Expanding to the peripheries: A corpus-based study of the development of the Japanese discourse marker toiuka

•Toiuka originally expressed the speaker's difficulty in lexical choice.•Subsequently, it shifted its position and gained new uses.•In the left periphery, it serves the purposes of repair, upgrade, and disagreement.•In the right periphery, it adds elaboration or weakens assertiveness.•The left periphery shows more vigorous change.

Many languages have common or stock phrases that are used when the speaker is unsure about how to say a certain thing, as with such English expressions as how should I put it? and something like X. In conversation, one strategy to avoid turning into a silence is to give a tentative choice with the hope that the addressee will understand the speaker's meaning. The Japanese discourse marker toiuka started as such a parenthetical expression that appears in mid-sentence and indicates the speaker's difficulty in lexical choice. It subsequently shifted to the utterance-initial and -final positions and gained new uses. The present article examines the diachronic development of this expression, using data from the National Diet Minutes Corpus [1], the Ninjobon 'Love Story Books' Corpus [2], and the Taiyo 'Sun Magazine' Corpus [3]. We keep track of the pragmatic-semantic and syntactic patterns over time quantitatively and show from a usage-based approach how this gradual process occurred.