Also known as: Pig Branch
Hai closes the twelve-branch cycle. It is yin water in name but holds yang stems 壬 (yang water) and 甲 (yang wood) — abundant flowing water carrying the seed of next spring's wood. It is the pig at the trough at first frost: contented, generous, simple-hearted, content to feed others. Hai Day Masters often appear easy-going on the surface but carry depth, philosophical reflection, and the seed-instinct that begins the next cycle.
Hai san-he with 卯 and 未 transforms to wood (亥卯未合化木), and six-unites with 寅 to wood (寅亥合木). Conflicted by 巳 (巳亥冲), and self-punished (亥亥自刑).
Hai has a philological history of its own. The Zuo Zhuan (左傳 Zuǒ Zhuàn) records an old man of Jiang county who stated his age by observing that the character 亥 has two strokes above and six below, letting the court scribes compute the days; and the Lüshi Chunqiu (呂氏春秋 Lǚshì Chūnqiū) preserves the story of a passage read as three pigs fording a river when it should have said the jihai day — the origin of the standard phrase for a copying error. The Shuowen Jiezi glosses Hai through 荄 gāi, a root, the faint yang of the tenth month meeting the fullness of yin.
Hai is the last branch, but the classical reading does not treat it as an ending. It stores Jia wood, the beginning of the next round, which is why the older glosses speak of roots and of concealed yang instead of exhaustion. Two calendrical cautions: the Hai month opens at Lidong, the start of winter, not at Xiaoxue in its middle; and the Hai hour runs 21:00 to 23:00, ending where Zi begins, so a birth at 23:30 is not Hai. The contented-pig imagery is again a later zodiac layer. Several points about Hai also remain open. Most tables give it Ren and Jia, but some assign the first days of the month to Wu earth, which changes whether Hai holds any earth at all. The Yin–Hai pairing is listed simultaneously as a union and a break, with no agreed order of resolution. Whether doubled Hai constitutes a self-punishment is rejected by some lineages. And whether the Jia wood inside Hai can actually feed fire depends on the same hidden-stem and storehouse arguments that divide the field elsewhere.
In a chart Hai is where water holds office and wood is conceived. Ren water takes its prosperity seat here and Jia wood begins its life cycle here, which is why classical readings describe Hai as abundant water already carrying next spring's growth. A water Day Master born in the Hai month is rooted but cold, and the standard traditional response is to look for fire as a seasonal regulator before adding any more water. Hai is also one of the four travelling-horse branches, read as a seat of movement and departure.
Beyond the wood frame, the Yin union, the Si clash and the self-punishment already listed, Hai harms Shen. Yin and Hai are also listed as a break, which makes them a second case, alongside Si and Shen, where one pair appears both as a union and as a source of friction, and lineages handle the contradiction differently. The Si clash sets two travelling-horse branches against each other and is traditionally read through movement and relocation more than through simple damage. The Shen-Hai harm is usually treated alongside those same punishments, and there too the reading turns on which side the chart supports.
The Hai month runs from Lidong (立冬 Lìdōng) to Daxue (大雪 Dàxuě) and holds Xiaoxue. Pentad almanacs of the Yueling tradition record water beginning to freeze, the ground beginning to harden, and, in the old figurative language, pheasants entering the water and becoming clams. Northern folk usage calls the warm spell that often falls in this month the little spring of the tenth month. On the compass Hai sits in the northwest with Xu and Qian, and the Hai hour, named for settling, is when the household was said to go quiet.
Traditional practice treats Hai and Zi as different in kind, not ranked by size. Zi is the cardinal seat of water, holds Gui alone, and is where Ren water reaches its imperial stage: concentrated, still, deep. Hai holds Ren and Jia, is the prosperity seat of Ren, and is read as abundant moving water that already carries wood inside it. As for a Hai-month birth, Hai is the first month of winter and water commands the season, so water is strong by season. Whether it is excessive is a separate judgement resting on the Day Master and the other seven characters. Traditional practice for a cold, water-heavy chart typically looks for fire as a seasonal regulator and for earth or wood to channel the water, instead of declaring the water itself a problem. Strength and imbalance are not the same claim.
The Hai hour runs from 21:00 to 23:00, and the Zi hour begins at 23:00 — so a birth at 23:30 takes Zi, not Hai. Traditional practice also measures from apparent local solar time in place of a standard time zone, which can shift a borderline birth across the boundary. Charts cast near 23:00 are worth checking carefully, since the hour branch, and under some conventions the day pillar, both turn there.
Because both listings exist in the classical tables and neither was ever removed. The Yin–Hai six-union produces wood; the same pair is also given in the list of six breaks. Si and Shen present the identical problem. Practitioners resolve it differently — some read the union as dominant and the break as a minor qualifier, some hold that the two cancel into instability — and the honest answer is that this is a known unsettled point rather than an error in one of the books.
Because of what it stores. Hai is the twelfth and final branch, and the early glosses read it through roots and hidden yang, never through exhaustion. In the twelve-stage scheme Jia wood begins its life cycle at Hai, so the branch that closes the round already contains the first growth of the next one. The sovereign hexagram for the month is Kun, entirely yin — and in that same sequence the single returning yang line appears immediately afterwards.