Reconstruction of Ryukyuan tone classes of Middle Japanese Class 2.4 and 2.5 nouns

Abstract It is generally accepted that of the five tone classes reconstructed for disyllabic nouns in Middle Japanese (MJ), Classes 2.4 and 2.5 exhibit a split correspondence with proto-Ryukyuan (pR) tone Classes B and C. This split correspondence is of tremendous importance for the reconstruction of the proto-Japonic (pJ) tone system, because, in the absence of a conditioning factor accounting for the split, it has led to the reconstruction of additional tone classes at the pJ level. However, of the approximately 100 nouns belonging to these classes, the tone class of only half of them has been reconstructed for pR. Before embarking on the reconstruction of the pJ tone system, we must therefore first reconstruct the pR tone class of the nouns belonging to MJ Classes 2.4 and 2.5. This study provides a reconstruction of the tone classes in pR for 75 cognates using the latest comparative data of Northern and Southern Ryukyuan dialects. The results confirmed the existence of a split correspondence, where Class 2.4 and 2.5 nouns are found to be roughly split in half between pR Classes B and C, demonstrating that it is not a merely sporadic irregularity.