Xun Kong (旬空), usually rendered in English as void or empty, is one of the few Liu Yao concepts with a purely mechanical definition — and correspondingly, one of the easiest to compute incorrectly.
How it is defined
Days run in an unbroken cycle of sixty stem-branch pairs. That cycle divides into six runs of ten days, each beginning on a day whose stem is Jia. The ten days of a run cover ten of the twelve branches; the two branches left over are void.
| Run | Begins | Void branches |
|---|---|---|
| 1 | Jia Zi | Xu, Hai |
| 2 | Jia Xu | Shen, You |
| 3 | Jia Shen | Wu, Wei |
| 4 | Jia Wu | Chen, Si |
| 5 | Jia Chen | Yin, Mao |
| 6 | Jia Yin | Zi, Chou |
The error to avoid
You cannot work out the run from the day's branch alone. Each run covers ten of the twelve branches, which means any given branch falls inside five of the six runs. Take the branch Shen: it appears in the Jia Zi run, the Jia Shen run, and three others. Only the stem tells you which run you are in, so the calculation has to start from the full sixty-day index.
In code this means dividing the sixty-jiazi index by ten, not looking up the branch. It is a one-line difference that produces silently wrong results.
What void does to a line
A void line is not null. It is better described as a line with reduced traction — the thing it represents is present but does not bite. Classical texts treat void as temporary: the condition resolves when the run advances past the void branches.
A void significator usually means the matter is not yet effective. A void line that restrains the significator is good news, because the obstruction has less force than it looks like it does.
Void and the month
Void is a function of the day; month break (月破) is a function of the month. They are independent and can apply to the same line. A line that is both void and broken is at its weakest — but note that a line that obstructs you being in that state is favourable.
This inversion is the single most common source of misread charts. Whether a condition is good or bad depends entirely on which side of the relation the line sits on.
When void resolves
Classical practice holds that void clears when the day cycle reaches the void branches, or when the month branch overrides it. This is why Liu Yao is often used for timing: void is a temporary state with a definable end.