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The mutual generation and restriction among the Five Elements—Water, Wood, Fire, Earth, and Metal—are essentially a cyclic rotation of Yin ascending and Yang descending. "Generation" (Sheng) refers to nourishment and growth, corresponding to the ascent of Yin; "Restriction" (Ke) refers to control and transformation, corresponding to the descent of Yang. However, it is necessary for Yin to ascend first before Yang can descend; similarly, it is necessary for Yang to descend effectively before Yin can turn and ascend again. If the Five Elements only generate without restricting, it would be like having a wife but no husband, which is untenable. While people generally understand the principle of generation, they often overlook the principle of restriction; let us discuss this in detail.

The Kidney governs the Earth, Yin, and Water; the five body fluids also belong to Earth, Yin, and Water. The True Yang Qi within the Kidney warms and nurtures, connecting upward to the Yang Qi of all other Zang-Fu organs. Meanwhile, the True Yin Qi within the Kidney, facilitated by the steaming and movement of Kidney Yang, connects upward to the Yin Qi of all other Zang-Fu organs. Yang assists Yin in ascending to nourish Liver Wood, causing Liver Qi to spread and flourish, resulting in abundant blood and smooth Qi flow. Consequently, the Liver receives ascending Yin to nourish Heart Fire, making Heart Qi warm and moist, leading to blood generation and pulse circulation. Subsequently, the Heart receives ascending Yin to nourish Spleen Earth, strengthening Spleen Qi's transportation and transformation, enabling it to control blood and distribute essence. Then, the Spleen receives ascending Yin to nourish Lung Metal, granting Lung Metal its regulatory function, harmonizing Yuan Qi, and assisting in metabolic transformation. Finally, Lung Metal receives ascending Yin, turns downward, and enters the Kidney, allowing water essence to distribute throughout the body and the five meridians to circulate together. This represents the mutual generation of the Five Elements as one Qi, starting from the Kidney and ending at the Lung, symbolizing the Earth's Yin ascending to unite with Heaven.

The Lung governs Heaven, Yang, and Qi, distributing Yin fluids to soften Liver Wood. When Liver Wood is controlled by descending Yang, it becomes gentle and mild, no longer dry and urgent. Consequently, Liver Wood soothes Spleen Earth; when Spleen Earth is controlled by descending Yang, it becomes loose and functional, no longer sluggish and dull. Then, Spleen Earth controls Kidney Water; when Kidney Water is controlled by descending Yang, it knows how to circulate and excrete properly, no longer flooding aimlessly. Next, Kidney Water assists Heart Fire; when Heart Fire is controlled by Yang that has ascended and then descended, Heart and Kidney interact harmoniously, no longer suffering from flaming fire and dry water. Furthermore, Heart Fire warms Lung Metal; when Lung Metal is controlled by Yang that has ascended and then descended, body fluids are distributed evenly, no longer cold and dry like metal and water. This represents the mutual restriction of the Five Elements as one Qi, starting from the Lung and ending at the Lung, symbolizing Heaven's comprehensive coverage of Earth.

Thus, although the generation of the Five Elements involves the sequential ascent of Yin in the five Zang organs, it is actually Kidney Yang assisting Kidney Yin in ascending sequentially. The ascent of Yin is led by Heaven and supported by Earth. Although the restriction of the Five Elements involves the sequential descent of Yang in the five Zang organs, it is actually Lung Yang leading Lung Yin in descending sequentially. The descent of Yang is supported by Earth and led by Heaven. Generation is indeed generation, and restriction is also generation; are not generation and restriction simply the endless cycle of Yin ascending and Yang descending?

