Ancient Chinese culture is the long-term precipitation and development of monistic system thought. Its fundamental theory is always about the change of the energy of Qi.
“Yi Jing” and “Tao Te Ching” both tell us: Everything is inseparable from Yin and Yang, and it must have both Yin Qi and Yang Qi. Changes in the four seasons, birth, old age, sickness, and death in life are the result of the growth and decline of Yin and Yang.
Qi is invisible and untouchable energy that runs through the whole universe. The world‘s change is all about the Qi energy flow between Yin and Yang. Chinese medicine is cosmic medicine; Qi is a kind of cosmic energy. This energy produces everything. Where there is life or no life, it exists.
“气聚则生, 气散则亡” tells when Qi gathers, life is produced, and when Qi is dispersed, life dies. The Buddha said: when the 5 elements of Qi: Wood, Fire, Earth, Gold, and Water come together under certain conditions, a life is born. Without Qi supporting humans, life is over.
Qi is not only reflected in the breath but in all things. Its energy is immensely large. Imagine how heavy the heaviest thing around us is, Qi can move it. Mountain is very heavy. Qi can definitely move it because the mountain is no heavier than the moon, the earth, and the sun. The ancients said: the atmosphere lifted the earth and the earth is nothing more than a table tennis ball floating in the sky. Universe Qi can hold up the earth, so can it the mountains. Not only can the earth, but the Qi can also move the solar system, the Milky Way galaxy, the whole universe. It is everywhere.
Wherever Qi goes, it controls everything. Without Qi, there is no agriculture, no medicine … no life.
How does this energy manifest a human life? Parents give birth, energy gives life. It is Qi that continuously supplies life. A person is constantly absorbing energy and growing. It is the same for humans, plants, and animals.
As the essence of ancient Chinese culture, the Yin and Yang theory covers all aspects of the universe. It explains: Why do we have four seasons? It is because of the conversion of Yin and Yang between the universe, the sun, and the earth. Why do people get sick? It is the imbalance between Yin and Yang in the human body.
Yin and Yang are two opposite sides of the same thing: up and down, left and right, north and south, white and black… Yin and Yang have a distinct character of the opposition. There is Yin in Yang and there is Yang in Yin. They are interdependent to each other, support each other, contain each other, transform into each other, and complement each other. Their relationship is best described in the image of Taiji. Refer to figure 2 below.
Observe them by eyes: Anything that is upward, sporty, warm, and positive belongs to Yang. Conversely, down, static, cold, and negative belong to Yin. The largest representative of Yin and Yang: Heaven and Earth. There are others like sun and moon, day and night, man and woman, male and female…

Modern philosophy tells us that things are relative, not absolute. Although the sky, the heaven, is Yang, divided by how the sky presents to humans through a day, it is Yang during daytime and Yin at nighttime. Although it is Yang during the daytime, it can be further divided into Yang in the morning and Yin in the afternoon.
Yin and Yang can be divided indefinitely. Eventually, it reaches the atomic level. An atom is very small. Inside it, the nucleus is Yin due to its static, and the electrons surrounding the core are Yang due to the movements. Can atoms be divided again into smaller Yang and Yin? YES. Nobody knows if there is a world inside a cell of our human body, just like our universe is like a cell of a huge person, or, a huge creature.
Take a human as an example: a man is Yang, a woman is Yin; on a person, the front is Yang, the back is Yin; the upper is Yang, the lower is Yin. On one hand, the thumb is Yang, and the other four fingers are Yin. The palm of the hand is Yang and the back of the hand is Yin. From a mathematical point of view, odd numbers are Yang, even numbers are Yin.
From traditional Chinese Medicine’s point of view, in the human body, Yang meridians are active, warm, and fast; Yin meridians tend to be still, cold, and slow. So, the meridian that runs on the inner side is called the Yin channel, and that on the outer side is called the Yang channel. With this principle in mind, let us raise the arm: the inner side of the arm is Yin with extraneous fat accumulated and the outer side is Yang of mostly muscles.
The function that runs the human body is Yang, and the food and drink are Yin. Food and drink can produce the essence of energy that maintains the function of the Yang of the body through biochemical actions and nourish the body Yin through gasification.
Very importantly, for a person, the spirit is Yang, the body is Yin. Why? The human spirit embodied through the human heart and brain exudes human vitality upward and outward. The introverted, precise, and stable human body is the carrier and material foundation of the human spirit.
Yin and Yang in the human body are relatively balanced. This means: human spirit and body are balanced; human functions and basic food and water energies are balanced.
When Yin and Yang are biased in the human body, excess of Yang energy or excess of Yin energy causes hyperactive or weak Qi and Blood, and causes meridians to go abnormal. Then, people are sick.