In the BaZi (八字, bā zì) system, interactions occur not only between the Earthly Branches (地支, dì zhī), but also between the Heavenly Stems (天干, tiān gān). Six pairs of stems form special combinations — 天干合 (tiān gān hé). In these combinations, one Yin and one Yang element are "drawn together" and theoretically give birth to a new element. The key word is "theoretically": transformation occurs only when the right conditions are present.
The principle of formation: each 天干合 unites the Yin and Yang forms of different elements — stems that are "neighbors" in the Wu Xing order (五行, wǔ xíng — "Five Elements"). Numerologically: the 1st stem (甲 jiǎ) combines with the 6th (己 jǐ), the 2nd (乙 yǐ) with the 7th (庚 gēng), the 3rd (丙 bǐng) with the 8th (辛 xīn), and so on. That is precisely why there are exactly six of them.
1 All six 天干合 and what they produce
甲 (jiǎ — "the first Heavenly Stem," Yang Wood) and 己 (jǐ — "the sixth stem," Yin Earth) form an Earth combination. The image: a mighty oak (甲) and fertile soil (己) merge — Earth nourishes and absorbs. In relationships: the attraction between a strong leader and a flexible, supportive partner.
乙 (yǐ — "the second stem," Yin Wood, a flexible vine) and 庚 (gēng — "the seventh stem," Yang Metal, a sword) — the image of a sword cutting down a vine. Metal "wins." The combination creates a sharp, clear Metal energy: clarity, discipline, decisiveness. In relationships: softness yields to strength.
丙 (bǐng — "the third stem," Yang Fire, the Sun) and 辛 (xīn — "the eighth stem," Yin Metal, a jewel). The most unexpected combination: Fire and Metal give birth to Water. Like hot metal that, as it cools, condenses moisture. The Water combination carries depth, intuition, mystery. It is often linked to the attraction of the "prominent" to the "refined."
丁 (dīng — "the fourth stem," Yin Fire, a candle) and 壬 (rén — "the ninth stem," Yang Water, the ocean). Water nourishes Wood — a combination of growth. In the classics, 丁壬合 is called the "romantic combination" (桃花合, táo huā hé — "Peach Blossom combination"): the flame of a candle reaches toward the depth of the ocean. The Wood transformation brings growth, expansion, creativity.
戊 (wù — "the fifth stem," Yang Earth, a Mountain) and 癸 (guǐ — "the tenth stem," Yin Water, mist/dew). Mountain and mist — the image of dawn over a mountain ridge. Water, heated by Earth (by fire in the depths), gives birth to Fire. A combination of transformation: out of silence, clarity is born. The Fire transformation brings visibility, recognition, publicity.
2 When transformation is real: the conditions
In the Joey Yap school there is an important rule: 天干合 does not always transform the element. For a real transformation, certain conditions are required:
- 🌿 Seasonal support (月令, yuè lìng — "the command of the month"): if the Month Branch supports the new element, the transformation is confirmed;
- 🔢 The presence of the new element's signs in the chart: if there are no signs of Earth at all, the 甲己 combination produces only "busyness," not Earth;
- 🚫 The absence of a block: if another stem stands between 甲 and 己, the combination is disrupted.
3 The combination as "busyness": the most important practical consequence
Regardless of transformation, 天干合 has one guaranteed consequence: both stems become "busy" — they are merged with each other and temporarily lose their independent function.
What does this mean in practice? If your 用神 (yòng shén — "Useful God," the chart's key resource) enters into a combination with another stem, its energy is "diverted" from performing its function. This is called 合而化 (hé ér huà — "combine and transform") — and it can be either a blessing or a problem.
4 天干合 and romance: attraction through the chart
In the practice of reading compatibility, a 天干合 between the stems of two people — especially between the Day Masters (日主, rì zhǔ) — indicates a chemical attraction. This is no guarantee of happiness, but it is a signal: two people are "drawn" to each other at the level of elemental nature.
Considered especially romantic are:
- 💫 丁壬合 (dīng rén hé): the most "romantic" of the combinations — in the classics it is linked to 桃花 (táo huā — "Peach Blossom");
- ✨ 丙辛合 (bǐng xīn hé): the attraction of the public to the refined, of brilliance to depth;
- 🌱 甲己合 (jiǎ jǐ hé): strength protects softness — the classic pair of "protector and protected."
5 天干合 vs 地支合 (dì zhī hé): the difference in scale
The Heavenly Stems (天干) are responsible for outward expression, visible life, the social sphere. The Earthly Branches (地支) are responsible for the inner life, destiny, deep processes. Therefore:
- 天干合 — affects professional relationships, public life, career alliances;
- 地支合 (六合, liù hé) — affects deep relationships, destiny, long-term partnerships.
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