This article aims to study the articulation of Oswald Külpe’s critical realism, with particular stress on the subject of categories doctrine and on the role that it takes on in opposing to objective idealism and, more broadly, to the overcoming of Kantian transcendentalism and the phenomenalism strictly related to it. Starting from an exploration concerning the Aristotelian conception of categories and the comparison that Heidegger makes with Külpe’s thought, an analysis of the whole Külpean Kategorienlehre has been done by taking (...) into consideration the principle of category differentiation, the criterion of their application and their fundamentally gnoseological function. The essay points out too as the Külpean layout is not able to provide a suitable solution to the problems it deals with, as the distance from a genuine notion of ontology shows the metaphysical naivety remaining in the philosophical and categorical project of Külpe. (shrink)