I Ching (Book of Changes)

At its core the Zhouyi is a divination manual: sixty-four hexagrams, each built from six broken (yin) or unbroken (yang) lines stacked in every possible combination, paired with a terse, often cryptic judgment and six individual line texts. Aristocrats in the Western Zhou consulted it through a yarrow-stalk counting procedure that generated a hexagram, then read the judgment and relevant line texts as guidance for the situation at hand, a system that likely developed out of the older tradition of oracle-bone and turtle-shell divination once cracked bone gave way to counted stalks as the preferred technology of inquiry.

Over the following centuries, particularly across the Warring States and into the Han, a set of ten commentarial essays known as the Ten Wings was added, elaborating the bare hexagram texts into a full cosmology built on the complementary interaction of yin and yang and the ceaseless mutual generation of the hexagrams as a model of both natural and moral process. These commentaries were traditionally, but incorrectly, attributed to Confucius; modern textual criticism, reinforced by a 1973 Mawangdui silk-manuscript version of the text whose hexagram order differs from the received one, treats them as the product of later Warring States and Han scholarship still actively reworking the text centuries after its core was fixed.

As a Confucian classic, later ranked first among the Five Classics in the standard imperial ordering (the earlier Han-era sequence instead placed the Odes first), the Zhouyi was read not as mere fortune-telling but as an ethical technology: correctly discerning the structure of a present situation, its hexagram, was thought to disclose the right timing and the right action, making divination compatible with, rather than opposed to, moral self-cultivation. This reframing is what let a divination manual sit alongside works like the Analects at the center of the Confucian curriculum.

Its vocabulary of yin-yang and the eight trigrams subsequently supplied the working language of Chinese cosmology, medicine, alchemy, and statecraft for the next two thousand years, and the text remains in active use as a divination manual into the present.