Zhuangzi holds that the relationship between the universe and man is "the unity of man and nature", and things are forgotten by me, so he has a well-informed view of life and death; Zhuangzi thinks that Tao gives us appearance and heaven gives us shape. What we should do is not to damage our nature because of likes and dislikes. He takes the complete life of human beings as the starting point to think about what kind of life journey people should spend. He transcended the limitations of any knowledge system and ideology, and stood in the circle of heaven and on the edge of life to reflect on life. His philosophy is a philosophy of life, and his thinking is of ultimate significance. Moreover, there are many ideas that are very advanced, such as "one foot beats, half of the day is inexhaustible", which is the extreme thought in mathematics. Plato believes that any philosophy must include a theory about nature and the universe if it is to be universal. Plato tried to grasp the eternal truth about individuals and nature, so he developed a natural philosophy that was suitable for and subordinate to his political and theological views. Plato believes that tangible things in nature are fluid, but the "form" or "idea" that constitutes these tangible things is eternal. Plato pointed out that when we say "horse", we don't mean any horse, but any kind of horse. The meaning of "horse" itself is independent of all kinds of horses ("tangible"), and it does not exist in space and time, so it is eternal. But a specific, tangible horse that exists in the sensory world is "mobile" and will die and rot. This can be used as a preliminary explanation of Plato's theory of ideas. Plato believes that we can't have a real understanding of those changing and flowing things. We only have opinions or opinions about them. The only thing we can really understand is the "form" or "idea" that we can use our reason to understand. Therefore, Plato believes that knowledge is fixed and certain, and there can be no wrong knowledge. But opinions may be wrong. In Plato's Republic, there is a famous cave metaphor to explain idealism: a group of prisoners are in a cave, their hands and feet are tied, and their bodies can't turn around, so they can only turn their backs on the hole. There is a white wall in front of them, and a fire is burning behind them. On that white wall, they saw the shadow of themselves and the things between them and the fire. Because they couldn't see anything else, the prisoners would think that the shadow was the real thing. Finally, a man broke free from the shackles and groped his way out of the hole. He saw the real thing for the first time. He went back to the cave and tried to explain to others that those shadows were just illusory things and showed them the bright way. But for those prisoners, the man seemed to be more stupid than before he escaped, and declared to him that there was nothing in the world except the shadow on the wall. Plato used this story to tell us that "form" is actually the real thing under the sunshine, and what our sensory world can feel is just the shadow on the white wall. Our nature is dark and monotonous compared with the bright world of reason. People who don't understand philosophy can only see those shadows, while philosophers see external things in the sunshine of truth. Plato's Republic also painted us an ideal utopia. Plato believed that the country should be ruled by philosophers. The citizens in Plato's ideal country are divided into three classes: patriots, soldiers and ordinary people. Defenders of the country are a few elites who manage the country. They can be inherited, but excellent children from other classes can also be trained as patriots, and the descendants of patriots may also be reduced to the class of ordinary people. The task of defending the country is to supervise the formulation and implementation of the code. Plato has a complete set of theories to achieve this goal. His utopia requires everyone to have his special function in society to meet the overall needs of society. But in this country, women and men have the same rights and there is complete sexual equality. The government can lie when it is in the public interest. Everyone should do his own thing and should not disturb others. Today, Plato's utopia is a terrible totalitarian country. But "the ideal country is actually the view of scientists who manage the country in the right way", Plato himself did not try to realize the state machine in the ideal country. Plato pointed out in The Laws that a "constitutional country" is the best country after an ideal country. He also pointed out in the book that women and men should receive the same respect and training. Plato tried to make astronomy a branch of mathematics. He believes: "Astronomy, like geometry, can be studied by asking and solving problems, regardless of the celestial boundaries." Plato thought that the beginning of the universe was an indistinguishable chaos. The development of this chaos is the result of the activities of a supernatural god. According to Plato, the universe has changed from chaos to order, and its most important feature is that the creator has formulated a rational plan for the world; The mechanical process of putting this scheme into practice is a natural event