Functionalism and the Metaphysics of Causal Exclusion

Given their physical realization, what causal work is left for functional properties to do? Humean solutions to the exclusion problem (e.g. overdetermination and difference-making) typically appeal to counterfactual and/or nomic relations between functional property-instances and behavioural effects, tacitly assuming that such relations suffice for causal work. Clarification of the notion of causal work, I argue, shows not only that such solutions don't work, but also reveals a novel solution to the exclusion problem based on the relations between dispositional properties at different levels of mechanism, which involves three central claims: (i) the causal work of properties consists in grounding dispositions, (ii) functional properties are dispositions, and (iii) the dispositions of mechanisms are grounded in the dispositions of their components. Treating functional mental properties as dispositions of components in psychological mechanisms, I argue that such properties do the causal work of grounding agent-level dispositions. These dispositions, while ultimately grounded in the physical realizers of mental properties, are indirectly so grounded, through a hierarchy of grounding relations that extends upwards, of necessity, through the mental domain.