Abstract

It has been a traditional claim that Descartes sought to construct a deductive scientific system in which everything could be deduced from a priori truths. I shall call this thesis strong a priorism. In view of the overwhelming amount of evidence that Descartes thought experience to be a necessary part of his method, the traditional interpretation has undergone several transformations. One interpretation resulting from this transformation holds that Descartes sought to prove the first principles of natural philosophy in an a priori manner. I will call this interpretation weak a priorismk.My task in this paper is to show that the thesis of weak a priorismk is false. With a view to proving this, I will show that one of the very general principles of Cartesian natural philosophy, namely, the claim that the essence of matter is extension, could not have been, and was not meant to be, established in a purely a priorik way.