This did not give the deathblow to rationalism alone, but also to bourgeois materialism which reigned among the French radical thinkers. Kant's researches refuted the negative as well as the positive assertions anent the supernatural and infinite. This cleared the field for faith, for intuitive conviction. God, freedom and immortality are concepts the truth of which cannot be proved by reason, like the natural truths derived from experience. But nevertheless their reality is no less certain, only it is of a different nature, being subjective and, therefore, necessarily a matter of personal conviction. The freedom of the will, for instance, is not a knowledge gained by experience, because experience never teaches us anything but lack of freedom and dependence on the laws of nature. But nevertheless freedom of will is a necessary conviction of every one who feels it in the categorical imperative: Thou shalt! of every one possessed by a sense of duty and of the knowledge that he can act accordingly: therefore freedom of will is unconditionally certain and requires no proof by experience. And from this premise there follows in same way the assurance of the immortality of the soul and of the existence of God. It gives the same kind of certainty to all ideas which were left in a state of uncertainty by the critique of pure reason. At the same time freedom of will determines the form of the theory of understanding. In the entire world of phenomena there was no room for freedom, for these phenomena follow strict rules of causality, as demanded by the organization of our mind. Therefore it was necessary to make room for freedom of will somewhere else, and so "things in themselves," hitherto a phrase without value and meaning, assumed a higher importance. They were not bound to space, time or categories, they were free: they formed so to say a second world, the world of noumena, which stood behind the world of phenomena and which solved the contradiction between the lawful dependence of things in nature and between the personal conviction of freedom of will. These opinions and reasonings were fully in accord with the conditions of science and the economic development of Kant's time. The field of nature was left entirely to the inductive method of science which based itself on strictly materialist experience and observation, classifying things systematically in their causal order and excluding all supernatural interference. But while faith was banished from the natural sciences forever, it could not be dispensed with. The ignorance as to the origin of the human will left room for a supernatural ethic. The attempts of the materialists to exclude the supernatural also from this field failed. The time had not come as yet for a materialist and natural ethics, for science was not yet able to demonstrate as an indisputable truth, founded on experience, in what manner ethical codes and moral ideas in general had a material origin.