天干地支
Tiāngān Dìzhī Heavenly Stems and Earthly BranchesThe ten Heavenly Stems and twelve Earthly Branches pair into a sixty-unit cycle that Shang dynasty scribes used to date oracle bone inscriptions around 1250 BCE — and that modern Chinese speakers still reach for when naming a year, booking an auspicious wedding date, or signing a contract as 甲方 Party A.
The lowest common multiple of ten and twelve is sixty, which is why the cycle runs sixty units before it resets. Ten Heavenly Stems (天干 tiāngān) are assigned numbers one through ten; twelve Earthly Branches (地支 dìzhī) are numbered one through twelve. Pair stem 1 with branch 1, stem 2 with branch 2, and so on — when the stems run out at ten, they restart, while the branches continue. After sixty pairings, both sequences return to their starting positions simultaneously.
Oracle bone inscriptions from the late Shang dynasty (c. 1250 BCE) show this system already in use to count days, not years. A Shang diviner recording a session would inscribe the stem-branch day name at the top of the bone — the same way a modern person writes the date at the top of a letter. The day names have not changed. The 甲子 day that a Shang priest recorded three thousand years ago and the 甲子 day in a contemporary Chinese almanac are produced by the same mechanism, counting the same positions forward from the same starting point.
How the system originated is contested. The ten stems may derive from an earlier Shang ten-day week (旬 xún) used to organise ritual cycles. The twelve branches likely tracked a twelve-month lunar year. The pairing into a sixty-unit cycle was probably already in place by the time the oracle bones began, since the bones show no signs of the system being new or experimental — the scribes use it with complete fluency from the earliest surviving inscriptions.
The ten stems in order: 甲 jiǎ, 乙 yǐ, 丙 bǐng, 丁 dīng, 戊 wù, 己 jǐ, 庚 gēng, 辛 xīn, 壬 rén, 癸 guǐ. Their original meanings, if any, are unclear — by the time they appear in oracle bone inscriptions they function as pure ordinal markers, not as words with independent semantic content. The mapping onto the Five Phases (五行 wǔxíng) came later, during the Han dynasty synthesis of correlative cosmology: 甲乙 = Wood, 丙丁 = Fire, 戊己 = Earth, 庚辛 = Metal, 壬癸 = Water. Each pair consists of a yang stem (the odd-numbered one) and a yin stem (the even-numbered one).
The first two stems, 甲 and 乙, drifted into general use as ordinals the way English speakers use A and B. School classes in Taiwan and mainland China are still labelled 甲班, 乙班, 丙班. Legal contracts in Chinese designate the two parties as 甲方 (jiǎ fāng) and 乙方 (yǐ fāng) — Party A and Party B — a usage so entrenched that 甲方 has acquired its own colloquial weight, often meaning "the client" or "the person with the budget and the opinions." 甲 alone has become a colloquial intensifier in younger Mandarin — 这家餐厅真的很甲 ("this restaurant is genuinely top-tier") — borrowed directly from its position as the first and therefore highest-ranked marker in the sequence.
甲乙 map to Wood (木 mù), yang and yin respectively. 丙丁 map to Fire (火 huǒ). These four are the stems most visible in everyday life: 甲方/乙方 in contracts, 甲班/乙班 in school grading, 丙 as the third rank in evaluation scales.
戊己 map to Earth (土 tǔ), the central phase in the Five Phases system, associated with the turning points between seasons rather than a single season. 庚辛 map to Metal (金 jīn). 庚 appears in 庚子年 (1960, 2020), the Year of the Rat with Metal quality — a pairing that recurs every sixty years.
壬癸 map to Water (水 shuǐ). 癸 is the least common stem in modern usage — it appears mostly in 癸亥 and other cycle-specific contexts. The rarity of stems 9 and 10 in everyday language reflects the fact that only the first few ordinals see enough use to acquire independent meaning.
