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The Round Diagram symbolizes Heaven, with the Qian trigram (Heaven) located in the Southeast and the Kun trigram (Earth) in the Northwest.
The Square Diagram symbolizes Earth, with the Qian trigram (Heaven) located in the Northwest and the Kun trigram (Earth) in the Southeast.

[Image: Round and Square Diagrams]
[Image: Sixty-Four Hexagrams Diagram]

The *Suwen* (Basic Questions), chapter "Shengqi Tongtian Lun" (Treatise on the Connection between Vital Qi and Heaven), states: "Human Yang Qi is like Heaven and the Sun; if it loses its proper place/function, lifespan will be shortened and vitality will not be manifest." (This passage clarifies that human life relies entirely on Yang Qi. If the sun is not bright, the sky becomes dark and gloomy; if Yang Qi is not secure, humans suffer premature death; these are all manifestations of Yang Qi losing its proper state. Thus, Heaven does not shine by itself; its brightness comes from the Sun and Moon. The moon's body is originally black and becomes bright only when illuminated by the sun. This illustrates that Heaven's operation depends on the Sun's brightness. When the sun reaches noon, it is day; the sun hangs high in the middle of the sky, revealing visible divine illumination, representing the Yang of the Li trigram being outside. When the sun reaches midnight, it is night; fire lies hidden in water, containing invisible primordial Qi, representing the Yang of the Kan trigram being inside. Heaven's operation takes the Sun as its root. Without this Sun, Heaven would have no distinction between day and night, the four seasons would lose their order, darkness would prevail, and all things would fail to manifest. In humans, only this Yang Qi is essential. Without Yang Qi, who would clarify the clear and turbid? Who would distribute Sanjiao (Triple Burner)? Who would facilitate respiration? Who would conduct circulation? How would blood be generated? How would food be digested? This is equivalent to Heaven without a Sun. Is it possible to preserve one's natural lifespan under such conditions? Among the 162 chapters of the *Neijing*, only this section elucidates the profound principles of the correspondence between Heaven and Humanity, making it most crucial for readers to study carefully.)

Generally, the key to Yin and Yang is that Yang must be dense/secure so that Yin can be solidified. If the two are not in harmony, it is like having Spring without Autumn, or Winter without Summer. Therefore, harmonizing them is called the standard of the Sages. (Yin governs internal retention, while Yang governs external protection. If Yang is dense externally, pathogenic factors cannot invade, allowing Yin to remain solid internally. Disharmony refers to bias: bias toward Yang is like having Spring without Autumn; bias toward Yin is like having Winter without Summer. Harmonization involves draining excess and tonifying deficiency, ensuring neither dominates, which is the method of the Sages.) Thus, if Yang is excessive and cannot maintain density, Yin Qi will perish. (If Yang is dense, Yin is solid; if Yang is hyperactive, how can it be dense? Yin Qi, disturbed, will suffer from Jian Jue [Frying Syncope] and exhaust itself.) However, if Yin is peaceful and Yang is securely retained, Jing and Shen (Spirit) will function properly. (Yin Blood is calm internally, Yang Qi is secure externally. Yin nourishes Jing, Yang nourishes Shen. With abundant Jing and complete Shen, this state is termed "Zhi" [Governance/Health].)

The *Suwen*, chapter "Wuchang Zheng Da Lun" (Great Treatise on the Normal Policies of the Five Constants), states: "Those where Yin Essence is offered up live long; those where Yang Essence descends die young." (Qibo originally discussed the Southeast as a Yang region, where essence descends and people often die young; the Northwest as a Yin region, where essence rises and people often live long. I have expanded upon this: this ultimate principle of Yin and Yang applies equally within the human body. Blood belongs to Yin; although stored by the Liver, it actually falls under the category of True Water of the Kidney Meridian. Water is the Root of Pre-Heaven. When Water is prosperous, Yin Essence is abundant and offered upward, thus enabling longevity; therefore, tonifying the Kidney should be urgent. Qi belongs to Yang; although governed by the Lungs, it is actually transformed from food and drink by Spleen Earth. Earth is the Root of Post-Heaven. When Earth declines, Yang Essence deteriorates and sinks downward, leading to premature death; therefore, tonifying the Spleen should be urgent. Ancient sages said, Water is the Origin of Tian Yi (Number One), and Earth is the Mother of All Things. Since ancient times, only Xue Lizhai deeply understood this meaning, frequently using Liuwei Dihuang Wan (Six-Ingredient Rehmannia Pill) to strengthen Water as a plan for offering upward, and simultaneously using Buzhong Yiqi Tang (Tonify the Middle and Augment the Qi Decoction) to support Earth as a prevention against sinking. This person likely penetrated the subtleties of ascending and descending and deeply comprehended the purport of creation.)

My commentary: Medical classics fill shelves, yet they do not exceed the scope of Yin and Yang. Indeed, regarding the Zang-Fu organs, abdomen and back, upper and lower, interior and exterior of the body; the pulse positions of left and right, cun and chi; the qualities of floating, sinking, slow, and rapid; the seasons of Spring, Summer, Autumn, and Winter; and the annual movements of South Governance and North Governance, if one observes the subtleties of Yin and Yang and regulates their deficiency and excess, then the roots of ten thousand diseases fall under control, and the richness of ten thousand volumes resides within the inch-pulse. Is this not concise yet comprehensive, simple yet reliable?