This paper examines the adverbization of Japanese degree Adverbs ‘Bakani’, ‘Iyani’ and ‘Yakeni’ and the process in which the degree meaning is established in adverb usage, in terms of synchronic and diachronic approaches.
As a result, (ⅰ)the first examples of the ‘Bakani’, ‘Yakeni’ appeared in the late modern period, and ‘Iyani’ appeared in the early modern period. Although only a few examples are seen before the early modern period, they come into use frequently. (ⅱ)In the development of the degree adverbial usage of ‘Bakani’, the adjective verb ‘Baka(na)’, which means ‘stupidity far from normal’, has lost its original substantive meaning(i.e. stupidity), and gets the derived meaning of ‘extremeness of degree’. It can be pointed out that the development of the degree adverbs of ‘Iyani’ and ‘Yakeni’ is derived from the substantive meaning of ‘abnormally unfavorable’. (ⅲ)The mechanism by which the meaning of degree in the adverbial usage is derived in common with ‘Bakani’, ‘Iyani’ and ‘Yakeni’ involves the semantic factor of ‘abnormality far from normal’ inherent in the original meaning of adjectives. (ⅳ)Furthermore, it also involves the syntactic factor that they are used as the adverbial usage of modifying an adjective or verb in sentences.