Tsou Yen (active late 4th century B.C.) was a Chinese philosopher important for developing the so-called Five Element theory, fundamental to Chinese philosophy and science.
Tsou Yen was born in Ch'i, a state in modern Shantung Province, where the Tsou family had established a reputation for scholarship early in the 4th century B.C. During this time the rulers of Ch'i had become active supporters of scholarly activities, and they established at the Ch'i capital an academy known as Chi-hsia, which was attended by hundreds of scholars from all parts of China. Tsou Yen was one of the most distinguished of these scholars and was held in particularly high esteem by the ruling family of Ch'i.
Little is known of Tsou Yen's life. He apparently became a popular figure in several of the states outside of Ch'i. He traveled to the neighboring state of Wei, where the ruler, King Hui (reigned 370-319), came out to the suburbs of the capital to greet him personally. Tsou was received with even greater respect by the minister of Chao, the Lord of P'ing-yüan, who walked at the side of his carriage and brushed the dust off his seat. In the northern state of Yen, King Chao (311-278) is said to have acted as Tsou's herald and even to have brushed the road before him. King Chao built a special palace so that he could take instruction from the great philosopher.
Tsou Yen is important primarily for his systematization of the Five Element theory, which has been one of the most influential ideas in Chinese philosophical and scientific thought. According to this theory, the dominant forces in the universe were the five elements, or agents (hsing), defined as fire, water, wood, metal, and earth. Tsou Yen conceived of these agents as operating as historical forces that govern the creation and the destruction of dynasties. He believed that each dynasty was ruled by a particular agent, which eventually would be replaced by another agent, thus creating another dynasty.
According to this theory, the dynasty of the legendary emperor Shun ruled by virtue of the element earth; the following dynasty, the Hsia, ruled by virtue of wood; the Shang, by metal; and Tsou Yen's own dynasty, the Chou, by fire. Tsou Yen combined this theory with the concepts of yin and yang. Yin, the dark and female principle, was said to alternate periodically with yang, the bright and male principle. Part of the year was governed by yin and the other part by yang.
How original Tsou Yen's theories were is not known. Similar ideas may have been circulating on the eastern seaboard of China about this time. Ch'i and Yen were the home of numerous magicians and alchemists who advocated many of the same theories as Tsou Yen. It is possible Tsou derived his system from these sources.
There is no single study of Tsou Yen in a Western language. The best summary of his life and ideas can be found in Joseph Needham, Science and Civilization in China (4 vols., 1954-1965).