grew up in an orthodox Jewish environment and studied philosophy, mathematics and physics in Marburg, Frankfurt am Main, Berlin and Hamburg, where he graduated under Ernst Cassirer. Having lived in Paris and Cambridge to study, he emigrated in 1938 to the United States, where he taught at the New School for Social Research in New York and, from 1949, at the University of Chicago, with guest professorships at Berkeley and Jerusalem. In 1965 he received an honorary doctorate from the University of Hamburg, and the Grosses Verdienstkreuz from the West German government. Following his retirement in 1968 he was appointed Guest Professor at Claremont and Annapolis. During his career he published numerous studies of well known philosophical and theological authors, such as Die Religionskritik Spinozas (1930), Philosophie und Gesetz (1935), The Political Philosophy of Hobbes (1936), On Tyranny (1948), Persecution and the Art of Writing (1952), Natural Right and History (1953), Thoughts on Machiavelli (1958), The City and Man (1964), Socrates and Aristophanes (1966), and Liberalism Ancient and Modern (1968).