The chant in question went "uenio, uenis, uenit, uenimus, uenitis, ueniunt". Occasionally, because my focus is on mediaeval Latin rather than classical and it doesn't really matter, it would go "venio, venis, venit", etc. The verb is "venire", "to come"[1], and I spell it with the "v" here because "venire" is also the modern Italian infinitive of "to come". What suddenly struck me as I was muttering, slurring syllables into musical chants, was the way "venio" can have three syllables ("ve-ni-o") or two ("ven-yo"). And this second form sounded oddly familiar. Not from modern Italian - today, the verb runs "vengo, vieni, viene, veniamo, venite, vengono". Italian "vengo" and "vengono" ("they come") are pronounced exactly as they look, each consonant alone ("ven-go", "ven-go-no").
And with one of those pleasing little moments when one more linguistic link falls into place, I realised where I'd heard the form "ven-yo" before:
I' son Beatrice che ti faccio andareAnd the third person plural derived from it:
vegno del loco ove tornar disio;
amor mi mosse, che mi fa parlare. (Inferno, ii.70-72)
I am Beatrice who bids you go,
I come from whither I long to return;
Love moves me, and moves my speech.
Quali colombe dal disio chiamateIt's not modern Italian, but Trecento Tuscan. In modern Italian, "gn" (as in "gnocchi", "agnello", "magno") is pronounced "ny", so Dante's "vegno" is pronounced "venyo" - ie, very similar to the way Florentines were probably pronouncing the Latin "venio" at the time, as "io" in Tuscan was almost invariably a diphthong[2].
con l'ali alzate e ferme al dolce nido
vegnon per l'aere, dal voler portate. (Inferno, v.82-84)
Like doves summoned by desire
wings lifted, then still, to the sweet nest
they come through the air, borne by will.
A quick search on Dante Online (which I adore) confirmed that the form "vengo" never appears in any of Dante's works, and "vengono" only twice, both in the Convivio.
But of course, this is a modern (online) edition of the text. The extant manuscripts - of which there are many - vary wildly in their spelling, abbreviations, punctuation, capitalisation, and aeration (where one word ends and the next begins), even if one confines oneself to manuscripts produced in Tuscany in the fourteenth century.
For example, comparing one line across nineteen manuscripts at Dante Online that fit those criteria, we have:
Sol con un lengno e co(n) quella co(m)pagnaLetters or words in brackets are rendered by abbreviations imported from Latin. Spelling of the sound rendered nowadays by "gn" varies between "gn", "gni" and "ngn". But it's worth pointing out that the "gn" in both "legno" and "compagna" are descended from the Latin "gn", rather than "ni". And in the same manuscripts, the spelling of "vegno" is actually far more stable (the text is Beatrice's speech quoted above):
sol chon un lengno e cchon quella chonpangna
sol con un lengno (et) con quella compagna
sol chon u(n) legno (et) co(n) quella compagna
sol con un legn (et) con quella compagna
sol con un legno (et) co(n) quella co(m)pagna
sol con un legno (et) co(n) quella co(m)pagna
sol con un legno,' et conquella compagna
sol con un legno (et) conquella co(m)pagna
sol conu(n) legno eco(n) quella co(m)pagna
sol con un legno (et) co(n) quella co(m)pagna
sol con un legno (et) cu(n) quella compagna
solchonun lengno eco(n)quella compangna,
Sol chon vn lengno et chon q(ue)lla (com)pagna.'
sol con un legno (et) co(n) q(ue)lla co(m)pagna
sol con u(n) lengno e con quella conpagna
sol con un legno et con quella compagnia
sol co un legno (et) con quella compagna
sol conun legno (et) co(n) quella co[m]pagna
Bibl. Medicea Laurenziana: Strozzi 152 2r
Bibl. Medicea Laurenziana: Ashburnham 828 2r
You could have hours of fun comparing the spelling of just those four little extracts. "Beatrice" appears twice as "Biatrice", "I'" appears once as "I" (without any indication of the elided "o", twice as "Io" and once as "Io" with the "o" subpuncted - marked for deletion by a discreet dot underneath. The "or" in "amor" and "tornar" appears in three of them with the half-r, which, in the fourth manuscript, is also irregularly used after "a". Not one is even internally consistent in how they join "che" to the following pronoun ("ti" in the first line, "mi" in the third). The consonant is sometimes doubled, sometimes not, and the second manuscript spells it "che" in the first line and "ke" in the third. Three of them change "di" to "del" and attach it with a doubled consonant to "loco", but the fourth doesn't, effectively omitting the definite article, which could be an interesting Latin-derived mannerism in itself, or just a mistake. One has "dove" for "ove", which means much the same thing but is more common in modern Italian.But one word that stays consistent - save for the immaterial distinction between "u" and "v" - is "vegno". Perhaps the "gn" in words derived from a Latin "gn" (such as "legno" and "compagna" above) was pronounced more nasally (ng+n), leading to irregular spelling, where the "io"-descended "gn" was harder to confuse as it was one consonant ("n") followed by a diphthong.
Nowadays you wouldn't distinguish "legno" from "vegno" - except, as I said before, that "vegno" has vanished. The consonants reversed, and hardened to "vengo". So at some point, farther down the track, the pronunciation was distinct enough to stratify in the spelling.
I wonder when that happened?
[1] Yes, I know it's conventional in Latin to use the first person singular indicative - "venio", "I come" - to "name" a verb. No, I don't care. To me, the infinitive of a verb is the name. Favouring one finite form over another is silly.
[2] Although, an exception occurs in both of the above quotes - both contain the word "disio", "desire", in which the primary stress falls on the second "i" and it is therefore a full syllable in its own right.
Except where specified as manuscript transcripts, quotes are from the Commedia seconda l'antica vulgata, Edizione Nazionale of the Società Dantesca Italiana, under the general editorship of Georgio Petrocchi (Florence 1994), accessed at Dante Online. Translations are mine.