Abstract: In the Transcendental Dialectic Kant reflects on the faculty of reason and its illusory claim to be able to get to know the thing-in-itself. Through paralogisms, antinomies and ideals Kant shows that the unifying aspiration of reason fails in the search for objective knowledge, but nevertheless plays an indispensable role in human progress, thanks to its regulative value. Jaspers recovers Kantian reflection to fight idealism and scientism and reads Kant in the light of the kierkegaardian and nietzschean enhancement of existence. In Philosophy Jaspers outlines a path in which the limits encountered by man in the search for a foundation lead to a fragmentation of knowledge and the different modes of existence must be kept in constant dialogue through reason, in order to experience the «Umgreifende». Hersch starts from Jaspers to elaborate a kantian ontology in which man’s essence is to make and create his own reality, giving shape to matter through his own grip. Man can not arrive at objective knowledge, but reason nevertheless pushes the subject to constantly overcome himself in free creation, to build that authenticity promised to him by his own nature. At the end of the path a “rational a-logic” is elaborated in which metaphysics is directly linked to praxis and capable of maintaining a dialectical relationship with the irrational.