 As a philosopher Descartes may be broadly characterized as a synechist. His philosophical system rests on two fundamental principles: the celebrated Cartesian dualism—the division between mind and matter—and the less familiar identification of matter and spatial extension. In the Meditations Descartes distinguishes mind and matter on the grounds that the corporeal, being spatially extended, is divisible, while the mental is partless. The identification of matter and spatial extension has the consequence that matter is continuous and divisible without limit. Since extension is the sole essential property of matter and, conversely, matter always accompanies extension, matter must be ubiquitous. Descartes’ space is accordingly, as it was for the Stoics, a plenum pervaded by a continuous medium.