Despite the fact that the nature of the properties of causation is rarely discussed within the mental causation debate, the implicit assumption is that they are universals as opposed to tropes. However, in recent literature on the problem of mental causation, a new solution has emerged which aims to address the problem by appealing to tropes. It is argued that if the properties of causation are tropes rather than universals, then a psychophysical reductionism can be advanced which does not face the problem of multiple realizability. However, the 'trope solution' rests upon the assumption that one can combine a trope monism with a type dualism. I argue that such a combination cannot be allowed. Given a plausible interpretation of types within a trope ontology, trope monism in fact entails type monism. Consequently, if one identifies mental tropes with physical tropes, one must also identify mental and physical types and in doing so face a modified version of the multiple realizability argument.