Yang Wood Rat (甲子) 甲子

In the 60 Jiazi sexagenary cycle, 甲子 (Yang Wood Rat) sits at position 1 of 60. It pairs the Heavenly Stem 甲 — the Yang expression of Wood, covered in depth in the Yang Wood Day Master entry — with the Earthly Branch 子 (the Rat), whose primary element is Water and which secondarily holds the hidden stems 癸 (Yin Water).

The classical character of any Jiazi comes from two structural questions: what relationship the branch element has to the stem element above it, and whether the stem has a “root” in any of the branch’s hidden stems. Both are deterministic and apply consistently wherever this Jiazi appears in a chart — Year, Month, Day, or Hour pillar — though the practical implication shifts with position.

The branch’s element produces the stem. 子 feeds 甲 — in BaZi terms, the branch acts as resource (印). 甲子 is nourished and supported from below; the stem has natural backing without having to earn it. This is read as an “auspicious” structural pairing only when the chart actually needs more of Wood; an over-resourced chart reads differently.

甲 is unrooted in this Jiazi: none of the hidden stems in 子 share Wood, so the visible stem floats on a foreign element. The stem’s strength comes from elsewhere in the chart (other pillars carrying Wood); without that support, the stem is read as “weak” or unstable.

子 carries 癸 (Yin Water) as hidden stems. In BaZi these are latent influences: they only surface when the rest of the chart triggers them — through combinations involving 子, through clashes that crack open the branch, or through transformations during specific Luck Pillars.

From 甲’s perspective, the hidden stems represent the following Ten God relationships: 癸 as 正印 Direct Resource. These determine what kinds of opportunity, pressure, or support emerge from 子 when it is activated.

In the classical Nayin (納音) system, every pair of consecutive Jiazis maps to one of 30 named “sounding elements” — an alternative elemental classification used alongside the standard Five Phases. 甲子 is classified as 海中金 (Hǎi zhōng jīn, “Sea Gold”), with an underlying element of Metal.

Nayin is read as a poetic, descriptive layer rather than a structural one: the imagery of the name (“Sea Gold”) implies how the Jiazi’s elemental quality manifests in practice. 甲子 shares its Nayin with one other Jiazi: 乙丑 (Yin Wood Ox). Together, this pair forms the 海中金 Nayin set.

Every Earthly Branch has exactly one combination partner (六合) and one clash partner (六沖). When a chart contains both members of a pair, the relationship transforms or destabilises that pillar. 子’s pairings:

In BaZi, the twelve Earthly Branches form four 3-Harmony groups (三合): trios that, when all three branches appear together in a chart, combine to produce a single elemental phase. 子 belongs to the 申+子+辰 group, which combines into Water. The other two branches in this group are 申 and 辰.

When 子 appears with both partner branches, the resulting elemental transformation can dominate the chart’s reading. Even a partial harmony (two of the three branches) creates a noticeable pull toward Water. Other Jiazis carrying the partner branches: 戊辰, 壬申, 庚辰, 甲申, 壬辰, 丙申, 甲辰, 戊申, 丙辰, 庚申.

The four direction sets (三會) group the twelve Earthly Branches by season and cardinal direction: 子 belongs to 亥+子+丑 — the Winter group, associated with North and the Water element.

Direction sets carry a “seasonal weight” that complements the 3-Harmony grouping. Where 3-Harmony combines distant branches into one element, direction sets combine three sequential branches representing the early/middle/late phase of one season. Other Jiazis sharing this direction set: 乙丑, 乙亥, 丁丑, 丁亥, 己丑, 己亥, 辛丑, 辛亥, 癸丑, 癸亥.

When 甲子 sits at the Year Pillar, its stem (甲) takes on a different Ten God meaning depending on the chart owner’s Day Master. Each row below is computed deterministically from the elemental and polarity relationship.

The 60 Jiazi cycle repeats every 60 years, so 甲子 appears at fixed intervals. Within the 1900–2030 reference range, the years carrying 甲子 are below. Each links to a full reference page for that calendar year.