Hobbes, in his metaphysical inquiry set out in Pat 2 of De Corpore, reduces the basic concepts of the Aristotelian metaphysics, such as substance, essence, and accident, to the concepts of body and accident, inparticular the two accidents of extension and motion. The point of his reduction consists of materialism, nominalism, and mechanism.（ i）Materialism: regarding body as the only substance, he reduces substance to body.（ii）Nominalism: regarding the distinction between essence and accident as relative to denomination, he reduces essence to accident.（iii）Mechanism: he reduces accidents to extension, the accident which characterizes body in general, and motion, the accident which explains change in bodies.This reduction, and hence his metaphysics, provides aconceptual framework for his physics. In this sense, his physics depends on his metaphysics. However,the dependence relation between metaphysics and physics is not unilateral but bilateral. For the reduction, and hence his metaphysics, is estimated to be successful only to the extent that his physics is able to explain the phenomena of nature by using the conceptual framework provided by his metaphysics. Therefore, Hobbes's metaphysics is characterized as a science placed before and completed after his physics.