The Roles of Internal and External Factors and the Mechanism of Analogical Leveling: Variationist- and Probabilistic OT approach to Ongoing Language Change in Japanese Voice System by

This thesis presents an exhaustive research about ongoing language variation and change in the Japanese voice system. Through the analysis I identify the roles of internal and external factors in human linguistic competence that govern the language variation and change, and I construct a model of grammar that inherently includes the language variation and change. This work aims at the formal theoretical analysis primarily built upon the empirical evidence: a huge amount of spontaneous speech data. Until now, a number of researches on language variation and change have been done from various perspectives: The sociolinguistic research, specifically from the perspective of the variationist approach (Labov 1963 et seq., Weinreich et al. 1968), has revealed much about language variation and change, particularly with respect to phonological aspects, focusing on various internal and external factors that govern the phenomena by the quantitative method. However, the formalization of the mechanism of language variation and change is insufficient; the generative grammatical approach (Chomsky 1957) can give a formal account of the phenomena based on the grammatical theory. However, this approach has focused on the language competence as the research subject, and the language use has been overlooked. Thus, the approaches have not cooperated and have not shared their insights. In the grammatical category voice in Japanese, language variation and change which reorganize the conjugation paradigm are currently underway. The process includes three variations: sa-Insertion, ra-Deletion and re-Insertion. The variation and change in voice are related to the functional demand and to morphophonology. Based on these facts, I conducted the research from the perspectives of a variationist approach (Labov 1963 et seq.; Weinreich et al. 1968), and also Optimality Theory (henceforth OT; Prince and Smolensky 1993/2004), specifically the