By Grandmaster Shou-Yu Liang and Master Wen-Ching Wu
Ancient Chinese philosophers believed that everything in the universe was interrelated. Everything in the universe has an opposing, yet inseparable counterpart. The counterparts are referred to as Yin and Yang. Yin-Yang is constantly changing. This is the reason for all activity in the universe. This concept of constant change became an approach to understand the laws of nature. The basic theory of Yin-Yang can be summed up briefly as: Yin-Yang Opposition (Yin-Yang Duili), Yin-Yang Interdependence (Yin-Yang Hugen), Yin-Yang Decreasing and Increasing (Yin-Yang Xiaozhang), and Yin-Yang Transformation (Yin-Yang Zhuanhua).
Yin-Yang Opposition explains that within all things in nature, there are opposing, but coexisting characteristics of Yin and Yang. For example, the sky in Yang and the earth is Yin; man is Yang and woman is Yin; fire is Yang and water is Yin. However, keep in mind that the terms: Yin and Yang, are abstract and relative; not absolute. Under specific conditions, the Yin and Yang characteristics may change and within the Yin or Yang, there are subdivisions of Yin and Yang.
Yin-Yang Interdependence refers to the interdependent characteristic of Yin-Yang. One cannot exist without the other. In distinguishing the characteristics of Yin and Yang, there needs to be a reference. This reference is the Yin or Yang counterpart. For example, when classifying a cup, the inside is Yin and the outside is Yang. If the cup doesn't have an outside (Yang), it would not be a cup and therefore would not have and inside (Yin). All Yin-Yang must coexists and depend on each other. Without one, there isn't the other.
Yin-Yang Decreasing and Increasing describes the interaction and potential exchange between Yin and Yang. The existence of Yin-Yang is not a static state. It is always changing, inter-changing potentials. It is always either Yin decreasing and Yang increasing or Yin increasing and Yang decreasing. For example, during a twenty-four hour period, the sun comes up the horizon (increase in Yang) as evening diminishes (decrease in Yin). In the afternoon, the sun begins to go down the horizon (decrease in Yang) as evening approaches (increase in Yin). Another example can be seen in the waxing and waning of the moon. This is true for everything in the universe.
Yin-Yang Transformation describes the way Yin-Yang properties change into each other. Thetransformation occurs under extreme conditions of Yin-Yang Decreasing and Increasing. For example, if you were to throw a ball straight up, the upward velocity is classified as Yang. This speed slows down as it reaches its maximum height (decreasing Yang). At the maximum height, the velocity becomes zero (extreme condition), and begins to fall (Yang velocity become Yin velocity).
There is no conclusive evidence on when and how the Yin-Yang philosophy was first introduced to the Chinese culture. Some say it is at least 5,000 years old, some recent archaeological findings suggest that the Yin-Yang concept may be over 10,000 years old, from the discovery of ancient clay pots with markings that may represent Yin-Yang. This concept was explained in detail during the Zhou Dynasty (1122-249 B.C.) when the Zhou Dynasty's Book of Changes (Zhouyi) was complied. The contents of Zhouyi consisted of two parts. The first part contains the Book of Changes (Yijing or I Ching), which is about prediction and probability. The second part, Yichuan, contains the "theoretical and philosophical" explanation of the Book of Changes. Zhouyi is the oldest and most influential book of the Chinese classics, containing information about everything from astrology, meteorology, geology, to human relationships. It used the Yin-Yang concept to explain the rules of the universe and to analyze everything in it.