This paper probes the elements of theoretical necessity, starting with the word ruo (若) in Duan Yucai’s Shuo Wen Jie Zi Zhu (段玉裁《說文解字註》). From the prospective of theoretical methods of “Ruo (若) ,” the theoretical necessity of “Ruo (若) ,” the exegesis functions of “Ruo (若) ” and different intonations with different modal particles, the author conducted multi-level and multi-dimensional analysis on “Ruo (若) ” in Duan Yucai’s Shuo Wen Jie Zi Zhu (段玉裁《說文解 字註》) so as to explore the concepts of theoretical necessity from Duan Yucai.

歷年以來，學者皆首推段玉裁《說文解字注》為闡釋許慎《說文解字》的文字工具書。然而，段《注》亦不免有不少漏錯之處。近年來，徐《箋》中的一些說法受到學界的認同和徵引，徐《箋》逐漸得到學術界的接受和肯定。徐《箋》雖為段《注》作箋，但徐氏不像一般的注釋家，把自己的工作局限在解釋原文方面，盲目跟從和維護段《注》對《說文》的解釋。徐《箋》的撰寫目的在於表識段說，在段《注》含混之處加以說明，簡略之處加以補充，有時更會另提己見，其識見甚或比段《注》更精確。本文試從「馬」、「䠶」、「臣」三字為討論中心，闡釋比段《注》精準之處。