TL;DR: When casting a hexagram, any line carrying the number 9 (lão dương, old yang) or the number 6 (lão âm, old yin) is a moving line, while 7 and 8 are not moving. Chu Hy in the Dịch học khải mông laid out a method for judging change according to the number of moving lines: with one moving line you read that line's text of the original hexagram, with two you read both moving line texts and take the upper line as master, with three you read the Thoán text of both the original and the changed hexagram, with four you read the two non-moving line texts of the changed hexagram and take the lower line as master, with five you read the single non-moving line text of the changed hexagram, and with six, Kiền and Khôn read the Dụng cửu and Dụng lục texts while other hexagrams read the Thoán text of the changed hexagram. This is a school convention, not a law, and other books such as Tăng san bốc dịch use an entirely different method of interpretation.
Which text do you read when a divination produces many moving lines?
The short answer: according to the method for judging change that Chu Hy set out in the Dịch học khải mông (易學啟蒙), the number of moving lines determines which text you read. With one moving line you read that line's text of the original hexagram; with two moving lines you read both moving line texts and take the upper line as master; with three moving lines you read the Thoán text of both the original and the changed hexagram; with four moving lines you read the two non-moving line texts of the changed hexagram, taking the lower line as master; with five moving lines you read the single non-moving line text of the changed hexagram; with six moving lines, Kiền and Khôn read the Dụng cửu and Dụng lục texts, and other hexagrams read the Thoán text of the changed hexagram. This whole system sits in the Khảo biến chiêm (考變占) chapter of the Dịch học khải mông, and the Ngự toản Chu Dịch chiết trung, compiled by Lý Quang Địa by imperial order in 1715, copied it verbatim[1].
Why are only 9 and 6 used, and not 7 and 8?
Because in the yarrow-stalk method, only 9 and 6 produce moving lines. The four numbers 7, 8, 9, 6 correspond to four images: 7 is thiếu dương (young yang), 8 is thiếu âm (young yin), 9 is lão dương (old yang), 6 is lão âm (old yin). The old changes, the young does not change, so any line carrying 9 or 6 is a moving line, and any line carrying 7 or 8 is a static line. Chu Hy wrote in the Khảo biến chiêm chapter: "用九用六者變卦之凡例也" (Dụng cửu and Dụng lục are the general rule for judging the changed hexagram), meaning every yang line uses the number 9 and not 7, and every yin line uses the number 6 and not 8[1].
This mechanism comes from the yarrow-stalk method. In the Minh thi sách (明蓍策) chapter of the Dịch học khải mông, each line is formed through three changes, and each change has four steps (tứ doanh). Eighteen changes in total form six lines. The number of stalks left after three changes determines whether that line is 6, 7, 8, or 9. Because the number 9 (old yang) requires all three changes to be odd and the number 6 (old yin) requires all three to be even, the probability of getting 9 and 6 is markedly lower than that of 7 and 8. This is recorded in the Dịch học khải mông thông thích of Hồ Phương Bình, which quotes Âu Dương Tu's remark that when casting, "七八常多而九六常少" (seven and eight are often many, nine and six are often few)[2].
What are the steps in Chu Hy's method for judging change?
The method divides into seven cases, from no moving lines to all six lines moving. The table below summarises the original text of the Khảo biến chiêm chapter in the Dịch học khải mông, as copied in the Ngự toản Chu Dịch chiết trung[1]:
| Number of moving lines | Which text to read | Chu Hy's note |
|---|---|---|
| 0 (all six lines static) | Thoán text of the original hexagram | The inner trigram is trinh, the outer trigram is hối |
| 1 moving line | The text of that moving line in the original hexagram | Cites six examples from the Tả truyện |
| 2 moving lines | The two moving line texts of the original hexagram, taking the upper line as master | Not recorded in the Kinh Truyện; Chu Hy inferred the rule |
| 3 moving lines | Thoán text of both the original and the changed hexagram, original as trinh, changed as hối | The first ten hexagrams take trinh as master, the last ten take hối |
| 4 moving lines | The two non-moving line texts of the changed hexagram, taking the lower line as master | Not recorded in the Kinh Truyện; inferred the rule |
| 5 moving lines | The single non-moving line text of the changed hexagram | Cites the Mục Khương example from the Tả truyện |
| 6 moving lines | Kiền reads Dụng cửu, Khôn reads Dụng lục, other hexagrams read the Thoán text of the changed hexagram | Cites the Thái Mặc passage in the Tả truyện |
One point needs noting: in the two-moving-line and four-moving-line cases, Chu Hy himself notes that the Kinh Truyện does not record them, and he only "dĩ lệ suy chi" (inferred from the rule)[1]. This is an important point for the reader to distinguish which rules have roots in the Kinh Truyện and which are conventions Chu Hy added.
What did Chu Hy base the method for judging change on?
