五行（wǔ xíng）包括：金(jīn)、木(mù)、水(shuǐ)、火(huǒ)、土

(tǔ) 及其运动。

 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.These five kinds of substances are of the relationships of generation and restriction (相生相克：xiāng shēng xiāng kè) and are in constant motion and change.

 

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. 

 

  Among the five-elements, there exist the relationships of generation and retriction. 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.  

（木生火、火生土、土生金、金生水、水生木）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. 

（木克土、土克水、水克火、火克金、金克木）

 

Generation and restriction have the correlations inseparable in the five elements.And they oppose each other （相互对立: xiāng hù duì lì）and yet also complement each other（相互补充: xiāng hù bǔ chong）.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.Thus,the relative balance maintained between generation and restriction ensures normal growth and development of things.