Yin and Yang

In Chinese cosmology, yin and yang are two opposite but complementary principles that regulate the functioning of the cosmos. Their repeated alternation provides the energy necessary for the cosmos to sustain itself, and their continuous joining and separation is at the origin of the rise and the disappearance of the entities and phenomena that exist within the world of the "ten thousand things" (wanwu).

According to a celebrated statement, which is found in one of the appendixes to the Book of Changes (Yijing), "one yin and one yang, this is the Dao." This sentence refers to the Dao that first determines itself as the One (or Oneness) and then through the One gives birth to the two complementary principles. As each of these stages generates the next one, yin and yang are ultimately contained within the Dao itself. At the same time, the phrase "one yin and one yang, this is the Dao" refers to the continuous alternation of yin and yang within the cosmos. When one of the two principles prevails, the other yields, but once one of them has reached the height of its development, it begins to recede; in that very moment, the other principle begins its ascent. This mode of operation is especially visible in the time cycles of the day (alternation of daytime and nighttime) and of the year (alternation of the four seasons).

The origins of these notions are impossible to ascertain. Scholars generally deem that the terms yin and yang originally denoted the shaded and sunny sides of a hill and later began to be used in an abstract sense as cosmological categories. The earliest extant text that contains a list of items arranged according to their yin and yang qualities is a manuscript found in Mawangdui entitled Designations (Cheng), likely dating from the third century B.C.E. Examples of yang and yin items, respectively, mentioned in this text include heaven and earth; above and below; day and night; summer and winter; spring and autumn; man and woman; father and child; elder brother and younger brother; ruler and minister; soldiers and laborers; speech and silence; giving and receiving; action and nonaction.

Between the third and the second centuries B.C.E., the notion of yin and yang became one of the main pillars of correlative cosmology, a feature of which is the coordination of several preexistent patterns of emblems, including, besides yin and yang, the five agents (wuxing) and the eight trigrams and sixty-four hexagrams of the Book of Changes. Each of these patterns represents a particular way of explicating the features and functioning of the cosmos. In the system of correlative cosmology, for instance, yin is related to the agents Metal (west/autumn) and Water (north/winter), while yang is related to Wood (east/spring) and Fire (south/summer), and the balance between them is represented by the central agent Soil. The association with the five agents is likely at the origin of the view that yin and yang are further subdivided into two states each: "minor yang" (Wood), "great yang" (Fire), "minor yin" (Metal), and "great yin" (Water).

The relations among the different cosmological configurations that intervene between the Dao and the "ten thousand things" are illustrated in the well-known Diagram of the Great Ultimate (Taiji tu), which was discussed at length by both Daoist and Neo-Confucian authors. This chart depicts on top the Absolute (wuji) as an empty circle. Below it is another circle that represents the Great Ultimate (taiji) as harboring the Two, or yin and yang, shown as two semicircles that mirror each other. Each of them is made of black (yin) and white (yang) lines that enclose each other to depict yin containing yang and yang containing yin. The empty circle within these lines corresponds to the empty circle on top; this alludes to the notion that yin and yang are the "function" or "operation" (yong) of Emptiness, which in turn is their "substance" or "core" (ti). Following this are the five agents, which constitute a further stage in the progressive differentiation of Oneness into multiplicity. The lines that connect them to each other show the sequence in which they are generated, namely Wood, Fire, Soil, Metal, and Water. In this cosmological configuration, the Great Ultimate is represented by the central Soil (which is said to have a "male" and a "female" aspect) and reappears as the small empty circle below, which represents the conjunction of Water and Fire ("great yin" and "great yang") and of Wood and Metal ("minor yang" and "minor yin"). The circle below the five agents represents heaven and earth or the active and passive principles that respectively give birth to and support the existence of the "ten thousand things," represented by the circle at the base of the diagram.

The notions of yin and yang have deeply affected Chinese culture as a whole. Representations of these notions are found in religion, art, and several other contexts; as part of the system of correlative cosmology, moreover, yin and yang have played a central role in traditional sciences and techniques, such as divination, medicine, and alchemy. Beyond this, the search for the balance and harmony of yin and yang has had, and continues to have, a pervasive influence on the everyday lives of Chinese people.