Substance, Reality, and Distinctness

Descartes claims that God is a substance and that mind and body are two different and separable substances. This paper provides some background that renders these claims intelligible. For Descartes, that something is real means that it can exist in separation, and something is a substance if it does not depend on other substances for its existence. Further, separable objects are correlates of distinct ideas, since an idea is distinct (in an objective sense) if its object may be easily and clearly separated from everything that is not its object. It follows that if our idea of God is our most distinct idea, as Descartes claims, God must be a substance in the Cartesian sense of this term. Second, if we can have an idea of a thinking subject that does not in any sense refer to bodily things, and if bodily things are substances, then mind and body must be two different substances.