In ancient times, people thinking over various phenomena of nature came to a conclusion that the universe is reigned by two opposing origins. In China, this concept is referred to as “Theory of Yin – Yang”.
Yang is a male active origin, while Yin is its passive female counterpart having opposite features. Yang includes everything elevated, bright and all that relates to the surface of the things and phenomena as well as strong, mobile, light, volatile, and unpredictable like day, sky, sun, fire etc. whereas Yin includes all low, dark, thick and deep as well as weak, motionless, heavy, constant and recurring like night, earth, moon, water etc.
Everything that is below or inside is Yin, while everything that is above and outside is Yang. Thus, the feet are Yin as they are located below and touch the ground and hands are Yang as they are positioned higher and hanging in the air. The sole of the foot is Yin, while dorsal surface of foot is Yang. A line between the Yin-Yang surfaces is clear Yin-Yang Border Line. The Yin-Yang Theory provides a key to many natural phenomena, though it may not answer all the questions. For example, it does not explain the law of similarity.