First, we can only know what natural science has made us realize, and philosophy is of no more use than helping us to clarify the necessary conditions for making knowledge possible. Kant completely reversed this problem from Plato. Before that, people made knowledge conform to external things. Kant said, what if we make things conform to our knowledge in turn? Kant compared this way of thinking with Copernicus's "Heliocentrism": Before Copernicus, people thought that all the planets revolved around our earth, but Copernicus said that our earth revolved around other planets.

Secondly, it is considered that the criticism of practical reason is to examine the essence of "will" that stipulates moral behavior and the principles it follows. The book includes two parts: the original theory of pure practical reason and the methodology of pure practical reason. It highlights the problem of human subjectivity, emphasizes the dignity and loftiness of personality, and shows a strong humanistic spirit.

Thirdly, if I want to be a truly moral person, I must assume that God exists, and not everything is over after the end of life. In Critique of Judgment, Kant also pays attention to the purpose, significance and mode of action of people's spiritual activities, including people's aesthetic appreciation and fantasy ability.

Kant brought about a Copernican transformation in philosophy. He said that things are not affecting people, but people are affecting things. We are building the real world. In the process of understanding things, people are more important than things themselves. Kant even thinks that we can't know the truth of things, only the appearance of things. Kant's famous assertion is that man is the measure of everything. His argument has something in common with modern quantum mechanics: the characteristics of things are related to observers.