In Chinese philosophy, the concept of Yin and Yang, in the era of the Early China, applies to many more philosophical categories than merely the relationship between the sunny side and the shady side of the sun. A whole series of possible interactions between the Yin and Yang in life is contained in the Chinese Book of Changes, the I Ching. The philosophical theory and the origin of natural sciences of the I Ching is imbued in the Nei Ching. having absorbed and developed the essence of Book of Changes, the Nei Ching reflects the spirit of science. Under the influence of Book of Changes, as well as its idea of Yin and Yang, peculiar at the time, the Nei Ching adapts the essences of the theory of Yin and Yang. The contribution made by the Nei Ching to the development of the philosophical concepts of Yin and Yang lies in that it combines those philosophical concepts with medicine and makes this the basic theory of Chinese medicine. In the Nei Ching, the Yin and Yang theory asserts that the human body is an organic whole, and there exists an organic connection between all tissues and structures. Therefore, the Yin and Yang functions as an essential life that plays a major role of the organic interrelation, the mutual control, and the mutual assistance. Yet, at the same time, each of them can be divided into the opposite aspects of yin and yang. Yin and yang depend on each other for existence. Without yin, there would be no yang, Without yang, there would be no yin. Neither can exist in isolation. Thus the interrelation of Yin and Yang is premised on the two opposite forces and aspects as the underlying cause of all change of Yin and Yang.