《孟子•盡心上》首章所言：「盡其心者，知其性也。知其性，則知天矣。」提綱挈領地說明了「心」、「性」、「天」三者之關係，然而也正因為該章語彙之精簡扼要，故亦同時造成了理學家詮釋上之分歧。故本文擬就此方向著手，從語法學的角度作一嘗試，以便對此文句之詮釋提供另一視角，冀望有助於該語義理上之討論。 文中首先就關係詞「則」字展開討論，提出了若分別依語法學中之「順遞關係」與「假設關係」之理解，則可以發現其中之差異處在於：若以順遞關係解之，則「知性」與「知天」之關係較以假設關係解之者直截，而沒有分成兩截立說。至於「者」字，則由於「盡其心」是帶有實踐意味的，故其背後所隱涵之實踐主體「人」無法被忽略，因此學者多以為「盡其心者」即是「盡其本心之人」。 其次，對於語氣詞「也」與「矣」字之討論，則是透過學者之分析，提出了以下看法：「盡其心者，知其性也」、「知其性，則知天矣」有可能皆重於靜態之判斷，兩並列語間應為本然之關係。 最後，再透過朱子之註解此語，試著理解何以朱子認為此語中之關係不僅不是「順遞關係」，而是順序相反的「假設關係」，即先經由知性、知天，而後始能言盡其心。希望藉由本文之討論，能從分析思想家對於古漢語的理解模式出發，進而提出由另一視角探索理學家如何詮釋經典之可能。

Mencious said: "If one makes the fullest use of his 'Xin' (mind, 心), he can understand his own 'Xing' (nature, 性). When he understand his own 'Xing', he thereby knows the will of 'Tian' (heaven, 天)." These two sentences were wrote at the beginning of Chapter 13 of "The Discourses of Mencious", which could help us to concentrate on the main points about the relation among "Xin", "Xing" and "Tian". Scholars who study in "Neo-Confucian", however, always have different interpretation of these sentences. One of the reasons might be the brief and concise of classical Chinese. From the perspective of grammar, we try to analyze these two sentences in the other way. First, according to the discussion on the conjunction "Ze" (則)，we can realize the second sentence as a conditional or a hypothetical clause. Through the analysis in the text, we might understand the relation between "understand his own 'Xing'" and "knows the will of 'Tian'" more clearly. Second, analyzing the auxiliary "Zhe" (者), "Ye" (也) and "Yi" (矣), could also help us realize the true meaning of these two sentences. Finally, after the discussion from the perspective of grammar, we try to realize the annotations of "The Discourses of Mencious" from Zhu Xi, and figure out his interpretation of Confucian Classics. After all of these analysis, we might have a new vision of the hermeneutics.