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2026-10-13

Greek ei and ou: actually diphthongs?

With apologies to readers who prefer the Greek alphabet, I’m going to present the Greek in transliteration here. Most of this brief post is background information that Greek readers probably know already anyway.

Classical Greek ei and ou each spell what were originally two separate sounds:

Original diphthongs, as in teîchos ‘wall’ (PIE root: *dʰeiǵʰ-) and spoudḗ ‘haste’ (PIE root: *speud-). These were always spelled with ei and ou.
“Spurious diphthongs”, resulting from vowel contraction and vowel lengthening, as in einaî ‘to be’ < *esnaî, Moûsa ‘muse’ < *mónsā. In pre-Classical Greek, these are spelled with e and o, respectively. They probably represented long, close-mid vowels, /eː/ and /oː/.

The merger in spelling that happens in Classical Greek suggests that the original diphthongs and the original monophthongs merged. So far, so good. We can imagine two scenarios:

The original monophthongs became diphthongs: /eː/ > /ei/ and /oː/ > /ou/. This merged them with the original diphthongs. Hence, their spelling was (usually) updated to ei and ou.
The original diphthongs contracted to monophthongs: /ei/ > /eː/ and /ou/ > /oː/. This merged them with the original monophthongs, providing a new, distinctive spelling to distinguish them from the corresponding short monophthongs, /e/ and /o/. Hence, /eː/ and /oː/ were now spelled ei and ou regardless of their etymology. Words with “spurious diphthongs” like einaî and Moûsa never actually contained a diphthong.

Somewhere in the fourth century BCE, the merged sounds develop further into /i:/ (at first not before vowels) and /uː/, which is also how they are borrowed into Classical Latin. I think this is equally compatible with both scenarios.

Otherwise, Scenario 1 seems simpler to me, as it just involves spelling what you hear: ei is /ei/ and ou is /ou/. It also receives some support from ancient grammarians explicitly calling ei and ou diphthongs. Yet, Classicists universally accept Scenario 2.

Why?

The only argument I can find in Allen’s Vox Graeca (p. 68) is that “since the tendency of Greek at all periods is to monophthongization rather than diphthongization, only the second supposition is realistic.” This assumes a kind of ahistorical linguistic essence pushing a certain language in a given direction at all times. I don’t think it’s a good way to decide between the two possibilities. Allen also concludes (p. 79) that ei before vowels probably was a diphthong /ei/ (and, p. 80, that prevocalic ou probably was /ow/ by extension). So the standard position asks us to accept:

Although Greek does not distinguish purely quantitative contrasts between /a/ and /aː/, /i/ and /iː/, and /y/ and /yː/, Classical Greeks decided to spell /eː/ and /oː/ as diphthongs once the possibility arose. They did not use this clever trick a second time to distinguish etymological /i/ from etymological /iː/ after ei also became /iː/, as far as I can tell.
Ancient grammarians were wrong to call these sounds diphthongs, although they’re pretty explicitly talking about sounds.
Greeks were not troubled by the use of ei for /ei/ before vowels but for /eː/ before consonants and word-finally, nor did the grammarians remark upon this.

The evidence isn’t clear-cut, but of the two possibilities, Scenario 1 seems clearly preferable. What makes Scenario 2 the uncontested winner?

Here lies the spurious diphthong hypothesis. #alphabet #Greek #linguistics #ProtoIndoEuropean

#alphabet #greek #linguistics #protoindoeuropean