Immanuel Kant (1724–1804) is the founder of German classical philosophy, the most important thinker after Plato and Aristotle. In an effort to determine the boundaries of human knowledge, Kant pointed out that a person cannot know reality, but only obtain a subjective idea of it. The philosopher of “duty” and the “categorical imperative”, Kant easily overturned all speculative theories, as a result, philosophy after him became completely different.