 All of the cosmogonies include cycles and processes of return. One prominent model was the four seasons. The change of seasons places cycles of growth and decay into a broader context of continuous vitality. The change of seasons itself, though, was seen as expressing a more fundamental cycle between poles such as yin and yang. Cyclical change could also be theorized through the progressions of generation (sheng 生) or overcoming (ke 克) among the five phases (wuxing 五行): wood, earth, fire, air, and metal. Another version of this cycling between poles was the claim that when processes reach an extreme, they reverse. Yet another manifestation is that things emerge from a common source and ultimately return to that source. In all of these cases, cyclicality explains the sustainability and predictability of natural patterns.