In antiquity, oracles were everywhere in use; the oldest among them confined themselves to the answers yes and no. This type of oracular pronouncement is likewise the basis of the Book of Changes.

"Yes" was indicated by a simple unbroken line (-), and "No" by a broken line (- -).

Yin and Yang: dualism and complementarity

Yang: Yes, masculine, light, strength , firm, heaven, creative
Yin: No, feminine, dark, weak, yielding, earth, receptvie

Thus, in the sky, morning and evening make a day by the alternation of the dark (yin) and the light (yang)

However, the need for greater differentiation seems to have been felt at an early date, and the single lines were combined in pairs:

Old Yang

Old Ying

Young Yang

Young Yin

These pictures correspond to the four seasons

To each of these combination, a third line was added.

In this way the eight trigrams came into being. These eight trigrams were conceived as images of all that happens in heaven and on earth. At the same time, they were held to be in a state of continual transition, one changing into another, just as transition from one phenomenon to another is continually taking place in the physical world. Here we have the fundamental concept of the Book of Changes. The eight trigrams are symbols standing for changing transitional states; they are images that are constantly undergoing change. Attention centers not on things in their state of being-as is chiefly the case in the Occident-but upon their movements in change. The eight trigrams therefore are not representations of things as such but of their tendencies in movement.

These eight images came to have manifold meanings. They represented certain processes in nature corresponding with their inherent character. Further, they represented a family consisting of father, mother, three sons, and three daughters, not in the mythological sense in which the Greek gods peopled Olympus, but in what might be called an abstract sense, that is, they represented not objective entities but functions.

A brief survey of these eight symbols that form the basis of the Book of Changes yields the following classification:

Name Attribute Image Family relationship
Ch'ien - the Creative strong heaven father
K'un the Receptive devoted yielding earth mother
Chên the Arousing inciting movement thunder first son
K'an the Abysmal dangerous water second son
Kên Keeping Still resting mountain third son
Sun the Gentle penetrating wind, wood first daughter
Li the Clinging light-giving fire second daughter
Tui the Joyous joyful lake third daughter

The sons represent the principle of movement in its various stages -beginning of movement, danger in movement, rest and completion of movement.

The daughters represent devotion in its various stages-gentle penetration, clarity and adaptability, and joyous tranquillity.