Kant's revolutionary way of thinking and the subsequent discussions of German idealism about the issues and the relevance of philosophy have gained a central position which endured all succeeding stages of spirit until the present day. Oldenburg´s main research emphasis on Classical German Philosophy takes up this claim and involves discussions of Kant, Fichte, Schelling, Hegel, and Hölderlin. Special attention is paid to the continued effects of Classical German Philosophy in the discourse of current philosophy. The issues and problems to deal with, if one sticks to the not purely formal notion of reason (which includes the claim as well as the forms of aesthetical experience), cannot be adequately discussed without reference to the standard of reflection in Classical German Philosophy.