Abstract

How does Descartes justify his claim that conceiving of a mind as a thinking thing and a body as an extended thing show that mind and body are distinct substances? The paper attempts to answer that question by following a clue Descartes gave Arnauld that virtually everything in Meditations Three through Five is germane to the real distinction between mind and body. The paper develops the distinction between material truth and formal truth from Descartes’s discussions of falsity in Meditation Three. In Meditation Three, clear and distinct ideas are materially true. They are consistent. They represent the possibility that there is something that corresponds to the idea (de dicto possibility). God is not a deceiver. Since it is psychologically impossible to doubt a clear and distinct idea, Descartes concludes Meditation Four by arguing that clear and distinct ideas are formally true (representative). Clear and distinct ideas represent true and immutable natures (essences). It is in virtue of true and immutable natures that it is possible that there are things of determinate kinds. Hence, in Meditation Five, clear and distinct ideas represent de re possibilities. Since the mind/body distinction is a distinction between true and immutable natures, Descartes takes clearly and distinctly conceiving a thinking thing as distinct from an extended thing to be sufficient for claiming a real distinction between mind and body.