日本語の方言
The vowels , , and have been obtained by internal reconstruction from Old Japanese, with the other Old Japanese vowels derived from vowel clusters. The mid vowels and are required to account for Ryukyuan correspondences. In Old Japanese, they were raised to "i" and "u" respectively except word-finally. They have also left some traces in eastern Old Japanese dialects and are also found in some early "mokkan" and in some modern Japanese dialects.