The Yarrow-Stalk Method and the Coin Method: How to Cast with Yarrow Stalks and How the Two Differ

The text

The number of the Great Expansion is fifty; forty-nine of them are used. Divide them into two, to stand for the two. Set one apart, to stand for the three. Count them off by fours, to stand for the four seasons. Return the remainder to between the fingers, to stand for the leap month. ... Thus four operations complete one change, and eighteen changes complete a hexagram.

This is the account in the first part of the Xici (the "Great Commentary"), and it is the oldest and most orthodox casting method that survives. Zhu Xi turned it into steps that can actually be followed, in the Shiyi ("Procedure for Divination") at the front of his Zhouyi Benyi ("Original Meaning of the Zhouyi").

The steps

1. Take fifty yarrow stalks. Pull one out and set it aside unused, leaving forty-nine to work with.
2. Divide in two: split the stalks at random into a left pile and a right pile.
3. Set one apart: take one stalk from the right pile and tuck it by the little finger of the left hand.
4. Count by fours: count through the left pile four stalks at a time and hold the remainder between the fingers (the remainder is one to four; if the pile divides evenly, it counts as four). Count through the right pile the same way and take its remainder.
5. Return the remainder: the stalk set apart plus the two remainders always add up to five or nine. Remove them. This is the first change.
6. Do two more changes with the stalks that are left. Each time, the number removed is always four or eight.
7. After three changes, divide the number of remaining stalks by four. The result is 9, 8, 7 or 6, and that gives one line.
8. Repeat six times, eighteen changes in all, to complete a hexagram.

The odds are not the same

With both methods, the chance of a yang line and the chance of a yin line are one half each, and the chance that any given line is a changing line is one quarter. The difference lies in whether the changing lines are yin or yang: with yarrow stalks, old yang turns up more easily than old yin (three to one), while with coins the two are symmetrical.

Zhu Xi noticed long ago that the two methods differ. In the Zhuzi Yulei ("Classified Conversations of Master Zhu") he says: "People today use three coins in place of counting the stalks, and that cannot bring out all the changes." The difference comes from the asymmetry created by setting one stalk apart in the first change; it does not mean that one method is "more accurate" than the other. The ancients treated the yarrow stalks as the proper method because they valued its solemnity and the time it takes. Working through eighteen changes takes a quarter of an hour, and by then the mind has settled of its own accord. For the steps of the coin method, see How to cast with three coins.