Essence-Function (體用) is a key concept in Korean Buddhism. The Awakening of Mahayana Faith, attributed to Aśvaghoṣa (?80-?150 CE), employs Essence-Function. Essence-Function forms a fundamental syncretic and ecumenical application in the philosophy of Wonhyo (617–686 CE). Chinul (1158–1210) and Kihwa (1376–1433) also employ and develop this idea of Essence-Function in their writings in particular ways. Wonch'uk (613–696) employed the conceptual and analytical tool, Essence-Function, as an exegetical, hermeneutical and syncretic device.
A. Charles Muller is one of the first scholars to open the discourse of Essence-Function in English.