To understand and describe the universe the ancient Chinese used the Yin-Yang and Five Element theories to describe everything in the cosmos. The five elements are Wood, Fire, Earth, Metal and Water.

The basic theory behind the five elements can be summed up by two normal and three adverse interactions. Mutual nourishment and mutual restraint are normal cyclic patterns. Mutual over-restraint, reverse-restraint and mutual burdening are the adverse conditions. By understanding the cyclic patterns in the human organs (elements) and the possible adverse conditions, the illness of one organ can also indicate problems in the corresponding organs.

Mutual nourishment refers to the cyclic enhancement of the five elements. In this normal cycle each element gives and receives nourishment in order to keep each other in check and balance. Mutual nourishment and restraint cycles are not independent, they interact with each other and are closely related.

The inner arrows display the mutual restraint cycle and the outer ones the mutual nourishment cycle.