Yin cannot exist without Yang, nor can Yang exist without Yin. They depend on each other to exist. Just as we saw in the Law of Opposition, being opposite poles they need each other mutually to exist. This quality is called the interdependence of Yin and Yang.
It is not possible to rest if there was not previously a period of activity. A door only opens if it is closed. Fire only burns while there is fuel... One without the other loses the condition for its existence, Yin cannot be produced in isolation and Yang cannot grow alone. The separation of opposites is equal to death. See: disappearance of Yin and disappearance of Yang.
The organs are divided into Yin and Yang forming pairs Zang Fu. Each pair represents one of the elements of nature in the human microcosm (water, fire, wood, etc), which make up other pillar theories of Acupuncture.
- The Yin organs store life and nourish the entire body.
- The Yang organs produce the necessary energy or Qi from respiration and food.
The Yin organs need the function of the Yang organs, and the Yang organs need the nourishment of the Yin organs. Yin needs Yang and Yang needs Yin.
As for vital substances, blood belongs to Yin and energy belongs to Yang. Without the energy to propel it, blood would be motionless and could not nourish, and without blood, energy would have no material aspect, way to manifest itself and nourish the body.
Each organ, regardless of whether it is Yin or Yang, has a physical structure which is the organ in question (its Yin aspect, material) and a function (Yang aspect, energetic). For example, the Liver organ has a physical structure (Yin) which is the organ itself, but its functions encompass storing blood and ensuring the free circulation of Qi throughout the body (Yang). The correct function of an organ needs a correct state of its physical structure and vice versa.
In Traditional Chinese Medicine it is important to keep in mind the interdependence since nothing is separate from the whole. Thanks to this we can know what happens inside by observing what is outside or cause an effect above by treating below, for example.
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