Also known as: Yang Wood · Great Tree Wood
Jia (甲, Jiǎ) is the first of the ten Heavenly Stems (天干) used in Bazi and the Chinese calendar, and represents yang wood.
Jia heads the Ten Heavenly Stems and represents yang wood — the rising, structural, pioneering quality of wood. Classical texts compare it to a tall tree (大林之木): straight trunk, deep roots, branches reaching to heaven. As a Day Master it gives leadership instincts, principled bearing, and a pioneering temperament that breaks new ground but resents being directed.
Jia is favored by water for nourishment and by metal for shaping, but fears flood (too much water rotting the roots) and dislikes earth too dry. The classical pairing 甲己合化土 (Jia-Ji union transforming to earth) is the first of the five stem combinations, signaling marriage between heaven's yang wood and earth's yin soil.
The great-tree image is a later arrival. Han-dynasty writers who explained the names of the stems read Jia (甲 jiǎ) as a seed splitting its husk: the Han shu treatise on harmonics and the calendar glosses the name in exactly that way, and the Shuowen jiezi places Jia at the head of the east, where yang qi first stirs and the sprout still wears its shell. On that older reading Jia names the instant of cracking open; the finished timber came afterwards, once image-based reading took hold in the Song and Ming. Both layers survive in practice: the push through the surface, and the form that grows out of it.
The Ming-era Di Tian Sui opens its portrait of Jia with a trunk reaching skyward, then warns that spring wood cannot take metal and autumn wood cannot take earth: young growth is injured by the axe, old growth is buried under heaped soil. A second thread comes from the Jing Fang system of matching hexagrams to stems, where the first hexagram, Qian, pure yang, takes Jia. Calendrics, image-and-number studies, and fate calculation each hook the same character onto a different frame. That is why Jia carries such a thick set of associations, and also why old manuals slide between three vocabularies without announcing it.
In practice the first question about a Jia day master is whether it has roots. Jia holds its salary position at Yin (寅), its blade at Mao (卯), its growth stage of birth at Hai (亥), and its grave at Wei (未). If none of those branches appear below, the Jia written on top is floating. Only then does the month matter: born in Yin or Mao it holds the season, born in Shen or You it is under pressure. Working in that order also clears away two habitual errors. Jia does not outrank Yi, since yin and yang describe mode and carry no ranking, and a rootless Jia is far weaker than a well-rooted Yi. Strength by itself is likewise neither fortunate nor unfortunate until placed against what the chart wants. Jia also says nothing about height or build, and it is not a zodiac animal: day master and birth-year animal belong to separate systems.
In the Ten Gods scheme Jia meets Geng as Seven Killings and Xin as Direct Officer, glossed classically as the axe and the pruning knife, while Bing becomes Eating God and Gui Direct Resource, sunlight and rain. The general likes and dislikes set out above hold only as a default, and the seasonal-adjustment tradition supplies the proportions: spring Jia is tender and wants warmth from Bing with metal kept measured; summer Jia wants water against the heat; autumn Jia, pressed by strong metal, usually takes fire to restrain it with water to mediate; winter Jia wants Bing first to break the freeze. As for the Jia-Ji bond, combining is a relationship and transforming an outcome with its own requirements, so the presence of the pair settles nothing by itself.
The tradition does not read Jia with one voice. Image-based schools reason from the metaphor, picturing how a tree would fare in the surrounding conditions. Structure-based schools ask only which Ten God the month branch releases and what pattern forms, setting the imagery aside almost entirely; the two can stress very different things in the same chart. A longer-running dispute concerns whether yang stems follow qi and not force: when a weak Jia faces a chart crowded with metal and earth, schools differ on whether to abandon the day master or still support it. Where the tradition splits like this, setting both positions out is closer to the sources than picking one.
Each of the four pillars carries a heavenly stem, and the stem of the day pillar — the day master — stands for the person. When that stem is Jia (甲 jiǎ), the chart is described as a Jia wood chart, yang wood. The day master is only a starting point: the birth month, whether supporting branches appear below, and which Ten Gods surround it all have to be read before anything follows. “I am Jia wood” settles nothing on its own.
Jia is traditionally said to welcome water for nourishment, fire for expression, and a measured amount of metal for shape, while disliking flood that rots the roots, heavy earth that buries them, and unchecked metal. That general rule is already set out above. The working choice turns on season and temperature: winter-born Jia is usually said to need Bing fire first, summer-born Jia needs water against the heat, and autumn-born Jia often needs fire to restrain strong metal. The same stem can call for opposite remedies in different months.
No. Both are wood, and they differ in mode with neither ranking above the other: Jia describes upward, structural growth and Yi describes spreading, adaptive growth. How strong wood actually is in a given chart depends on the birth month, whether the branches supply roots, and what feeds or drains it, and not on which character is written. A rootless Jia surrounded by metal and earth is far weaker than a Yi born in the Mao month with roots below.
No. The tradition separates combining from transforming. Two stems combining establishes a relationship; the pair actually turning into earth is a further claim that normally requires the month branch to be earth, the transforming phase to be in season and well supported, and no other stem breaking the bond or competing for it. When those conditions fail, the usual reading is combined but not transformed: the two stems tie each other up and lose some freedom of action without becoming earth.
Autumn birth is not a verdict in itself. Metal is strong and wood confined in autumn, so a Jia day master sits under pressure, and the classical procedure checks three things: whether fire is present to restrain the metal, whether water mediates between them, and whether any wood roots sit in the branches. With those in place, autumn Jia is often read as timber being shaped into something useful; only when all three are missing does the reading turn to damage.