 Another novel area of philosophical speculation was that related to spiritual forces. Confucius said little about them, other than that people’s proper concern should be how to live in the world of humanity. Yet following the Buddhist discourses on the afterlife, rebirth, and various heavens and hells, Neo-Confucians were compelled to articulate various understandings of the spirit world. One of the more commonly accepted positions defined ghosts and spirits (C: guishen; J: kishin) in terms of the spontaneous activities of yin and yang in the world. Without denying that there were spiritual forces, this account provided for a kind of naturalistic understanding of spiritual phenomena.