 Although these names belong to the vocabulary of the "Book of Changes", in the "Cantong qi" they denote formless principles that serve to explicate how the Dao generates the world and manifests itself in it.The corresponding trigrams (Qian ☰, Kun ☷, Kan ☵, Li ☲) and hexagrams (Qian ䷀, Kun ䷁, Kan ䷜, Li ䷝) are symbolic forms used to represent those principles.Qian is the active ("creative") principle, essence, Yang, and Heaven; Kun is the passive ("receptive") principle, substance, Yin, and Earth.