 Earlier Confucian scholars lacked a sophisticated metaphysical and cosmological basis for their ethical codes, and so were motivated to “offer a cosmology that could compete with the Buddhists” (Creel 1971: 205). This would eventually lead to the development of Neo-Confucianism, which had already permeated Korea by the end of the Koryŏ dynasty (918–1392), when discussions on human nature (K. sŏng) were starting to be discussed in great detail. The Chinese scholar Han Yu (768–824) initiated the resurgence of interest in Confucianism, especially the ideas of Mencius, evident in An Inquiry on Human Nature, while at the same time rejecting Buddhism. These ideas that would make their way into Korean diatribes against Buddhism, also propelling them towards debates about human nature (SB-Chan: 452–455; SB-BB: 583–585). One of Han Yu’s disciples, Li Ao (died ca. 844), also wrote on Mencian ideas in Returning to the Nature, focusing on how to become a sage: a theme that would be developed by Koreans to a much more sophisticated degree during the Chosŏn dynasty (see Fung 1937 [1983: 413–415]). However, his writings are indebted to Buddhist ideas about the recovery of one’s inherent good nature or Buddha Nature (佛性, C. foxing, K. bulsŏng), influential at that time, although he reorients them to advocate Confucian sagehood, especially important for Korean Confucianism.