that is taken for granted. Plato's cosmology is basically a mathematical cosmology. He imagined that there were two kinds of right triangles at the beginning of the universe, one was half of a square and the other was half of an equilateral triangle. From these triangles, four kinds of regular polyhedrons are reasonably produced, which constitute particles of four elements. Fire particles are regular tetrahedrons, gas particles are regular octahedrons, water particles are regular icosahedrons, and soil particles are cubes. The fifth regular polyhedron is a dodecahedron formed by a regular pentagon, which is the fifth element that makes up the matter in the sky and is called ether. The whole universe is a sphere, because the sphere is symmetrical and perfect, and any point on the sphere is the same. The universe is also alive and moving, and there is a soul that fills all the space. The motion of the universe is a circular motion, because circular motion is the most perfect and does not need hands or feet to push it. The quantity of each of the four elements in the universe is as follows: the ratio of fire to gas is equal to the ratio of gas to water and the ratio of water to soil. Everything can be named by a number, which is the proportion of the elements they contain. In "The Republic", Plato designed a picture of a just country: the country is moderate in scale, with a panoramic view of the whole country from a high place in the city, and the Chinese people know each other. Plato believed that the country originated from the division of labor, so he divided the citizens in the ideal country into three levels: the ruler, the warrior and the laborer, representing the three qualities of wisdom, courage and desire respectively. Rulers rely on their own philosophical wisdom and moral strength to rule the country; The samurai assisted in governing the country and defended the security of the country with loyalty and courage; Laborers provide material means of subsistence for the whole country. Each of the three grades has its own duties and its own place. In such a country, the statesmen are highly respected philosophers, and only philosophers can understand ideas, have perfect virtue and superb wisdom, understand where justice lies, and govern the country fairly under the guidance of reason. Rulers and samurai have no private property and family, because private property and family are the root of all selfish evil thoughts. Workers are never allowed to own luxury items. The utopia also attaches great importance to education, because the quality and morality of the people determine the quality of the country. Plato even imagined that all people over the age of 1 would be sent abroad at the beginning of the founding of the People's Republic of China, because they had been influenced by the old culture and could not be changed. All citizens should receive lifelong education from music, physical education, mathematics to philosophy from childhood. The content of education must be strictly selected, and the epics of Homer and Hersiod and the works of tragic poets are not allowed to be introduced into the country, because they will poison the hearts of young people. Plato claimed that this was the "first-class good" ideal country, and other regimes were the metamorphosis of this ideal regime. Due to the poor marriage, the ideal regime caused the three levels to be mixed, which led to the struggle and the rise of the military regime. In the military regime, a few powerful people gather wealth and form an Oligarchy. The sharp contradiction between the rich and the poor leads to the revolution of the people and Democracy. Democracy will be replaced by tyrannical regime when it reaches the extreme. The statesman was written between Plato's last two trips to Syracuse (367 BC ~ 361 BC), which was a period when his political practice in Syracuse was frustrated and his thoughts changed. The main idea of Politician is to discuss the definition of true politician and politics. Plato put forward the concepts of political mean and mixing in this dialogue; For the first time, the role of law is clearly discussed and the law is used as the standard for dividing the regime. He believes that true politicians (the king of philosophy) do not need to be ruled by law, but in reality true politicians are extremely rare, and even if there are true politicians, the law still has a certain role. Because politics is not only an art, but also a science. Law is just like the training plan and prescription of coaches and doctors for politicians. Although it is absurd in theory, it is necessary in practice. Plato further developed his thoughts on the role of law in his last work, Laws. From the ideal, he respected the rule of the king of philosophy, "no law or regulation is more powerful than knowledge"; Proceeding from reality, he emphasized that human beings must have laws and abide by them, otherwise their lives would be like the most savage beasts. Under the guidance of this thought, he designed his "second-class city-state" in the 12-volume Law, including geographical environment, territory size, population size and source, national economic life, class structure, political system, laws and other detailed rules. Due to the change of guiding ideology, the second-class