First, the proposition of knowledge When we see the proposition that "knowledge is power", the first thing that comes to mind is that it belongs to the category of epistemology. In the western traditional thinking, westerners especially emphasize the epistemological research at the philosophical level, which leads to the proposition that "virtue is knowledge" by Socrates, the ancient Greek philosopher who first put forward the proposition of knowledge. In ancient Greece, the problem of knowledge has always been the main issue discussed by philosophers. Protagoras believes that everyone can only be satisfied with what the object world presents to him, and personal feeling is the only thing that everyone can trust. "Man is the measure of all things" (1), and he demonstrated the impossibility of universal knowledge with the help of individual differences in feelings. Gorgias further demonstrated this view: "First, there is nothing; Second, even if things exist, they cannot be grasped; Third, even if they can be caught, it is impossible to tell others about it. " ② These three propositions deny the possibility of existence, cognition and language communication respectively. It is regarded as the beginning of skepticism in the history of western thought. In this way, the question of whether we can acquire knowledge about the objective world becomes inevitable. With Socrates as the forerunner and Plato and Aristotle as the main force, this paper systematically and profoundly demonstrates and analyzes the nature of knowledge, thus laying the theoretical foundation of western epistemology. Plato was the first philosopher who systematically studied epistemology.