「字異而義同」為王念孫《讀書雜志》習見之訓話術語之一，唯過去對其涵義、特徵、演變等相關問題，皆缺乏深入之探討。本文因擬針對其術語作一全面而宏觀之探究。 本文首先運用定量分析之方式，逐一梳理《雜志》「字異而義同」之訓詁條例凡三十五則，以歸納、分析其術語之涵義，結果發現本術語乃以讀音之同近為其先決條件，屬「因聲求義」之術語。且其主要論述諧聲字組間之關係，由此可知其所謂之「字異」，乃是指字形具諧聲關係之「微異」，而此亦即本術語之最大特色。 其次，上溯其淵源，考察本術語自唐至清在不同訓詁學家詮釋之下其意義之生成。並藉此略窺其中所反映之王氏訓詁觀念，從而對其「詁訓之旨，本於聲音」、「引伸觸類，不限形體」等主張有更深一層之理解與認知。

"Zi Yi Er Yi Tong" is one of the scholium terminologies in Wang Nian - Sun's "Du Shu Za Zhi". Due to lack of in - depth discussion over the denotation, characteristics, and transformation of the terminology, this study probes into the terminologies comprehensively. First, quantitative analysis was employed to sort 35 scholium notes of "Zi Yi Er Yi Tong"in "Du Shu Za Zhi", and then the terminological denotations were generalized and analyzed. The results show that similar pronunciation is the prerequisite condition; those are homophonous terminologies. Since "Du Shu Za Zhi" expounds the relationship between "Xie Sheng" words, "Zi Yi" terminologies with slightly different character form are the main characteristics. Moreover, the terminologies originated from varied denotations interpreted by different scholium scholars between Tang to Ching Dynasty. This study not only probes into Wang's philosophy on scholium but also gains an in - depth understanding of principles of scholium.