Stella Moon

Descartes’s doctrine of clarity and distinctness states that whatever is clearly and distinctly perceived is true. This paper looks at his early doctrine from Rules for the Direction of the Mind, and its application to the demarcation problem of curves in Descartes’s Geometry. This paper offers and defends a novel account of the demarcation criterion of curves: a curve is geometrical just in case it is clearly and distinctly perceivable. This account connects Descartes’s rationalist epistemological programme with his ontological views about mathematics.