Yin and yang

Taoists affirm yin and yang, the two complementary and interdependent principles whose interplay constitutes and moves all things. Yin is the receptive, dark, yielding, and cool; yang the active, bright, firm, and warm; neither is good or evil, and each contains the seed of the other, as the familiar diagram shows. All phenomena arise from their alternation and balance, and health, harmony, and the right ordering of life consist in their proper proportion rather than in the triumph of one over the other.

Yin and yang predate organized Taoism as a systematic concept: the terms appear in early form in the I Ching, the Book of Changes, and were developed into a more elaborate cosmological system during the Warring States period by thinkers associated with the Yin-Yang school, traditionally linked to the philosopher Zou Yan in the fourth and third centuries BCE, who combined the paired forces with the theory of the Five Phases (wood, fire, earth, metal, water) to explain cosmic and historical change. Taoism absorbed and integrated this already-developed cosmological vocabulary rather than originating it, one reason yin-yang thought pervades traditional Chinese medicine and Confucian cosmology as much as it does specifically Taoist philosophy.

Yin and yang give Taoism (and Chinese thought more broadly) a way of understanding change as the ceaseless, cyclical interaction of paired forces flowing from the Tao. The concept underlies Taoist cosmology, medicine, alchemy, and self-cultivation, and it is shared across the Taoist schools, including the Zhengyi, Quanzhen, and Shangqing traditions. Its vision of a world made of complementary rather than warring opposites contrasts with dualisms of good against evil, and it connects to the Taoist ideal of harmony and to the practice of wu wei, action attuned to the balance of forces.

The now-ubiquitous circular black-and-white taijitu symbol is considerably later than the concept itself: its familiar form is generally traced by scholars to Song dynasty Neo-Confucian diagrams, particularly Zhou Dunyi's eleventh-century Taijitu Shuo, an explanatory treatise on a cosmological diagram illustrating the generation of yin and yang from the Supreme Ultimate (taiji), rather than to any ancient Taoist or Zhou-era source. The popular assumption that the graphic symbol itself is of great antiquity is a common misconception historians of Chinese philosophy have worked to correct, even though the underlying paired concept of yin and yang it depicts is genuinely ancient.