The modern compound tone rules of Japanese are usually seen as recent innovations, without any link to the tonal history of Japanese. Since the Middle Japanese tone system is not reconstructed correctly, there is no resemblance between compound tone in Middle Japanese and compound tone in the modern dialects. The outcomes of the project show that there is, in fact, a close link between the tone of compounds in Middle Japanese (and by extension proto-Japanese) and the tone of compounds in the modern dialects, but only if the Middle Japanese tone system is reconstructed in accordance with Ramsey's ideas. This proves beyond any doubt that the upside-down reconstruction of Japanese tonal history that is still prevalent in Japan needs to be abandoned.
The insight that a Gairin type tone system is the result of an innovation, but need not be seen as belonging to a separate lineage, based on its rules for compound tone, has solved a puzzle concerning three dialect areas along the Sea of Japan coast that has intrigued researchers since the 1950s. The widely separated dialects of Izumo, the Noto peninsula and the northeast of Japan share a very distinct segmental phonology. There are strong resemblances between the Gairin type tone systems of Izumo and the northeast, but the tone system of the Noto peninsula in-between the two is very different. Following my reconstruction of Japanese tonal history based on Ramsey’s theory, the Noto tone system is archaic, while the tone systems of Izumo and the northeast are innovative.
These three areas can now be regarded as representing different stages in a single dialect, separated through different waves of migration. The first migration took place in the 1st century CE, and brought a dialect with a distinct segmental phonology and an archaic tone system from the ancient kingdom of Izumo to the Noto peninsula. After innovations resulted in a Gairin-type tone system in Izumo, a second migration in the 6th century CE by-passed the Noto peninsula and brought rice farming culture and the distinct Gairin type tone system and segmental phonology of Izumo to the northeast of Honshu. This sequence of events explains the resemblances in segmental phonology between the three areas, and the archaic nature of the Noto tone system. It also explains why the resemblance in tone between Izumo and northeast Honshu is much closer.
Distinctive resemblances in the shape of burial tombs as well as mythology offer supporting evidence for the first migration and resemblances in DNA and folk music for the second. The most complete overview of the result of the project will be published open access in:
De Boer, Elisabeth M. 2022. “What tonal data can tell us about the history of the Japanese language: Concentrating on evidence from the Tokyo type tone systems.” Current Issues in Linguistics Theory, John Benjamins Publishing Company.