 One of the many terms used in East Asian philosophical discussions to refer generally to the ideas of the Song philosophers of the Cheng-Zhu tradition and their exponents in later dynastic periods, was seirigaku (C: xinglixue), or “the school of human nature and principle.” The two words “human nature” (C: xing; J: sei) and “principle” (C: li; J: ri) were joined in part as a reflection of the Neo-Confucian identification of human nature with principle. In Japan, this position, equating human nature and principle, was affirmed by orthodox proponents of the Cheng-Zhu teachings such as Hayashi Razan and later, Yamazaki Ansai and their followers. In many respects, their accounts of human nature can be construed as an egalitarian affirmation of the commonly shared nature of all people. The grammar of most statements asserting the identity of human nature and principle support this understanding: they leave little room for doubt that orthodox Cheng-Zhu thinkers were saying that all people have the same human nature, and that that human nature is principle. To the extent that they explained the myriad differences in humanity, they did so by reference to variations in the clarity or turbidity of the generative force (ki) of particular individuals.