
The Chinese observed that everywhere in nature there is dynamic interchange. The seed (Yin) grows into the plant(Yang),which itself dies back into the earth (Yin). This takes place within the changes of the seasons-Winter (Yin) transforms through the Spring into Summer (Yang), which in turn transforms through the Fall into Winter again. The Chinese medical system draws extensively on these metaphors. This is most fully articulated in the system of the "Five Elements" or "Five phases" : water,fire,wood,metal,and earth.
The characteristics described here are merely examplars of how the elements can be seen,but the important feature is that they will all contain both Yin and Yang aspects,thus reflecting the underlying principle of mutually interactive duality, so central to Chinese thought.
Each Element is seen as having a series of correspondences relating both to the natural world and to the human body . Fire, for example, corresponds to Heat and to The Heart. A pattern of interrelationships between the Five Elements is used as a model for the way in which the processes of the body support each other. These are defined mainly through the Sheng and Ke cycles.