Within the tonal classes in ruibetsu-goi (which is referred to here as “Classified Vocabulary”) developed for the diachronic study of Japanese accent, classes 3, 4, and 5 for two-mora nouns exhibit distinctive patterns of split and merger into two distinct types in Ryukyuan. These two types are called “ita-group” and “iki-group” in this paper. The paper attempts to show that these two groups are distinguished by the vowel length of the first syllables in certain Ryukyuan dialects (e.g. Shuri in mainland Okinawa Island), while they are distinguished by different accentual patterns in some other Ryukyuan dialects (e.g. Tokuwase in Tokunoshima). This paper proposes that such distinction of accentual patterns developed as a result of the transference of the phonological distinctions in Ryukyuan dialects from the vowel length of the first syllable to the accent patterns.
This paper argues that the vowels in the first syllable in “iki-group” nouns were once long, but were subsequently shortened in various Ryukyuan dialects, while their accent patterns retained their former distinctions between "ita-group" and “iki-group”. Thus, being a newly developed accent class in Ryukyuan, formed as a result of the above mentioned process of transference of phonological distinctions, the “iki- group” is a marked category for the two-mora nouns of classes 3, 4, and 5. Thus, the unmarked accentual patterns for classes 4 and 5 are not those of the “iki-group” as most of the previous studies have proposed, but actually “ita-group” patterns. The collorary of this assertion is that, contrary to the traditional analyses that assert that the patterns of tonal mergers in proto-Ryukyuan of 2-mora nouns in the Classified Vocabulary is 12/3/4 5, it is actually 1 2 / 3 4 5/3 4 5, with the newly developed "iki-group" represented by 3 4 5.