city-state is quite different from the just state in the Republic in specific measures. There are mainly: the political system has changed from the sage regime ruled by the king of philosophy to a mixed regime to prevent individual dictatorship. "Republic" advocates that the rulers implement the system of public property, public wife, public meals and public education, while "Law" restores private property and family. In the Republic, citizens are classified according to their innate endowment, while in the Law Chapter, they are classified according to the acquired property. Plato is also the first person in the history of western education to put forward a complete pre-school education thought and establish a complete education system. Plato began to engage in educational research activities in middle age. Starting from the philosophical thought that ideas exist before matter, he emphasized rational exercise in his education system. He asked children aged 3-6 to be supervised by nannies, and they would gather in the temple of the village to play games, listen to stories and fairy tales. Plato thinks these are of great educational significance. After the age of 7, children will begin to learn all kinds of knowledge and skills needed by soldiers, including reading, writing, calculating, riding, throwing guns, archery and so on. From the age of 2 to 3, those students who show special interest in abstract thinking will continue their studies, studying arithmetic, geometry, astronomy and acoustics, so as to exercise their thinking ability and make him begin to explore the mysteries of the universe. Plato pointed out the significance of each subject to the development of abstract thinking. He advocated that future rulers should further study dialectics after the age of 3 to gain insight into the world of ideas. After five years, he can become the king of philosophy who rules the country. In his slave owner pedagogy system, physical education occupies an important position. Plato also attached great importance to women's sports. He thinks: "girls should practice all kinds of dancing and wrestling;" After marriage, they will take part in battle drills, camp and use weapons ... because once all the troops are out to fight the enemy, they can defend the children and the city "(Plato's Theory of Education). In Plato's exposition, almost all aspects of sports at that time were involved. He believes that sports should include educational means and health skills. He gave a fierce attack on the tendency of sportsmanship and professionalism in Athens at that time, and also criticized the citizens' thoughts and attitudes of despising sports. He advocates the harmonious development of mind and body, emphasizing "exercising with physical exercise and cultivating the mind with music". Plato's rich sports thoughts have a far-reaching influence on the development of sports in later generations. Plato and Aristotle were the most influential philosophers in ancient Greece, and among them, Plato had a great influence on future generations. Plato wrote a book in the mouth of his teacher Socrates, saying that when the mind abandons the body and yearns for the truth, then the thought is the best. When the soul is infected by the sin of the body, people's desire to pursue truth will not be satisfied. In Europe, there has long been Platonic love called "spiritual love" by China people. This kind of love thinks that the combination of the flesh is impure and dirty, and that love and lust are two opposite States. Therefore, when a person is really in love, it is impossible for him to think of physically combining with the object he loves. In people's eyes today, Plato's view of love is incredible. An American scholar, on the other hand, has put forward a new view of Plato's love as understood by modern people. Ira·reiss, the president of the East-West Social Society of the United States and the author of The American Family System, believes that the spiritual love advocated by Plato actually refers to a kind of love between the same sex, that is, "homosexuality". The ancient Greeks believed that the process of homosexuality was more spiritual communication and spiritual communication than physical communication. In ancient Greek society, where women received little education, it was difficult for men to find spiritual opponents from women. This is why Plato emphasized the love between men. Plato firmly believes that "true" love is a persistent emotion, and only time is the touchstone of love, and only extraordinary love can stand the test of time. Sociologists in the United States have different opinions on whether Platonic love is pure love with only spiritual intercourse or elegant love with physical intercourse but emphasis on spiritual intercourse. But one thing is certain, that is, Plato believes that love can make people sublimate. He said that for a man who lives a noble life, it is not blood, honor, wealth, but love that guides his behavior. There is no emotion in the world so deeply rooted in people's hearts as love. If a person who is in love has committed disgraceful acts and is seen by his father, friends or anyone else, he will not be as pale as his lover, losing everything and being unable to face the person he loves and the person who loves himself.