A well-known ``overdetermination''argument aims to show that the possibility of mental causes of physical events in a causally closed physical world and the possibility of causally relevant mental properties are both problematic. In the first part of this paper, I extend an identity reply that has been given to the first problem to a property-instance account of causal relata. In the second, I argue that mental types are composed of physical types and, as a consequence, both mental and physical types may be causally relevant with respect to the same physical effect, contrary to the overdetermination argument. In further sections, I argue that mental types have causal powers, consider some objections and reject an alternative version of part-whole physicalism. Throughout I assume that causal relata are tropes and property types are classes of tropes.