Chapter One: The Origins of the Earthly Branches -- The Ancients' Cognition of Time and Space

Section 1: The Initial Naming of the Earthly Branches

The names of the Twelve Earthly Branches -- Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai -- when exactly did they arise$6 This question appears simple but in truth involves exceedingly broad considerations.

In the oracle bone inscriptions of the Shang dynasty, the Heavenly Stems and Earthly Branches were already used extensively for day-reckoning. As seen in the oracle bone script, the Shang people paired the ten Heavenly Stems with the twelve Earthly Branches in a sixty-unit Jiazi cycle for recording days -- an established system. The Shangshu (Book of Documents), in the "Canon of Yao" (Yao Dian), records that in the time of Emperor Yao, observations of "the sun at its midpoint" (ri zhong), "the longest day" (ri yong), "the equal night" (xiao zhong), and "the shortest day" (ri duan) for the solstices and equinoxes were already practiced -- and determining these required a precise timekeeping system.

The forms of the Earthly Branch characters in oracle bone script differ considerably from those of later Small Seal script, yet their fixed sequence never varied. The oracle bone form of "Zi" resembles an infant; "Chou" resembles a hand grasping and twisting; "Yin" resembles an arrow about to be released from a bow... Though the original meanings of each character are much debated, one point can be confirmed: by the Shang dynasty, these twelve symbols had already formed a complete and closed cyclical system.

Why twelve$7

This question is of the utmost importance. The Heavenly Stems number ten, the Earthly Branches twelve; the least common multiple of ten and twelve is sixty, hence the sixty-unit Jiazi cycle. The reason for ten Stems is still comprehensible -- the Shang people counted ten days as one "ten-day week" (xun), with three such weeks per month. But why should the Earthly Branches number precisely twelve$8

The answer can be stated with near certainty: the number twelve originates from the orbital period of Jupiter (the Year Star, Suixing).

Jupiter takes approximately twelve years to complete one circuit of the heavens (the actual period being 11.86 years). The ancients of high antiquity observed that Jupiter traversed one specific celestial region each year, returning to its original position in about twelve years. They therefore divided the sky near the ecliptic into twelve zones, the so-called "Twelve Jupiter Stations" (shi'er ci). The Zuozhuan (Commentary of Zuo), in the twenty-eighth year of Duke Xiang, records:

"The Year Star is in the Station of Stellar Record" (sui zai Xingji).

Here "the Year Star" (sui) refers to Jupiter, and "Stellar Record" (Xingji) is one of the Twelve Stations. The Guoyu (Discourses of the States), in the "Discourses of Jin," likewise records:

"The Year Star is in the Great Beam" (Suixing zai Daliang).

The Twelve Stations are: Stellar Record (Xingji), Murky Ladle (Xuanxiao), Mound of Zou (Juzi), Descending Lou (Jianglou), Great Beam (Daliang), True Sinking (Shichen), Quail's Head (Chunshou), Quail's Fire (Chunhuo), Quail's Tail (Chunwei), Star of Longevity (Shouxing), Great Fire (Dahuo), and Timber-Splitting (Ximu). These twelve stations correspond to the twelve Earthly Branches, forming the basic framework of ancient Chinese astronomical calendrics.

The Erya (Approaching Elegance), in the section "Explaining Heaven" (Shi Tian), records the alternate names of the twelve Earthly Branches in the Jupiter chronological system:

"When the Grand Year is in Yin, it is called She-ti-ge; in Mao, Dan-e; in Chen, Zhi-xu; in Si, Da-huang-luo; in Wu, Dun-zang; in Wei, Xie-qia; in Shen, Tun-tan; in You, Zuo-e; in Xu, Yan-mao; in Hai, Da-yuan-xian; in Zi, Kun-dun; in Chou, Chi-fen-ruo."

These twelve names are archaic and difficult to parse. Scholars have variously attributed them to ancient languages or to descriptions of stellar phenomena. Yet regardless of their etymology, the intimate connection between the Twelve Earthly Branches and astronomical observation is here plainly visible.

