The “substance” in substance dualism and its denial

Substance dualism is meant to be a theory of thought, but how does it work as a theory of substance?

Both the theory and its critics seem to assume mind is a substance since it is a subject of properties or performs operations. Socrates, however, would be a substance for the same reason, so we get a Socrates/ mind-of-Socrates substance dualism even if we are materialists.

Or not. Assuming materialism wants to avoid a matter/emergent Socrates substance dualism, it can always just deny that Socrates or mind are substances. The only subject of properties is matter, with both Socrates and mind being accidents of these basic building blocks. Which accident is Socrates? Maybe position? Relation? Just arrange matter in the right order and you can frankenstein yourself any Socrates you want, right? So Socrates is the relation of substances arranged Socrates-wise.

Somewhere along the way, however, the definition of substance shifted. It started out as a subject of action but it came to mean any smallest part of some acting whole. Assuming we’re not speaking past each other, at some point we took it as axiomatic that the actions of wholes are nothing beyond the actions of their parts. 

It follows that an ultimate or complete analysis of things would reduce them to partless realities. But – and this is the crucial point – if analysis gives us substance it hits something ultimate. And so any analysis of physical things into substance cannot be into an extended body but only into Leibnizian monads, i.e. into substantial forms.

Materialism is in one sense right that Socrates and mind are not substances, but they’re wrong that entities with mass, charge, motion, inertia, etc. could serve as the substance of things. More exactly, matter can serve as substance only when appropriated by form, though this appropriation is probably made so as to constitute the whole that arises from the combination of the formal and material parts. And so substance, as Aristotle shows in Metaphysics Z, is first of all substantial form, then matter, then the composite of the two.


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