動爻、本卦與之卦是什麼？
作者：Wei Chun Chuang・2026-10-15
用銅錢或其他方法起卦時，常會聽到「動爻」「本卦」「之卦」這幾個詞。它們描述的是：一個卦在起卦當下的樣子，其中哪些爻正在轉變，以及轉變之後會成為哪一卦。這篇用三枚銅錢的方法說明它們的關係。
起卦時，一爻是怎麼得出來的？
最常見的是「三錢法」：三枚銅錢同時擲出，每擲一次得到一爻，共擲六次，由下往上依序排出初爻到上爻。
常見的約定是正面記 3、反面記 2（也有人反過來記，只要前後一致即可），三枚相加會得到 6、7、8、9 其中一個數字：
- 7：少陽，陽爻，不變。
- 8：少陰，陰爻，不變。
- 9：老陽，陽爻，會轉為陰爻。
- 6：老陰，陰爻，會轉為陽爻。
更古老的方法是用蓍草推演，〈繫辭傳〉有「大衍之數五十」的記載，同樣會得到 6、7、8、9 四種結果。
什麼是動爻？
數字是 9 或 6 的爻，就是「動爻」，也叫「變爻」。傳統的理解是「老」到極點就會轉向：老陽轉為陰，老陰轉為陽；7 與 8 是「少」，還在成長，所以保持不變。
一個卦可能沒有動爻，也可能有一個、幾個，甚至六爻全動。
本卦和之卦有什麼關係？
六次擲完後，照原本的陰陽畫出的卦，叫「本卦」。把所有動爻翻轉，陽變陰、陰變陽，得到的新卦叫「之卦」，也常叫「變卦」。
「之」在古文中有「往、到」的意思，所以之卦可以理解為「本卦往哪裡去」。如果沒有任何動爻，就只有本卦，沒有之卦。
可以舉個例子嗎？
假設六爻都是陽，只有初爻擲出 9。本卦是六爻皆陽的乾卦，動爻是初九。把初爻由陽翻成陰，下卦從乾 ☰ 變成巽 ☴，上卦仍是乾，於是之卦是「天風姤」。
閱讀時，可以先讀乾卦初九的爻辭「潛龍勿用」，再看姤卦的卦辭作為參照。
有動爻時，要讀哪一段文字？
不同的書與流派有不同規則，沒有唯一標準。宋代朱熹在《易學啟蒙》中整理過一套常被引用的做法，例如：
- 沒有動爻：讀本卦的卦辭。
- 一個動爻：讀本卦那一爻的爻辭。
- 六爻全動：乾卦讀「用九」，坤卦讀「用六」，其他卦讀之卦的卦辭。
兩到五個動爻的情況另有細則。初學者不必一開始就全部記住，先掌握這個框架即可：本卦是現在的樣子，動爻是變化的位置，之卦是變化的方向。
為什麼說起卦是用來反思？
卦辭與爻辭多半是意象與處境的描寫，而不是具體答案。把起卦當成一面鏡子，問自己：「這段文字讓我想到目前的哪件事？」「哪個地方正在改變？」比起把它當成結論，更能幫助你整理想法。
常見問題
- 沒有動爻代表什麼？
- 代表六爻都是 7 或 8，只有本卦，沒有之卦。常見做法是以本卦的卦辭為主來閱讀。
- 之卦和錯卦、綜卦一樣嗎？
- 不一樣。之卦只翻轉動爻；錯卦是六爻陰陽全部互換；綜卦是把整個卦上下顛倒。三者是不同的觀察角度。
- 銅錢正反面一定要記成 3 和 2 嗎？
- 這是常見約定，也有人反過來記。重要的是同一次起卦前後一致，並清楚記錄每一爻的數字。
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What are changing lines, the primary hexagram and the resulting hexagram?