A further question: if the Branches originated from astronomy, why are they called "Earthly" (di) Branches$9

This apparent contradiction in fact holds deep meaning. The Hanshu (Book of Han), in the "Treatise on Pitch-Pipes and the Calendar" (Luli Zhi), citing Liu Xin, states:

"Heaven bestows from above; Earth receives from below. Heaven distributes through the six harmonies; Earth sustains through the six harmonies."

And the Huainanzi, in the "Treatise on Celestial Patterns" (Tianwen Xun), says:

"Heaven has nine layers; Earth has nine provinces. Heaven has ten Stems to reckon days; Earth has twelve Branches to reckon months."

The Heavenly Stems correspond to Heaven; the Earthly Branches correspond to Earth. For Heaven's course is vigorous -- the sun travels one degree per day, reckoned by the ten Stems. Earth's nature is receptive -- the moon travels thirteen and a fraction degrees per day, reckoned by the twelve Branches. The sun is yang, the moon is yin; Heaven is yang, Earth is yin. The ten Stems are the warp and weft of Heaven; the twelve Branches are the meridians and vessels of Earth.

Yet the meaning of "Earth" here does not refer merely to the physical ground. "Earth" (di) signifies bearing, containing, receiving. The Way of Heaven flows ceaselessly without fixed abode; the Way of Earth receives and sustains in ordered pattern. The Twelve Earthly Branches are like the earth bearing the myriad creatures, each in its proper place, each presiding over its proper season. Hence, though they originated from celestial observation, they are named "Earthly Branches" precisely because they possess the quality of bearing, positioning, and containing.

Section 2: The Pairing of the Twelve Earthly Branches with the Twelve Months

In ancient calendrics, the twelve months were reckoned by the Twelve Earthly Branches -- a system of great antiquity. Though the Liji (Book of Rites), "Monthly Ordinances" (Yueling), was compiled at a later date, the monthly ordinance system it records was inherited from pre-Qin or even earlier traditions. It takes the month whose "establishment" is Yin (the so-called Xia calendar system) as the first month of the year.

The Huainanzi, in the "Treatise on Celestial Patterns," details the pairing of the twelve months with the Earthly Branches:

"The first month points to Yin; the second month to Mao; the third to Chen; the fourth to Si; the fifth to Wu; the sixth to Wei; the seventh to Shen; the eighth to You; the ninth to Xu; the tenth to Hai; the eleventh to Zi; the twelfth to Chou."

The word "points to" (zhi) here refers to the direction indicated by the handle of the Big Dipper (Beidou). The Dipper's handle rotates once around in a year, pointing each month to a specific direction corresponding to an Earthly Branch. This is what is known as "the Dipper's establishment" (doujian).

Why is the Yin-month the first month$10

This question pertains to the doctrine of the Three Calendrical Standards (san zheng). The Shiji (Records of the Grand Historian), in the "Treatise on the Calendar" (Li Shu), states:

"The Xia calendar begins with the first month; the Yin (Shang) calendar with the twelfth month; the Zhou calendar with the eleventh month."

The Xia dynasty established Yin as the first month; the Shang established Chou; the Zhou established Zi. Through the succession of the Three Dynasties, the start of the year varied. Yet regardless of which month began the year, the fixed correspondence between the Twelve Earthly Branches and the twelve months never changed: the Zi-month always contains the winter solstice (roughly mid-November to mid-December in the modern solar calendar), and the Wu-month always contains the summer solstice (roughly mid-May to mid-June).

On what basis was this fixed correspondence established$11 It rests upon the actual astronomical phenomena of the sun's apparent annual motion and the Earth's revolution. At the winter solstice, the sun is directly above the Tropic of Capricorn -- the moment when yang qi is at its weakest and yin qi at its apex. Hence it is paired with Zi -- Zi being the place where yang qi first stirs, where the single yang returns. At the summer solstice, the sun is directly above the Tropic of Cancer -- yang qi at its apex, yin qi just arising. Hence it is paired with Wu -- Wu being the place where yin qi first appears, where the single yin begins its descent.

The Yijing (Book of Changes), in the Tuan commentary on the hexagram Fu (Return), states:

"Returning and repeating its way, in seven days comes the return -- this is the movement of Heaven" (fanfu qi dao, qi ri lai fu, tian xing ye).

