 The fundamental aspects of Hobbes’ materialism are well known. Hobbes believed that everything that exists is a body, and that bodies are sometimes in motion and sometimes at rest. Furthermore, he held that the only essential property of body is extension, or magnitude. All other apparent properties of bodies, such as those of color, taste, and firmness, are the result of motions from bodies being continued through media to humans’ sense organs. These motions, when continued into the bodies of perceivers, are constitutive of conceptions, or  ideas.[2]  Ideas of the objects of sense are caused by motions from things outside of perceivers and those continued motions constitute ideas and serve to individuate one idea from another. Thus, all ideas in the human mind are either from sense perception or derived from ideas gained from sense perception (Leviathan I; LEV 22).