What is the theory of Yin and Yang since ancient times?

Yin-yang theory holds that everything in the universe has two aspects, namely Yin and Yang, which are both opposite and unified, and constantly moving and interacting. This kind of movement and interaction is the root of the movement and change of everything. The ancients called this constant movement and change "biochemical infinity" Su Wen said: "Yin and Yang are the way of heaven and earth (the existence of unity of opposites is the fundamental law of all things), the discipline of all things (everything cannot exist against this law), changing parents (the change of things is formed by the constant movement and interaction of Yin and Yang), the source of life and death (the production and destruction of things come from this fundamental law), and gods. It is expounded that the growth, development and extinction of all things in the universe are the result of the continuous movement and interaction of Yin and Yang. Therefore, the theory of Yin and Yang has become a way of thinking to understand and master the laws of nature. Medicine belongs to the category of natural science, and it is believed that the physiological activities of the human body and the occurrence and development of diseases cannot go beyond yin and yang. Therefore, in order to master the development process of the disease, explore the essence of the disease and obtain satisfactory curative effect, we must explore the changes of yin and yang in the human body.

Significance and universality of Yin and Yang: Ancient thinkers believed that everything in the universe was composed of two opposing and interdependent aspects. These two aspects are called yin and yang.

Generally speaking, Yang represents things with dynamic, positive and strong attributes, such as: dynamic, strong, dynamic, exciting, positive, bright, invisible, functional, ascending, dew, light, heat, growth, life activities and so on. Yin represents the other side of things with static, immobile and soft attributes, for example, static, soft, immobile, restrained, negative, gloomy, tangible, material, declining, inward, heavy, cold, reducing and physical.

When two things are related, they can be divided into yin and yang. For example, the sky is yang, the earth is yin, the day is yang, and the month is yin; Fire is yang, water is yin, male is yang and female is yin; It's sunny during the day and cloudy at night.

Take an animal as an example, its body is yin and its life activity is yang; Its internal organs are yin and its exposed fur is yang; Its abdomen is yin and its back is yang.

From the above example, Yin and Yang refer to the most basic and highest differences and generalizations of all things in the universe.