"Qi" and "li" operate together in mutual dependence. They are mutually aspective in all creatures in the universe. These two aspects are manifested in the creation of substantial entities. When their activity is waxing (rapid or expansive), that is the "yang" energy mode. When their activity is waning (slow or contractive), that is the "yin" energy mode. The yang and yin phases constantly interact, each gaining and losing dominance over the other. In the process of the waxing and waning, the alternation of these fundamental vibrations, the so-called five elements (fire, water, wood, metal, and earth) evolve. Zhu Xi argues that "li" existed even before Heaven and Earth