 It is in the Rules that Descartes introduces the simple natures. The simple natures are not only what our ideas are of—that is, they not only constitute the contents of our ideas, the “objects” immediately presented to the mind—but are also the natures possessed by things. (AT X 399; CSM I 32) Examples of simple natures are colors, sounds, smells, shapes, sizes, extension, and the like. He says, for example, in Rule Twelve, “if I judge that a certain shape is not moving, I shall say that my thought is in some way composed of shape and rest; and similarly in other cases.” (AT X 420; CSM I 45) In the First Meditation, Descartes mentions similar ideational elements “from which all the images of things” are formed. (AT VII 20; CSM II 13–14) In the Second Meditation, in his analysis of the adventitious idea of a piece of wax, Descartes again provides a list of such ideational elements. (AT VII 30–32; CSM II 20–21) In the Third Meditation, he refers to such items as “elements in my ideas.” (AT VII 44; CSM II 30) And, in the Sixth Meditation, when revisiting some of what he had established in the Second Meditation, talk of these qualities that are “the only immediate objects of my sensory awareness” is again introduced. (AT VII 75ff; CSM II 52ff) So, although Descartes does not employ the “simple natures” terminology in later work, the philosophical notion certainly looks to be present in his later work. 