In Chinese philosophy, the concept of yin yang (often referred to in the west as yin and yang) is used to describe how polar or seemingly contrary forces are interconnected and interdependent in the natural world, and how they give rise to each other in turn. The concept lies at the heart of many branches of classical Chinese science and philosophy, as well as being a primary guideline of traditional Chinese medicine, and a central principle of different forms of Chinese martial arts and exercise, such as baguazhang, taijiquan (tai chi), and qigong (Chi Kung) and of I Ching divination. Many natural dualities - e.g. dark and light, female and male, low and high, cold and hot - are thought of as manifestations of yin and yang (respectively).
Yin yang are complementary opposites within a greater whole. Everything has both yin and yang aspects, although yin or yang elements may manifest more strongly in different objects or at different times. Yin yang constantly interacts, never existing in absolute stasis. The concept of yin and yang is often symbolized by various forms of the Taijitu symbol, for which it is probably best known in western cultures.
There is a perception (especially in the West) that yin and yang correspond to good and evil. However, Taoist philosophy generally discounts good/bad distinctions as superficial labels, preferring to focus on the idea of balance. The idea that yin and yang has a moral dimension originated in the Confucian school (most notably Dong Zhongshu) around the second century BCE.