In this article, the possibility of a koine in the dialect of the Bonin Islands is discussed by analyzing the verbs and adjectives of the older speakers of those islands. Abe (1999) has previously dealt with the verbs and adjectives spoken in the Bonin Islands. These forms originate from the Hachijojima dialect forms investigated in "The Linguistic Atlas of Japan".
The conclusions of the analysis of the data gained through interviews in Bonin (Abe 1999) are as follows: 1) Traditional Hachijojima dialect forms are changing to the forms of the common language of Japanese. 2) The changes were caused by contact with the dialects other than the Hachijojima dialect and languages other than Japanese of the Western-descent (Obeikei) islanders.
Abe (1999) discussed only the change itself and named it as "Ogasawara dialect".
This article tries to find the mechanism of the occurrence of the "Ogasawara dialect" by the application of the theory of koine to the data. In order to accomplish this purpose, the evidence that supports the assertion that the dialect in the Bonin Islands is a koine will be pointed out.
Though the conclusion that dialect experiences dialect leveling (the loss of marked and/or minority variants) and that a stabilized variety has derived from the leveling should be waited for in the future analysis, the following evidence as a koine is obtained:
1) Dialect experiences the dialect mixing of any linguistic subsystems such as regional dialects, literary dialects, and sociolects. The mixing subsystems satisfy one of following conditions. That is, they should be mutually intelligible, or they should share genetically related superseding systems such as a standard variety or literal variety.
2) Dialect contact is caused by the political, social, economic, demographic change in a community.