本文旨在透過譚獻的學術評論，重新反省吾人對清代學術既有的認識與評價。在道問學風氣濃郁的清代晚期，作為一個泛覽博觀的傳統文人，譚獻既不免於深受漢學考據之風之吹拂，卻又能堅守其以文章觀學術優劣的立場，所以其評價學術之出發點，也就迥異時流，而頗具特色。從價值立場言之，譚獻最欣賞的是常州莊氏高標西漢的經術文章；從批評角度言之，譚獻又頗能運用實齋的流略學眼光排比學術之演變。值得注意的是，譚獻成功綰合二家學說，成為其觀察學術優劣的基本模式：先以流略學眼光對學問作歷時性與共時性之檢驗，再以能否表出微言大義作為學術優劣之判準。譚獻既然在批評立場上有其特殊視域，其於學術高下優劣之評，也就呈現出獨特之風格。如以文章轉變的角度論清初至乾嘉學術的變化，又如從對經典出以政治論述的視野，而批評戴震專與理學家較勁，辨析毫釐之間，是見地不高，格局不廣的表現，至於對常州學派的批評，雖有溢美之嫌理當細繹之外，譚獻讓我們明白了常州經學其學術關懷的傳統性。簡言之，其論學的假想敵並非國勢日落時的東漸西學，而是傳統學術內部演變而成的乾嘉考據大潮。至於譚獻對清初諸大儒的抑揚高下，對程朱宋學的隱隱排斥，又不必皆是非之準，而有賴學者善加採擇。

This study aims to re-examine our previous critiques of Qing research by looking at Tan Xian's diary. As one of the erudite traditional literati in the late Qing, ”following the path of inquiry and study” (dao wenxue), he could not help but be deeply influenced by sinological textual research; yet in addition he adopted methods of literary criticism to assess academics. In this light, his criticism is distinctive from that of his contemporaries. From the standpoint of value, Tan Xian most agreed with Zhuang Shuzu of the Changzhou line, in his high estimation of the Confucian political thought in the Western Han Dynasty. Critically, he was also able to utilize Zhang Xuecheng's method of ”exploring academic development from bibliography” (liuluexue) to rank the evolution of academics. Tan Xian uniquely combined these two perspectives in judging academics. This is the basis of a model for observing academic value: first, one investigates its diachronic and synchronic aspects through ”exploring academic development from bibliography”; then, one decides whether or not one can draw out the subtleties of its expression as a criterion for judging academic superiority or inferiority. For example, by investigating how written articles evolved, he could discuss academic developments from early Qing to the Qian-Jia period. And based upon the degree of involvement of political discourse in classical studies, he criticized Dai Zhen, who often challenged neo-Confucian scholars on small points, on the grounds that his viewpoints were too narrow and restricted. Even though his critique of the Changzhou School seems to be an overestimation that deserves scrutiny, it at least provides us with a way to know what concerned Changzhou scholars. In sum, what concerned him was Qian-Jia textual-critical research rather than the process of bringing western science and technology to China. In a word, Tan Xian's critiques of Great Scholars of the early Qing and of the Cheng-Zhu school require further study and investigation.