The five elements refer to wood, fire, earth, metal, and water and their motions. The five element theory resulted from the observations and studies of the natural world by the ancient Chinese people in the course of their lives and productive labor. Since ancient time, wood, fire, earth, metal and water have been considered as basic substances to constitute the universe and they are also indispensable for life. Zuo’s Interpretation of the Spring and Autumn Annals (Zuo Zhuan) says:” The five kinds of materials in nature are all used by people. None of them cannot be dispensed with”. Another classical work Shang shu states: “water and fire are used for cooking, metal and wood are used for cultivating and earth gives birth to all things, which are used by people.” These five kinds of substances are of the relationships of generation and restriction and are in constant motion and change. In TCM the five-element theory, as a theoretical tool, is used to explain and expound different kinds of medical problems by analogizing and deducing their properties and interrelations. It also used to guide clinical diagnosis and treatment. The theory, like the theory of yin-yang, has become an important component of the theoretical system of TCM.

Classification of Things in Light of the Five-Element Theory.

In ancient China, the five-element theory was unceasingly developed and gradually became perfected. In time it came to recognize that everything in nature might be respectively attributed to one of the five elements. For instance, wood has the nature of growing freely and unfolding. So, anything that is similar to the characteristics is attributed to the category of wood. Fire has the nature of flaring up. Thereby the things similar to the nature of fire are classified into the attribute of fire. Earth has the nature of giving birth to all things. Thus, those that possess the nature of earth are attributed to earth. Metal has the nature of purifying and descending. Hence, those with the nature of metal can be attributed to metal category. Water has the nature of moistening and flowing downwards. For this reason, the things that have moistening, downward movement and coldness correspond to water. The following table shows the classification of partial things according to the five-element theory.(See Tab. 1)

Among the five-elements, there exist the relationships of generation, restriction, subjugation and counterrestriction, and mutual affection between mother-organ and child-organ. Generation implies that one kind of thing can promote, aid or bring forth another, i. e., wood generates fire, fire generates earth, earth generates metal, metal generates water, and water, in turn, generates wood. Each of the five elements contains the dual nature -”being generated” and “generating”. This relationship of the five elements is called the “mother-child” relationship. The element that generates is called the “mother”, while the element that is generated is called the “child”. Take wood for example, because wood produces fire, it is the mother of fire; but it is produced by water, so it’s water’s child.

Tab. 1 the Classification of Things According to the Five Elements

Restriction means bringing under control or restraint.The order of restriction goes as follows: wood restricts earth, earth does water, water does fire, fire does metal, and metal, in turn, does wood. Any one of the five elements has two aspects-being restricted and restricting. For example, the element restricting wood is metal, and the element that is restricted by wood is earth.
Generation and restriction have the correlations inseparable in the five elements.And they oppose each other and yet also complement each other.Without generation,there would be no growth and development of things;without interrestriction there would be no balance and coordination during development and change,and excessive growth would bring about harm.For example,on the one hand,wood generates fire,and,on the other hand,it restrains earth;while earth, in turn,generates metal and restricts water.Precisely because generation resides in restriction and restriction resides in generation,the natural world and life processes are full of vitality,on the one hand and excessive growth will not bring about harm on the other hand.Thus,the relative balance maintained between generation and restriction ensures normal growth and development of things.

That is, ecological equilibrium in nature and physiological balance in the human body result from such relationships of generation and restriction. These relationships are illustrated in the following figure.

Fig. 2 Relationship of generation and restriction (or subjugation) of the Five Elements

However, once any one of the five elements becomes excessive or insufficient, there would appear abnormal intergeneration and counter-restriction known as subjugation and counter-restriction (or reverse restriction). By subjugation is meant that one of the five elements overacts upon another one when the latter is weak. Therefore, it is also called “double restriction”. For instance, excessive wood may over-restrict earth, resulting in insufficiency of earth, so called wood subjugates earth. This is the abnormal manifestation of disorder of inter-restriction among things.

Counter-restriction means that the strong bulliesthe weak. It is also a morbid condition in which one element fails to restrict the other in the regular order, but in reverse order. It is clear that the order of counter-restriction is just the opposite to that of inter-restriction. For example, under normal conditions, metal should restrict wood, but in case of wood-qi excess, or metal-qi deficiency, wood will counter-restrict metal instead of being restricted by metal, which is known as “wood counter-restricts metal.” Therefore, Su Wen states :”When qi of a certain element is sufficient, it will encroach the restricted element and counter-restrict the restricting element. When qi of a certain element is insufficient, it will be subjugated by the restricting element and counter restricted by the restricted element,” This is another manifestation of the disturbance of the equilibrium between substances (see Fig. 3).

Fig. 3 Relalionship of subjugation and Counterrestriction of the Five Elements

“Affecting between mother and child” refers to abnormal intergeneration in the five elements. The generated element is considered as the child, and the generating element as the mother. Here “affecting” means having harmful influence, including both “the diseased mother-organ affecting the child-organ” and “the diseased child-organ involving the mother-organ.” The former is same as the order of intergeneration, and the latter is just the reverse order of intergeneration. For instance, normally, water generates wood, which is called “mother organ’s disorder affecting its child-organ”; but abnormally, water involves wood, which is called “child organ’s disorder involving its mother organ” when wood affects water. (See the following figure).
Fig. 4 Subjugation and Counter-restricting Among The Five Elements .

Special phrases

1.reinforcing the spleen (earth) to strengthen the lung (metal)

2.failure of water (kidney) to nourish wood (or failure of the kidney to nourish the liver)

3.five movements and six climates

4.wood tending to spread out freely

5.Depression of the liver (wood) generating fire

6.fire of the liver (wood) impairing the lung (metal)

7.fire tending to flare/flame upward

8.excessive fire impairing the lung (metal)

9.failure of fire to generate earth

10.coordination between water (kidney) and fire (heart)

11.incordination between the kidney (water) and the heart (fire)

12.”being restricted” and “restricting”