(b) In conjugation, analogy plays a part, and fiamos follows fiar (with the i and the a in distinct syllables), cambiamos follows cambiar (with the i and the a in the same syllable).
Synæresis readily takes place for vowels ordinarily in distinct syllables (fió, etc.); but diæresis hardly obtains for the vowels of a true diphthong (cambió, etc.).
(c) The combinations ió and iè are usually diphthongs in the terminations of the preterite indicative, the future subjunctive, the past tenses of the subjunctive, and the gerund, of verbs of the second and third conjugations: e.g., murió, muriere, muriese, muriera, muriendo. In rió, deslió, rieron, deslieron, the vowels seem to be considered as forming separate syllables, the i being treated as part of the stem and not of the suffix.
(d) The substantival ending -ión (acción, etc.) is generally a diphthong, and rarely suffers dissolution.
(e) In derivatives analogy operates: e.g., naviero and brioso with their i in a separate syllable because of navío and brío (cf. [rule 4]); but glorieta and ambicioso with a diphthong because of gloria and ambición. Ordinarily, such ie and io combinations permit of synæresis if they are properly dissyllabic, and if properly diphthongal they remain indissoluble. Still, adjectives in -i.oso and -u.oso sometimes dissolve their diphthong; e.g., as in Espronceda:
El majestüoso río
Sus claras ondas enluta,
Garcilaso:
El árbol de victoria
Que ciñe estrechamente