 A key feature of Neo-Confucian philosophical discussions of ghosts and spirits is their naturalistic metaphysical character. Rather than purporting to describe particular spirits, many Neo-Confucians, following Cheng Yi, explained ghosts and spirits as “traces of the creative transformations of the world.” More specifically, Neo-Confucians often interpreted what appeared to be ghosts and spirits as “the spontaneous activities of the two generative forces,” yin and yang. As yin and yang expanded and contracted, spiritual forces purportedly emerged with yang, and ghostly forces with yin.