This paper presents a view of the phoneme /i/, which has never been discussed in the vowel system of the dialects of the main island of Okinawa. The phoneme /i/ has [+ back, + high, -labial] as its main distinctive features, but phonetically is realized as [ i ] (front high vowel) ; hence, it is necessary to posit a rule of changing /i/ into [ i ]. However, the postulation of /i/ brings about a great simplification in the phonological system.
The postulation of /i/ provides a principled basis for the contrast of [waki] 'reason' and [wat_??_i] ‘armpit’, or [tii] ‘hand’ and [t_??_ii] 'blood', where palatalization applies not to /waki/ or /ti/, but to /waki/ or /ti/. The addition of /yi/ to the distribution of /y/ and subsequent vowels in the Yonabaru dialect does not change such a restriction-effective in Standard Japanese as well-that /y/ occurs only with [+back] vowels. Rather, the establishment of yi makes it possible to give a simpler account of the alternation of -yi and -yu in the non-past morpheme /yu/, sinceyi need not be derived directly from /yu/. In addition, only when [_??_ikiN] 'the world' is derived from /syikin/ does the presence of /i/ give an account of why, as in [_??_it_??_a] ‘down’ being derived from /sita/, the expected progressive palatalization is not applied to /k/. The incorporation of /i/ into the phonological system provides a means of making a phonological distinction between homophonous words; /kwi/ ‘voice’ and /kwi/ ‘stake’ derive the same phonetic form [kwii] through the application ofThe postulation of /i/ brings about a typological simplification in that Ryukyuan dialects typically have a 6-vowel system, and also contributes to the comparison of correspondences between phonological systems of related dialects.