This volume, originally published in 1990, delineates the transition Descartes effects from a prevalent medieval conception of understanding to a modern conception of it. Through the examination of the continuities and discontinuities between Descartes' account of the understanding and that of high scholasticism, a characterization emerges of two way in which the understanding is autonomous in Descartes' view. These two sorts of autonomy shed light on the origin of a set of related concerns that give modern philosophy its coherence, setting it apart from medieval philosophy as a distinct tradition. The first sort - the independence of the understanding of the senses - creates the modern problem of scepticism with regard to the external world. The second sort, concerning the ontological status of the mind, provides the background against which modern discussions of the mind/body problem take shape.