漢字之發展延綿數千年，漢字之使用橫跨眾多國家，字形之演變，往往千支萬派，異彩紛呈，以致點橫稍縱，即形似他字；兼之文字之使用，音義常相糾纏變化，導致一字之異體常見與他字互有糾葛。正如曾榮汾《異體字字典．總編輯序》所論：「整理中國文字，形音義必須兼顧。表面看來，異體歧衍，形體為重。或隸變，或草省，或減形，或增旁，自有其道。但是實際上的演變卻與音義糾纏難分。或甲為乙之異，乙復為丙之異；或甲為正字兼作乙異，乙亦為正字兼作甲異。」本論文以《異體字字典》中正異體彼此糾結之「甲為正字兼作乙異，乙亦為正字兼作甲異。」之「互為異體」類型為探討主題，稽究歷代文獻，藉以一窺兩正字如何互相成為彼此異體，並探討相關文字學理。

The Ministry of Education's "Dictionary of Chinese Character Variants" is a large-scale book of Chinese characters that had offered scholars lots of benefits. This research project is based on "The Two Words are Variants of Each Other" in the book. This historical document explained the theory of Chinese characters. The research results can be used as a reference for related research and dictionary editing.