 In fact, there were some core Kantian ideas that the Neo-Kantians self-consciously rejected. They rejected the doctrine of the thing-in-itself as incoherent and unnecessary (Windelband 1910: 323), or radically reinterpreted talk of things-in-themselves as talk of a postulated final and complete theory of the world (Cohen 1885: 503ff.). Their rejection of Kant’s dualism of appearances and things-in-themselves was closely related to their rethinking of Kant’s distinction between two “stems” of cognition: sensibility and understanding. The Marburg philosophers came to fundamentally reject this distinction, while the Southwest Neo-Kantians (while maintaining the irreducibility of intuitions to concepts) still rejected the idea that intuitions are the result of a mind-independent thing-in-itself affecting sensibility. Though the Neo-Kantians took as fundamental to their philosophies the existence of substantive a priori concepts and principles that make knowledge possible, they did not accept that the categories and principles identified in the Critique of Pure Reason were complete or fixed for all time. In particular, Marburg Neo-Kantians believed that some of the categories and principles that Kant identified were relative to the scientific theories of Kant’s day, and that the categories and principles could change as scientists develop new empirical theories. Southwest Neo-Kantians, on the other hand, were keen to argue that history is just as much a science as mathematical physics, and they thought that Kant’s critical project had to be extended in order to identify the a priori elements in history. Last, the classical Neo-Kantians held that transcendental philosophy is distinct and independent of empirical psychology, even though (they argued) Kant himself was not always innocent of psychologism, despite the fact that Kant’s philosophy when rightly interpreted is the basis for a sound anti-psychologism (Cohen 1883: §8).