My aim in this thesis is to explain how a non-reductionist metaphysics can accommodate the causal relevance of the psychological and of the special sciences generally. According to physicalism, all behavior is caused by brain-states; given "folk-psychology", behavior is caused by some psychological state. If psychological states are distinct from brain states, then our behavior is overdetermined and this, it is claimed, is unacceptable. I argue that this consequence is not unacceptable. I claim that our explanatory practice should guide our (...) ontological commitment. If we can offer true explanations that appeal to more than one event, then we are committed to overdetermination for the event explained. I argue that accepting overdetermination is not absurd and that we can give an adequate account of causal relevance for psychological and other supervenient properties. The result is a partial defense of both property and event pluralism. Recent work by Davidson, Fodor, Jackson, Kim, Pettit and Yablo receives explicit and critical discussion. (shrink)