「誠」是儒家道德哲學裡重要的觀念之ㄧ；在春秋以前的典籍中，「誠」字多當作助詞用；到了《孟子》，「誠」已具道德的意涵；在《孟子》一書裡「誠」有作真誠、誠懇，亦有作真正、實在之意義者；孟子將「誠」與人的道德修養聯繫起來，〈離婁上〉言：「誠者，天之道也；思誠者，人之道也。至誠而不動者，未之有也；不誠，未有能動者也。」「誠」可以作為自然、社會的道德原則；而〈盡心上〉：「反身而誠，樂莫大焉。」則說明了能反躬自省，自己真誠踏實地達到「誠」，便是最大的快樂。人們通過「思誠」、「至誠」的克己自律，達到「天道」的「誠」的境界，正《中庸》所謂：「誠者，天之道也；誠之者，人之道也。誠者，不勉而中，不思而得，從容中道，聖人也。」「天之道」的「誠」是「真實無妄」的善道，而「人之道」則在於瞭解天所賦與人之本心的善，並真實無妄地面對自己，通過道德修養，排除人欲之私，以藉由「誠」來貫通天人之道。本文將從：壹、「誠」的起源問題；貳、《孟子》的「誠」與「善」：所欲「明」之「善」為何？「善」的自明性、可欲性，及「善」作為價值根源的意義；參、《孟子》的「誠」與「動」：「動」、「不動」和「至誠」、「思誠」、「反身而誠」所帶來的「誠」之「動」與「善」之化所指涉的意義；肆、《孟子》的「誠」與「覺」：「思誠」、「反身而誠」與「覺」的關係；伍、《孟子》與《中庸》論「誠」的反思；以及《孟子》「誠」思想的價值等面向作一論述，並希冀從此一探究中能對《孟子》論「誠」的思想及其價值有扼要的理解。

Genuineness is one of the most important concepts in Confucian philosophy of morality. In the texts before the Spring-Autumn period, the word “cheng” was usually utilized as an auxiliary word, while in Meng-zi “cheng” already took on the meaning of morality. In Meng-zi, “cheng” means genuineness, sincerity and truthfulness. Meng-zi associated “cheng” with the moral cultivation of human beings. On the one hand, “cheng” could be taken as the moral principle of nature and society; on the other hand, it is the greatest happiness to reflect on oneself and achieve “cheng” sincerely. Through the discipline of “thinking about cheng” and “complete cheng,” one can reach the realm of the “heavenly way” and “cheng.” In The Doctrine of the Mean, the “heavenly way” is “genuineness” and “truthfulness,” and the “human way” is to understand the inherent good that one is bestowed by the heaven, face oneself truthfully and eliminate the selfish desire through moral cultivation, so as to understand thoroughly through “genuineness the heavenly way and the human way.” This paper is to understand concisely the thought and value of “genuineness” in Meng-zi through the following sections: first, the origin of “genuineness”; second, “genuineness” and “good” in Meng-zi; third, “genuineness” and “dynamics” in Meng-zi; fourth, “genuineness” and “jue” (feeling) in Meng-zi; fifth, the reflection of Meng-zi and The Doctrine of the Mean on “genuineness”; and finally an statement on the value of “genuineness” from Meng-zi.