（《素问·至真要大论》）
帝曰∶愿闻阴阳之三也何谓？（厥阴少阴太阴，三阴也。少阳阳明太阳，三阳也。）岐伯曰 ∶气有多少异用也。（易
曰一阴一阳之谓道，而此曰三者，以阴阳之气各有盛衰，盛者气多，衰者气少。《天元纪大论》曰∶阴阳之气各有多少，
故曰三阴三阳也。按阴阳类论以厥阴为一阴，少阴为二阴，太阴为三阴，少阳为一阳，阳明为二阳，太阳为三阳，数各
不同，故气亦有异。）帝曰∶阳明何谓也？岐伯曰∶两阳合明也。（两阳合明，阳之盛也。《阴阳系日月篇》曰∶辰者三月，
主左足之阳明∶巳者四月，主右足之阳明，此两阳合于前，故曰阳明。丙主左手之阳明，丁主右手之阳明，此两火并合，
故曰阳明。）帝曰∶厥阴何也？岐伯曰∶两阴交尽也。（厥，尽也。两阴交尽，阴之极也。《阴阳系日月篇》曰∶戌者九
月，主右足之厥阴；亥者十月，主左足之厥阴。此两阴交尽，故曰厥阴。详经络类三十四。）
帝曰∶幽明何如？岐伯曰∶两阴交尽故曰幽，两阳合明故曰明，幽明之配，寒暑之异也。（幽明者，阴阳盛极之象也。
故《阴阳系日月篇》以辰巳为阳明，戌亥为厥阴。夫辰巳之气暑，戌亥之气寒。如夜寒昼热，冬寒夏热，西北寒、东南
热，无非辰巳戌亥之气，故幽明之配，为寒暑之异。）帝曰∶分至何如？岐伯曰∶气至之谓至，气分之谓分，至则气同，
分则气异，所谓天地之正纪也。（分言春秋二分，至言冬夏二至。冬夏言至者，阴阳之至极也。如司天主夏至，在泉主冬
至，此六气之至也。夏至热极凉生，而夜短昼长之极，冬至寒极温生，而昼短夜长之极，此阴阳盈缩之至也。春秋言分
者，阴阳之中分也。初气居春分之前，二气居春分之后，四气居秋分之前，五气居秋分之后，此间气之分也。春分前寒
而后热，前则昼短夜长，后则夜短昼长；秋分前热而后寒，前则夜短昼长，后则昼短夜长，此寒热昼夜之分也。至则纯
阴纯阳，故曰气同。分则前后更易，故曰气异。此天地岁气之正纪也。）
The Yellow Emperor said: I wish to hear about the division of Yin and Yang into three. What does this mean? (Jueyin, Shaoyin, and Taiyin constitute the Three Yin; Shaoyang, Yangming, and Taiyang constitute the Three Yang.) Qibo replied: This is because there are differences in quantity and function due to the varying degrees of Qi. (The *I Ching* states, "One Yin and one Yang is called the Dao," but here it speaks of three, because Yin and Yang Qi each have varying degrees of abundance and decline. Abundant Qi is considered "many," while declining Qi is considered "few." The *Tianyuanji Dalun* states: "Yin and Yang Qi have different quantities, hence they are called Three Yin and Three Yang." According to the *Yinyang Leilun*, Jueyin is ranked as First Yin, Shaoyin as Second Yin, and Taiyin as Third Yin; Shaoyang as First Yang, Yangming as Second Yang, and Taiyang as Third Yang. Since their numerical rankings differ, the quantity of Qi also varies.)
The Yellow Emperor asked: What is meant by Yangming? Qibo replied: It means the combination of two Yangs illuminating each other. (The combination of two Yangs represents the peak of Yang. The *Yinyang Xi Riyue Pian* states: "The month of Chen (the third lunar month) governs the Yangming meridian of the left foot; the month of Si (the fourth lunar month) governs the Yangming meridian of the right foot. These two Yang energies converge anteriorly, thus it is called Yangming. Bing Fire governs the Yangming of the left hand, and Ding Fire governs the Yangming of the right hand. These two Fire energies merge, thus it is called Yangming.")
The Yellow Emperor asked: What is Jueyin? Qibo replied: It means the exhaustion of two Yins. ("Jue" means exhaustion. The convergence and exhaustion of two Yins represent the extreme limit of Yin. The *Yinyang Xi Riyue Pian* states: "The month of Xu (the ninth lunar month) governs the Jueyin meridian of the right foot; the month of Hai (the tenth lunar month) governs the Jueyin meridian of the left foot. These two Yin energies converge and exhaust themselves, thus it is called Jueyin." See detailed discussion in the Meridians category, Chapter 34.)
The Yellow Emperor asked: What are You (Darkness/Hidden) and Ming (Brightness)? Qibo replied: The exhaustion of two Yins is called You; the combination of two Yangs is called Ming. The pairing of You and Ming corresponds to the difference between Cold and Heat. (You and Ming are manifestations of the extreme abundance of Yin and Yang. Therefore, the *Yinyang Xi Riyue Pian* associates the months of Chen and Si with Yangming, and the months of Xu and Hai with Jueyin. The Qi of Chen and Si is hot (summer heat), while the Qi of Xu and Hai is cold. Just as nights are cold and days are hot, winter is cold and summer is hot, and the northwest is cold while the southeast is hot, these are all influenced by the Qi of the months Chen, Si, Xu, and Hai. Thus, the pairing of You and Ming manifests as the distinction between Cold and Heat.)
The Yellow Emperor asked: What are Fen (Equinox/Split) and Zhi (Solstice/Arrival)? Qibo replied: When Qi arrives at its peak, it is called Zhi; when Qi divides, it is called Fen. At Zhi, the Qi is uniform; at Fen, the Qi differs. This constitutes the regular chronology of Heaven and Earth. (Fen refers to the Spring and Autumn Equinoxes, while Zhi refers to the Winter and Summer Solstices. Winter and Summer are termed Zhi because they represent the extreme limits of Yin and Yang. For instance, the ruling Qi of the Siantian (Heavenly Ruler) corresponds to the Summer Solstice, and the ruling Qi of the Zaiquan (Earthly Ruler) corresponds to the Winter Solstice; this is the arrival of the Six Qi. At the Summer Solstice, heat reaches its extreme and coolness begins to arise, marking the extreme of short nights and long days. At the Winter Solstice, cold reaches its extreme and warmth begins to arise, marking the extreme of short days and long nights; this is the extremity of Yin and Yang's waxing and waning. Spring and Autumn are termed Fen because Yin and Yang are equally divided here. The first Qi period precedes the Spring Equinox, the second follows it; the fourth precedes the Autumn Equinox, and the fifth follows it; this is the division of the intermediate Qi. Before the Spring Equinox, it is cold turning to hot; previously days were short and nights long, afterward nights are short and days long. Before the Autumn Equinox, it is hot turning to cold; previously nights were short and days long, afterward days are short and nights long; this is the division of Cold/Heat and day/night length. At Zhi, there is pure Yin or pure Yang, hence "Qi is uniform." At Fen, there is alternation between preceding and succeeding phases, hence "Qi differs." This is the regular chronology of the annual Qi of Heaven and Earth.)