Kant's inaugural paper "Forms and Principles of the Sensed World and the Rational World" put forward in 1770 marked the beginning of the transitional period. He believes that people's feelings are just a phenomenon, and the rational world represents the real world. Space and time are the internal conditions of the soul, and sporadic feelings of isolation from each other become a phenomenon under the arrangement of the innate laws of space and time. Phenomenon is how things behave in the relationship with the subject. Only pure concepts can understand the real world. Kant believes that Newton's absolute theory of time and space is fictitious, that G.W. Leibniz's view of time and space is the relationship between things can not be established, and that this view of time and space is obviously incompatible with Euclidean geometry. The new theory of time and space put forward in this article is an important step for him to change his direction.

In this period of critical philosophy, Kant established a unique critical philosophy system, including epistemology with transcendentalism, dualism and agnosticism as its basic characteristics, as well as ethics and aesthetics on this basis.

From the perspective of epistemology, Kant firmly believed in the reliability of natural science, directly criticized the one-sidedness of rationalism and empiricism, and tried to combine the reasonable aspects of the two philosophical schools. It is advocated that human beings should know themselves, know nature and make use of it. In Kant's view, mathematics and natural science are important achievements of pure reason and perfect models of human understanding, which are inevitable and universal. If we can explain the inevitability and universality of mathematics and natural science, we can gain insight into the inside information. Based on this belief, Kant not only opposed Hume's skepticism, but also believed that Locke's empiricism could not explain this problem.