本文目的在探討朱子學中是否有相當於亞里斯多德的「本質」概念，這個問題涉及朱子是否運用這個概念來說明其「人性、物性同異」之辨。牟宗三與勞思光在這個問題上的看法迥異，牟宗三認為朱子學中並沒有「本質」概念，勞思光則認為朱子學中有「本質」概念。牟宗三的看法頗具爭議性，引起若干學者的批判。為釐清此爭議，筆者首先以他們對朱子「枯槁有性」說的解讀做為切入點，分析他們二人的看法，指出牟宗三對朱子學的詮釋最具效力。隨後以韓國「湖洛論爭」中的「人性、物性同異」論辯做為參照的對象，通過「人性、物性同」論者對「人性、物性異」論者的批判，指出在朱子的「理氣論」中並沒有安置「本質」概念的空間。最後，筆者指出牟宗三認為唯有將「本質」概念歸諸知識的領域，才能使其在朱子學中獲得獨立意義的看法具有合理性。

“Essence” is a critical concept in Aristotle’s philosophy. It is important to ask whether it was employed Zhu Xi’s philosophy--in his elaboration of the issue “the difference between the human nature and the thing’s nature.” As for this question, contemporary scholar Lao Sze-kwang and Mou Zong-shan reached opposite conclusions. Lao Sze-kwang confirmed that Zhu Xi had the concept of essence in his theory; whereas Mou Zong-shan denied that Zhu had it, and Mou’s remark caused some criticism. By clarifying their arguments about the Zhu Xi’s “death matters have nature”, the author argues that Mou’s interpretation is more persuasive than Lao’s. Furthermore, the author employs the Korean Confucians’ debates on “the difference of the human nature and the thing’s nature” as reference, and shows that there is no room for the concept of essence in Zhu Xi’s theory of Li-Qi. The paper concludes that only in the field of epistemology, Zhu Xi’s concept of essence has its independent meaning and reasonableness.