Yi Hai Pillar (乙亥) — Yin Wood over Pig
What the Yi Hai pillar (乙亥) is in BaZi: yin Wood on the Pig branch, its hidden stems, its nayin Fire on the Mountain Top, and when it returns.
What is the Yi Hai pillar?
Yi Hai is the pair 乙亥: the Yi stem standing over the Hai branch. It is number 12 of the sixty possible combinations. The same pair can appear as a year pillar, a month pillar, a day pillar or an hour pillar, and which one it is changes how it is read — a year pillar is read as the environment someone was born into, a day pillar as the person themselves.
What the two characters are
乙 Yi — The second stem: the vine. Yi people are flexible, persuasive and grow around obstacles rather than through them.
亥 Hai — the Pig, a Water branch covering 21:00 – 23:00. As a branch it is the third of the four layers a chart is read through: the animal name people know is only this one character, with no stem attached.
Yi Hai is the last of the twelve and the one with the most support. Yin Wood on Hai stands directly on Jia, the Yang Wood hidden in the branch, which gives it a genuine root, and the branch's own Ren Water feeds it on top of that. It is rarely the part of a chart that reads as under-resourced.
How the two meet
Inside a pillar the stem and the branch are not equal partners. The convention is to read them as a relationship: one of them is doing something to the other. Here, the branch generates the stem.
The branch feeds the stem. The support is real and it shows up as a pillar that holds its own without strain — the quality of the stem is available to the chart rather than being spent. Whether that translates into anything lasting still depends on whether the stem has an actual root in the more hidden layers.
The stem does have a root in this branch — one of the hidden stems matches its element, so what the stem is survives being used.
What is hidden in the branch
A branch is not one element. Each of the twelve carries up to three stems inside it — the main qi that gives it its name, and one or two lesser ones. Those hidden stems are where most of the actual weight in a chart comes from, and they are read even though nothing of them appears in the four visible characters.
| Hidden stem | Element | Role in the branch |
|---|---|---|
| 壬 Ren | 水 Water · Yang | main qi — the element the branch is named for |
| 甲 Jia | 木 Wood · Yang | middle qi |
When a practitioner says a pillar is strong or weak, this table is usually the reason — a stem with a hidden ally below it behaves nothing like the same stem sitting on an empty branch.
Where this pillar sits in the sixty
乙亥 is number 12 of the sixty combinations. Its nayin — the classical image assigned to it — is 山头火 Fire on the Mountain Top, a Fire image. The Fire images run from the furnace up to the sky. They share the property of having to be fed, and of being visible wherever they are.
As a day pillar, this pair comes round every sixty days. The next six:
As a year pillar, the pair returns only once every sixty years — these are the recent and coming ones:
The day dates are calculated from the same engine that runs the chart calculator. Note that the Chinese day starts at 23:00: a birth late in the evening belongs to the next day pillar, which shifts the whole calculation by one.
Reading a pillar on its own
A single pillar is not a reading. What this page describes is the internal structure of 乙亥 — which element is on top, what is underneath it, and whether the support is there. To turn that into something about a person you need the other three pillars and a day master to read them against, because the ten gods that carry the actual meaning are relationships to the day master rather than properties of a pillar.
The other pillars in this set
Common questions
See your four pillars
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