Since everything in the life can be classified according to its Yin and Yang components, it is said:
“Now the Yin/Yang has a name but no form. Thus it can be extended from one to ten, from ten to a hundred, from a hundred to a thousand, from a thousand to ten thousand (i.e. it can embrace all things).” – Ling Shu (Spiritual Pivot)
Each component not only opposes but also contains its opposite, for:
“There is Yin within the Yin and Yang within the Yang. From dawn till noon the Yang of the Heaven is the Yang within the Yang; from noon till dusk the Yang of heaven is the Yin within the Yang; from dusk till midnight the Yin of heaven is the Yin within the Yin; from midnight till dawn the Yin of heaven is the Yang within the Yin.” – Su Wen (Plain Questions)
Thus ”functional movement” belongs to Yang, ”nourishing substance” to Yin, nor can the one exist without the other; for, if the intestines and other internal organs do not move, ”nourishing substances” can not be digested and, if over a long period ”nourishing substances” are not provided, the organs cease to move.
“yin in the interior is the guardian of Yang; Yang in the exterior is the activator of Yin.” – Su Wen (Plain Questions)
The opposition of Yin and Yang is not static; it is a perpetually changing rhythm of movement, whose interplay produces growth, transformation and death.
“The relation of Yin and Yang is the means whereby the myriad things are able to come to birth, Yin and Yang react upon each other, producing change”. – Su Wen (Plain Questions)
This changing rhythm in the balance of Yin and Yang ensures that there is never an excess of either of these polar opposites, for overactivity of Yang is a once adjusted by the yielding passivity of Yin.\
“In winter on the 45th day (the beginning of spring) the Yang Qi is slightly superior and the Yin Qi slightly inferior; in summer on the 45th day (the beginning of autumn) the Yin Qi is slightly superior, the Yang Qi slightly inferior”. – Su Wen (Plain Questions)
In the former case, Yang Qi waxed with the upsurge of spring as Yin Qi Waned; in the latter, Yin Qi waxed with the decline to winter as Yang Qi waned.
”When speaking of Yin and Ynag, the exterior is Yang, the interior is Yin; when speaking of Yin and Yang in the human body, the back is Yang, the abdomen is Yin; when speaking of Yin and Yang of the Zang and Fu in the body, then the Zang are Yin, the Fu are Yang; liver, heart, spleen, lungs and kidneys are all Yin, the gall bladder, stomach, large intestine, small intestine, bladder and triple warmer are all Yang.”
Thus the back is Yang and the Yang within the Yang is the heart.
The back is Yang and the Yin within the Yang is the lungs.
The abdomen is Yin and the Yin within the Yin is the kidneys.
The abdomen is Yin and Yang within the Yin is the liver.
The abdomen is Yin and the extreme Yin within the Yin is the spleen” – Su Wen (Plain Questions)
If this balance of Yin and Yang is upset there is a reaction:
“Excess of Yin causes a Yang disease, excess of Yang a Yin disease. Yang in excess produces heat and Yin in excess produces cold; If the heat is extreme, it will produce cold; and if the cold is extreme, it will produce heat.” – Su Wen (Plain Questions)