What is the I Ching?

Tze-Ki Hon, writing in the Stanford Encyclopedia of Philosophy, describes the book as three layers. The first is the set of 8 trigrams and 64 hexagrams, the figures of broken and solid lines. The second is the short statements attached to each hexagram and to each of its lines. The third is a group of commentaries known as the Ten Wings.

The first two layers make up the old core, known as the Zhou yi (周易), the Changes of Zhou. The Ten Wings draw philosophical readings out of those symbols and statements.

A person holds a question in mind and builds a hexagram one line at a time, from the bottom up. Today this is often done by tossing three coins six times. A coin method is reported to have become widespread in the Tang dynasty.

An older procedure uses yarrow stalks. The commentary called the Xici describes sorting 50 stalks by counting and setting aside. Modern practice follows a reconstruction, much of it owed to the Song scholar Zhu Xi.

Any line that changes points to a second hexagram, so a cast may give two texts to read. Hon notes that early divination was used as an aid to decisions, and that the book came to be treated as a way of reflecting on oneself.

Hon calls the core text oracles from the Western Zhou period. Scholars date its assembly in roughly its present form anywhere from the 10th to the 4th century BCE. Edward Shaughnessy, comparing its language with dated bronze inscriptions, placed it in the last quarter of the 9th century BCE.

Excavated and purchased manuscripts give approximate dates for copies of the text. The Shanghai Museum bought a set of bamboo strips in 1994, looted from a tomb. Its 58 strips hold about a third of the text. A carbon-14 test gave 306 BCE, plus or minus 65 years, and the writing points to the state of Chu around 300 BCE. Shaughnessy argues the text was already stable by then.

A silk copy from Mawangdui, found in 1973, was probably made in the 170s BCE and puts the hexagrams in a different order from the received text. Bamboo strips from Fuyang were buried in 165 BCE.

The Ten Wings are seven writings from between the 5th and 2nd centuries BCE, divided into ten parts. In 136 BCE the emperor declared the book a Confucian classic, and the core and the Wings were joined into one work in the same period.

Han dynasty scholars built an elaborate cosmology around it, matching hexagrams to the calendar. Most of their writing is lost. Wang Bi (226 to 249) wrote a commentary that later became the standard one. Zhu Xi (1130 to 1200) argued that the book's original purpose was divination and set the hexagrams apart from the Wings again.

The historian Richard J. Smith traces its influence on philosophy, religion, art, science and medicine across East Asia, and shows how Japan, Korea, Vietnam and Tibet each adapted it to local beliefs.

Jesuit missionaries brought word of the book to Europe in the 17th century, and Leibniz wrote about it. Richard Wilhelm, a theologian who had spent more than two decades in China, published a German translation in 1924 with the help of the Chinese scholar Lao Naixuan. Cary Baynes, a student of Carl Jung, based her English version of 1950 on it, and the book found a large American readership in the 1960s.

Tradition gives the trigrams and hexagrams to the mythical Fu Xi, the statements to King Wen and the Duke of Zhou in the 11th century BCE, and the Wings to Confucius. Early texts repeat parts of this tradition, and the Xici credits Fu Xi with the trigrams. No evidence from the periods named confirms any of it. The Wings are much later than the core text, and the credit to Confucius is historically shaky.

A figure of more than three thousand years is often quoted for the book's age. The oldest dated copy we found is the Shanghai manuscript of around 300 BCE, and scholarly dates for the core text cover six centuries. Older divination practice is a separate question from the age of this text.

Some details stay open. The strips of the Shanghai manuscript were scattered, so its original order is not known, and no proposed explanation of the red and black symbols in it has convinced Shaughnessy. Sources also differ on the year the core and the Wings were combined. The Stanford entry gives both 135 and 125 BCE.