We will examine central themes in the philosophical systems of some 17th Century `rationalist’ philosophers: René Descartes, Princess Elisabeth of Bohemia, Nicolas Malebranche, Benedict de Spinoza, Gottfried Leibniz, and Émilie du Châtelet. The issues taken up by these philosophers, and how they came to grip with them, helped define modern conceptions of the world and our place in it. We will focus on what these philosophers wrote about metaphysics and epistemology. Topics to be discussed include: skepticism about the external world; free will; the mind-body problem; the existence of God; causality and substance; the nature of philosophical explanation.