The hexagram Fu, with a single yang line at the bottom, corresponds precisely to the image of the Zi-month at the winter solstice. The hexagram Gou (Encounter), with a single yin line at the bottom, corresponds to the image of the Wu-month at the summer solstice. Though the doctrine of the Twelve Sovereign Hexagrams (shi'er pi gua, also called the twelve "waxing and waning" hexagrams) may have taken form between the Warring States and the Han dynasty, the principle of pairing twelve hexagrams with twelve months is in fact the obverse side of the Branch-month reckoning system.

The sequence of the Twelve Sovereign Hexagrams is:

• Zi-month: Fu (Return) -- one yang, five yin
• Chou-month: Lin (Approach) -- two yang, four yin
• Yin-month: Tai (Peace) -- three yang, three yin
• Mao-month: Dazhuang (Great Strength) -- four yang, two yin
• Chen-month: Guai (Breakthrough) -- five yang, one yin
• Si-month: Qian (Heaven) -- six yang, pure yang
• Wu-month: Gou (Encounter) -- one yin, five yang
• Wei-month: Dun (Retreat) -- two yin, four yang
• Shen-month: Pi (Stagnation) -- three yin, three yang
• You-month: Guan (Contemplation) -- four yin, two yang
• Xu-month: Bo (Stripping) -- five yin, one yang
• Hai-month: Kun (Earth) -- six yin, pure yin

This sequence clearly displays the complete process: yang qi sprouts in the Zi-month, gradually grows through Chou, Yin, Mao, and Chen, and reaches pure yang in the Si-month; yin qi sprouts in the Wu-month, gradually grows through Wei, Shen, You, and Xu, and reaches pure yin in the Hai-month. This is the rhythm of yin-yang waxing and waning -- and the most fundamental temporal information carried by the Earthly Branches.

Section 3: The Twelve Earthly Branches and Directional Positions

The Earthly Branches do not merely reckon time; they also mark directions. Zi is due north, Wu due south, Mao due east, You due west, and the remaining branches distribute between the four cardinal points, forming twelve directional positions. These are the so-called "Twelve Chronograms" (shi'er chen).

The Zhouli (Rites of Zhou), "Spring Official -- Director of Celestial Observations" (Fengxiang Shi):

"The Director of Celestial Observations presides over the twelve years, the twelve months, the twelve chronograms, the ten days, and the positions of the twenty-eight constellations."

Here, "twelve chronograms" refers to the twelve directional positions (or double-hours) represented by the Twelve Earthly Branches.

Why is Zi in the north$12

Zi is the place where yang qi first stirs, and the north is the domain of Water and the direction of winter. On the winter solstice, the sun is at its lowest point in the southern sky; viewed from the ground, sunlight is at its weakest, and all things lie in dormancy. Yet it is precisely within this extreme yin that a single yang begins to move. This is what the Most High (Laozi) meant:

"The myriad creatures carry yin on their backs and embrace yang" (wanwu fu yin er bao yang).

And the Yijing, "Explaining the Trigrams" (Shuogua Zhuan):

"Kan is Water, the trigram of due north, the trigram of toil. It is where all things return."

Kan represents Water, winter, north, and Zi. Yet the image of Kan -- outer yin enclosing inner yang -- shows a single yang line trapped between two yin lines, corresponding precisely to the meaning of the single yang returning in the Zi-month.

The directional arrangement of the Twelve Earthly Branches constitutes a complete spatial coordinate system:

This spatial arrangement is not an arbitrary human convention but a natural correspondence based on astronomical observation and the principles of yin-yang and the Five Phases. Spring belongs to Wood and is in the east; Summer to Fire and the south; Autumn to Metal and the west; Winter to Water and the north. The seasonal transitions belong to Earth and occupy the four inter-cardinal directions (northeast, southeast, southwest, northwest) -- this is the fundamental rule for matching the Five Phases with the four seasons and four directions.

Here we must press further: what is the significance of the four Earth-branches (Chou, Chen, Wei, Xu) occupying the inter-cardinal positions$13

Earth is the center of the Five Phases, the mother of all things. Yet in the directional system of the Twelve Earthly Branches, Earth does not occupy the center (no Branch is placed at the center) but is distributed among the four inter-cardinal positions. This arrangement carries deep significance.

