The existence of the Dao 道(the Way), according to the Yizhuan 易传 (the Commentary), is something intangible. The connotation of the Dao is the law of change caused by the interaction between yin and yang. The main functions of the Dao are “to change” and “to generate”. The intangible refers to the law of change caused by the interaction between yin and yang, and the law is expressed by the divinatory symbolic system (卦爻 符号, the trigrams or hexagrams). It is through the unique permutation of yin and yang lines of a trigram or hexagram that the law of change is explained as a universal model uniting celestial, terrestrial and human laws. The symbolic system is used to express the universal nature of continual generation of life.