Hans Leisegang (March 13, 1890 – April 5, 1951) was a German philosopher and a professor at the University of Leipzig (1920), Jena (1930–34) and Berlin (1948). He was imprisoned for his views on Adolf Hitler during the Nazi era. He identified philosophy as an interdisciplinary concept of the world and as being synthetic and not analytic. He studied physics and was able to write on the interface of theoretical physics and philosophy.

Leisegang was born in Blankenburg, son of Otto a military pastor. He studied philosophy, languages and history at Strasbourg, Paris and Leipzig. In 1911 he received a doctorate at Strasbourg under Clemens Bäumker and Theobald Ziegler with a dissertation titled “The Concepts of Time and Eternity in later Platonism” (1913) which received a university award. He taught at schools near Markranstädt for some time. He habilitated from the University of Leipzig in 1920 and became a professor in 1925. In 1930 he became a professor of philosophy at the University of Jena. He had written about Gotthold Ephraim Lessing and his worldview in 1931 and Lessing was hated by the National Socialists as a friend of Jews. Leisegang made some derogatory remarks about Hitler who gave a speech at a memorial event for President Hindenburg in 1934. He was then given a six-month prison sentence. Theodor Litt and a few friends stood by him. He was released after a trial but dismissed from service. He studied physics along with his son and completed his doctorate in 1942 from the University of Jena with a thesis on diode galvanometers for measuring high frequency AC. He then worked in the industry as a physicist. After World War II he was able to resume teaching in Jena on December 1, 1945, but he was dismissed by the university administrators on October 29, 1948, for his opposition of the Soviet governance, non-democratic structures in the university and refusal to teach Marxism and Leninism. He had to flee from East Germany to West Berlin to avoid arrest. ^[1] From 1948 he lectured at the Free University in Berlin. ^[2]

Leisegang wrote extensively about thinking and world view. Leisegang wrote several books including on the history of philosophy in Germany. ^[3] His major books were Denkformen (1928) and Die Gnosis (1924) which went into several editions. ^[4] Leisegang classifies all philosophical thought into (A) thought-circles (Denkform des Gedankenkreises) - (B) circles of circles (Denkform der Kreis von Kreisen) - (C) conceptual pyramid (die Begriffspyramide) and (D) Euclidean-mathematical thought-form (die euklidisch-mathematische Denkform). ^[5]

Leisegang married Erna Mehlhose in 1914 and they had a son Siegfried (born 1916) and a daughter Gertrud (1922). ^[6]