Schelling.
Sibbern had long been interested in the philosophy of G.W.F. Hegel but had never written any extended analysis of it. When Johan Ludvig Heiberg unveiled his new philosophical journal Perseus in 1837 as part of his Hegelian campaign, he provided Sibbern with the occasion that he had been waiting for. In a series of eight installments in the journal, Maanedsskrift for Litteratur, Sibbern published an extensive critical account of Hegel's philosophy under the guise of a review of the first volume of Heiberg's Perseus. In the fall of 1838 he collected the first four installments of this review and published them as an independent monograph entitled Remarks and Investigations Primarily Concerning Hegel's Philosophy. This work represents arguably the most exhaustive, detailed and profound analysis of Hegel's philosophy ever to appear in the Danish language, anticipating many aspects of Kierkegaard's famous criticism.