I'm looking at a set of data right and I'm a bit confused on how to tackle this. The data is showing a stem alternation of some verbs with [e] and [o] and no change in others. I know this is due to Latin and I've done some research on it but the answers I've found have left me confused. What rule makes a verb like "poder" conjugate with a stem change (puedo) but a similar verb such as "rentar" not (rento)? We're learning about abstract analysis right now and I'm quite sure that has something to do with it, but I don't know the steps to get there. Is there some sort of underlying vowel that never comes to surface that we can use in a rule? I've noticed that the dipthongization happens if the first syllable is stressed and has [e] or [o] but of course this doesn't apply everywhere, which is the problem. Thank you!

  • There are verbs that change (or not) on meaning. follar: follo (I fuck), fuello (I fart). aforar: afuero (legal term), aforo (I measure/calculate). You cannot predict when a stem change will happen by looking only at modern Spanish — you can only say definitively when it will not, or when it could. You'd need to look to Latin to get better predictions, but it's not perfect. correr, for instance, should be cuerro based on the Latin->Castilian rules, but it just doesn't. Dec 5, 2016 at 3:00
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    Oops — I saw this and thought it was in the Spanish.SE and not in Linguists.SE, so my previous comment isn't helpful. But, basically, you can think of there being eight vowels in Spanish: A, E₁, E₂, E₃, I, O₁, O₂, and U. Of these, A, E₁, I, O₁, and U allow for permanent rising and falling diphthongization, but are unaffected by stress. E₂, E₃, and O₂ appear as E₁ and O₁ when not stressed, but when stressed, they become /je/ (E₂), /i/ (E₃), and /we/ (O₂). Weirder things happen to them if of the -ir verb group, with E₂ and E₃ at times being /i/ and O₂ as /u/ Dec 5, 2016 at 3:20
  • @guifa I'm quite curious about your E³, since I haven't come across that pattern before (I'm a Latin speaker who knows these distinctions only through historical changes). Would you mind giving an example of a word containing it, that I could trace back? I'd like to improve my answer if I've left out something relevant.
    – Draconis
    Jan 4, 2017 at 5:34
  • @Draconis for example, pedir (pido, pides, pide, pedimos, pedís, piden). AFAIK, there's no pattern to predict when E goes to IE or just I, and some verbs can even go both ways, like erguir (yergo/irgo). Jan 4, 2017 at 5:59
  • @guifa Most curious. Thank you! I shall research further.
    – Draconis
    Jan 4, 2017 at 6:02

3 Answers 3


Classical Latin had a system of ten native vowels + two foreign vowels + two important diphthongs, for a total of twelve (a, ā, e, ē, i, ī, o, ō, u, ū, y, ȳ, æ, œ). This is quite a lot of vowels to keep straight; for later Romance speakers, it was too many.

In the precursor to Spanish (aka "Late Iberian Vulgar Latin", the Latin spoken in Spain right before it became not-Latin-any-more), this twelve-vowel system simplified to seven: a, e, i, o, u, ɛ, ɔ. (ɛ and ɔ are phonetic symbols; they were never actually written that way at the time. ɛ is the vowel in English "met", ɔ the vowel in "hot".)

a ← a, ā
e ← ē, i, œ
ɛ ← e, æ
i ← ī, ȳ, y
o ← ō, u
ɔ ← o
u ← ū

This change was nicely universal and predictable. Similar things happened in other vulgar Latin dialects, which would become the other Romance languages.

Then, the system simplified again. In unstressed syllables, or before syllable-final nasals, ɛ and ɔ turned into e and o.

e ← ɛ
o ← ɔ

In any other places, they broke into diphthongs.

je ← ɛ (spelled "ie")
we ← ɔ (spelled "ue")

For instance, Latin metus → Spanish miedo, Latin focus → Spanish fuego.

And this is the source of your mysteriously appearing diphthongs. When the first syllable is stressed, a historical /ɛ/ becomes /je/; when unstressed, it becomes /e/. Similarly, a historical /ɔ/ in a stressed syllable becomes /we/; in an unstressed syllable, /o/. But a historical /e/ or /o/ never changes its form, always remaining /e/ or /o/ regardless of stress.

Unfortunately there's no good way to predict where these ɛs and ɔs are, except by knowing the vowel lengths in the Latin words. So the best option for analysis is to take them as separate underlying phonemes, even though only these few remnants are visible now.

Source 1
Source 2

(See also guifa's comment on your question: what they call E² I call ɛ, and what they call O² I call ɔ. The "weirder things" they mention in the -ir conjugation come from a later process of vowel-raising, which I haven't gone into here; the first source link has some excellent information on that as well.)

  • To make it also a little bit more fun, I believe it is worth to mention the vowel raising you mentioned. If the verb with original /ɛ/ or /ɔ/ has infinitive with -ir, it evolves to /i/ and /u/ in finite forms, e.g. pedir,concebir etc. conjugate as pido, concibo etc. Also the whole thing cannot be explained purely synchronically since in the evolution there were analogies (see adiestrar and amueblar from reply of user6726) and there are cases of inherited difthongs (piedad from Latin pietatem).
    – Eleshar
    Jan 4, 2017 at 19:02

The problem is that there are three classes of behavior, when only two make sense under normal assumptions about what the underlying segments of the language are. One pattern is the diphthongizing patterns of "be able" /pod/, where when stressed you get [we] as in [pwéðo] "I can". The second is the non-alternating pattern of "eat" /kom/ as in [kómo] "I eat". So far so good, yuo have a distinction between underlying diphthongs and underlying monophthongs, and diphthongs monophthongize when unstressed. But that can't be totally true, because of piedád "piety" where you do in fact have unstressed diphthongs. The abstract analysis "solves" the problem by saying that only specially-marked stressed vowels are diphthongized, so the unstressed diphthong of piedád is not a problem since the rule is that stressed vowels diphthongize, not that unstressed diphthongs monophthongize. There are basically two specific proposals for that special marking. One is that the special vowels are tense or long; the other is that they have an arbitrary diacritic [+D] (which is abstract since you can't hear it).

What seems to force some abstract analysis is this third class of vowels, exemplified by piedád: if only we could deal with unstressed diphthongs, the matter would be very simple – /pwed/ versus /kom/. As far as I know, the class of unstressed diphthongs is circumspect. There are prefixed stems like adiestrar, amueblar, and some nouns like piedad (also vienés), but to the best of my knowledge, no verb roots like puevár, pientér.


As an aside to all that's been said already: traditional Spanish grammar divides all verbs into three conjugation classes based on their endings (-ar, -er, -ir), but I've read (the source escapes me) that it would be more sensible to add three more for the stem-changing verbs discussed here, since there are so many.

Another aside: alternation of -e- and -i- based on the original Vulgar Latin vowel is of course not confined to Spanish. Italian has e → ie and o → uo, Romanian has e → e̯a and o → o̯a, etc. Neither French (which has fixed last-syllable stress) nor Portuguese have vowel alternation of this kind.

  • French has some vowel alternation based on stress (e.g. vous venez, je viens), although nowhere near as much as Spanish. See here: books.google.com/… Jan 5, 2017 at 16:48
  • The French situation is the result of analogical levelling (OF tu aimes, vous amez; MF t'aimes, vous aimez) and in some cases of the split of the two stems into two semantically distinct verbs (ie ployer to flex, plier to bend) Jan 5, 2017 at 23:35

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