The movements of "Posing as an Archer Shooting Both Left-and-Right-Handed" in Health Qigong· Ba Duan Jin are virtual and real, loose and stretch, powerful and soft, all of which embody the cultural connotation of yin-yang philosophy. Therefore, learning the knowledge of yin-yang theory and guiding the practice with the movement law of yin and yang is important for grasping the movement essentials of Health Qigong and improving the exercise effect of Health Qigong.

First, the interpretation of Yin and Yang

Yin and yang is the simple theory of the unity of opposites in ancient China, which belongs to the ancient Chinese materialism and dialectics category. The initial meaning of yin and yang refers to the distribution of sunlight, yang means facing sun and yin means being shady, which have manifested in the warm and cold of the climate, and up and down, left and right, inside and outside of the orientation, restlessness and tranquilization of motion state, etc. Ancient Chinese philosophers have recognized that the phenomena in the nature are all in the relationship of mutual opposition and interaction, therefore the concept of yin and yang has been used to explain the opposite and interdependent substances in the nature. And they also believed that the world has the material nature, and the world is the result of unity of opposites of yin and yang. For example, "Guo Yu· Zhou Yu" has observed, experienced, comprehended and generalized various phenomena in the nature with the view of yin and yang, it considered that yin and yang are not only the basic properties of the world (moving, extraverted, rising, warm and bright are generally considered as yang; and relative static, introverted, falling, cold and dark are generally considered as yin), but also are the fundamental of generation, change and development of materials in the world. Lao Tzu also said, "All things on earth face sun with shade in the back, which achieves harmony in conflict". He believed that, with the contradictory nature, everything is constituted by opposite two aspects, namely the opposite and unified yin and yang, which is the condition of mutual existence of things, and also the source of the development and change of things. And "Huang Di Nei Jing Su Wen· Yin Yang Ying Xiang Da Lun" said," Yin-yang is the law of heaven and earth, the guiding principle of all things, the source of changes, and the origination of life and death, and the House of spirits". It also said, "Clear yang corresponds to heaven and turbid yin corresponds to earth, earth qi goes upward to be cloud, and heaven qi goes downward to be rain", which means everything in the universe contains yin and yang, and the world itself is the result of unity of opposites of yin and yang.

The properties of yin and yang of things are not absolute, but relative, mainly reflecting in the following aspects: Firstly, opposite things in the nature do not stand still, but interact in the motion changes. The interaction of yin and yang is also known as mutual development of yin and yang, which is manifested as mutually opposing and constraining, interdependent and mutually promoting, waxing and waning, balance and mutual transformation of yin and yang. Under certain conditions, yin and yang can be transformed to each other, that is, extreme yin begets yang and extreme yang begets yin, and yin and yang are interdependent. Such as, day and night, sunny and rainy, hot and cold, rigid and soft of muscles, as well as the climate changes of warm heat, cool and cold in the four seasons. Secondly, there are primary and secondary status between yin and yang. When yin contains yang, yin is primary, and the substance mainly show the attribute of yin. When yang contains yin, yang is primary, and the substance mainly show the attribute of yang. Thirdly, it is the infinite divisibility of things. All things can be divided into two aspects, namely yin and yang, which can be subdivided into yin and yang. As "Su Wen· Yin-yang Li He Lun" said, "Yin and yang can be infinitely divided into yin and yang, which is countless".

Thus, yin-yang theory is the philosophy to guide understanding and analyze the properties of things, as well as deduce the formation, development and change of things for ancient Chinese philosophers.

（By Cui Jian）