In Chinese thought Yin-Yang represent the two great opposite but complementary forces at work in the cosmos. Yin is the female, cold, dark, passive power. Earth, rain, soft, evil, black, small, even (numbers), are yin. Yang represents masculinity, light, and warmth. 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.