 Natorp and Cohen find general affirmation of this train of thought in Kant’s project of seeking the conditions of possibility of the “fact” of mathematical natural science (cf. Kant Prolegomena). However, the similarities end there, for by rejecting or modifying several basic aspects of Kant’s philosophy, they also end up with a radically transformed conception of the nature of scientific experience and the meaning of knowledge. The first of their modifications stems from an anti-psychologistic critique of Kant himself, namely of what they see as a confusion in the first Critique between the task of a transcendental grounding of the sciences and that of a transcendental logic of human cognition (Stolzenberg 1995: 25. But compare Holzhey 1984: 137). The former is in their view the genuine critical enterprise, for it promises to reveal the autonomous sources of objective knowledge, whereas the latter threatens to trace science back to psychological, and therefore contingent, subjective (albeit a priori)  wellsprings.[14]  Second, they deny any scientific role to intuition as conceived by Kant, either pure or empirical. Partly this is a result of their anti-psychologism, which forbids them from grounding the objectivity of science in the subjective faculties of cognition; but it is also because they see, with Kant, the essence of thinking in its activity and spontaneity, whereas intuition (at least as defined by Kant) is passive and receptive (cf., e.g., Kant, Kritik der reinen Vernunft (KrV), A68/B93). Hence, intuition thus conceived threatens to introduce a heteronomous, and therefore rationally unacceptable, factor into science. Finally, the Marburgers follow their German Idealist predecessors in dismissing all talk of things in themselves, conceived as things existing independently of knowledge. We can see how these three important modifications of Kant’s philosophy stem from the same basic concern with rational autonomy. For reason to be autonomous, its activity must be spontaneous; but this spontaneity cannot be conceived of psychologically, because human cognition as a matter of fact has a passive, and therefore heteronomous, intuitive element, namely sensibility. Furthermore, things in themselves can play no explanatory role here because they are ex hypothesi alien to reason.