The concept of Yin and Yang
The concept of Yin and Yang: a living principle for a living body
Yin and Yang are not merely abstract philosophical categories. They form a practical framework through which Traditional Chinese Medicine interprets reality. The Su Wen expresses the central principle clearly: everything can be analysed through the opposites of Yin and Yang, yet neither is absolute. Everything changes continuously within the enduring framework of the Yin-Yang relationship.
Relational, not absolute
The most fundamental characteristic of Yin and Yang is their relational nature. Nothing is absolutely Yin or absolutely Yang; everything is Yin or Yang in relation to something else. A useful example is climate: Barcelona is Yang compared with Stockholm because it is warmer, yet Yin compared with Algiers because it is cooler. The same phenomenon may therefore be Yin and Yang depending on the point of reference.
In clinical TCM this means that a symptom or condition should not be evaluated in isolation. It is interpreted in relation to the rest of the body, the patient's constitution and the clinical context. Yin-Yang analysis is always contextual.
The qualities of Yin and Yang
Although Yin and Yang are relative, they are associated with recognisable groups of qualities. Yin is associated with inwardness, darkness, stillness, cold, materiality and downward movement — earth, moon, mist, water, night and winter. Yang is associated with expansion, brightness, activity, warmth, function and upward movement — heaven, sun, light, fire, day and summer.
Within the human body, upper regions are relatively Yang and lower regions Yin; the exterior is Yang and the interior Yin; the back is Yang and the front Yin; function is Yang and structure Yin; Qi is relatively Yang, while Blood and Body Fluids are relatively Yin.
The symbol: movement within a circle
The familiar Yin-Yang symbol, the taijitu, represents a dynamic cycle rather than a static division. As Yang reaches fullness, Yin gradually begins to grow. As Yin reaches its maximum, Yang begins to return. The small circle of the opposite colour within each half symbolises that the seed of the opposite is always present. There is therefore never completely isolated Yin or Yang.
The emperor and the directions
In ancient China the Yin-Yang principle was also applied spatially. During ceremonies the emperor traditionally faced south, the direction associated with the sun and Yang. North behind him was Yin; east to the left was associated with Yang because the sun rises there, while west to the right was associated with Yin because the sun sets there. This spatial symbolism expressed the idea that human order should reflect the broader order of nature.