Translated by Pete Ferreira
Third, Heidegger examines the thesis of modern ontology according to which the two fundamental ways of being are the being of nature (res extensa) and the being of the spirit (res cogitans). Heidegger's nexus in the discussion of the idea of being in modern ontology is again Kant because Kant is halfway between the start (Descartes) and the latter's fulfilment (Hegel) and represents the keystone of its development following rationalism and idealism. Now, taking that thesis as the fundamental determination within the horizon from which modern ontology understands the problem of being and that of subjectivity, Heidegger examines how Kant understands and determines the structure of the subject. In particular, he describes the Kantian determinations of personalitas transcendentalis (the I of perception), of personalitas empirica (the I of understanding) and personalitas moralis (the I as a person and as an end in itself), seeing in the Kantian understanding of the subject an implied and almost unaware understanding of the temporal structure of human life. While not going so far as to explicitly thematize in this sense the way of being of the subject, Kant does however give a determination, that of person and of end in itself, which is very close to capturing it in its specific ontological character. And yet, even the Kantian understanding remains unsatisfactory in the eyes of Heidegger, because it remains in the end the Cartesian split of res cogitans and res extensa. In addition, according to Heidegger the Kantian understanding of the subject as finite substance implicitly refers to an understanding of being in the sense of being-produced, as for Kant "finitude is being referred necessarily to receptivity, that is, the impossibility of being oneself the creator and producer of another being. Only the creator of a being knows this being in its proper being. The being of things is understood as being-produced".59
59 GA 24, 214 [The Basic Problems of Phenomenology, p. 151.] (and in general, for the interpretation of the thesis of modern ontology, see §§ 13-15).