Abstract

Lady Mary Shepherd’s account of the mind-body relation is interactionist: she holds that bodies cause sensations in our immaterial minds, which in turn cause motions in our material bodies through actions of the will. Yet Shepherd does not explain how immaterial and material things interact with each other. She instead simply asserts that mind-body interaction does not raise any conceptual difficulties. In this chapter I argue that Shepherd’s dismissal of the interaction problem is underpinned by her rejection of the early modern conception of substance, which sees substances as the metaphysical bases for their qualities or states. Shepherd’s approach to naturalism instead involves a chemical conception of substance, defining substances as masses of ‘qualities,’ which, for Shepherd, are capacities to interact in different circumstances. On this ontology, the nature of a substance is derived from its capacities to interact, and not the other way around. This ontological reversal dissolves the objections that had been raised against mind-body interaction. Shepherd’s metaphysical interpretation of the ‘chemical philosophy’ thus allows her to overcome one of the central aspects of the mind-body problem in its early modern formulation.