The five elements refer to five categories in the natural world, namely wood, fire, earth,
metal and water. According to the theory wood, fire, earth, metal and water are the basic
substances that constitute the material world. These substances are not only of the relations
with generation and restriction but set in a state of constant motion and change for example
wood promotes fire, fire promotes earth, earth promotes metal, metal promotes water, and
water, in turn, promotes wood.