Analysis of information sources in references of the Wikipedia article "Yōkai" in English language version.
[...] although it is tempting to think in terms of a simple opposition - kami good and yōkai bad - the line between the two is blurry. Yanagita Kunio, the father of folkloristics in Japan, suggested that yōkai are kami that have 'degraded' over time, an idea that suggests an intimate relationship between the two. [...] Folklorist-anthropologist Komatsu Kazuhiko has suggested that yōkai are 'unworshipped' kami and kami are 'worshipped' yokai. [...] Both kami and yōkai reflect a way of thinking often called animistic, meaning that the things in the world around us - rocks, rivers, even musical instruments - can possess animating forces or spirits. Within such an animistic world, we can imagine a continuum. On one end, where yōkai cluster, we have everything that seems troublesome, undesirable, unworshipped. The other end contains helpful, desirable, and worshipped things - generally called kami. But these are extremes, and any individual entity can move along this continuum. If a 'bad' yōkai does something 'good,' we might consider it a kami, and vice versa.
