  These contrasting views of Descartes' intellectual development suggest different relations between his metaphysics and physics.  Schuster (1980) treats Descartes' metaphysical arguments as a kind of afterthought. Machamer and McGuire (2006) see Descartes' alleged “epistemic turn” and his retreat from realism as a response to philosophical criticism in 1641; they find more continuity between Descartes' Rules and his writings up to 1641 than does Garber, or than is presented herein. One way of understanding this earlier discontinuity is to grant that Descartes was working on physical problems first,  while emphasizing that his metaphysical insights of 1628–9 allowed him to achieve a general conception of matter as having only “geometrical” properties, viz., size, shape, position, and motion.