Yarrow Stalk Divination Method for the I Ching

The Yarrow Stalk Method dates to high antiquity and is the standard casting procedure recorded in the Great Commentary (系辞传). Preparation begins with 50 yarrow stalks (one is set aside to represent the Taiji, "Supreme Ultimate"), leaving 49 for the "Grand Expansion Number" operation. Each operation goes through three rounds of "divide in two, set one aside, count by fours, gather remainders," yielding four possible values: 6, 7, 8, or 9. The critical difference lies in probability: in the yarrow method, Old Yang (9) has ~3/16 probability, Old Yin (6) ~1/16, Young Yang (7) ~5/16, and Young Yin (8) ~7/16. This differs dramatically from the coin method (each value at 1/4 probability) — the yarrow method makes Yin lines (especially Young Yin 8) more frequent and Old Yin extremely rare, better reflecting nature's tendency toward "abundant Yin, rare dramatic reversals."

In modern practice, the coin method dominates due to its speed and simplicity, but serious traditional I Ching scholars insist on the yarrow method or its mathematical equivalent. The core difference lies in signal frequency: the coin method produces changing lines with 50% probability (values 6 and 9 each at 25%), while the yarrow method produces them at only ~25% (Old Yang 3/16 + Old Yin 1/16 ≈ 4/16). This means yarrow-cast hexagrams are "quieter" — fewer changing lines, more precise signals, less noise. The coin method's high changing-line rate often creates chaotic "everything is mutating" readings, whereas the yarrow method's low rate ensures each change signal is a high-value true signal.