 Cartesian philosophy also ignites various controversies in the latter decades of the seventeenth century that provide the context of intellectual tumult out of which the Enlightenment springs. Among these controversies are the following: Are mind and body really two distinct sorts of substances, and if so, what is the nature of each, and how are they related to each other, both in the human being (which presumably “has” both a mind and a body) and in a unified world system? If matter is inert (as Descartes claims), what can be the source of motion and the nature of causality in the physical world? And of course the various epistemological problems: the problem of objectivity, the role of God in securing our knowledge, the doctrine of innate ideas, and others.