Interdependence between Yin and Yang

Yin and Yang are opposed to and yet, at the same time, depend on each other. Neither can exist in isolation without its opponent's existence. In other words, without Yin there would be no Yang, and it's the same the other way round.

So either Yin or Yang is the prerequisite for the other`s existence. And this kind of coexistent relationship is stated in TCM, "solitary Yin or Yang failing to live". This interdependence is also reflected in the relationship between substances and functions. The substance corresponds to Yin and the function, to Yang.

The function is the result of material motion, and nothing in the world is not in a state of motion. Thereby, there is not any substance which can't produce its function and there is also not any function which doesn't originate from the motion of its substance. Therefore, Neijing says: "Yin in the interior is the basis for Yang; while Yang in the exterior is the activity for Yin".

"Yin" refers to the material, basis of functional activity of Yang and "Yang" refers to functional activity. The substance and function are interdependent and inseparable. Here is just an imaginable and vivid figure of speech. However, when the interdependent relationships between substances, between functions as well as between substances and functions are abnormal, life activities will be broken, thus bringing about dissociation of Yin and Yang, depletion of essence-qi and even an end of one's life.

Yin and Yang always coexist in a dynamic equilibrium in which one waxes while the other wanes. In other words, waning of Yin will lead to waxing of Yang and vice versa. Take the seasonal and climatic variations as an example; it gets warm from winter to spring, and hot from spring to summer.

This is the process of "Yang waxing and Yin waning," Conversely, it gets cool from summer to autumn, and cold from autumn to winter-the process known as "Yin waxing and Yang waning". Under normal conditions, the waning-waxing relation of Yin and Yang is in a state of relative balance. If this relation goes beyond normal limits, the relative balance of Yin and Yang will not be maintained, thus also resulting in either excess or deficiency of Yin or Yang and the occurrence of disease, so far as to endanger one's life.