 We finally turn to the Marburg thesis that philosophy, as philosophy of science, must also be the philosophical history of science. For science, as a fieri (a doing) evolves over time; hence the activity of its basic functions and the regulated mutation of its laws can only be observed through time. Yet this historical tracing of the progress of science must be philosophically informed, that is, grounded in the transcendentally isolated system of basic functions. As mentioned above, Natorp holds that the entire value of the transcendental method is normative: having laid bare the categorial functions in their purity, science can be judged as to its rigor, i.e., its submission to rational legislation. The Marburgers, with this criterion in hand, enthusiastically apply it in praise and blame.