Yin-Yang and the Five Elements: The Foundation

Yin-yang and the five elements are the two ideas the whole East Asian calendar is built on. Every stem, branch and pillar is described with them, so once they are clear, the rest of this series reads much more easily.

Yin and yang: two sides of one thing

The old image behind yin and yang is a single hill in the sun. The bright slope is yang and the shaded slope is yin, yet it is one hill, and as the day moves the light and shade trade places. Yang stands for what is outward, active, bright and expanding; yin for what is inward, quiet, cool and gathering. Neither is better. Each only makes sense next to the other.

In the calendar every sign carries one of the two. The ten heavenly stems alternate strictly: 甲 is yang, 乙 is yin, 丙 is yang, and so on, which gives five yang stems and five yin stems. The twelve earthly branches alternate the same way, six yang and six yin. The haru engine marks a branch as yang when its place in the order is even, counting 子 as position 0, so 子 is yang, 丑 is yin and 寅 is yang again.

Five phases, not five substances

The five elements are Wood, Fire, Earth, Metal and Water (木火土金水). The Chinese word used for them, 行, means to move or to go, so many teachers prefer to call them five phases. They are less like chemical ingredients and more like five stages of any process that grows, peaks, turns, gathers and rests.

The tradition links each phase to a season and a mood of movement:

Wood: growth that pushes upward and outward, like spring shoots.
Fire: full expression and warmth, like midsummer.
Earth: steadying and turning, the ground that holds the change between seasons.
Metal: gathering, trimming and sorting, like the autumn harvest.
Water: storing and resting, like seeds waiting through winter.

How yin-yang and the elements combine

Put the two ideas together and the ten stems appear naturally: each of the five elements has a yang form and a yin form, and 5 times 2 makes 10. The branches are sorted by element too, but not evenly. Wood, Fire, Metal and Water each have two branches, while Earth has four: 丑, 辰, 未 and 戌. Those four sit in lunar months 12, 3, 6 and 9, the last month of each season, which is why the tradition describes Earth as the hinge between seasons rather than a season of its own.

The five elements with their stems, branches and seasons (from facts.json stems and branches)
Element	Hanja / Korean	Yang stem	Yin stem	Branches	Season
Wood	木 / 목	甲	乙	寅卯	Spring
Fire	火 / 화	丙	丁	巳午	Summer
Earth	土 / 토	戊	己	丑辰未戌	Last month of each season
Metal	金 / 금	庚	辛	申酉	Autumn
Water	水 / 수	壬	癸	亥子	Winter

Counting the elements in a chart

A Four Pillars chart has four pillars of two characters each, so eight characters in all, or six when the birth hour is unknown. The haru engine counts the elements in two ways. The surface count simply looks at which element each visible character belongs to. The weighted count also adds the stems hidden inside each branch and lets the month branch count double, because it stands for the season (see the page on hidden stems).

Take example B from the engine's test set: Seoul, 1 July 1988, 13:10, with the pillars 戊辰, 戊午, 丁巳 and 丙午. The surface count is Fire 5, Earth 3, and zero for Wood, Metal and Water. The weighted count gives Fire 51.5%, Earth 41.5%, Wood 3.3%, Metal 2.6% and Water 1.1%. Notice that the hidden stems let the three absent elements show up as small traces instead of a flat zero.

The tradition reads a lopsided picture like this as a question rather than a verdict: which phase is plentiful, which is thin, and what would bring the whole into better balance? It does not treat Fire as good or Water as bad.

Balance is the whole point

Yin-yang and the five elements describe relationships, not fixed labels. Too much of anything, even something pleasant, is read as out of balance, and yin always holds a seed of yang and the other way round. The next page, on the cycles of generation and control, shows how the five phases feed and restrain one another so that no single one runs away with the whole.

Questions

Is yang good and yin bad?

No. The tradition treats them as partners. A yang stem is simply more outward and a yin stem more inward; both appear in every complete cycle.

Why is Earth given four branches when the others have two?

Earth is read as the turning point between seasons, so it takes the last month of each of the four seasons: 丑, 辰, 未 and 戌.

Is Metal only about metal objects?

Not really. The phase stands for gathering, cutting away and refining, the mood of autumn harvest, and hard things like rock and iron are its images.

Does a missing element in a chart mean something is lacking in a person?

The tradition reads it only as part of the overall balance, and a surface zero often still appears as a small share once hidden stems are counted. It is a way of describing a pattern, not a judgment about anyone.