The purpose of this paper is to reflect on the concepts of reality and possibility on the basis of a study of the categorial display of Kant's modal Ontology. This reflection will take us to a consideration of the confrontation between Aristotle and Heidegger regarding the problem of possibility which leads to a deeper opposition between the relevance of the Chapter on Transcendental Eschematism in Kant's Critique of Pure Reason; diverse conceptions of the specific task of Philosophy or, more generally, the relation between the problem of being and the problem of time.