NOTE: In diphthongs a dominates o and e; and o dominates e. Any strong vowel dominates a weak one.
Ex. In Bo^abdíl, if a were not dominant, the diphthong would be dissolved.
There are with regard to accent three possible conditions under which two contiguous vowels may occur within a word.
a. The contiguous vowels may precede the accented syllable.
b. One of the contiguous vowels may be accented.
c. The contiguous vowels may come after the accented syllable.
a. Two contiguous vowels before the accent.
(1) Of the twenty-five possible combinations all are admissible in diphthongs in a syllable preceding the accented syllable.
(a) Diaeresis may be employed to dissolve the diphthong.
Ex. _Sobre una vi|oleta_, p. 169, XIII, l. 8.
b. One of two contiguous vowels accented.
(1) _When two contiguous vowel's are strong._
(a) There is no diphthong if one of two contiguous strong vowels receives the accent.
Ex. _Chispë|ando el sol hiere_, p. 173, XXVI I, l. 17.
Ex. _Tú, sombra a|érea que, cuantas veces_, p. 170, XV, l. 7.
By synaeresis, however, a diphthong may be formed, especially in the combinations á^o, á^e, ó^e--_c^a^o^s, c^a^e, ro^e_. But in order to diphthongize oa, ea, and eo, when the accent naturally falls on the first vowel, the accent must shift to the second, which is a dominant vowel. Such diphthongization is harsh. For example, _loa_ would shift the accent from o to a in order to form a diphthong. The accent would also shift in _cre^a, fe^o_.
(2) _When one of the contiguous vowels is weak and the other strong._
(a) There is no diphthong if an accented weak vowel precedes a strong.
Ex. _Yo, que á tus ojos en mi agoní|a_, p. 171, XV, l. 18. Synaeresis is, however, sometimes employed to overcome this rule. The accent must then shift.
(b) There is no diphthong if an accented weak vowel follows a strong.
Ex. _¿Cómo puede re|ir?_ p. 182, XLIX, l. 4.
Synaeresis serves sometimes to overcome this rule. The result is usually harsh.
Ex. _En re^ir á costa ajena, les prepara._
(c) If an accented strong vowel precedes a weak, they form a diphthong. The diphthong is rarely dissolved, and is usually marked with a diaresis, if dissolution takes place.
Ex. _Beso del aura, onda de luz_, p. 170, XV, l. 5.