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Yin originally meant "shady, secret, dark, mysterious, cold." It thus could mean the shaded, north side of a mountain or the shaded, south bank of a river.

Yang in turn meant "clear, bright, the sun, heat," the opposite of yin and so the lit, south side of a mountain or the lit, north bank of a river.

From these basic opposites, a complete system of opposites was elaborated. Yin represents everything about the world that is dark, hidden, passive, receptive, yielding, cool, soft, and feminine. Yang represents everything about the world that is illuminated, evident, active, aggressive, controlling, hot, hard, and masculine.

Everything in the world can be identified with either yin or yang. Earth is the ultimate yin object. Heaven is the ultimate yang object. Of the two basic Chinese "Ways," Confucianism is identified with the yang aspect, Taoism with the yin aspect.