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How does the Yijing use 64 configurations related to the number 8?

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Close-up of a sunflower head showing seeds arranged in a spiral pattern that follows the Fibonacci sequence. — number symbolism The head of a sunflower arranged in a Fibonacci sequence.

In the Yijing, the 64 configurations are derived from the number 8 through the combination of eight fundamental trigrams, known as bagua.1

These hexagrams are formed by stacking these eight trigrams in pairs, one above the other, resulting in $8 \times 8 = 64$ unique configurations. This mathematical structure is deeply embedded in the system's cosmology, which seeks to explain all existence and change through the interaction of yin and yang principles.12

Furthermore, the number 8 holds specific cultural significance in Chinese thought regarding the human life cycle. Just as the number 8 dictates the progression of a man’s development—such as the loss of sexual virility occurring at $8 \times 8 = 64$ years—the Yijing utilizes this same numerical relationship to organize its divinatory system.2