Descartes was both metaphysician and natural philosopher. He used his metaphysics to ground portions of his physics. However, as should be a commonplace but is not, he did not think he could spin all of his physics out of his metaphysics a priori, and in fact he both emphasized the need for appeals to experience in his methodological remarks on philosophizing about nature and constantly appealed to experience in describing his own philosophy of nature. During the 1630s, he offered empirical (...) support for the basic principles of his natural philosophy, while also promising to provide a metaphysical justification. He offered the metaphysical justification in the Meditations and Principles. and claimed absolute certainty for it. At the same time, he recognized that the particular postulated mechanisms of his natural philosophy did not reach that standard of certainty. These mechanisms were supported by empirical testing or confirming of causes through observed effects. (shrink)