摘要
自甲、金、簡牘文字大量出土後，討論文字形體之古今異同蔚為風氣，因而古文獻中關於「古今字」的材料亦引起眾人的注意，成為考釋文字的重要根據之一。本文檢證《古今字》的著錄及前人經傳注釋用語，指出使用古今字有二種不同的路線，其一以用字為基點，如段玉裁對「古今字」的討論等，其二以造字為基點，如徐灝對「古今字」的討論等。二者不僅定義寬嚴不同，範疇亦有歧異，與今人所稱之同源字、異體字、通假字等當分別觀之。
段玉裁在文字學發展史中無疑是起重要作用之人，《說文解字注》中云「古今字」者數百見之多，常為後人稱引。卻往往忽略了段氏使用此一術語仍嚴守經、注的分際，承襲鄭注之傳統，站在訓詁的立場；從《毛詩訓詁傳定本小箋》、《詩經小學》、《周禮漢讀考》等著作互證之，尤為清晰。徐灝《說文段注箋》雖是疏段注之作，在「古今字」的認識上卻站在文字學的立場，破《說文》之約束，直探文字之本原，與段氏迥別。這個趨勢一直發展至今。
Since the unearthing of oracle bone, bronze and bamboo slip writings began on a massive scale, comparison of the forms of ancient and modern characters has become a popular topic of discussion. As a result, materials in ancient documents on "ku-chin-tzu" have attracted public attention, and have become the most important source in the interpretation of characters.
In this paper I trace the term "ku-chin-tzu" etymologically, and examine "ku-chin-tzu" writings and their transmission and commentary. There have been two lines of research on "ku-chin-tzu." The first, represented by the work of Duan Yu-ts'ai, takes views of Commentariology (訓詁學) as its starting point. The other, represented by Hsu Hao, takes views of Writing (文字學) as its starting point. The two differ not only in the narrowness or looseness of their definitions, but in the categories they use.