Abstract
I undertake to examine how Descartes understood the relationship between physics and mathematics. My thesis is that what distinguishes the objects of mathematics from those of physics on Descartes's view is that the former are considered in abstraction from a material substratum while the latter are considered as involving a material substratum. Since it has often been maintained that Descartes identified matter with extension, and hence rejected the notion of a material substratum, I attempt in the first part of my paper to establish the textual basis for ascribing a substratum view to Descartes. In the second part of the paper, I present the case for my thesis concerning Descartes's account of the difference between the objects of mathematics and those of physics