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Qi (vital energy) is acquired from Heaven and Earth, and inherited from parents. Qi acquired from Heaven and Earth is called True Qi (Zhen Qi), while Qi inherited from parents is called Ordinary Qi (Fan Qi).

Regarding True Qi: When a human embryo forms, it acquires the Qi of Heaven and Earth. This Qi interacts with the body's Qi through similarity, combining to form the human body. The nature of Qi varies in clarity/turbidity and density/thinness, leading to differences in human strength/weakness and firmness/gentleness.

Regarding Ordinary Qi: When a person first receives their physical form, the embryo is formed by the conglomeration of father's essence and mother's blood, naturally generating warm Qi. After ten months when the Qi is sufficient, birth occurs. A point of Ordinary Qi resides in the Qi Acupoint of the Lower Dantian (Lower Elixir Field), and the respiration of the entire body's Qi emanates from here.

Prenatal Original Qi (Yuan Qi) belongs to Yang Qi, while Postnatal Grain Qi (from food) belongs to Yin Qi. If one keeps the Original Qi circulating internally, and if Yang Qi becomes strong, then Yin Qi will naturally diminish. When Yang is strong and Yin is weak, various diseases will not arise.

Briefly stated: If a person indulges in sleep, Shen (Spirit/Mind) separates from Qi, leaving Qi without a master, causing it to rush out and scatter uncontrollably.

Those whose intake of Grain Qi exceeds their Original Qi tend to be obese; thus, those who are extremely obese often have shorter lifespans. Humans rely on the Qi of water and grain to nourish the body. The clear Qi of water and grain that circulates within the vessels is called Ying Qi (Nutritive Qi); the turbid Qi of water and grain that circulates outside the vessels is called Wei Qi (Defensive Qi). Ying Qi benefits the joints, while Wei Qi fills the skin.

Regarding Shen (Spirit): Before a person is born, when parents unite their essence, the sign begins to appear as a single point. The initial condensation of a thought is what constitutes Shen. This initial appearing point is the basis for forming the physical shape; this initial intersection of thought is the source of generating Shen.

Shen is the child of Qi. Just as Qi forms the body, so does Shen provide perception and movement. This refers to the stage from the beginning of having a body.

Shen is the commander of Qi. Where Shen moves, Qi moves; where Shen rests, Qi rests. This refers to the stage after the body has already been formed.

When Shen is tranquil, the Heart (Xin) is harmonious; when Shen is agitated, the Heart is turbulent, and turbulence in the Heart damages the physical form. To preserve the physical form, one must first regulate the Spirit. Cultivate the Spirit with tranquility and harmony to keep it secure within; dwell in the Heart with purity and emptiness so as not to be tempted by external things.

The *Dai Yi Bian* states: The body is like a house, and Shen is like the owner. If the owner dies, the house has no guardian, becoming empty and liable to collapse. The body is like a boat, and Shen is like the boatman. If the boatman leaves, the boat cannot move, becoming empty and subject to decay. People busy themselves merely nourishing the physical flesh, while neglecting the critically important Shen, much like steering a boat without a boatman or serving a house while abandoning its owner. Is this not dangerous?

In the past, Kang Zhongjun was eighty-six years old and extremely robust. He claimed that when he was young and reading the *Thousand Character Classic*, he gained some enlightenment regarding the four characters "Heart moves, Spirit fatigues" (Xin Dong Shen Pi). Throughout his life, he knew to exercise caution and moderation in all matters, avoiding prolonged mental exertion and spiritual fatigue, thus remaining vigorous in old age.