TL;DR: Tuần không is the two earthly branches that do not appear in ten consecutive sexagenary days, for example in the Giáp Tý week, Tuất and Hợi are void. To find them, combine the can chi of the day the hexagram is cast and look it up in the six Giáp weeks. Tăng san bốc dịch holds that one should not rush to a conclusion based on không vong, but should also weigh movement, stillness and prosperity or decline, and it permits casting the hexagram again to verify.
What is tuần không (void in the ten-day cycle) in Lục Hào?
Tuần không (void in the ten-day cycle) refers to the two earthly branches that do not appear within the ten consecutive sexagenary days of a Giáp week. The book Tăng san bốc dịch opens the chapter "Tuần không" by listing six statements: in the Giáp Tý week, Tuất and Hợi are void; in the Giáp Tuất week, Thân and Dậu are void; in the Giáp Thân week, Ngọ and Mùi are void; in the Giáp Ngọ week, Thìn and Tỵ are void; in the Giáp Thìn week, Dần and Mão are void; in the Giáp Dần week, Tý and Sửu are void[1]. These six statements follow directly from the method of pairing ten heavenly stems with twelve earthly branches.
Two easily confused characters need to be distinguished. "Tuần" here is a group of ten sexagenary days, not a seven-day week. "Không" means empty, absent, and is not a type of spirit star placed separately into a chart. This is a lookup convention, not an observable natural phenomenon.
How to find the two void branches in a Giáp week
To know which week applies, first take the stem-branch of the day the hexagram was cast. That day falls within a ten-day week beginning with the stem Giáp, and the two branches missing from that week are the void ones. Tăng san bốc dịch explains briefly: from Giáp Tý to Quý Dậu is one week, and within those ten days there is no Tuất and no Hợi, so a line meeting Tuất or Hợi is called void, also called tuần không[1].
The table below looks up the six weeks directly, so readers can quickly cross-check against the day they are examining:
| Giáp week | Ten days in the week | Two void branches |
|---|---|---|
| Giáp Tý | Giáp Tý to Quý Dậu | Tuất, Hợi |
| Giáp Tuất | Giáp Tuất to Quý Mùi | Thân, Dậu |
| Giáp Thân | Giáp Thân to Quý Tỵ | Ngọ, Mùi |
| Giáp Ngọ | Giáp Ngọ to Quý Mão | Thìn, Tỵ |
| Giáp Thìn | Giáp Thìn to Quý Sửu | Dần, Mão |
| Giáp Dần | Giáp Dần to Quý Hợi | Tý, Sửu |
A quick way to remember: the two void branches always stand immediately before the branch that opens the week, following the cycle of twelve branches. A week beginning with Tý has the two branches immediately before Tý, namely Tuất and Hợi; a week beginning with Dần has the two branches immediately before Dần, namely Tý and Sửu. This mnemonic matches the table above and is convenient when no reference book is at hand.
Why do ten stems and twelve branches produce two empty branches?
Ten heavenly stems pair with twelve earthly branches to form a cycle of sixty sexagenary days, called lục thập hoa giáp (the sixty-year cycle). Because ten and twelve meet completely only after sixty combinations, each week of ten stems pairs with only ten branches, leaving two branches unused in that week; the next week begins with the first of those leftover branches, so after the Giáp Tý week comes the Giáp Tuất week.
Tăng san bốc dịch also records many different names for void that earlier books had established: chân không (true void), giả không (false void), động không (moving void), xung không (clashing void), điền không (filling void), vô cố tự không (void without cause), hữu tán nhi không (void through scattering), mộ không (tomb void), tuyệt không (extinction void), hại không (harm void), an không (peace void), phá không (destruction void). The author himself remarks that the books discuss this far too elaborately, then sets out his own way of handling it[1].
How should a line falling into tuần không be interpreted?
Tăng san bốc dịch does not accept the mechanical reading that meeting tuần không means losing everything. The book sets out the principle: a prosperous line is not counted as void, a moving line is not counted as void, a line supported by the day stem or by a moving line is also not counted as void; a moving line that transforms into void, or a hidden line that is prosperous, are likewise not counted as void. Conversely, a line broken by the month is counted as void, a static line that does not move is counted as void, a hidden line that is overcome is counted as void, and a true void is counted as void. True void is defined by season: earth in spring, metal in summer, wood in autumn, fire in the three winter months[1].
