宋明理學乃是承續先秦儒學的。然而，理學提出的許多概念和思維方式與先秦儒學是有所區別的，周敦頤(1017-1073)論「誠」便是一個顯著的例子。先秦儒學論「誠」，均是指真實無妄之意，無論是孟子抑或是《中庸》，「誠者，天之道也」，「誠」只是用來形容天道的一個側面，並非等同；「誠之者，人之道也」，實現如天道般的真實無妄，亦只是實踐人道的一個側面，亦非等同。但到了周敦頤，其藉《易傳》的乾坤思維加以引申，認定整個宇宙本身已然就是真實無妄的「誠」，同時賦予「純粹至善」的價值蘊義。既然人是宇宙中的一分子，故其原初面貌亦是真實無妄的。但人會產生「邪暗」之心，即處於「幾」狀態中會產生善惡之別，故人的一切努力，無論是「主靜」抑或是「無欲」，均是以回復到真實無妄的狀態為標宗。所以，濂溪學思的宗旨在於「存誠」。周敦頤如是的詮解，開創出與先秦儒學不一樣的氣象。統言之，理學自周敦頤起，注視到宇宙的安排與定位，並對人心人性於此定位中找尋安頓之所。先秦儒學則專注於人間世事如何實踐的議題。但《易傳》是較為特殊的，其藉由乾坤概念指出宇宙之定位，並隱含提出人心人性的安頓處，因此理學家常發揮《易傳》作為論述佐據。是以從周敦頤論「誠」的內蘊，我們便能見及理學不同於先秦儒學而開展出的新理論以及所引出的新氣象。本文區分三部分立論，一論周敦頤之「誠」的蘊義，二論先秦儒家「誠」字的意義，三，由之探討理學呈顯出的新開展與新氣象。最後作一結論。

Neo-Confucianism purposed to persist Pre-Chin’s Confucianism, but it differs from Pre-Chin’s in many concepts and ways of thinking, e.g. Chou Dun-Yi’s “Cheng”. In Pre-Chin’s Confucian texts such as Mencius or Doctrine of the Mean(中庸), Cheng means “true and not mendacious”. As an adjective, it pictures only some aspects of Tian-Dao(天道), but not equivalent to it. And it is also one aspect of human practice that he should act as truly as Tian-Dao. But Chou Dun-Yi Developed the thought in Commentaries on The Book of Changes(易傳), identified the universe with the truth, so “Tian-Dao” with “Cheng”, then labeled it “the supreme good”── a value-term. Human beings are originally true and good (since they are constituents of the universe), but evil crises from slight wicked aspects in human mind. All human efforts should aim at going back to the good origin, that is, “holding the Cheng”(存誠).To sum up, Pre-Chin’s Confucianism exclusively focused on how to establish human practice, but Neo-Confucianism payed attention to the whole order of the universe, arranging the location of person in the universe. This new atmosphere began since Chou Dun-Yi.