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On the Dayan Yarrow Stalk Method

Exploring the philosophical significance and operational principles of the Great Expansion divination method from the I Ching

Tianwen Editorial Team January 27, 2026 7 min read PDF Markdown
On the Dayan Yarrow Stalk Method

II. The Four Operations and Eighteen Changes: A Ritual of Divine Communication

The operation of the Da Yan method is extremely complex, known as the "Four Operations and Eighteen Changes."

  • The Four Operations: Dividing into two, Suspending one, Counting by fours, and Returning the remainders. These four actions constitute one "operation" (one change).
  • The Eighteen Changes: It takes three operations (three changes) to produce a single Yao (line). A hexagram has six lines, thus $3 \times 6 = 18$ changes are required to complete a hexagram.

This process is not just about finding a number; it is designed to help the diviner collect their thoughts and enter a state of "Sincerity" (Cheng) through meticulous labor.

Preparation

  • Tools: 50 yarrow stalks (ancient people used stalks of Achillea millefolium; today, bamboo sticks or Go stones are often used).
  • Setting: A clean desk, sitting facing south (or north, depending on tradition), with a heart full of reverence.

【Calculating the First Line】 (Requires Three Changes)

The First Change

  1. Extract the Taiji: Remove 1 stalk from the 50 and set it aside. 49 stalks remain.
  2. Divide into Two (Symbolizing the Two Forces): Randomly divide the 49 stalks into two piles (left and right). This symbolizes the initial separation of Heaven and Earth, Yin and Yang.
  3. Suspend One (Symbolizing the Three Powers): Take one stalk from the right pile and place it between the pinky and ring finger of the left hand. This symbolizes "Man" born between Heaven and Earth, forming the "Trinity" (Heaven, Earth, Man).
  4. Count by Fours (Symbolizing the Four Seasons):
    • First, count the left pile in groups of four. The remainder will be 1, 2, 3, or 4 (Note: if it divides evenly, the remainder is 4, not 0). Place this remainder between the ring finger and middle finger.
    • Next, count the right pile in groups of four. Place that remainder (1, 2, 3, or 4) between the middle and index finger.
  5. Return the Remainders (Combined Remainder): Combine all stalks currently held between the fingers of the left hand (the 1 suspended + left remainder + right remainder) and set them in the corner of the desk. These are "discarded" for this change.

Mathematical Validation: The total stalks removed in the first change can only be 5 or 9. (The stalks remaining in hand will be 44 or 40).

The Second Change

Combine the remaining stalks (44 or 40) and repeat the steps:

  1. Divide into two.
  2. Suspend one from the right.
  3. Count by fours on both sides.
  4. Return the remainders to a separate pile.

Mathematical Validation: The stalks removed in the second change can only be 4 or 8. (The stalks remaining in hand will be 32, 36, or 40).

The Third Change

Repeat the process one last time with the remaining stalks.

Mathematical Validation: The stalks removed in the third change can only be 4 or 8.

Determining the Line (Yao)

After three changes, count the remaining stalks held in hand. The total will only be one of four numbers. Divide this number by 4 to get the Line Number:

  • 24 stalks left: $24 \div 4 = 6$ —— Old Yin (Changing line, marked as X).
  • 28 stalks left: $28 \div 4 = 7$ —— Young Yang (Unchanging, marked as —).
  • 32 stalks left: $32 \div 4 = 8$ —— Young Yin (Unchanging, marked as --).
  • 36 stalks left: $36 \div 4 = 9$ —— Old Yang (Changing line, marked as O).

With this, the first line (the bottom line) is drawn. Repeat this "Three Changes" process six times total, moving from bottom to top, to complete the hexagram.