In Chinese thought, the Yin and Yang are counterbalancing forces. Beginning in the early 4th century BC, Chinese philosophers defined Yin and Yang in their books. They stated that Yin and Yang combine in various proportions to produce all the objects in the universe. Everything in the world is identified with either Yin or Yang. Earth is the ultimate Yin object. Heaven is the ultimate Yang object.
The characteristics of Yin cannot exist without those of yang, or the characteristics of yang without yin. Chinese philosophers stressed the importance of balance between the two to ensure social and political harmony. All problems and catastrophes are caused by an imbalance of Yin and Yang. Restoring harmony in relationship to Yin and Yang is important in Chinese lives.
Yin signifies murky, dark, the moon, cold. It thus could mean the shaded, north side of a mountain or the shaded, south bank of a river. Yin represents everything about the world that is dark, hidden, passive, mild, cool, soft and feminine.
Yang in turn signifies, clear, bright, the sun, heat, or the opposite of Yin. Thus the bright, south side of a mountain or the bright, north bank of a river is Yang. Yang represents everything about the world that is illuminated, evident, positive, aggressive, hot, hard and masculine.