The most notable point in the chapter "Tuần không" is that the author admits that when he first learned divination, whenever he met tuần không he did not know how to interpret it: if he wanted to treat it as completely empty, he would see it manifest on the day it was filled and so not empty; if he wanted to treat it as not empty, there were cases where it was thoroughly empty. The book therefore proposes the method of multiple casting: when meeting tuần không, cast an additional hexagram; if the later hexagram is good, it promises that once the week passes the void will end; if the later hexagram is bad, it is treated as truly empty[1].
Examples in Tăng san bốc dịch of a wealth line meeting tuần không
The book recounts the case of the day Ất Mão in the month of Thìn, divining for wealth, obtaining the hexagram Gia Nhân changing to Bí. The wealth line Sửu holding the World position met tuần không; although there was a Tỵ line generating it, Tỵ in turn transformed into being overcome, so it could not generate. The book records that the wealth line Sửu still had qi because it was in the month of Thìn, and ancient method says that if it has qi it is not counted as void, so the author did not dare decide conclusively and cast an additional hexagram. The later hexagram was Khuê changing to Tổn, where the wealth line Tý was void and hidden beneath the Mùi line, both hidden and void and also overcome. Combining the two hexagrams, the author concluded there was no wealth, and it proved true that there was none[1].
Another example: on the day Tân Hợi in the month of Tý, divining about travelling far to seek wealth, obtaining the hexagram Đại Súc. The World line Dần wood was generated by both the month of Tý and the day Hợi as wealth, and moreover World and Response generated each other, so at a glance the hexagram was flawless. But the World was meeting tuần không; according to ancient method, "vô cố tự không" (void without cause) is a sign of great misfortune. The author did not conclude immediately but cast an additional hexagram, then used the second hexagram to decide[1].
The marriage case is also worth noting. On the day Quý Dậu in the month of Tý, divining for oneself about marriage, obtaining the hexagram Hằng changing to Đỉnh. The wealth line Tuất moved in the Response palace to generate the World, and moreover World and Response generated each other. Although Tuất met tuần không, because it was a moving line it was not counted as void; indeed the next day, exactly the day it left tuần không, the marriage proposal was accepted[1]. The judgment in this example uses precisely the phrase "động bất vi không" (動不爲空) stated in the chapter "Tuần không".
Why must an additional hexagram be cast when meeting tuần không?
The method of multiple casting in Tăng san bốc dịch is not a decorative technique, but a way of handling cases when the rule of tuần không alone is not enough to decide. Dã Hạc wrote that the method of multiple casting dispels many doubts (多占之法，能消許多疑惑); Lý Ngã Bình added that when a hexagram meets void, one cannot immediately treat it as void (凡占遇空，不可卽以爲空也)[1]. This approach places tuần không on the same level as other signals such as month breaking, day stem, movement and stillness, rather than giving it sole veto power.
It should also be remembered that Tăng san bốc dịch repeatedly refutes the rigid readings of earlier books, for instance in the section discussing marriage, Giác Tử (Lý Văn Huy) criticises the books Hoàng kim sách and Dịch mạo for taking the Response as the wife and then holding that whenever the Response is prosperous the bride's family must be wealthy and noble, calling this a perverse line of argument (種種悖謬)[1]. That spirit applies equally to tuần không: it is one variable in the system, not a verdict.
Suggestions from Nhật Nguyệt
Suggestions from Nhật Nguyệt: when you look up tuần không for a hexagram, follow this order. One, write down clearly the stem-branch of the day of casting, because without the day you cannot look up the week. Two, look it up in the table of six Giáp weeks to get the two void branches. Three, examine whether the line to be interpreted is static or moving, whether it is supported by the day stem or by a moving line, whether it is broken by the month, and only then conclude. Four, if that line is the deciding point of the question and the signals still overlap, cast one more hexagram and compare the two, exactly in the spirit of multiple casting in Tăng san bốc dịch.
It should be stated clearly that this is a convention of one school of hexagram divination, not a conclusion about human destiny. Tăng san bốc dịch is a Lục Hào book from the Qing dynasty: the original text only proves what the book says, not that what it says is true. Readers who want to use it as a way of organising their own thoughts should keep that spirit, and not turn the two words tuần không into a pronouncement about anyone's finances, health or marriage.
