In the Romance languages, metaphony was an early vowel mutation process that operated in all Romance languages to varying degrees, raising (or sometimes diphthongizing) certain stressed vowels in words with a final /i/ or /u/ or a directly following /j/.
Metaphony in central and southern Italo-Romance (i.e. excluding Tuscan) affects stressed mid-vowels if the following syllable contains /i/ or /u/.
In these languages, as in Tuscan, final /u/ was lowered to /o/; it evidently happened prior to the action of metaphony.
In most Italian languages, most final vowels have become obscured (in the south) or lost (in the north), and the effects of metaphony are often the only markers of masculine vs. feminine and singular vs. plural.
Examples: In some of the Astur-Leonese dialects, in northern Spain, a distinction between mass and count nouns appeared at an early stage.
Some of those dialects also lost metaphony and the noun count/mass distinction altogether, keeping it only in their pronoun systems, others, such as Pasiegu from Eastern Cantabria closed all their mid-vowels in word ending syllables, and relied on metaphony as a means for distinguishing mass/count nouns.
), preterites (vini < PIE veni, I came) and demonstratives (isti < esti, this; isi < esi, that).
Furthermore, the mass/count distinction is expressed very differently: Only a few "mass neuter" demonstratives exist, and they have a higher rather than lower vowel (tudo "everything" vs. todo "all (masc.
Romanian shows metaphony of the opposite sort, where final /a/ (and also /e/, especially in the case of /o/) caused a diphthongization /e/ > /ea/, /je/ > /ja/, /o/ > /oa/:[5] cēram "wax" > ceară; equam "mare" > /*ɛpa/ > /*jepa/ > iapă; flōrem "flower" > floare; nostrum, nostrī, nostram, nostrās "our (masc.