Sixty instead of a hundred and twenty: stems, branches and the great cycle

Everyone knows the twelve animals; hardly anyone knows the great cycle behind them. That the Chinese calendar is built from ten heavenly stems and twelve earthly branches is still written everywhere. Why that makes sixty years and not a hundred and twenty is something almost no one explains – and yet it is a two-minute sum, and once it has been worked through it confuses no one again. This page originally belonged to an audio series; here the material is set down to be read.

Every stem and every branch is yang or yin

What most accounts leave out is the polarity. The ten stems are the five phases in two versions each – wood, wood, fire, fire, earth, earth, metal, metal, water, water – and in every pair the first counts as yang, the second as yin.

With the twelve branches it is the same, only without the doubling: rat yang, ox yin, tiger yang, rabbit yin and so on down to the pig. Six animals are yang, six are yin, strictly alternating.

The name of a year is made of both, stem first, branch second. “Metal rooster” and “water tiger” are translations of exactly that double designation.

Why not a hundred and twenty

Ten times twelve would be a hundred and twenty. But there are only sixty combinations, and the reason is the polarity: a yang stem always meets a yang branch, a yin stem always a yin branch. The other half of the conceivable pairs simply does not occur.

The check can be made in both directions. Over the course of the cycle each animal meets five stems – one per phase, always in the same polarity. Twelve animals times five gives sixty. The other way round, each stem meets six animals; ten times six gives sixty as well. Mathematically it is the lowest common multiple of ten and twelve: the two wheels come back into line only after sixty steps.

From this follows a rule of thumb that saves a great deal of confusion: there is no yin dragon and no yang rabbit. Anyone who reads such a thing is reading a mistake.

Not only years

That the same cycle counts days as well is usually dealt with in a subordinate clause. Yet the counting of days is the oldest part of the whole system: it is attested on the oracle bones of the Shang dynasty and has run on ever since, untouched by every calendar reform. If you have a birth chart worked out, you get a stem-branch combination for your day of birth out of this very long chain.

For the years the beginning can be named exactly: the present cycle of sixty started in 1984, a year of the wood rat, and runs to 2043. It is therefore a good half of the way through.

The sixtieth birthday

Here the cycle touches everyday life. When you turn sixty, the stem-branch combination of your birth year comes back for the first time. In China, Korea and Japan that is an occasion in its own right: the sixtieth birthday is celebrated more grandly than the fiftieth, because with it one whole round is closed and, in the tradition's image, a new one begins.

One need not believe in astrology to find something fine in that. A calendar that counts age not as a mark on a straight line but as a round gives the date a different meaning from a merely larger number. How stems, branches and the five phases turn into an interpretation is set out under Chinese astrology.