In Chinese thought the two great opposite but complementary forces at work in the cosmos. Yin is the female, cold, dark, passive power, yang represents masculinity, light, and warmth. Earth, rain, soft, evil, black, small, even (numbers), are yin; heaven, sunshine, hard, good, white, large, and odd are yang. The interplay of the two forces makes up chi, or the material principle governing the universe. Their balance is essential to harmony and health. The Yin/Yang School of Chinese philosophy, perhaps founded by Tsou-Yen (c.305–240 bc), is an early attempt at a cosmology, based on the opposition of yin and yang and a doctrine of Five Elements (metal, wood, water, fire, and earth), operating in ordered cycles in the production of nature and history.