Certainly a most important aspect of the philosophical treatment of any problem concerns the relationship between that treatment and the philosopher's theory of human nature. Initially Descartes was keenly aware of one phase of this relationship, and the outcome of this awareness was his partly successful revolt against the anthropomorphisms of the Scholastic metaphysics and physics of his day.¹ He was, however, only partially, but I think increasingly, aware of another aspect of this relationship. This aspect refers us to the apparent ambiguity of many of the concepts commonly utilized to deal adequately with human nature and experience. In this regard Descartes' own theory of human nature radically affected his metaphysical outlook. That he was increasingly cognizant of this effective connection is evidenced by the development within his thought of two discernibly different metaphysics and philosophies of science; for as internal difficulties in the earlier version of his thought became manifest, he was forced to modify his doctrine in the direction of utilizing participatory and less mathematical-like concepts. This essay is intended to clarify the frequently unnoticed distinction between these two kinds of metaphysics.