I Ching: TCM Concept Guide

Name and origins

The I Ching (Yijing), also called the Book of Changes or Zhou Yi, is one of the oldest Chinese classics and the best known of the Five Classics. The character yi means change. A traditional reading, associated with Zheng Xuan, holds that the world is simple in its givenness, always in motion, and yet stable in the long run.

History

Shang and Zhou rulers used tortoise shell and animal bone for divination. After a reading, scribes carved the date, the names of those present, the question and the result onto the shell. The questions ranged from state affairs to sacrifice, weather, war, illness and travel. The verdict, auspicious or not, was meant to guide what people did next.

Later tradition assigns the eight trigrams to Fu Xi, their expansion to 64 hexagrams to Yu of Xia, and an early arrangement in the Gui Cang with Kun first. King Wu of Zhou overthrew Shang; his brother, the Duke of Zhou, is credited with the line statements (yao ci) that explain each line of a hexagram. By about 256 BCE the sequence often began with Qian. The Yi Zhuan commentaries, long linked with Con***ius, helped the text travel under the name Zhou Yi.

After 1279, scholars grouped three related traditions, Lian Shan, Gui Cang and Zhou Yi, and spoke of li (pattern), xiang (image) and shu (number). A tomb text from the second century BCE is often cited as evidence that the Zhou-period core was already in use.

Structure

A common schematic runs like this: taiji gives rise to the two modes (liang yi), those to the four images (si xiang), and those to the eight trigrams, which then pair into 64 hexagrams.

Wuji is treated as the undivided one; taiji as yin and yang, the two modes; the four images as greater yang, lesser yang, lesser yin and greater yin. Each hexagram is six lines (yao), stacked from the bottom, each line yin or yang. A hexagram is two three-line trigrams (gua).

Yin and yang in the text

Yin-yang is the core idea of the I Ching: paired opposites that replace and complete each other. In nature, yang is linked with sky, sun, heat and brightness, and yin with earth, moon, cold and dark. In the social language of the classic, yang was tied to ruler and gentleman and yin to commoner, a historical usage rather than a medical rule. The same polarity is used for vigorous and yielding, advance and retreat, expansion and contraction. Human life and natural events are read as having two sides.

Influence on Chinese medicine

Yin-yang in the I Ching is the background for yin-yang in TCM. Ideas of right time and right place, treating this patient rather than a generic disease, and matching a formula to a cause all sit in that lineage. Terms such as midnight-noon ebb and flow (zi wu liu zhu), the eight principles and the six excesses draw on the same habit of pairing.

The Huangdi Neijing is the classic example. The Shennong Bencao Jing used trigram thinking in early drug classification. Zhang Zhongjing joined yin-yang and taiji in the six-channel framework of the Shanghan Lun, which later clinical medicine still uses.