Abstract

The two studies comprising this dissertation focus upon the contribution of Dietrich von Freiberg, O.P. to late mediaeval problems concerning identity and change in nature. The first study presents Dietrich's theories of the elements and prime matter, and features an extended historical and philosophical critique of Thomas Aquinas' notion of virtual being. It is with this notion that Aquinas attempts to resolve the apparent tension between Aristotle's theory of the chemical mixture and Aquinas' own doctrine of the unity of substantial form. It is argued that virtual being is not a genuine Aristotelian mode of being and in any case does not resolve this apparent tension. Dietrich's own solution follows that of Averroes, maintaining that the elements in the mixed body are diminished from pure act to some degree of potency. It is argued that Dietrich mis-applies aspects of his theory of substantial generation in arriving at this solution. Such diminishment is possible, argues Dietrich, because of the elements' proximity to prime matter. The doctrine of proper form in its proper matter entails that prime matter must be complex, and those "natures" comprising prime matter be punctually indistinct. Thus are the elements themselves punctually indistinct in the homeomerous mixed body. Dietrich's solution is thus problematic precisely because it requires that the elements be capable of interpenetration. ;The second study evaluates, and attempts to situate in its historical context, Dietrich's theory that numerical identity is not preserved in intensive qualitative change. Rather, each new degree of intensity introduces a numerically distinct quality. This is because qualities lack the interiority of essence that substances possess. A survey of contemporaneous sources shows that while there was much opposition to this position, it was not uncommon. The discussion continues with an analysis of Dietrich's arguments that such change also neither is continuous nor entails an infinity of degrees. Degrees of intensity do not correspond with each "now" in the continuum of time. Rather, there must be an indivisible minimum, and intensive qualitative change must therefore be understood as stepwise and discontinuous