Kant's "three criticisms" constitute his great philosophical system, which are: Critique of Pure Reason (178 1 year), Critique of Practical Reason (1788) and Critique of Judgment (1790). The question to be answered in Critique of Pure Reason is: What can we know? Kant's answer is: we can only know what natural science makes us realize. Philosophy is of no use except to help us clarify the necessary conditions for making knowledge possible. The metaphysical problems since Plato are actually unsolvable. For Kant, to answer the question of what we can know, we must first look at the relationship between the knower and the known. Truth in classical philosophy is regarded as the consistent correspondence between language and things. Kant asked: How is this consistency possible? Things are concrete and materialized, while language is abstract. How can these two things be consistent? In fact, human perception only provides some characteristics of objects, such as mass, volume, shape, quantity, weight, speed of movement and so on. Without these characteristics, we can't imagine objects. This is the main feature of an object. Objects also have other subordinate characteristics, such as color, sound, taste and temperature sense. Although these subordinate features are part of the object, people can imagine them differently. For example, we can imagine a blue table as a green table. This difference between the main features and the secondary features makes people further ask: What is the real situation of the external world? Because if I can imagine some features of objects in different ways, that is to say, these features seem to exist only in my perception, how can I be sure that the world exists only in my mind? Therefore, the consistency (truth) between language and things seems to be only possible in people's minds. This is, of course, desperate extreme skepticism. What should people do if they are unwilling to accept this view? Maybe an external world that we can't recognize does exist, so what should we do? Before Kant, the philosopher's answer to this question was to push this question to God: our thoughts are consistent with the outside world because God is willing to arrange it this way. But the question is: how do we know that what God shows us is true? Kant reversed the problem. Before that, people let knowledge look at external things. Kant
And Kant said, what if we turn things upside down and make them conform to our understanding? 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. 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: intellectuality legislates for nature. His argument has something in common with modern quantum mechanics: the characteristics of things are related to observers. In Critique of Pure Reason, Kant studied the forms of human perception, namely space and time. Matter existing in time and space is processed into experience by human cognition, and Kant calls the form of human cognition "(absolute) category". These forms of human reason include people's assumptions about the soul, the world and God. Kant understands them as some restrictive principles, and people's experience world is constructed through these principles. Critique of Pure Reason studies how human beings know the outside world, while Critique of Practical Reason published by Kant in 1788 answers the ethical question: What should we do? In short, Kant tells us that we should do our duty. But what do you mean by "due diligence"? In order to answer this question, Kant put forward the famous "(absolute) Kategorischer Imperativ": "If you do this, you will always make the criterion of your will a universal law-making principle." Kant believes that man is morally independent. Although his behavior is limited by objective cause and effect, the reason why he becomes a man lies in his moral freedom, his ability to transcend cause and effect, and his ability to be responsible for his actions. The question to be answered by "judgment criticism" is: What hope can we have? Kant's answer is: if I want to be a real morality, I must assume that God exists and everything is not 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. In fact, Kant tried to reconcile empiricism and rationalism in order to unify thinking and object. He thinks that Hume's extreme empiricism must be refuted. For the first time, Kant attributed the identity of object and thinking to "the initiative of subject", which is a milestone in German philosophy. Fichte developed this initiative into an extremely morbid solipsism on the basis of Kant. Because Kant didn't realize that contradiction is the driving force of things, it caused the duality of his own system. However, at this stage of Kant, the identity of subject and object is temporarily attributed to the initiative of subject, while German classical philosophy was gradually established after later generations criticized and developed Kant's philosophy. I have to say that Kant's contribution is great. On Permanent Peace, published in 1795, should be Kant's last book with far-reaching influence on mankind. The ideas of world citizens, world confederations and sovereign countries' non-interference in internal affairs are still of practical significance today. Emmanuel Kant (1724- 1804) is a German philosopher, astronomer, one of the founders of the nebula theory and the founder of German classical idealism. 1754, Kant published a paper on whether the earth's rotation changes and whether the earth will age, which boldly questioned the "theory of cosmic invariance". 1755, Kant published the book General History of Nature and Theory of Celestial Bodies, and put forward the theory of the origin of the solar system for the first time. Kant pointed out in his book that the solar system evolved from nebulae. This nebula consists of solid particles of different sizes. Celestial bodies began to form in the most attractive places. Gravitation makes particles close to each other, and large particles attract small particles to form bigger lumps, which are getting bigger and bigger. The central part with the strongest gravity attracts the most particles and forms the sun first. The motion of the outer particles falling to the central body under the gravity of the sun changes direction due to the collision of other particles and becomes a circular motion around the sun. These particles orbiting the sun gradually form several centers of gravity and finally condense into planets orbiting the sun. The formation process of satellites is similar to that of planets. However, due to the rejection of metaphysical view of nature at that time, this theory did not attract people's attention and was buried for a long time. It was not until 1796 that P.S. Laplace, a famous French mathematician and astronomer, independently put forward another nebula hypothesis about the origin of the solar system in his book On the Cosmic System. People remember that Kant put forward this theory 4 1 years ago, so later generations called this theory Kant-Laplace theory, which is often called Kant-Laplace nebula hypothesis. Throughout the nineteenth century, this theory has been dominant in astronomy. He also made great influence and contribution to astronomy. Although most of Kant's works are difficult and it takes courage to read his books, Kant is an unavoidable peak in philosophical research. His influence on German thought is enormous. His attitude of strictly observing discipline and ensuring accuracy is very common in Germans today, and the most sophisticated instruments come from these serious and almost stupid people. More importantly, he set an example for German philosophical speculation, making philosophy a popular science in Germany, so that the proportion of the most famous philosophers and thinkers in the world with German symbols is too high. Hegel, Fichte, Marx, Nietzsche ... In many countries, as long as one person can appear, it is enough to boast of the world's famous names, but it has appeared one after another in Germany. Heine said: "Germany was introduced into the philosophical path by Kant, and philosophy became a national cause. A group of outstanding thinkers suddenly appeared on the land of Germany, just like being summoned by magic. "