Aquinas’ philosophy is revolutionary, especially his doctrine of essence within the context of natural philosophy has transcended that of Aristotle. The principal distinctions between the doctrines of Aquinas and Aristotle are demonstrated in four layers which are entity-nature, compositeness, particularity and potentiality of essence. Aquinas not only overturns and reforms the Western traditional view of essence, but also constructs a prominent “joint” connecting essentialism to existentialism in Western philosophy.

Aquinas’ doctrine of materia signata or “designated matter” is an important deviation from the traditional doctrines on matter. Through in-depth typological and genetic analyses of the related concepts, this essay explores materia signata’s ontological qualities, generative mechanism and function, as well as its academic significance in the history of both Christian theology and Western philosophy.