He based it on three sources. The first source is the Dụng cửu and Dụng lục texts attached to the Kiền and Khôn hexagrams, regarded as the general rule for all hexagrams when all six lines change. The original text: "乾卦用九見羣龍无首吉" (Kiền hexagram, Dụng cửu: seeing a flock of dragons without a head, auspicious) and "坤卦用六利永貞" (Khôn hexagram, Dụng lục: beneficial to persist in correctness)[1].
The second source is the examples recorded in the Tả truyện and Quốc ngữ, that is, divinations from the Spring and Autumn period that survive in writing. For example, Tất Vạn met the Truân hexagram changing into the Tỉ hexagram, corresponding to a moving Sơ cửu (first nine) line; Tấn Văn Công met the Đại Hữu hexagram changing into the Khuê hexagram, corresponding to a moving Cửu tam (nine three) line; Nam Khoái met the Khôn hexagram changing into the Tỉ hexagram, corresponding to a moving Lục ngũ (six five) line. Chu Hy cites all six examples to illustrate the one-moving-line case[1].
The third source is the discussion of earlier Confucian scholars, especially Âu Dương Tu. Âu Dương Tu held that not all six lines carry the number 9 or 6; only a line that moves is called 9 or 6, while a static line remains 7 or 8; and because in actual casting "七 八 常 多 而 九 六 常 少", one must distinguish clearly. Chu Hy judged this remark to be "phát minh tiên nho sở vị đáo, tối vi hữu công" (a discovery of what earlier Confucians had not reached, the greatest merit)[1].
When three lines move, why read both hexagrams?
Because Chu Hy held that one should not abandon the original hexagram entirely and look only at the changed hexagram. In the Khảo biến chiêm chapter he wrote: "三爻變則占本卦及之卦之彖辭，而以本卦為貞之卦為悔" (when three lines change, consult the Thoán text of both the original and the changed hexagram, taking the original as trinh and the changed as hối)[1].
The Dịch học khải mông thông thích adds Chu Hy's explanation: when three lines change, there is no longer a single line to take as master, so the Thoán texts of both hexagrams are consulted[2].
How is the case of all six lines moving handled?
For the Kiền hexagram with all six lines moving, one reads the Dụng cửu text: "見羣龍无首吉" (seeing a flock of dragons without a head, auspicious). For the Khôn hexagram with all six lines moving, one reads the Dụng lục text: "利永貞" (beneficial to persist in correctness). For other hexagrams with all six lines moving, one reads the Thoán text of the changed hexagram[1].
Chu Hy explains why only Kiền and Khôn have Dụng cửu and Dụng lục texts: because those two hexagrams stand at the head of the sixty-four hexagrams and are the pure yang and pure yin hexagrams. When Kiền changes into Khôn, all six lines being 9, then "quần long vô thủ" is the image of yang all changing into yin; when Khôn changes into Kiền, all six lines being 6, then "lợi vĩnh trinh" is the meaning of yin all changing into yang[1].
Why is Chu Hy's method for judging change not the only rule?
Because different divination books use different systems of convention. The book Tăng san bốc dịch (增刪卜易) by Dã Hạc lão nhân, in the Vĩnh Cao translation printed by the Information and Culture Publishing House in 2008, interprets hexagrams by an entirely different system: it uses the five phases (ngũ hành) generating and overcoming, the six spirits, the Host and Guest lines, the monthly and daily spirits, and does not read line texts according to the number of moving lines[3]. In this system, when a hexagram has many moving lines, one interprets by the interaction of the five phases among moving lines, changed lines, and static lines, rather than consulting Chu Hy's table for judging change.
Even within the Confucian tradition, Chu Hy's method was not always applied exhaustively. Lý Quang Địa in the Ngự toản Chu Dịch chiết trung records Hồ Nhất Quế's remark that when examining the divinations in the Tả truyện, the ancients did not necessarily take only one moving line but also looked at the hexagram body and the Thoán text; so one can see that the method for judging change is only one way of systematising, not an absolute description of what the ancients did[1].
Quick lookup summary
When a hexagram has been cast, the first thing is to count how many lines carry the number 9 or 6. If none, read the Thoán text of the original hexagram. If one, read that line's text. If two, read both line texts and take the upper line as master. If three, read the Thoán text of both the original and the changed hexagram. If four, read the two non-moving line texts of the changed hexagram and take the lower line as master. If five, read the single non-moving line text of the changed hexagram. If six, Kiền reads Dụng cửu, Khôn reads Dụng lục, and other hexagrams read the Thoán text of the changed hexagram.
Nhật Nguyệt's suggestion: Chu Hy's method for judging change is a tightly structured system, but it belongs to the methodology of one school, not a binding law. Learners should grasp this method as a standard for reading the Kinh Dịch in the Confucian manner, while also knowing that other divination systems such as Tăng san bốc dịch have their own method of interpretation. When casting for oneself, the important thing is consistency within one system, avoiding mixing systems and then drawing arbitrary inferences.
