Based on observations of nature, ancient Chinese people recognized patterns of transformation and change in the universe. Initially, these observations were interpreted using yin yang logic, but later these interpretations were expanded using a theory called the five phases. The five phases theory evolved from the study of various processes, functions, and phenomena of nature. The theory asserts substances can be divided into one of five basic phases: wood, fire, water, metal and earth, which contain their own specific characteristics and properties. Today, the five phases theory is still used as a tool for grouping objects, and as a method for analyzing changes of natural phenomena.

The key thing to keep in mind with the Chinese medical application of the five phases is that it is only a model, and it is known to have exceptions.

Within five phase theory there are four main relationships or ways in which the phases interact. The first of these is the generating (sheng, mother-child) cycle. This cycle describes the ways in which each phase, serving as a mother, promotes the growth and development of the following child phase.

Examples of this cycle are the Wood phase providing the generative force for Fire, Fire providing the generative force for Earth, etc. This relationship provides the foundation for understanding five phase theory and, consequently, where imbalances may arise within the cycle. If Earth, for example, is weakened from a poor diet and overwork you will see that more nourishment is requested from the Fire phase to nourish Earth. Additionally, if Earth is weakened the Metal phase may also be effected.

From a clinical perspective you may see people develop digestive issues from irregular eating, excessive worry and overwork which leads to a proliferation of dampness which then effects the Metal phase. Within this case you may see a combination of bloating, gas and poor energy with the development of Metal (Lung) symptoms such as sinusitis or phlegm-type asthma.

The controlling (ke, grandparent-grandchild) cycle provides for a check and balance system among all of the phases. Within this cycle Earth, for example, provides a control for Water and is controlled by Wood. An example of this relationship within the body is in cases of anxiety (Fire) which are related to LV Qi Stagnation (Wood) where, over time, you begin to see more Kidney (Water) related signs as the Water phase attempts to control the overactive Fire.

The overacting cycle (cheng) is an imbalance within the controlling cycle where the grandmother phase provides too much control over the grandchild and weakens the phase. Within nature you may see Water putting out Fire, Earth soaking up Water and so on.

A clinical example of this relationship would be Liver (Wood) overacting on the Spleen (Earth). In this case you have an overactive Wood phase over controlling Earth leading to disruptions in the digestive system.

The insulting cycle (wu) is also an imbalance within the controlling cycle where the grandchild insults or returns the controlling force generated by the grandmother. Using examples from nature you can see Fire burning up Water and Water washing away Earth and so on.

Clinically you may see this in cases where people have long-term psychological problems (Fire) which eventually effect the Kidneys (Water) as seen in the development of more Yin (Water) deficiency signs.