The Ten-Day Xun and Void
Last updated 5/21/2026
Every cast happens inside a ten-day calendar window. Wen Wang Gua calls that window a xun.
Inside each xun, only ten of the twelve Earthly Branches appear as day branches. The two that do not appear are called void branches. If a line carries one of those two branches, the line is still present in the chart, but the calendar is not backing it right now.
That is the whole rule: void means temporarily unfunded, not deleted.
The day stem-branch pair sits inside one of six ten-day windows.
Each xun uses ten branches. The two branches outside that window are void.
Any line carrying a void branch gets tagged as void for this reading.
The six xun
The 60-day ganzhi cycle divides cleanly into six ten-day xun. Each xun begins on a Jia day. Because there are ten stems but twelve branches, every xun leaves two branches outside the window.
Void branches: Xu and Hai.
Void branches: Shen and You.
Void branches: Wu and Wei.
Void branches: Chen and Si.
Void branches: Yin and Mao.
Void branches: Zi and Chou.
Source basis: Yehe Laoren, Zengshan Buyi, Xun Void chapter; Bushi Zhengzong, chapter 17. Technical source labels stay out of the lesson flow unless they change the reading.
You can memorize the table, but you do not have to. The working logic is simple: find the Jia day that opened the current xun. The two branches not reached before the ten stems run out are void.
Case 1
In Case 1, the cast happens in the Chen month on a Wu-Shen day. The source header gives the answer directly: the void branches are Yin and Mao. But we should be able to re-create that answer from the calendar.
The case begins here. Wu is the fifth stem, so walk back four days.
These are the three days immediately before the cast day.
This is the opening Jia day, so Case 1 sits inside the Jia-Chen xun.
Jia-Chen xun has two void branches: Yin and Mao.
Now scan the cast. Line 2 carries the Yin branch, so line 2 is void in this reading.
Void branches: Yin and Mao.
Branch: Yin. Element: Wood. The line exists, but the current xun does not fund it.
Case 1 later uses this line when day pressure triggers Dark Moving. That comes in 3.6.
Line 2 is not the target line for the father’s illness question. The target line is the Parent line, and we will formalize target-line selection in Act 4. For now, the important habit is visual: compute the void, then look through the six lines and mark any branch that matches.
What void means
Void is not absence. The line is drawn. Its role, branch, and element are still part of the chart. The point is that the calendar is not supplying that branch during the current xun.
Think of void as no current running through the line yet. A weak line may be helped by support from another line. A void line needs the calendar to change. The void clears when the time condition changes; the exact timing rules come later in Act 8.
That distinction matters. Weakness is a strength condition. Void is a timing condition. If a line is weak, you ask whether support, motion, or the Day can help it. If a line is void, you also have to ask when the void resolves. Support may gather around the line, but the line still needs the calendar to supply the missing branch before it can deliver cleanly.
This is also different from Month Breaker. Void comes from the day’s ten-day xun. Month Breaker comes from the month branch clashing a line. They can overlap, but they are not the same status.
Void belongs to the xun, not to a single stem. The full stem-branch day pair is what tells you which xun you are in.
Walk back from the cast day to the Jia day that opened the ten-day window. Then use the xun table.
Where this lands us
You can now read the void from a case header and derive it yourself from the day. More importantly, you have the right mental model: void is temporary, calendar-based, and unresolved until time moves.
Next we need the physics that make non-void branches interact.
→ 3.3 The Five Phases: Generation and Control.