The order of the 64
The 64 hexagrams of the I Ching come in a fixed order, the one you'll find in almost any edition. It opens with hexagram 1, Activity, and hexagram 2, Passivity, and closes with hexagram 63, After the End, and hexagram 64, Transition. This order is called the King Wen sequence, because tradition credits it to King Wen, the founding figure of the Zhou dynasty.
There's no evidence that King Wen actually arranged it. What we do know is that it's the order of the received text, and that it's very old. It isn't the only one: a silk manuscript found at Mawangdui, buried in the second century BCE, arranges the hexagrams differently, grouping them by trigram.
Everything comes in twos
The first thing you notice in the sequence is that the hexagrams come in pairs: 1 and 2, 3 and 4, 5 and 6, all the way to 63 and 64. That's 32 pairs, and each pair follows one of two rules.
Inversion. In 28 of the 32 pairs, the second hexagram is the first one turned upside down. Take hexagram 3, Initial Obstacles. From the bottom up, its lines are yang, yin, yin, yin, yang, yin. Flip it and you get yin, yang, yin, yin, yin, yang, which is hexagram 4, Immaturity. A hexagram turned over like this is called the inverted hexagram.
Complement. Eight hexagrams look the same either way up, because they're symmetrical: 1, 2, 27, 28, 29, 30, 61 and 62. Flipping them changes nothing, so each one is paired with its opposite, with every line switched, yang for yin and yin for yang. That's the opposite hexagram. These make the four remaining pairs: 1 and 2, Nourishment (27) and Excesses (28), Water (29) and The Flame (30), Inner Integrity (61) and Success in Small Matters (62).
Some pairs follow both rules at once, like 11 and 12 or 63 and 64: the second is both the first turned over and its opposite.
There's a lovely lesson in this for reading: every situation has a partner that looks at it from the other side. When you get a hexagram, reading its pair can show you the same scene from the opposite point of view.
The two halves of the book
The sequence is split into two parts, the upper canon and the lower canon.
- The upper canon runs from 1 to 30. It opens with Heaven and Earth in 1 and 2, and ends with Water and Fire, in 29, Water, and 30, The Flame.
- The lower canon runs from 31 to 64. It opens with hexagram 31, Attraction, and hexagram 32, What Lasts, which tradition reads as people meeting and staying together, and ends with 63 and 64.
That's why people often say the first half is about the natural order and the second about human affairs. It's a traditional reading, useful as an image, though every hexagram mixes both worlds.
The split looks uneven, 30 against 34, but here's a detail: if you count each inverted pair as one figure, since it's the same figure seen from two sides, each canon has exactly 18 figures. We don't know whether the authors meant it, but it's a striking balance.
Is there a logic to it?
Within each pair the rule is clear. The order between pairs is another matter. One of the Ten Wings, the Sequence of the Hexagrams (序卦), explains it as a story in which each hexagram leads to the next: 有天地，然後萬物生焉, "there are heaven and earth, and after that all things are born." It's a beautiful reading, but it was written long after the sequence itself. To this day no one has found a simple mathematical rule that explains the whole order.
There are other famous orders, such as the one Song dynasty scholars credited to Fu Xi, which arranges the hexagrams like binary numbers and caught the eye of Leibniz in the eighteenth century. But the King Wen sequence is the book's own, and it's the numbering almost every edition uses, Cambios included.
Why it's useful to you
You don't need to memorize the sequence to consult the I Ching. But knowing it gives you two things: the numbers stop feeling arbitrary, and every hexagram comes with a partner. To learn about the commentaries that try to explain it, go on to The Ten Wings.