The ancient Chinese have observed that everything in existence has polar opposites or two extremities. These are interdependent and cannot exist without each other. They are interrelated and intertwined. Yet nothing is completely pure so at their extremes the opposites still contain some trace of the other. This seemingly simple yet highly complex concept is called Yin and Yang. The duality of things such as light and dark, positive and negative, high and low are just some of the physical manifestations of Yin and Yang. Both are equally important and necessary, very much unlike the concept of good and evil
where good champions all.
This Taiji symbol is the graphic depiction of Yin (black) and Yang (white), constantly in motion. Within Yin there is Yang and vice versa.
All things soft, passive, yielding, slow, cold, dark; and is associated with water, the earth, the moon, night time and femininity is what represents Yin.
On the other hand, all things hard, aggressive, focused, fast, hot, bright; and is associated with fire, the sky, the sun, daytime and masculinity is what represents Yang.
The relationship between Yin and Yang can be summarized by the following principles.
Interdependence
Both Yin and Yang exist together and are interdependent on each other. For example, darkness cannot exist without light, warmth cannot exist without cold, etc.
Ascension and Declination
Yin and Yang are in constant motion, during which there is mutual ascension and declination of both. For example, a sunrise is the gradual ascension of Yang and declination of Yin, and the transition from summer to autumn to winter is the gradual ascension of Yin and declination of Yang.
Coordination
A balance of Yin and Yang is ideal. The ascension and declination of both should occur in a controlled and coordinated manner to maintain that balance, otherwise imbalances of Yin and Yang can occur in the form of excess and deficiency which leads to obstacles and dissonance.
Transformation
By applying certain catalysts and under specific conditions, Yin and Yang can transform into the other. For example, cold water (Yin) can be boiled to transform into hot steam (Yang).
Subdivision
Within Yin and Yang there exist subdivisions of Yin and Yang. In other words, Yin and Yang can each be further divided into Greater (Yang) and Lesser (Yin). For example, daytime is representative of Yang, however a hot high-noon sun would be Greater Yang whereas a cooler evening sun would be Lesser Yang.
Presence in absence
Nothing in existence is purely Yin or Yang. Because they are constantly in motion therefore even at their extremities there can be found small traces of the other. At the height of Yang, Yin is already beginning to manifest and vice versa. For example, the middle of the night represents the extreme of Yin, but at that same moment it is already on its way toward sunrise (Yang).