 Neo-Confucians also took up the Buddhists concepts of noumena-phenomena (i-sa) and transformed it into the i-ki 理氣 (Principle and Vital Force) framework, which is then used to explicate the nature (sŏng 性) and feelings (情) of human beings. It is in Chosŏn Korea where the most advanced discussion of the relationship between the original human nature and the emotions took place in the form of the so-called “Four-Seven Debate” (see below), and it is the originator of the Four-Seven Debate, Yi Hwang 李滉 (1501–1570 pen name: T’oegye 退溪), who provides what is probably the most detailed examination of the Essence-Function paradigm in the entire East Asian tradition (Muller forthcoming). 