 Among the many students of Cohen and Natorp’s who identified themselves with the Marburg school, the most accomplished and influential was undoubtedly Ernst Cassirer (1874–1945). After writing his dissertation under Cohen in 1899 on Descartes’s philosophy of mathematics and science, Cassirer moved to Berlin, where he worked as a Privatdozent (though not a Professor, which was ruled out by institutional  anti-Semitism[10]).  His most important works before 1914 are in the history of philosophy (especially the massive, two volume Problem of Knowledge (Cassirer 1906, 1907a), which follows the development of the philosophy of science from the late Renaissance to Kant), and the philosophy of the exact sciences (Substance and Function, 1910; Einstein’s Theory of Relativity, 1921). Starting in 1921, Cassirer’s philosophy broadened into a “philosophy of symbolic forms”, which differs in some fundamental ways from the classic works of his teachers.