作者：Wei Chun Chuang・2026-10-15
When you cast a hexagram with coins or another method, you soon meet three terms: changing lines, the primary hexagram and the resulting hexagram. Together they describe what the hexagram looks like at the moment of casting, which lines are in the process of changing, and which hexagram it becomes after the change. This article explains how they fit together using the three-coin method.
How is each line produced when you cast?
The most common method uses three coins. Toss all three at once to get one line; toss six times, building the hexagram from the bottom line to the top.
A common convention counts heads as 3 and tails as 2 (some people reverse this; just stay consistent). The three coins add up to 6, 7, 8 or 9:
- 7: young yang, a yang line that stays.
- 8: young yin, a yin line that stays.
- 9: old yang, a yang line that turns into yin.
- 6: old yin, a yin line that turns into yang.
An older method uses yarrow stalks; the Great Commentary mentions "the number of the great expansion is fifty". It produces the same four results: 6, 7, 8 and 9.
什麼是動爻？
A line that comes out as 9 or 6 is a changing (moving) line. The traditional idea is that what is "old" has reached its extreme and turns around: old yang becomes yin and old yin becomes yang. Seven and eight are "young", still growing, so they stay as they are.
一個卦可能沒有動爻，也可能有一個、幾個，甚至六爻全動。
How are the primary and resulting hexagrams related?
After six tosses, the hexagram drawn from the lines as they fell is the primary (original) hexagram. Flip every changing line, yang to yin and yin to yang, and the new figure is the resulting hexagram, also called the relating or changed hexagram.
In classical Chinese the word used for it means "going to", so you can think of the resulting hexagram as where the primary hexagram is heading. With no changing lines there is only the primary hexagram.
Can you show an example?
Suppose all six lines are yang and only the bottom line came out as 9. The primary hexagram is Qian, all yang, with the first nine changing. Flip that bottom line to yin: the lower trigram changes from Qian ☰ to Xun ☴ while the upper stays Qian, so the resulting hexagram is Gou, "Coming to Meet" (Heaven over Wind).
You might first read the first-nine line of Qian, "hidden dragon, do not act", and then read the judgment of Gou alongside it.
Which text do you read when lines are changing?
Books and schools differ; there is no single standard. One frequently cited set of guidelines comes from the Song-dynasty scholar Zhu Xi in his Introduction to the Study of the Changes, for example:
- No changing lines: read the judgment of the primary hexagram.
- One changing line: read that line's statement in the primary hexagram.
- All six changing: for Qian read "using nines", for Kun read "using sixes", for any other hexagram read the judgment of the resulting hexagram.
Two to five changing lines have their own detailed rules. Beginners don't need them all at once. Start with this frame: the primary hexagram is how things stand now, the changing lines show where change is happening, and the resulting hexagram shows the direction of change.
Why is casting described as a tool for reflection?
Judgments and line statements mostly describe images and situations, not concrete answers. Treat a casting as a mirror and ask yourself: "What in my life does this passage bring to mind?" "Where is something changing?" Used this way, it helps you sort out your own thinking rather than giving you a verdict.
常見問題
- What does it mean if there are no changing lines?
- All six lines came out as 7 or 8, so there is only a primary hexagram and no resulting hexagram. A common approach is to read mainly the primary hexagram's judgment.
- Is the resulting hexagram the same as the opposite or inverted hexagram?
- No. The resulting hexagram flips only the changing lines; the opposite hexagram swaps yin and yang in all six lines; the inverted hexagram turns the whole figure upside down. They are different ways of looking.
- Must heads be 3 and tails 2?
- That is a common convention; some people reverse it. What matters is staying consistent within a casting and recording each line's number clearly.
Practise with an app
To practise these ideas, YiJian is an iPhone course that teaches the I Ching from zero, with eight interactive beginner lessons (the first three free) and illustrated guides to all sixty-four hexagrams. Casting in the app is a practice feature for checking what you have learned and reflecting on your situation; it does not make decisions for you.