The Institute of History and Philology, Academia Sinica, possesses a set of manuscripts titled “Guanglu guancha gong Duan shi Shuowen qianji” 光祿觀察公段氏 說 文 簽 記 that contains Wang Niansun’s 王 念 孫 (1744–1832) thoughts on Shuowen 說文. Contrasting Wang’s manuscripts with Duan Yucai’s 段玉裁 (1735– 1815) Shuowen jiezi zhu 說文解字注, the present article points out the broad disagreements between these two leading Qing 清 (1644–1912) philologists in four sub-fields of Chinese philology. First, Wang and Duan disagreed on paleography. They had different theories about the six categories of Chinese characters, particularly about the overlap between semantic and phonetic compounds. Second, their reconstructions of the Old Chinese rhymes and initials are different. Third, they disagreed on historical semantics, including the original semantic analyses of characters by Xu Shen 許慎(ca. 54–ca. 125), loan graphs, the dialects’ original characters, the use of philological evidence, and the semantics of function words. Fourth, they took different approaches to textual criticism, valuing different editions and using different sources and methodologies in collating Shuowen. This article compares Wang and Duan’s methodologies and provides insights into dozens of controversial philological cases with the help of excavated materials and linguistic tools.