The theory of yin and yang
The theory of yin and yang turned up in 800 B. C. It didn't contribute its due share to philosophy until the end of the period of the Warring States. The Book of Changes said, “Change comes from the applied force between softness and hardness; light comes from the applied force between softness and the moon; season comes from the transition between hotness and coldness.” It is thus evident that everything of nature grows and changes under the force of yin and yang . “Yin and yang reflects Tao ” had symbolically represented all changes in the cosmos. Scientists of later generations inherited this philosophy to expound human life and activities. Zhang Jiebin, a medical scientist of the Ming Dynasty pointed out in his Book of Categories, “Yin and yang is Tao . They are two opposite. According to taiji, yang grows in mobility and yin grows in immobility.” It proved that Chinese traditional medical science took the two complementary interactive forces as the base of human activity. In other words, even nature is the product of the interaction between yin and yang. Its theorization, composition and characteristics are all created on this basis. As far as movements and composition are concerned, both of them are linked to yin and yang that are opposite, interdependent and mutually restricting. The interaction between yang and yin can be seen everywhere—in activity and inertia, in hardness and softness, in excess and deficiency. For instance, opposite yet interdependent moves as in “Playing the Lute” in the traditional routine of Tai Chi Chuan, integrating yin and yang , echoes the application of the yin and yang theory in Tai Chi Chuan.