In this seminar, we examine a certain style of natural philosophy in the 17thC, which emphasizes metaphysics and rational principles, as found in Descartes, Hobbes, and Leibniz. Topics covered include speculations on the nature of body, the laws of nature, the notion of force, and large-scale principles that were taken to govern the material world. We study the mechanist thought in Descartes and Hobbes, and how it evolves into Leibniz’s dynamics.