The principals of Yin and Yang apply to everything from the movement of stars and planets to the most minute cellular functions of the body.
Yin controls internal surfaces, lower region and front parts, both on the body as whole and on each individual organ, while Yang governs external surface, upper regions and back parts. Yin descends, Yang ascends. Yin controls blood, Yang controls energy. Innate instincts belong to Yin, acquired skills to Yang. Eating is a nourishing Yin activity, while drinking alcohol is a depleting Yang activity. In breathing, inhalation is Yin, exhalation is Yang. In the seasons, cool autumn and cool winter belong to Yin, warm spring and hot summer belong to Yang.
The list of complements is endless; nothing exists or function except indirect conjunction with its own essential opposite, and all abnormal phenomena, from disease to thunderstorms, are caused by a critical imbalance between these two primordial forces.