 Given his rejection of the Scholastic qualitative tradition in physics, Descartes’ depiction of centrifugal effects as due to a “tendency” or “striving” of moving bodies thus raises a host of intriguing ontological questions (and may even reveal a vestigial influence of his earlier Scholastic training). That is, even as his penchant for a geometrical world view increased, as manifest in the identification of extension as matter’s primary quality, Descartes continued to treat inertial motion and its accompanying force effects as if they were essential characteristics of bodies. Descartes’ own remarks on the ontological status of inertial force, furthermore, disclose a certain degree of ambiguity and indecision. In a 1638 letter, (six years before the Principles), he concludes: