? After considering and rejecting various proposals, I advance my own, which focuses on what grounds the causal closure of the physical realm. A metametaphysical implication of my proposal is that philosophers working without the notion of grounding in their toolkit are metaphysically impoverished. They cannot do justice to the thought, encountered in every (...) introductory class in the philosophy of mind, that dualism has a special problem accounting for mental causation. (shrink)