Yarrow Stalks & the Great Expansion

The Great Treatise says, "The number of the Great Expansion is fifty; of these, forty-nine are used." You take fifty yarrow stalks — dried, straight, long-lived, the ancients' plant of choice — set one aside and never touch it again (it stands for the still center of things), and work with the other forty-nine.

That single withdrawn stalk is the whole method's hidden hinge: every change unfolds from the one point that does not change. It is why the yarrow cast has always been held to come closest to the mind of heaven and earth.

Those four operations together make one "change." Set aside the hung and remainder stalks, gather what is left, and run the four again — that is the second change; once more is the third. After three changes, the stalks in hand come to exactly 36, 32, 28, or 24.

Divide by four for 9, 8, 7, or 6: nine is old yang (moving), eight young yin, seven young yang, six old yin (moving). That fixes one line. A hexagram has six lines, so it takes three changes six times over — eighteen changes — to reach a whole one. Hence the old name: "eighteen changes make a hexagram."

A full yarrow cast runs fifteen or twenty minutes even for a practiced hand. The slowness is the point: the endless dividing, counting, and returning works like a quiet ceremony, gathering the mind onto the question stalk by stalk, leaving no room to rush.

Coins and numbers caught on precisely because they swap this elaborate procedure for a faster roll of chance. Mathematically the two don't produce old and young lines at quite the same odds as the stalks — but for almost any question they are more than enough. Learning the yarrow method is not about doing it daily; it is so that when you tap Cast, you remember how grave this craft once was.