本文嘗試追溯中國傳統哲學概念——「誠」，在禮學上的根源。將「誠」一義所表明的天人心性主體，以一種禮學與人類學式的眼光切入，追溯至古代祭禮中的齋戒行為，並與「誠」之哲學內涵作一對應式的探討，說明從祭禮到義理轉化的軌跡。主要關鍵即於「齋戒」的儀節功能，在培養專一凝鍊的敬神意識；並齋戒的主要內涵，在天人溝通時的「齊」「定」狀態：通過變食、沐浴、防欲等儀節，求其敬慎，並修身致思。因著宗教禮儀所引導出宗教情感的落實，「齋戒」於是從致祭的形式意義轉趨於脩身、致思，進而省覺出面對鬼神、宇宙、天地時的自我定位，即能夠自「明」而「誠」，乃至由「誠」而「明」，心性誠體的意義於焉完成。

This article tries to trace the origin of the Chinese traditional philosophical concept, Cheng, as it is recorded in the ancient Book of Propriety, Li Ji. The turn from the ritual practice to philosophy is studied by reflecting on the parallel development of the meaning of Cheng, and the practice of abstinence in the ancient cult. Cheng is an attitude of respect and recollection before God; and the practice of abstinence aims at the maintenance of an attitude of Zhai Ding during the ceremony. With the completion of the ceremonies, religious sentiments become reality. People are thus moved to practice the virtues of prudence, and to Cosmos. This awareness leads to insight. From mind-nature to Cheng, from Cheng to insight, the meaning of mind-nature takes shape and the religious attitude of Cheng become a philosophical notion.