the concept of yin-yang reveals two propositions that explain the nature of Tao. First, everything is constantly changing. And, secondly, opposites complement each other. The pure yang substance manifests in the sky; the muddy yin substance transforms into the earth... The sky is the yang substance, and the earth is the yin substance. The sun is yang substance and the moon is yin substance... Yin substance is stillness and yang substance is mobility. The yang substance gives birth, and the yin substance nurtures. The yang substance transforms the breath-qi, and the yin substance forms the bodily form. The purpose of human existence is the balance and harmony of opposites. There can be no "fi...