As a major founder of Contemporary Neo-Confucianism, Mou Zongsan (1909-1995) is also well-known for introducing the threefold typology of Song-Ming Neo-Confucianism. According to Mou, besides the School of Principle (li) as represented by Zhu Xi (1130-1200) and the School of Mind (xin) as represented by Lu Xiangshan (1139-1193) and Wang Yangming (1472-1529), a third lineage was formed by Hu Wufeng (1105-1162) and Liu Jishan (1578-1645). However, despite the fact that Mou’s typology has revolutionized our understanding of Chinese philosophy, thus far no one has tried to identify its possible sources. In fulfilling this gap, this paper will argue that there are some hidden sources of this provocative typology. First of all, it can be traced to the influence from the early Heidegger’s idea of the threefold transcendence (or difference) in his manuscripts for the second volume of Being and Time. Secondly, to some extent, Heidegger’s distinction of three types of ethics also contributes to Mou’s classifying of Song-Ming Neo-Confucianism. All this will not only uncover Heidegger’s decisive influence upon Mou other than his appreciation of Heidegger’s interpretation of Kant’s schematism, but also give rise to a deeper understanding of the distinction between the early and the later Zhu. Besides, in terms of Liu’s appreciation of Zhu’s early affinity to Hu Wufeng’s school, one can counterbalance the thesis that the de facto lack of Liu’s reference to Hu implies the elimination of any de jere connection between their doctrines. Given the recent challenges raised by different scholars, in terms of this clarification of its origins one can develop a new defense of Mou’s typology.