Heads or tails in the I Ching: which side of the coin is yang?

In the traditional three-coin method, the inscribed side of a Chinese coin (字, the face with the characters) counts 2, which is yin, and the plain or reverse side (背) counts 3, which is yang. Three plain sides make 9, old yang; three inscribed sides make 6, old yin. Books do not all agree, and with modern coins you have to choose for yourself, but the choice matters far less than people fear: what matters is that you decide before you toss and never switch.

The line values

Toss three coins, add the faces, and you get one of four totals. With the plain side as 3 and the inscribed side as 2:

• 6 — three inscribed sides (2 + 2 + 2): old yin, a broken line that is moving.
• 7 — one plain side, two inscribed (3 + 2 + 2): young yang, a solid line at rest.
• 8 — two plain sides, one inscribed (3 + 3 + 2): young yin, a broken line at rest.
• 9 — three plain sides (3 + 3 + 3): old yang, a solid line that is moving.

Notice the small trap: one plain side gives a yang line and two plain sides give a yin line. The total decides, not the majority of faces. Chinese manuals remember this with four old words, 單拆重交: one plain side is "single" (單, young yang), two are "split" (拆, young yin), three are "doubled" (重, old yang) and none is "crossed" (交, old yin).

With fair coins, 6 and 9 each turn up one time in eight, 7 and 8 three times in eight. The full method — six throws, built from the bottom line up — is explained in the three-coin guide, and what to do with the moving lines in the changing-lines guide.

Why three for yang and two for yin

The numbers come from the oldest number symbolism attached to the book. The Shuogua (說卦) says the sages "took three for heaven and two for earth" (參天兩地而倚數): odd is heaven and yang, even is earth and yin. Three coins of value 3 or 2 can only total 6, 7, 8 or 9, the same four numbers the far older yarrow-stalk method produces, so the coins were designed to plug into the existing system.

Which face of the coin should carry the 3 is a separate question, and here the tradition is a matter of practice rather than scripture. The mainstream Chinese convention, and the one Richard Wilhelm describes in the instructions to his translation, makes the inscribed side yin with the value 2 and the reverse side yang with the value 3. That is the convention this site uses, as the three-coin guide explains.

A minority of modern teachers reverse it, usually on the reasoning that the inscribed side is the "front" (正面) of the coin and should therefore be yang. You will meet both in books and online.

Heads and tails on ordinary coins

Modern coins do not have a 字 side and a 背 side in the old sense, and on many old Chinese coins the "plain" side is not even plain: the reverse of a Qing coin usually carries a mint mark in Manchu script. So with any coin you simply have to decide. Common choices:

• Heads = 3, tails = 2, treating the portrait side as the bright, yang face. This is a frequent convention in English-language books.
• The side with more text = 2, mapping the modern coin onto the old inscribed side. This keeps faith with the Chinese convention.

Either is fine. If you want to settle it once and forget about it, choose the second, which matches the traditional rule and this site. There is more on choosing and marking coins in what coins to use for the I Ching.

Why the choice matters less than you think

Here is the reassuring part. Swapping the convention swaps 3 and 2 on every coin, so every 7 becomes an 8 and every 6 becomes a 9, and the reverse. Two things follow:

• The odds are identical. Old lines still come up one time in eight each, young lines three in eight. Neither convention makes moving lines more or less likely.
• The same physical toss gives the opposite hexagram. Every solid line becomes broken and vice versa — the relation the commentaries call the opposite hexagram (錯卦), explained in nuclear, inverse and opposite hexagrams. The moving lines stay in the same places.

For example, if your six throws give, bottom to top, one, two, three, zero, two and one plain sides, the traditional convention reads 7, 8, 9, 6, 8, 7: fire below, mountain above, Hexagram 22, Bi, with lines 3 and 4 moving. Read with the opposite convention, the same coins make Hexagram 47, Kun. That sounds alarming until you remember that the coins are random: before you toss, both conventions give every hexagram exactly the same chance. Neither is hiding the "real" answer from the other.

What does damage a reading is changing the rule after seeing the result, or switching from one cast to the next. That turns the method into a way of choosing the answer you prefer, which is precisely what a fixed rule is there to prevent.

A few small practical questions

• Can you toss one coin three times? Yes. The throws are independent, so one coin tossed three times gives 6, 7, 8 and 9 with exactly the same odds as three coins tossed together.
• What if a coin lands on its edge or rolls away? Toss that line again. It is not an omen, and there is no need to restart the whole cast.
• Do the three coins have to match? No, as long as you know which face counts 3 on each, though matching coins make mistakes less likely.

On this site

On the I Ching page you do not have to decide: the server makes each toss with a cryptographic random source and applies the traditional values, plain side 3 and inscribed side 2. The on-screen coins animate a result that has already been recorded.

Putting it into practice

• Pick your convention now, write it in the front of your notebook or journal, and keep it.
• Remember the four totals rather than counting heads: 6 and 9 move, 7 is solid, 8 is broken.
• Record each throw as a number, bottom line first, before you look anything up.
• If you have been using the other convention for years, there is no need to switch. Your past casts were valid under your rule; just do not mix the two.