Up to 1950, Schelling was almost a forgotten philosopher even in Germany. In the 1910s and 1920s, philosophers of neo-Kantianism and neo-Hegelianism, like Wilhelm Windelband or Richard Kroner, tended to describe Schelling as an episode connecting Fichte and Hegel. His late period tended to be ignored, and his philosophies of nature and of art in the 1790s and first decade of the 19th century were the main focus. In this context Kuno Fischer characterized Schelling's early philosophy as "aesthetic idealism", focusing on the argument where he ranked art as "the sole document and the eternal organ of philosophy" ("das einzige wahre und ewige Organon zugleich und Dokument der Philosophie"). From socialist philosophers like György Lukács, he was regarded as anachronistic. An exception was Martin Heidegger, who found in Schelling's "On Human Freedom" central themes of Western ontology - being, existence, and freedom - and expounded on them in his 1936 lectures.