The Guanzi, "Chapter on the Five Phases" (Wuxing Pian):

"Earth is the root and origin of the myriad things, the garden-plot from which all life springs."

The Chunqiu Fanlu (Luxuriant Dew of the Spring and Autumn), "The Meaning of the Five Phases":

"Earth dwells in the center and serves as Heaven's moisture. Earth is the child of Fire; none of the Five Phases is more honored than Earth."

Earth is the mother of the other four Phases -- Metal, Wood, Water, and Fire all depend upon Earth for their generation. Yet if Earth were to remain solely in the center without extending to the four directions, the qi of the four directions could not be harmonized. Therefore the ancient sages placed four Earth-branches at the four inter-cardinal positions, making them the pivots of seasonal transition: Chou at the junction of winter and spring, Chen at the junction of spring and summer, Wei at the junction of summer and autumn, Xu at the junction of autumn and winter. This is the meaning of "Earth of the Four Seasons" or "Earth flourishing in all four seasons."

The last eighteen days of each season are governed by Earth. This doctrine appears in the Huainanzi, "Treatise on Celestial Patterns":

"Earth is born in Wu, flourishes in Xu, ages in Yin, and dies in Shen."

And also:

"The center is Earth; its days are Wu and Ji... Earth encompasses all four seasons."

The four Earth-branches occupy the inter-cardinal positions like four joints, enabling the qi of the four seasons to flow and connect in succession. Without these four Earth-points, Wood, Fire, Metal, and Water would stand isolated, unable to generate and succeed one another. Herein lies the exquisite ingenuity of the Earthly Branch system.

Section 4: The Earthly Branches in Oracle Bone Script and Their Early Use

Tracing back to the oracle bone inscriptions of the Shang dynasty, the use of the Twelve Earthly Branches was already highly mature. The Shang people reckoned days by the stem-branch system, cycling continuously through the sixty Jiazi units, as attested in vast numbers of divination records. Several examples:

"On Guisi, divination; the Diviner Ke inquired: Will this ten-day week be free of misfortune$14" (Heji 1)

"On Jiawu, divination; the Diviner Zheng inquired: Will it rain today$15" (Heji 12)

"On Yiwei, divination; the Diviner Bin inquired: If the king hunts at Mai, will there be no disaster$16" (Heji 28)

In such divination records, "Guisi," "Jiawu," and "Yiwei" are stem-branch day-names. The Shang diviners recorded the day's stem-branch designation in virtually every divination, demonstrating that this system was already fully institutionalized.

One must ask: did the Earthly Branches already carry Five-Phase attributes in the Shang dynasty$17

This question is difficult to answer definitively. No clear records of Five-Phase correspondences for the Earthly Branches have been found in oracle bone inscriptions. The Five-Phase doctrine is generally believed to have germinated at least by the Western Zhou period. The Shangshu, "Great Plan" (Hongfan), records Jizi's words to King Wu:

"The Five Phases: the first is Water, the second Fire, the third Wood, the fourth Metal, the fifth Earth. Water is said to moisten and flow downward; Fire to blaze and rise upward; Wood to bend and straighten; Metal to yield and reshape; Earth to receive seed and yield harvest."

Whether this passage truly represents Jizi's original words may be debated by scholars, yet the sequence and properties of the Five Phases it describes have been transmitted in unbroken succession to later ages. By the Spring and Autumn and Warring States periods, the doctrine of the Five Phases matched with four seasons and four directions was widely current.

The Zuozhuan, twenty-ninth year of Duke Zhao, records the words of Cai Mo:

"Therefore there are officials of the Five Phases, called the Five Officials. They in truth received their clan names and were enfeoffed as highest lords, sacrificed to as honored spirits. In the sacrifices of soil and grain and the Five Domestic Rites, they are revered and honored. The Director of Wood is called Goumang; of Fire, Zhurong; of Metal, Rushou; of Water, Xuanming; of Earth, Houtu."

Officials of the Five Phases, each governing one direction -- this is an early record of the Five Phases matched with directional positions. Yet this passage does not explicitly state a one-to-one correspondence between the Five Phases and the Twelve Earthly Branches. The explicit matching of Branches with Phases may have been systematized only in the late Warring States period.

