Sequences

Two adjacent vowel sounds occurring in the speech chain lead to hiatus or diphthongs, depending on whether their pronunciation is heterosyllabic or homosyllabic. There has always been a tendency towards vowel reduction, both in hiatus and diphthongs. There are also frequent secondary vowel sequences produced by the loss of certain intervocalic consonants (mainly [β̞, ð̞, ɣ̞, ɾ]).

Most diphthongs correspond to decreasing sequences such as [ei̯], [eu̯], [ai̯], [au̯], [oi̯] o [ui̯], among others.The absence of rising diphthongs has been a traditional feature of the language; instead, a number of hiatus, consonant epenthesis or reductions occurred; however, the presence of rising diphthongs is increasingly common. 

There are different types of hiatus occurrences: inside the lexical element by derivation and composition, in verbal forms, etc.; in these cases, hiatus or its phonetic results are generally fixed.Another type of hiatus is produced by adding a morpheme to a lexematic or verbal base; in such cases, the use of this morpheme is optional and, therefore, so is the occurrence of hiatus and its different diatopic variations.The latter group includes sequences produced when determiner [-a] is combined with each of the vowels in word-final position: [-ia], [-ea], [-aa], [-oa], [-ua] and also [-ya] for the Souletine dialect; these sequences have a great variety of results, so there may even be cases of polymorphism, both social and individual, in a same location.