The twelve branches in order: 子 zǐ, 丑 chǒu, 寅 yín, 卯 mǎo, 辰 chén, 巳 sì, 午 wǔ, 未 wèi, 申 shēn, 酉 yǒu, 戌 xū, 亥 hài. Like the stems, they appear in Shang oracle bones as pure ordinal markers. Each branch was assigned a two-hour period of the day, a month, a cardinal direction, and, later, one of the twelve zodiac animals.
The two-hour period system (时辰 shíchen) divided the twenty-four-hour day into twelve equal segments anchored at the branches. 子时 runs from 11 pm to 1 am — the dead of night, which is why 子夜 (zǐyè) means midnight. 午时 runs from 11 am to 1 pm — the midpoint of the day, which is why 午饭 (wǔfàn) means lunch and 上午/下午 mean morning and afternoon. These words have been in daily use for so long that most speakers never connect them to the branch system that generated them.
The twelve zodiac animals (生肖 shēngxiào) were overlaid onto the branch sequence during the Han dynasty, almost certainly as mnemonic aids. The branches are older; the animals are labels. Rat corresponds to 子, Ox to 丑, Tiger to 寅, Rabbit to 卯, Dragon to 辰, Snake to 巳, Horse to 午, Goat to 未, Monkey to 申, Rooster to 酉, Dog to 戌, Pig to 亥. The animals do not explain the system; they help people remember which position they were born in.
子时 (11 pm–1 am) and 午时 (11 am–1 pm) are the most linguistically productive branches. 子夜 midnight, 午夜 (a synonym), 午饭 lunch, 上午 morning, 下午 afternoon, 正午 high noon — all derive from these two positions. The 子午线 (zǐwǔxiàn) is the meridian line, named because it runs between midnight-north and noon-south.
Rat 鼠, Ox 牛, Tiger 虎, Rabbit 兔, Dragon 龙, Snake 蛇, Horse 马, Goat 羊, Monkey 猴, Rooster 鸡, Dog 狗, Pig 猪. A person's birth year determines their 生肖, and this is one of the first personal facts exchanged in Chinese social introductions. The twelve animals cycle every twelve years; the full sixty-year cycle requires the stem as well — a Dragon year (辰) can be 甲辰, 丙辰, 戊辰, 庚辰, or 壬辰, and the stem carries additional elemental and astrological character.
The first pairing is 甲子 (jiǎzǐ), which gives the entire cycle its common name. The sequence continues: 乙丑, 丙寅, 丁卯, 戊辰, 己巳, 庚午, 辛未, 壬申, 癸酉 — then the stems restart at 甲 while the branches continue — 甲戌, 乙亥, 丙子, and so on. After sixty pairings, 甲子 appears again. Each of the sixty combinations is unique; no two years in a given cycle share the same name.
The year 2024 is 甲辰年 — a 甲 stem (Wood, yang) paired with the 辰 branch (Dragon). The previous 甲辰 year was 1964. The one before that was 1904. Going backward through 甲子 years: 1984, 1924, 1864 (the final year of the Taiping Rebellion), 1804. The Shang scribes dating their oracle bones in the twelfth century BCE were counting forward through the same sixty positions, looping back to the same 甲子 starting point, and that chain has never broken.
Completing a full sixty-year cycle is 花甲 (huājiǎ), from a classical description of the cycle's sixty combinations as "flowers" — the many-coloured pairings of the recurring sequence. A person's 花甲 birthday, their sixtieth, is one of the significant milestone celebrations in Chinese life, alongside the 古稀 (gǔxī) at seventy and the 耄耋 (màodié) at eighty. The sixtieth birthday is understood as a completion: one full revolution of the cosmic clock, and the beginning of a second.
花甲 refers to the sixty named combinations of the stem-branch cycle; 之年 is the classical possessive construction meaning "the year of." The phrase dignifies the sixtieth birthday as a cosmic milestone rather than simply a number — the person has outlasted one complete revolution of the mechanism that names time.
From the Analects (论语 Lúnyǔ), 2.4: Confucius describes his own development decade by decade. At sixty, he says, he could hear any word and immediately understand its truth without inner friction. The line is cited as the classical warrant for treating the sixtieth year as a threshold of wisdom, independent of the stem-branch calculation — though both traditions converge on sixty as a meaningful turning point.