The Lushi Chunqiu (Annals of Lu Buwei), "The Twelve Annals" (Shi'er Ji), matches the Five Phases with the twelve months in a sequence identical to that of later tradition:

• Month of Early Spring (Yin-month), Mid-Spring (Mao-month), Late Spring (Chen-month) -- Spring, season of Wood
• Month of Early Summer (Si-month), Mid-Summer (Wu-month), Late Summer (Wei-month) -- Summer, season of Fire
• Month of Early Autumn (Shen-month), Mid-Autumn (You-month), Late Autumn (Xu-month) -- Autumn, season of Metal
• Month of Early Winter (Hai-month), Mid-Winter (Zi-month), Late Winter (Chou-month) -- Winter, season of Water

Though this text does not explicitly say "Yin belongs to Wood" or "Zi belongs to Water," its system of matching the Five Phases with twelve months implicitly contains the Five-Phase attributes of the Earthly Branches.

Section 5: The Yin-Yang Attributes of the Earthly Branches

The Twelve Earthly Branches are divided into yin and yang:

• Yang Branches: Zi, Yin, Chen, Wu, Shen, Xu (those in odd-numbered positions)
• Yin Branches: Chou, Mao, Si, Wei, You, Hai (those in even-numbered positions)

This division assigns yin or yang by positional parity. Yet there is another understanding: division by the yin-yang quality of their Five-Phase attribute. Thus Zi is yang Water, Hai is yin Water; Yin is yang Wood, Mao is yin Wood; Wu is yang Fire, Si is yin Fire; Shen is yang Metal, You is yin Metal; Chen and Xu are yang Earth, Chou and Wei are yin Earth.

Why is Zi yang Water while Hai is yin Water$18

This must be understood from the directional position and temporal sequence of each Branch. Zi occupies due north, the proper seat of Water; Hai occupies a position northwest-of-north, an oblique seat of Water. The proper is yang; the oblique is yin. Considered temporally, the Hai-month (tenth month) is governed by pure yin, its sovereign hexagram being Kun (Earth, pure yin) -- hence it is yin Water. The Zi-month (eleventh month) sees the return of the single yang, its sovereign hexagram being Fu (Return) -- though its Five-Phase attribute is Water, yang qi has already begun to stir, making it yang Water.

This reasoning is subtly beautiful. Yang Water is water containing yang; yin Water is water containing yin. The water of the Zi-month, though the sky is cold and the earth frozen, already has subterranean springs stirring beneath the ice, with yang qi secretly budding -- hence it is yang Water. The water of the Hai-month, when heaven and earth are sealed shut with no yang qi at all, is purely yin water -- hence it is yin Water.

The same logic extends to the rest:

• Yin is yang Wood: the wood of the first month, yang qi first rising, plants budding, vitality surging forth
• Mao is yin Wood: the wood of the second month, at the spring equinox, yin and yang in equilibrium, wood qi gentle and supple
• Si is yin Fire: the fire of the fourth month, fire qi just arising, not yet at its peak
• Wu is yang Fire: the fire of the fifth month, the summer solstice at the apex of yang, fire qi at its greatest
• Shen is yang Metal: the metal of the seventh month, autumn qi first arising, the beginning of severity
• You is yin Metal: the metal of the eighth month, at the autumn equinox, metal qi at its purest

The distinction of Yin as yang Wood while Mao is yin Wood, and Si as yin Fire while Wu is yang Fire, may seem to defy common expectation. But Yin stands at the very beginning of yang qi's ascent -- its tendency is active and initiating, hence yang. Mao, though wood qi is at its height, comes after the spring equinox when yang qi has passed its halfway mark, and Mao stands in an even-numbered position in the Branch sequence, hence yin. Si, though fire qi is just arising, occupies an even-numbered position and its tendency is still gentle, hence yin. Wu occupies the seat of yang's apex and an odd-numbered position, with fire qi at its most potent, hence yang.

This yin-yang distinction is critically important for understanding the Six Combinations and Qi Transformation. For the method of the Six Combinations typically pairs one yang with one yin -- yin and yang in intercourse, achieving a state of peace and harmony, and only then does qi transformation occur. This will be discussed in detail below.