  There are also differences among interpreters concerning the relative priority in Descartes' philosophical endeavors of epistemology or the theory of knowledge as opposed to metaphysics or first philosophy. In the account of Descartes' development from Sec. 1, he was interested in epistemological and methodological questions first, and these interests came to a head in the Rules. Thereafter, his aim was to establish a new natural philosophy based on a new metaphysics. In the extant works from the 1630s, the World and Discourse plus essays, he argued for the general principles of his physics, including his conception of matter, on empirical grounds. He argued from explanatory scope and theoretical parsimony. As regards parsimony or simplicity, he pointed out that his reconceived matter had only a few basic properties (especially size, shape, position, and motion), from which he would construct his explanations. He claimed great explanatory scope by contending that his explanations could extend to all natural phenomena, celestial and terrestrial, inorganic and organic. But throughout the 1630s, Descartes claimed that he also was in possession of a metaphysics that could justify the first principles of his physics, which he finally presented in  the Meditations and Principles.