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[Diagram of the Six Qi and Solar Terms]
The verse states: The first Qi begins at Dahan (Great Cold), the second at Chunfen (Spring Equinox), the third at Xiaoman (Grain Full), the fourth at Dashu (Great Heat), the fifth begins at Qiufen (Autumn Equinox), and the sixth concludes at Xiaoxue (Minor Snow).

The six Qi of the four seasons have fixed solar term deadlines; warmth, heat, coolness, and cold each have their proper season in the year. The *Book of Yunqi* states: Yin and Yang intersect, divided into six positions, with the sun and moon advancing accordingly; the relaxation and tension of cold and heat operate through the four seasons, causing the climatic commands to change. Therefore, for any given year, the Qi starts at Dahan when the Wind-Wood First Qi is exchanged, then proceeds to Chunfen when the Minister-Fire Second Qi is exchanged, then to Xiaoman when the Minister-Fire Third Qi is exchanged, then to Dashu when the Damp-Earth Fourth Qi is exchanged, then to Qiufen when the Dry-Metal Fifth Qi is exchanged, and finally to Xiaoxue when the Cold-Water Final Qi is exchanged. Each Qi governs for 60 days and 87.5 ke (a traditional unit of time). This is called the "Six Steps." Within each step, there are four solar terms, totaling twenty-four solar terms, which serve to divide the six steps. In total, the six steps comprise 365 days and 25 ke to form one year. Thus, the *Suwen: Chapter on the Great Principles of the Six Subtle Meanings* states: To the right of Xianming (the place where the sun rises), is the position of Minister-Fire. To the right of Minister-Fire, moving back one step, is the governance of Minister-Fire. Moving back another step, Earth Qi governs. Moving back another step, Metal Qi governs. Moving back another step, Water Qi governs. Moving back another step, Wood Qi governs. This precisely describes the Fixed Main Qi of the six positions. "Xianming" refers to the place where the sun rises, i.e., the Mao position (due East). "Right" means that since Mao is in the East, when facing east, Minister-Fire, as the Second Qi, is located to the right of Mao. "Moving back" means that after Minister-Fire moves one more step to the right, it corresponds to the position of the Third Qi, Minister-Fire. The rest follows this pattern. For detailed meaning, refer to Yunqi Chapter 6.

[Diagram of Annual Main Qi]
This shows the positional order of the Main Qi year by year. The six Qi respectively govern the four seasons, remaining constant every year, hence they are called "Main Qi."

Main Qi belongs to Earth Qi. It takes shape on the earth, remains static, and holds its position. It refers to Wood, Fire, Earth, Metal, and Water, which respectively govern the four seasons and oversee earthly transformation, constituting the regular seasonal commands of Spring, Summer, Autumn, and Winter. However, the Main Qi follows the sequence of the generation cycle of the Five Elements, with Taiyin Damp-Earth succeeding Shaoyin Minister-Fire. For example, Jueyin Wind-Wood governs the First Qi because spring Wood represents the beginning of new life. It governs for slightly more than 60 days before Chunfen, starting from the middle of the Doujian Chou (Ox) position and ending at the middle of the Mao (Rabbit) position. When the celestial degree reaches here, wind Qi begins to move. Spring Wood generates Fire, so Shaoyin Minister-Fire becomes the Second Qi, governing for slightly more than 60 days after Chunfen, starting from the middle of Doujian Mao and ending at the middle of Si (Snake). When the celestial degree reaches here, warm and gentle weather begins to move. Since Minister-Fire and Duke-Fire share the same nature and follow each other, Shaoyang Duke-Fire succeeds Minister-Fire as the Third Qi, governing for slightly more than 30 days before and after Xiazhi (Summer Solstice), starting from the middle of Doujian Si and ending at the middle of Wei (Goat). When the celestial degree reaches here, intense heat begins to move. Summer Fire generates Earth, so Taiyin Damp-Earth becomes the Fourth Qi, governing for slightly more than 60 days before Qiufen, starting from the middle of Doujian Wei and ending at the middle of You (Rooster). When the celestial degree reaches here, clouds and rain become abundant, and damp evaporation arises. Long Summer Earth generates Metal, so Yangming Dry-Metal becomes the Fifth Qi, governing for slightly more than 60 days after Qiufen, starting from the middle of Doujian You and ending at the middle of Hai (Pig). When the celestial degree reaches here, clear and crisp Qi begins to move, and all things become dry. Autumn Metal generates Water, so Taiyang Cold-Water becomes the Final Qi, governing for slightly more than 30 days before and after Dongzhi (Winter Solstice), starting from the middle of Doujian Hai and ending at the middle of Chou (Ox). When the celestial degree reaches here, cold Qi begins to move. This constitutes the Main Qi of a year, which has regularity without variation. As for the annual Shen (Spirit), there are differences between Taishao (Excess and Deficiency); the six steps have distinctions in direct opposition. Keqi (Adventitious Qi) distributes the heavenly command, superimposing upon the Main Qi. Thus, the upper and lower interact and call to each other, giving rise to changes. The diagrams of Main Qi and Keqi should be consulted together.