Tao, Sunny Side Up
In Chinese philosophy, the concept of yin-yang (simplified Chinese: 阴阳; traditional Chinese: 陰陽; pinyin: yīnyáng), which is often referred to in the West as "yin and yang", literally meaning "shadow and light", is used to describe how polar opposites or seemingly contrary forces are interconnected and interdependent in the natural world, and how they give rise to each other in turn in relation to each other. The concept lies at the origins 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 (t'ai chi), and qigong (Chi Kung) and of I Ching. Many natural dualities—e.g., dark and light, female and male, low and high, cold and hot, water and fire, earth and air—are thought of as manifestations of yin and yang (respectively).
Yin and yang are not opposing forces (dualities), but complementary forces, unseen (hidden, feminine) and seen (manifest, masculine), that interact to form a greater whole, as part of a dynamic system. Everything has both yin and yang aspects as light could not be understood if darkness didn't exist, and shadow cannot exist without light. Either of these aspects may manifest more strongly in a particular object depending on the criterion of the observation. 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 evil and good. However, in Daoist metaphysics, good/bad distinctions and other dichotomous moral judgments are perceptual and not real, and yin-yang is an indivisible whole. In the ethics of Confucianism on the other hand, most notably in the philosophy of Dong Zhongshu, (c. 2nd century BCE) a moral dimension is attached to the idea of yin and yang.