The present study aimed to investigate vowel hiatus resolution and its relation to vowel shortening in Persian and Central Kurdish within an Optimality-Theoretic framework. The results showed that both Persian and Central Kurdish use glide formation through vowel shortening to resolve hiatus in certain environments. Persian has its own way to resolve vowel hiatus. The two high vowels /i/ and /u/, as a result of glide formation through vowel shortening, are changed into a short vowel and the glides /j/ and /w/, respectively. In Central Kurdish, glide formation occurs in high vowels /iː, uː/ and mid-high vowels /ēː, ōː/. In Persian, glide formation involves a quantitative reduction in the long vowel /iː/ and a quantitative and qualitative alteration in the long vowel /uː/. On the other hand, glide formation in Central Kurdish involves only a quantitative reduction in long vowels. Based on an OT analysis, the main factor in resolving vowel hiatus in both Persian and Central Kurdish is the obligatory presence of onset in the syllable structure. In contexts in which glide formation occurs through vowel shortening, the ranking of the active constraints in Persian and Central Kurdish is: ONSET, AGREE(place) >> MAX, DEP >> IDENT(µ).
