Kant's life can be divided into the early and later periods, with the early period focusing on the natural sciences and the latter on philosophy.

The main achievements of the early period were the publication of the General History of Nature and the Theory of Celestial Bodies in 1755, which proposed the nebula hypothesis of the origin of the solar system.

In the nine years that followed, beginning in 1781, Kant published a series of great works of great originality covering a wide range of fields, which revolutionized the philosophical thought of the time, including the Critique of Pure Reason, the Critique of Practical Reason, and the Critique of Judgment.

The publication of the "Three Critiques" marked the completion of Kant's philosophical system. The three critiques explore epistemology, ethics, and aesthetics, respectively.

Politically, Kant was a liberal who supported the French Revolution and the republican form of government, and in 1795 he published On Perpetual Peace, in which he proposed the idea of a parliamentary government and a commonwealth of the world.

The last representative work during his lifetime was Anthropology, which is generally considered to be a summary and summary of his entire doctrine.

In his later years, Kant was already known as an outstanding philosopher. Kant never married.

Kant's philosophy covers a wide range of topics, from aesthetics and ethics to metaphysics. His doctrine refers to the research methods of modern natural science, emphasizing the combination of experiment and mathematics, experience and reason, criticizing the old-style metaphysics that rationalism insists on not combining with experience, and at the same time criticizing empiricism that denies the necessary truth.

In the preface to the first edition of the Critique of Pure Reason, Kant states that the necessity of a critique of reason lies first in determining whether metaphysics in general is possible or impossible, and in defining the source, scope, and boundaries.

But Kant is in the preface to the second edition. Instead of focusing on the conditions for rational criticism, the new concept of "not knowledge according to the object, but the object according to knowledge", led Kant to launch the "Copernican revolution" in philosophy.

In the introduction, Kant proposes the general outline of the book: the general task of pure reason is to solve the problem of "innate synthetic judgment", that is, the question of "how possible" true scientific knowledge which is universal and inevitable and which expands the content of knowledge, and subdivides the following four questions according to this general question:

How is mathematics possible?How is natural science possible?How is metaphysics possible as a tendency of nature?How is metaphysics possible as science?

The book is roughly divided into five parts: "1 Transcendental Sensibility, 2 Transcendental Logic, 3 Transcendental Analysis, 4 Transcendental Dialectics. 5 Transcendental Methodology"

The "transcendental sensibility" is primarily to elucidate. Only through the innate intuitive form of human perceptual knowledge (receptivity), that is, "space" and "time", can we organize the sensory materials that stimulate the senses of the things in ourselves (the appearance of the phenomenal world), and at the same time, space and time are also the innate intuitive forms of mathematical knowledge.

The "transcendental logic" states that "the sensibility must be combined with the intellect. Intuition must be combined with thinking. in order to produce knowledge of the natural sciences." Thus there must be a transcendental logic, as distinct from formal logic, to explore the structure of intellect and its principles in relation to empirical objects.

A priori logic is based on the relationship between knowledge and objects, that is, the content of knowledge, rather than a mere form of thought. This marks the germ of dialectical logic in modern times.

"A priori analytical" (the logic of truth) states that the innate concepts and principles of intellect are the basis and conditions for the possibility of natural science.

In conceptual analysis, through the analysis of logical functions in intellectual judgments. The principle analysis theory in the transcendental analysis theory mainly clarifies the laws by which the intellect guides the judgment to apply the category to the phenomenon.

"Transcendental dialectics" (the logic of illusions) mainly explains that reason inevitably has to transcend phenomena to know the ontology, and that the resulting metaphysics as a natural tendency is nothing more than a priori illusions, and cannot be true science.

In the introduction to transcendental dialectics, Kant pointed out that the generalizing power of reason is due to the fact that it is necessary to know the unconditional by inference, starting from the conditional.

The "transcendental methodology" first states that although the empirical use of pure reason has the correct use of laws (the principle of intellectual precedence), its theoretical (speculative and transcendental) arcane use has no laws to speak of, so it is necessary to train its methods of use a priori (the four aspects of assertiveness based on definition, skepticism from the argument and falsification of both sides, and methods of hypothesis and proof) to establish some "negative" rules, in order to limit the tendency of pure reason to expand beyond possible experience, thus preparing methodological principles for the establishment of a metaphysics of experience.

Although Kant used critical philosophy, he himself established a complete set of philosophical theories.

In Kant's time, there were two main theories of European philosophical thought: empiricism, developed by John, Locke, David, Hume, and others, and rationalism, such as Descartes.

Empiricists believe that human knowledge and knowledge of the world comes from human experience, while rationalists believe that human knowledge comes from human reason.

Kant combined the two views to a certain extent. Kant believed that knowledge is acquired by human beings through both the senses and reason.

Experience is necessary for the production of knowledge, but it is not the only element. To convert experience into knowledge, reason is required (Kant, like Aristotle, called this reason "categories"), and reason is innate.

Human beings gain experience of the outside world through the framework of categories, and without categories they cannot perceive the worldly realm. Thus category is as necessary as experience for the acquisition of knowledge.

But there are also factors in the human realm that can change man's perception of the world, and he realizes that things are different from what people see, and that people can never know for sure what things really are.

In Kant's view, time and space are two inherently special concepts. In the Critique of Pure Reason, Kant pointed out that no one can imagine an object that exists in the world without time and space, and therefore he emphasized that experience is impossible without time and space, and that these two precede all experience.

In addition, Kant believed that experience must come from outside the mind. In other words, a person can perceive and understand the world around him, but he can never perceive and understand himself, because the generation of knowledge requires three elements: time, space, and scope.

In terms of the law of cause and effect, Kant also overturned Hume's view. Hume believed that there was no law of cause and effect, and that it was only by habit that human beings thought that there was a connection between the two phenomena.

In other words, we can only perceive the motion of the white ball and the black ball, but we cannot perceive the cause of the white ball's movement.

It is precisely because we cannot perceive the law of cause and effect itself that Hume argues that we cannot prove the existence of the law of cause and effect. But Kant believed that the law of cause and effect was the result of human reason, and Kant agreed with Hume that the law of cause and effect did not come from experience, but he believed that the law of nature could be proved, because the law of nature is the law of human cognition. The law of cause and effect is actually a manifestation of human reason.

On the question of religion, Kant acknowledged that neither experience nor reason could prove the existence of God. But he argues that for moral reasons, we must assume the existence of God and the soul.

He called these beliefs "practical assumptions," i.e., a hypothesis that cannot be proved, but which must be true for the sake of practice.

In terms of philosophical ethics in the Critique of Practical Reason, Kant rejects the claim that the will is governed by external factors, but argues that the will legislates for itself, and that the human ability to distinguish between right and wrong is innate, not acquired.

This set of natural laws is a supreme command, applicable to all situations, and a universal moral code. Kant believed that a true moral act is an act done purely on the basis of obligation, and that doing something to achieve a certain personal utilitarian purpose cannot be considered a moral act.

Thus, Kant argues that the moral conformity of an action does not depend on the consequences of the action, but on the motivation for taking it.

We are only free if we follow the moral law, because we follow the moral code that we have made ourselves, and if we do it only because we want to do it, there is no freedom at all, because you become a slave to all kinds of things.

In its own terms, his doctrine mainly answers four questions: What can I know, what should I do, what do I want, what is man? (to be continued......