The stem-branch system survives in several distinct registers, from the highly formal to the entirely mundane. In legal and commercial language, 甲方 and 乙方 appear in virtually every Chinese contract — lease agreements, employment contracts, service agreements. The usage is so routine that most signatories have no awareness they are invoking a 3,000-year-old ordinal sequence.
In the traditional almanac (黄历 huánglì, also written 皇历), stem-branch day names appear alongside assessments of whether the day is auspicious for weddings, funerals, travel, construction, or haircuts. The 黄历 is still published annually and still consulted — including through smartphone apps with millions of downloads. The app interface is modern; the underlying calculation is unchanged from the Song dynasty printed almanacs.
Traditional Chinese medicine (TCM) uses the branch-based time system (时辰 shíchen) in a theoretical framework that associates each two-hour period with the peak qi circulation of a specific organ. Practitioners may ask patients about symptom timing using 时辰 language. Feng shui calculations for architecture and burial also use the full stem-branch designation of a date, drawing on the elemental qualities of both the stem and the branch to assess compatibility with a site's orientation.
The zodiac animal system (生肖 shēngxiào), now the most globally recognised element of the stem-branch tradition, is the branch sequence stripped of its stems. Chinese New Year merchandise, horoscope columns, and personality discussions operate on the twelve-year animal cycle alone, which is structurally incomplete — it identifies a branch but not a stem, and therefore cannot locate a year within the full sixty. The full 甲辰 designation is used when precision matters: in almanacs, TCM, formal ritual contexts, and the calligraphy on traditional New Year couplets (春联 chūnlián), where the year is always written with both its stem and its branch.
The ten-unit sequence: 甲乙丙丁戊己庚辛壬癸. 天 (sky/heaven) + 干 (trunk, stem). The "heavenly" designation reflects the cosmological pairing with 地支 — heaven above, earth below.
The twelve-unit sequence: 子丑寅卯辰巳午未申酉戌亥. 地 (earth) + 支 (branch, limb). The "earthly" designation pairs with 天干 in a cosmological hierarchy, though the two sequences are structurally equal components of the cycle.
Both the name of the first stem-branch pairing (甲 + 子) and the common name for the full sixty-unit cycle. 一个甲子 means sixty years. The phrase appears in formal historical writing when describing the passage of a full cycle: 又一甲子过去了 "another sixty years has passed."
From the "flowery" or "variegated" appearance of the sixty combinations written out in full. Used to refer to a person's sixtieth birthday (花甲之年) and, by extension, to the completion of any sixty-year period. 花甲老人 is a respectful way to refer to someone in their sixties.
Each of the twelve Earthly Branches corresponds to a 时辰, a two-hour block of the day. The full set divides the twenty-four-hour day into twelve equal periods named by the branches. Still used in TCM, feng shui, and the 黄历; residually present in compounds like 子夜 and 午饭 that most speakers use without connecting them to the branch system.
The Shang calendar divided the month into three ten-day periods (上旬, 中旬, 下旬 — early, mid, and late). The ten Heavenly Stems may have originated as labels for the days of this ten-day week, which is why the sequence has exactly ten members. 旬 survives in modern Mandarin in expressions of time: 下旬 (the last ten days of a month), 年旬 (a decade of one's age in formal or literary usage).
生 (birth) + 肖 (resemblance, likeness). The twelve animals assigned to the Earthly Branches as mnemonic labels, probably during the Han dynasty. 你属什么? ("What do you belong to?") is a common question asking for someone's birth-year animal, and answering places the speaker in a twelve-year cycle. The full sixty-year system requires the stem; 生肖 alone gives only the branch.
Also written 皇历 (imperial almanac). A daily calendar that lists each day's stem-branch designation alongside assessments of its suitability for specific activities: marriage, travel, moving house, starting a business, cutting hair. Published annually by commercial presses and now available as a smartphone app. The stem-branch day names are the underlying structure; the auspiciousness assessments are a later interpretive layer.