However, generation and restriction must not be excessive. Excess means that instead of True Yin and True Yang generating life through their ascent and descent, pathogenic Water and Fire cause harm through theirs. Wood relies on Water for generation; if Water floods, Wood floats; if Wood floats, Fire becomes damp; if Fire is damp, Earth is trapped; if Earth is trapped, Metal is buried; if Metal is buried, Water floods further. With excess Water and lack of Fire in the interior, diarrhea, edema, and fullness arise, along with various damp diseases. Fire relies on Water for restriction; if Water is excessive, Fire extinguishes; if Fire extinguishes, Metal becomes cold; if Metal is cold, Wood becomes damp; if Wood is damp... [Note: Text implies Wood stagnation]. Wood generates itself; if Wood is excessive, it burns itself; if Fire burns, Earth dries; if Earth is dry, Metal withers; if Metal withers, Water dries up; if Water dries up, Wood burns more fiercely. With excess Fire and lack of Water in the interior, wind disorders, consumption, Gu distension, Ge dysphagia, and Sanxiao (Three Wasting-Thirsting) arise, along with various dry diseases. Earth relies on Wood for restriction; if Wood is strong, Earth is weak; if Earth is weak, Water floods; if Water floods... [Text implies Earth deficiency]; without Fire, Earth floods, causing chest stuffiness, swelling, and diarrhea (damp diseases); without Water, Earth dries, causing Gu distension, Ge dysphagia, and Sanxiao (dry diseases). Earth relies on Fire for generation; if Fire flares, Earth dries; if Earth is dry, Metal melts; if Metal melts, Water is deficient; if Water is deficient, Wood is vigorous; if Wood is vigorous, Fire flares more. With excess Fire and lack of Water, delirium, mania, and Ge Xiao arise. Metal relies on Fire for restriction; if Fire flares, Metal dries; if Metal dries, Wood is vigorous; if Wood is vigorous... [Text transitions to Wood trapped between Water and Fire], Wood is trapped between Water and Fire (Earth encompasses the Five Elements, so diseases often combine), causing chest stuffiness, distending pain, and mixed dry/damp diseases. Water relies on Earth for restriction; if Earth is dry... [Text implies Water constraint], leading to labor cough, sore throat, distress, and diarrhea (dry diseases). Water relies on Metal for generation; if Metal is cold, Water is cold; if Water is cold, Wood floods; if Wood floods, Fire becomes damp; if Fire is damp, Earth is trapped; if Earth is trapped... [Text repeats previous pattern] leads to labor cough, sore throat, distress, and diarrhea. If generation or restriction is excessive, restriction becomes restriction, and generation also becomes restriction. Moreover, the amount of True Yin and True Yang in the human body is fixed. Any appearance of excess is actually due to insufficiency. Excess and insufficiency transform into Turbid Yin and Dry Yang. Turbid Yin ceases to be Yin and becomes Pathogenic Water; Dry Yang ceases to be Yang and becomes Pathogenic Fire. The generation and restriction of the Five Elements revolve around Water and Fire; diseases caused by excess or insufficiency in generation and restriction also revolve around Water and Fire. Water flows toward moisture; Fire moves toward dryness. Therefore, Water and Fire are the foundation of the Five Elements' formation; Dryness and Dampness are the guidelines for all diseases.

Yin and Yang refer to Qi (energy/function), while Water and Fire refer to Form (substance/structure). Kan (☵) represents Water; Water is black, and black belongs to Yin. However, Water appears dark externally but bright internally, being empty and lively, thus representing Yang within Yin, hence Kan is solid in the middle (one solid line). Li (☲) represents Fire; Fire is red, and red belongs to Yang. However, Fire appears bright externally but dark internally, and returning to its root makes it black, thus representing Yin within Yang, hence Li is hollow in the middle (one broken line). From the perspective of substance, Water and Fire have void qualities, while Wood, Metal, and Earth have solid qualities. Thus, Water and Fire are the prenatal origins of Wood, Metal, and Earth. Fire has form but no substantial mass, requiring attachment to objects to manifest substance; Water has substance but is extremely void. Therefore, in discussing the order of Five Elements generation, it is Water 1, Fire 2, Wood 3, Metal 4, Earth 5; in discussing the order of Five Elements restriction, generation starts with Water, and restriction starts with Metal. Understanding the Qi and nature of the Five Elements, and the generation and restriction of Yin and Yang, reveals the principle of unity between Heaven and Humanity. Studying the other treatises in this collection will make this clear.