In ancient Greece, there was a theory of four elements. The four elements include fire, water, earth and air. A Greek philosopher Anaximander developed this theory, and he thought that a kind of original substance formed the four elements. At the same time, in ancient China, there was a theory of five elements. The five elements include wood (木), fire (火), earth (土), metal (金) and water (水). They were formed by a kind of original substance which was called Qi (气). In the Warring-States Period, Zou Yan (邹衍), a thinker of the Qi (齐) State, developed the theory of the five elements. He connected the theory of the five elements with the theory of Yin (阴) and Yang (阳), and founded the doctrine of the Yin-Yang and Five Elements (阴阳五行). Zou Yan gave a forced interpretation to this doctrine and used it to explain the events of the society and prophesy the future. Qin First-Emperor (秦始皇) accepted this doctrine, because he needed it to justify his imperial reign. Except political use and philosophical use, the theory of the five elements was also used widely by the traditional Chinese medical science.
Five elements are correlative. The relations of the five elements include promotion (生) and restraint (克). The wood promotes the fire, the fire promotes the earth, the earth promotes the metal, and the metal promotes the water. Why? The wood can be burning and become the fire, and the ash formed the earth. In the earth, there are mineral resources of the metal. The metal can melt and become liquid as the water.
As for the relations of restraint, the wood restrains the earth, the fire restrains the metal, the earth restrains the water, the metal restrains the wood, and the water restrains the fire. Why? A sprout breaks through the earth and becomes a big tree. A hoe or a spade has a wooden handle. The fire can melt the metal. The earth can be used for embanking rivers against floods. An ax or a saw has a metal blade. The water can extinguish the fire.
Five elements are abstracted to five attributes of many things such as seasons, climate, directions, colors, internal organs and taste so on. Spring, wind, east, green, liver and sour belong to wood. Summer, hotness, south, red, heart and bitter belong to fire. Autumn, dryness, west, white, lung and piquancy belong to metal. Winter, coldness, north, black, kidney and salt taste belong to water. Center, wetness, yellow, spleen and sweet belong to earth. The sixth month of the Chinese Lunar Calendar belongs to earth. In the Pre-Qin Era, heart belonged to earth. However, in the Han Dynasty, heart started to belong to fire because of political need. Since the Han Dynasty, the theory of five elements had been steady.
The theory of five elements is used for diagnosis, therapy and pharmacy of the traditional Chinese medical science. For example, the face of a patient who has a nephropathy is a little black. Recent years, an herb Guanmutong (关木通, Caulis Aristolochiae Manshuriensis) has been forbidden, because the excessive dose of this herb is nephrotoxic and even induces acute renal failure. The faces of the patients whose kidneys are damaged by Guanmutong are a bit dark.
The theory of five elements is very deep, and this article only can show some basic contents of it. In ancient times, the theory of five elements was used too widely. If a person couldn’t explain a thing or a phenomenon, he would easily attribute it to the movement of five elements. This kind of attitude seriously hampered the development of ancient Chinese science. Since the early days of the 20th century, many scholars started to be against the theory of five elements. Nowadays, the theory of five elements is only used by the traditional Chinese medical science, because leastways it is helpful and effectual in the traditional Chinese medical science. So we should treat it rightly.