  Descartes' arguments to establish the essences of these substances appeal directly to his clear and distinct perception of those essences.  The essence of matter is extension in length, breadth, and depth. One might speak here of “spatial extension,” but with this proviso: that Descartes denied the existence of space separate from matter. Cartesian matter does not fill a distinct spatial container; rather, spatial extension is constituted by extended matter (there is no void, or unfilled space). This extended substance possesses the further “modes” of size, shape, position, and motion. Modes are properties that exist only as modifications of the essential (principal) and the general attributes of a substance. In addition to its essence, extension, matter also has the general attributes of existence and duration. The individual parts of matter have durations as particular modes. All the modes of matter, including size, shape, position, and motion, can exist only as modifications of extended substance.