In Classical Latin, the diphthongs ae and oe were pronounced as /ai̯/ and /oi̯/, respectively.

Why was the letter e in these cases pronounced as /i/ instead of with an /e/ or /ɛ/?

  • Good question! I suppose you could alternatively ask why they are spelled ae and oe instead of ai and oi.
    – Joonas Ilmavirta
    Commented Apr 26, 2018 at 22:55
  • Hi! It may be because i can be pronounced as /j/, so using e instead would resolve this potential ambiguity. But I can't prove it.
    – Cerberus
    Commented Apr 26, 2018 at 23:03
  • It is not always the case that spelling accurately reflects pronunciation. Moreover, Latin constantly changed, like any other language. The diphthongs in question were no exception. I’m aware of at least four different phonetic realizations of these diphthongs.
    – Alex B.
    Commented Apr 27, 2018 at 14:44

1 Answer 1


The sources I remember reading say that in the Classical Period, the pronunciation of "ae" is likely to have been closer to [ae̯] or [aɪ̯] than [ai̯] (the difference between [e] and [ɪ] in the IPA is very small; people don't always agree about which of these two symbols is more appropriate even for vowels in living languages, so it's doubtful that we can determine with certainty the better transcription for Latin).

Part of the reason for thinking this is the change in spelling from the older "ai" digraph. Another reason is the eventual monophthongization of "ae" to /ɛ/ in Romance languages.

I've seen less discussion of "oe" in the literature, as this was a less common sound in Classical Latin, but Wikipedia marks "oe" as "oi̯ ~ oe̯", citing Allen.

I suppose some sources may write /ai̯/ as a phonemic transcription of the diphthong, similarly to how, when we're dealing with Latin accents that had contrastive vowel length, the "short i" phoneme can be transcribed as /i/ even if we reconstruct its phonetic quality as [ɪ]. This doesn't necessarily constitute a claim that a Classical Latin speaker would have thought of the sound as containing the independent vowel /i/, any more than transcribing the English diphthong in the word "price" as /aɪ/ constitutes a claim that an English speaker thinks of the sound as containing the vowel found in the word "kit".

  • Do any of the sources indicate when the pronunciation changed, assuming it was more /ai/ than /ae/ at some point in early classical or pre-classical Latin? I would not be surprised if the pronunciation changed during the classical era.
    – Joonas Ilmavirta
    Commented Apr 26, 2018 at 23:06
  • @JoonasIlmavirta This thread quotes Terence. Commented Oct 25, 2019 at 16:01

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