Immanuel Kant
Immanuel Kant (; ; 22 April 1724 – 12 February 1804) was a German philosopher who is a central figure in modern philosophy. In his doctrine of transcendental idealism, he argued that space, time and causation are mere sensibilities; "things-in-themselves" exist, but their nature is unknowable. In his view, the mind shapes and structures experience, with all human experience sharing certain structural features. He drew a parallel to the Copernican revolution in his proposition that worldly objects can be intuited "a priori" ("beforehand"), and that intuition is therefore independent from objective reality. Kant believed that reason is the source of morality, and that aesthetics arise from a faculty of disinterested judgment. Kant's views continue to have a major influence on contemporary philosophy, especially the fields of epistemology, ethics, political theory, and post-modern aesthetics.
Theodor Birt
When Birt was a professor in classics at Marburg University, its philosophy department was among the most important in Europe. Hermann Cohen and Paul Natorp there developed what came to be known as Neo-Kantianism. As the name suggests, this aimed to develop Kant's philosophy and apply it to a wide range of contemporary issues. In addition to Cohen and Natorp, Marburg's philosophy department was home during Birt's career to such important figures as Martin Heidegger, Hannah Arendt, Paul Friedlander, Ernst Cassirer, and José Ortega y Gasset. Birt contributed a section to one of Natorp's books, who thanked him as a 'great friend and colleague.' A letter from Kurt Wolff, who became a well-known German publisher, to the writer Boris Pasternak shows that Birt and the philosophers were part of the same social circle: