"Rationality must hold principles in one hand, the only principle that can make consistent phenomena regular in the other, and experiments designed according to those principles in the other hand, and go to nature for advice, but not as a pupil, the teacher can listen to what he likes, but as a judge, forcing the witness to answer his questions." _ _ _ _ Kant believes that all knowledge begins with experience, but not all knowledge comes from experience. Because knowledge is a combination of personal impression and innate cognitive ability, the phenomenon recognized by human beings is actually not the true face of things, because it has been processed by subjective conditions. Kant is in an era of constant debate between rationalism and empiricism. In his view, both views of these two factions have shortcomings. He accepted that knowledge must come from empirical judgment, but he also affirmed human rational reasoning ability. Kant believes that the key to the problem lies in understanding the subject. To ask what people know, it is better to ask what people can know first. Knowledge is mastered by people through three abilities: perceptual ability receives various phenomena of things through the stimulation of external things, intellectuality is the material provided by using concepts to master sensibility, and rationality is the logical thinking by using reasoning.