Five Elements: refers to the five substances of metal, wood, water, fire, and earth. Ancient Chinese thinkers used the theory of the Five Elements to explain the formation of all things in the world and their interrelationships. Traditional Chinese medicine uses the Five Elements to explain various phenomena in physiology and pathology. People who predict the future use the mutual generation and control of the Five Elements to calculate people's fate.

　　The theory of the Five Elements first appeared in Taoist philosophy. It emphasizes the concept of wholeness, aiming to describe the movement forms and transformation relationships of things. If yin-yang is the ancient theory of opposition and unity, then the Five Elements can be considered as the primitive general system theory. The theory of the Five Elements is a theory of the composition of matter in ancient China, similar to the four elements theory of earth, water, fire, and air in the West, but in the modern era that emphasizes pure science, this theory that integrates philosophy, science (physics, chemistry, biology), and sociology has not received the attention and research it deserves, let alone drawing on its essence and promoting it widely.
Generation of the Five Elements (Five Materials Theory) :
　　Metal generates water, water generates wood, wood generates fire, fire generates earth, and earth generates metal.
　　Metal generates water: melting of metal produces water;
　　Water generates wood: water nourishes wood;
　　Wood generates fire: dry wood produces fire;
　　Fire generates earth: fire burns wood to produce earth;
　　Earth generates metal: mineral deposits produce metal.
　　 Control of the Five Elements:
　　Metal controls wood, wood controls earth, earth controls water, water controls fire, and fire controls metal.
　　Hardness overcomes softness, hence metal overcomes wood; because tools can cut down trees;
　　Specificity overcomes dispersion, hence wood overcomes earth; because wooden stakes can be driven into the earth;
　　Substance overcomes emptiness, hence earth overcomes water; because dikes can prevent the flow of water;
　　Numerical superiority overcomes scarcity, hence water overcomes fire; because large amounts of water can extinguish flames;
　　Precision overcomes hardness, hence fire overcomes metal; because intense fire can melt metal.

The relationship between the Heavenly Stems and the Five Elements, directions:
　　Jia is timber for beams, East. Yi is timber for flowers and fruits, East.
　　Bing is the sun's fire, South. Ding is the fire of lamps, South.
　　Wu is the earth of city walls, Central. Ji is the earth of fields, Central.
　　Geng is the metal of axes and hammers, West. Xin is the metal of jewelry, West.
　　Ren is the water of rivers, North. Gui is the water of rain and dew, North.
　　The relationship between the Five Elements, directions, Heavenly Stems, colors, and mythical beasts:
　　Wood: East: Jia, Yi: Green: Azure Dragon
　　Metal: West: Geng, Xin: White: White Tiger
　　Fire: South: Bing, Ding: Red: Vermilion Bird
　　Water: North: Ren, Gui: Black: Black Tortoise
　　Earth: Central: Wu, Ji: Yellow: Yellow Lion
　　 The relationship between the Five Elements and the seasons
　　The Five Elements refer to the five modes of movement of gases.
　　Spring belongs to wood, representing the mode of gas spreading outward. In spring, grasses and trees grow vigorously, and the branches of trees spread outwards, with nutrients transported to the tops, so spring belongs to wood.
　　Summer belongs to fire, representing the mode of gas moving upward. Fire's characteristic is to move upward, and in summer, various plants grow rapidly upwards, so summer belongs to fire.
　　Autumn belongs to metal, representing the mode of gas contracting inward. Metal's characteristic is stability, and in autumn, harvests are made, and people store food for winter, and leaves fall, so autumn belongs to metal.
　　Winter belongs to water, representing the mode of gas moving downward. Water flows downward, and in winter, all things sleep, accumulating nutrients for spring, so winter belongs to water.
　　Because there are four seasons, there are four elements, but there should be a transitional period between summer and autumn, thus there is earth, which represents the stable movement of gas.
　　 The correspondence between the Five Elements and the Eight Trigrams
　　Metal---Qian, Dui: Qian is Heaven, Dui is Marsh;
　　Fire---Li: Li is Fire;
　　Wood---Zhen, Xun: Zhen is Thunder, Xun is Wind;
　　Water---Kan: Kan is Water;
　　Earth---Gen, Kun: Gen is Mountain, Kun is Earth.
　　 The correspondence between the Five Elements and the Earthly Branches
　　(1) The Three Combinations of Earthly Branches:
　　Zi (Rat), Chen (Dragon), Shen (Monkey) form the Water Element; Si (Snake), You (Rooster), Chou (Ox) form the Metal Element;
　　Yin (Tiger), Wu (Horse), Xu (Dog) form the Fire Element; Hai (Pig), Mao (Rabbit), Wei (Sheep) form the Wood Element.
　　(2) The Six Combinations of Earthly Branches:
　　Zi (Rat) and Chou (Ox) combine to form Earth; Yin (Tiger) and Hai (Pig) combine to form Water;
　　Mao (Rabbit) and Xu (Dog) combine to form Fire; Chen (Dragon) and You (Rooster) combine to form Metal;
　　Si (Snake) and Shen (Monkey) combine to form Water; Wu (Horse) and Wei (Sheep) combine to form Sun and Moon.
　　(3) The relationship between Earthly Branches and the Five Elements, directions:
　　Zi (Rat) belongs to Yang Water, North; Hai (Pig) belongs to Yin Water, North.
　　Yin (Tiger) belongs to Yang Wood, East; Mao (Rabbit) belongs to Yin Wood, East.
　　Si (Snake) belongs to Yin Fire, South; Wu (Horse) belongs to Yang Fire, South.
　　Shen (Monkey) belongs to Yang Metal, West; You (Rooster) belongs to Yin Metal, West.
　　Chen (Dragon), Xu (Dog) belong to Yang Earth, Central;
　　Chou (Ox), Wei (Sheep) belong to Yin Earth, Central.
Appendix: Categories of the Five Elements