The verb fieri has an unusual conjugation, and one of the weird aspects is the long I before many vowels: fīō, fīās, fīet… Why is the I long? Does the origin of the verb (which I have no idea of) explain this behavior?

I do not remember any other verbs that would have a long vowel before the in the first person singular present indicative, although short ones are common (facio, ruo, luo, eo…), and the long I is against my rule of thumb concerning vowel quantity in verbs. This particular I feels like an outlier in Latin conjugation, and I can't make any sense of it.

  • I am wholly unsure whether this is correct, but I always analyzed it as is canonically done with eius, namely containing a consonantal geminated i which may make the preceding vowel heavy regardless of its quantity. The consonantal i would then not be written to avoid fiio, which looks like an awkward double i before another vowel.
    – blagae
    Commented Jul 10, 2017 at 9:54
  • @blagae I had never thought of that option. So you would pronounce it as fijjō instead of fīō? It would be interesting to know if anyone can verify or falsify that idea.
    – Joonas Ilmavirta
    Commented Jul 10, 2017 at 10:09
  • I don't consciously pronounce eius as ejjus either, so no, but I would probably try to build the habit of extending the analogy to fijjo if I did.
    – blagae
    Commented Jul 10, 2017 at 10:24
  • 'Fio', 'fias', and 'fiet' are two-syllable words, therefore the first syllable needs the accent. Trying to make the 'i' short in quality but long in quantity actually kinds of hurts my English-formed throat. 'F-iiiihhh-o'. Oww. Commented Jul 10, 2017 at 17:40

1 Answer 1


The paradigm of fio is quite unusual - see its present indicative partial paradigm (fīmus and fītis are pretty much regular; from my undergrad textbook, Sobolevskii 1948):

enter image description here

Weiss writes that

"In Classical Latin fīo, fīunt, fīam etc. 'become' have been analogically restored" (p. 126).

It seems this explanation goes back to Sommer 1902 (at least, that's what Leumman 1977 mentions, a later edition though). Here's what Sommer suggested (p. 589):

enter image description here

So, Sommer hypothesized that ī was "restored" in the thematic forms with ī+V so that the paradigm of the verb would have fewer alternating forms. This is known as analogical restoration in historical linguistics.

cf. de Vaan "*fī - would develop phonetically in the 23s. and 12 p.pr. forms, and then spread to the other forms of the paradigm."

Sihler adds, cautiously though, that it could have happened because of a very special status of fio - "the only verb in -io with tonic accent on the i" (p. 546).

Of course, we won't find "hard evidence" - we are talking about Old Latin here, after all. But another source of indirect evidence comes from Plautus and Terence, where we can find both fĭerī (more common) and fīerī, fĭeret (more common) and fīeret etc. See Sihler (p. 546) for some interesting thoughts on this

Weiss also mentions, in footnote 10 on the same page, a very interesting observation made by Jan Safarewicz (Safarewicz 1974): ī tends to be used in those word-forms of fio when the following syllable is heavy. Tronskii 1960 argues that ī > ĭ occurred only before -er-. That being said, Leumann 1977 still writes, "Die Verteilung von fī- und fi- ist unregelmäßig" (p. 530).

  • Re Safarewicz: why doesn't this happen to capiō or other i-stem thirds?
    – Draconis
    Commented Jul 12, 2017 at 3:27
  • @Draconis Safarewicz proposed his (ad-hoc) explanation only for fio; at least, in Weiss' summary. I haven't checked it de visu yet.
    – Alex B.
    Commented Jul 12, 2017 at 3:39

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