I first asked this question in https://spanish.stackexchange.com/q/15929/11155

However the Spanish community has not found any answer yet and the phenomenon is observable in many Romance languages. I am wondering it anyone here in the Linguistics community will come with a plausible explanation.

As Comparative Grammar of the Romance Languages says:

To form the subjunctive, verbs normally switch their thematic vowel (a becomes e/i and e/i turns into a)

E.g. in Spanish the present subjunctive is formed by a kind of swapping the indicative endings between the verb declension classes: the 1st class (-a-) takes the indicative endings from the 2nd class (-e), and the 2nd and 3rd class (-i-) take the indicative endings from the 1st class:

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QUESTION: Is it only coincidental, or is there something deeper behind it? Something like "as the subjunctive often expresses uncertainty, let's make the verbs sound weird by deliberately using a wrong set of endings to emphasize that we are not sure"?

Is there any theory about the origin of this particular switch? I am aware that this is inherited from Latin. The question is not about how the Romance languages inherited it. By origin I mean rather an idea behind.

And a bonus question: is anything like this (swapping thematic vowel between tenses/moods) in non-Romance languages?

EDIT: I received a plausible answer at same question to the Spanish Stack Exchange site, see https://spanish.stackexchange.com/q/15929/11155

  • 2
    What makes you think there is an "idea behind" anything in languages?
    – fdb
    Aug 17, 2016 at 23:42
  • @fdb There often is. E.g. the "idea behind" the etymology of tomorrow is that "the next morning", which concept is btw kept in so many languages, Germanic, Romance, Slavic, even in Finnish. Isn't this an idea par excellence? Aug 18, 2016 at 5:51
  • Tomorrow is a content word, Honza Zidek, which has a meaning (and hence an idea). Grammaticalised morphemes generally don't have a "meaning" per se
    – Colin Fine
    Sep 24, 2020 at 13:37

3 Answers 3


From 280 of Benjamin W. Fortson's Indo-European Language and Culture:

The Italic subjunctive is not a continuation f the Proto-Indo-European subjunctive, which became a future. There are at least three subjunctive morphemes found in Italic, of which one continues the PIE athematic optative and the other two are of unknown origin.

For the details of how the distribution went you will have to consult various works. The question as to whether this pattern (the Romance pattern) appears elsewhere among I-E languages is answered by this shifting of functions of various morphemes, e.g. subjunctive to future, optative to subjunctive, and so forth. Deep stuff. The upshot is that "swapping" does not properly describe a process that occurred through a long and complex evolution among the I-E languages, although it does make it easier to teach the subjunctive to learners.

  • (1/2) From what I've read, the a-subjunctive seen in most of the Latin verb classes (e.g. pōnam from pōnere) comes from the IE optative, but if I understand the above quote right, the e-subjunctive seen in a-stem verbs (e.g. amem from amāre) is of unknown origin. Since we don't know where this -e- comes from, isn't it plausible that it arose through dissimilation from the -a- seen in other verb stems?
    – user8017
    Feb 24, 2016 at 23:50
  • (2/2) Without this dissimilation, the subjunctive of a-stems would (correct me if I'm wrong) have been indistingushable from the indicative, except in the 1st. person singular. If this theory is correct, then the OP's idea of "swapping" wouldn't be too far from the truth.
    – user8017
    Feb 24, 2016 at 23:51
  • I am just now reading Kuster's article on Old Norse transforming into Scandinavian where just such melding of endings is common. At some point, a disambiguation may occur, but the word "swap" makes me think of a conscious decision, as in, "Oh, I notice our singular preterits and plural futures sound the same; we need to swap endings with some other tense to avoid confusion." How these unconscious developments in a language occur is of immense interest, but languages do tolerate a large amount of ambiguities.
    – pbarrett
    Feb 25, 2016 at 22:17
  • 1
    (1/2) Sure, swapping is not the same as dissimilation: I just meant that the e-vocalism of the subjunctive in a-stems could have arisen through an impulse to choose a different vowel, to prevent a formal overlap with the indicative.
    – user8017
    Feb 25, 2016 at 22:34
  • 2
    (2/2) As far ambiguity, affixes can certainly fall together (via sound change) in the process of distinctions being lost, but the subjunctive as a category was fairly robust (and frequent) in Latin, so there would have been a motivation to "repair" potential ambiguities in some stem classes. Similarly, the difference between the future indicative of the 1st and 2nd conjugations (amābis, habēbis) and that of other classes (pōnēs) may be because a long-ē future would have looked the same as the subjunctive of the 1st conjugation, and the same as the indicative of the 2nd.
    – user8017
    Feb 26, 2016 at 11:59

This trait is directly inherited from Latin. A verb like laudare has subjunctive forms with an e: laudem, laudes, laudet, lauemus, laudetis, laudent while other verbs form their subjunctive with an a, e.g. vivere has: vivas, vivas, vivat, vivamus, vivatis, vivant.

  • 2
    Well, it is true, but not an answer to my question. I am aware that this is inherited from Latin. So the question is not about how the Romance languages inherited it. I had stated it in the question, and now I added an explicit note below. I think you may delete your post :) Feb 24, 2016 at 14:56

I got a plausible and quite exhaustive answer here in the Spanish Stackexchange: https://spanish.stackexchange.com/a/16541/11155

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