  Dietrich’s De ente et essentia which bears the same title as Thomas Aquinas’ opuscule is indeed a work that gives much evidence of having been prepared as a kind of rebuttal to certain doctrines of Aquinas. Both works open with a reference from Aristotle to the effect that care and caution must be taken early in the study of metaphysics with regard to fundamental notions. In fact Dietrich divides his treatise into two parts, devoting the first part to an analysis of the key metaphysical terms esse, ens, entitas, quid, and quiditas. In opposition to Aquinas he proposes the thesis that there is no real distinction between existence (esse) and essence (essentia). The existence of a thing expresses its essence and vice versa. The two notions differ only in the way they denote the thing of which they are predicated (in modis significandi)—existence expressing being in the mode of an act, essence in the mode of a possession and the term of an act.