During 207 B.C.- 9 A.D., the early Han dynasty devoted itself to homogenizing Chinese culture and philosophy. Towards this end, thinkers of those times attempted to combine all the rival schools of thought into a single system termed as the Han synthesis.

Han philosophers concentrated specifically on the Five Classics, attempting to derive from them, especially from the I ching, or Book of Changes, the principle of the workings of the universe, which is also called Tao or Great Ultimate. Tao explains the metaphysical workings of the entire universe and is the origin of the Five Agents school of Chinese thought or the YIN -YANG. The workings of Yin and Yang and the progress of the five material agents or wu hsing can explain each and every change that takes place in the universe. It can be it related to nature, the human body, human psychology, the finer arts, historical or political changes, scientific findings or natural calamities. The principle of Yin and Yang is the foundation of the entire universe. It underlies everything in creation. It brings about the development of parenthood and is also the root and source of life and death.

Yin originally meant "shady, secret, dark, mysterious, cold.” Yang, in turn meant, "clear, bright, the sun, heat," the opposite of Yin. From these basic opposites, a complete system of opposites was elaborated. Fundamentally, where 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 Yang and Taoism Yin. Yin and Yang oppose one another in their actions; every phenomenon that occurs in the universe can be reduced to one of these opposite forces.

Where Yang stands for peace and tranquility; Yin stands for chaos and turbulence.

Yang stands for destruction; Yin, for preservation.

Yang brings about disintegration; Yin creates

Water is an embodiment of Yin; fire is an embodiment of Yang.

Each of these opposite forces has the potential to produce the other; the concept of creation occurs under the principle of Yang, the completion of the created thing occurs under Yin, and vice versa.  This production of Yin from Yang and Yang from Yin occurs cyclically and constantly, so that neither Yin nor Yang is continually predominant over the other. Every phenomenon or state, and its opposite that we experience, be it poverty and abundance, sickness and health, success and failure can be explained with reference to the transient precedence of one principle over the other. Since neither of the two, Yin or Yang dominates endlessly, which means that all conditions are subject to change into their opposites.

This cyclical nature of Yin and Yang, the opposing forces of change in the universe simply mean that every phenomenon changes to its opposite in an eternal cycle of reversal. Furthermore, since each principle produces the other, all phenomena have, within them the potential to change into the opposite state, that is, joy can change to sorrow, sickness to good health, depression to elation and so on and so forth. Also, even though the opposite may not be apparent, since one state produces the other, no phenomenon/ state is completely devoid of its opposite state.

This cyclic and opposite nature of Yin and Yang is very aptly illustrated through the Yin-Yang or the Tai-Chi symbol which is derived from the universe. This familiar symbol of Yin and Yang flowing into each other, illustrates, with interior dots, the idea that each force contains the seed of the other, so that they do not merely replace each other but actually become the other. The Yin -Yang symbol is therefore, a Chinese representation of the entire celestial phenomenon. It contains the cycle of Sun, four seasons, 24- Segment Chi, the foundation of the I-Ching and the Chinese calendar.