Kantianism
Kantianism is the philosophy of Immanuel Kant, a German philosopher born in Königsberg, Prussia (now Kaliningrad, Russia). The term "Kantianism" or "Kantian" is sometimes also used to describe contemporary positions in philosophy of mind, epistemology, and ethics.
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: