「文以代變」是歷代文學必經的過程，政治力與社會力向來握有文學的解釋權。葉燮以進步的文學史觀所提出的「源流正變」，在詩學史、批評史上頗受推崇，但在有清一朝卻顯得曲高和寡，且不及門生沈德潛「格調說」的影響力，即回歸儒家詩教的「正變」說。本文試從「檢討」的角度切入，以葉燮的詩學為對照組，突顯沈德潛詩論更具實效性的關鍵原因。首先回顧葉、沈的生平與交集，並簡述二人詩論影響力的定案之說。往下，依次梳理二人詩論的根本不同，擬從詩歌發展的規律，到作品呈現的內容、具備的功能，聚焦到作者的修養與創作。結語除了觀照葉燮如何將詩論提昇到理論的高度，更總結沈德潛直駛在儒教的康莊大道，既符合官方的文藝思潮，也讓學子知所遵循，達到風行草偃的實踐效應

＂Literature Changing over Generations＂ is the necessary evolving process in ancient literature, and political and social power always cause impacton literary interpretation. From perspective of the Chinese poetic history and the history of Chinese literary criticism, the idea of ＂Positive Change from Origin and Development＂ raised through Ye Xie's outstanding historical sense on literature had been well regarded. But the idea was neither mainstream in Qing dynasty nor as influential as Shen De-qian's ＂Change Style＂ which was inclined to the Confucian poetic idea of ＂Independence of Positive Direction and Adaptive Evolvement＂. This paper is from review angle to study and highlight the key reasons that Shen De-qian's poetic was more effective than Ye Xie's. First of all, the article recalls the shared living story of Ye and Shan and briefly reviews their accepted influences each with their own poetics. Followed by combing their poetics and focusing on the fundamental differences, ranging from the laws of poetry, to the content of the works presented and functions served down to their cultivations and creations. The conclusion indicates the way of how Ye Xie was lifting poetics up to a theoretical level and summarizes the practical effects generated by Shan De-qian's poetic idea which fit official literary trend at that time as well as allowed students then to follow