Front rounded vowels are somewhat uncommon. If we focus on the high front rounded vowel /y/ and consider cases where it was lost, it seems most likely to shift to /i/ by losing its rounding or to shift to /u/ by changing its backness than it is to shift to any other vowel.

I find /y/ more acoustically similar to /u/ than to /i/. However, I can think of one example of the sound change /y/ > /i/ off the top of my head, namely Greek, but no examples of the sound change /y/ > /u/.

My question is twofold:

  • Are there known instances of the sound change /y/ > /u/?
  • Is the sound change /y/ > /i/ actually more common than /y/ > /u/?

The immediate motivation for this question is personal experience. I'm trying to square my intuition that /y/ > /i/ is probably a way more common change than /y/ > /u/ with the observation that /y/ sounds much closer to /u/ in real life than it does to /i/.

I have studied French and Mandarin to some degree, both of which have the /y/ phoneme. For me, at least, the /y/ sound in both these languages sounds much, much more like /u/ than it does like /i/.

I speak California English natively, so I guess my normal /u/ sound is fairly front.

  • 1
    English also had y > i (English "feet" ~ German Füße), but front rounded vowels are rare enough that I can't think of any other examples of them disappearing off the top of my head.
    – Draconis
    Commented Oct 16, 2022 at 5:47
  • In both Icelandic and Faroese, /y(ː)/ has also become /ɪ ~ iː/ and /i ~ ʊɪ/, respectively, though in Icelandic a new /y/ has developed secondarily from /ʏ/ before /jɪ/, so hugi is /hyːjɪ/, while hygi would be /hɪːjɪ/. It’s fairly common in various Southern Chinese dialects for /y/ to merge with /i/ as well. Commented Oct 16, 2022 at 9:15
  • 4
    Your native /u/ being the fairly fronted diphthong that most variants of English possess is likely the reason you find /y/ closer to /u/. People who speak languages that have ‘plain’ /u i/ but no /y/, such as Spanish speakers, generally hear and produce /y/ as /i/. — But do bear in mind that /y/ is often historically related to/comes from to /u/ within a language (e.g., virtually all cases of /y/ in Germanic languages are from umlauted /u/, French /y/ is the default outcome of /u/, Fenno-Ugric and Turkic /y/ pairs with /u/ in vowel harmony, etc.). Commented Oct 16, 2022 at 11:18
  • @Draconis Greek also lost its front rounded vowels (upsilon being classically /y/, and oi likely going through a mid front rounded stage) merging them all into /i/
    – Tristan
    Commented Oct 17, 2022 at 8:44
  • @Tristan That one’s mentioned in the question, though. Commented Oct 17, 2022 at 22:04

2 Answers 2


In Uzbek, Proto-Turkic > u, e.g.:

Proto-Turkic *üč (“three”) > Uzbek uch /utʃ/
Proto-Turkic *kün (“day”) > Uzbek kun
Proto-Turkic *yǖŕ (“face”) > Uzbek yuz

From among some two dozen Turkic languages that have ever existed, Uzbek seems to be the only one with that change being consistent, which is evidence of the rarity of that phenomenon.

  • 3
    it's because of the Persian substratum.
    – fdb
    Commented Apr 10 at 13:44
  • @fdb - Sure, and also due to the Persian influence Uzbek lost vowel harmony.
    – Yellow Sky
    Commented Apr 10 at 16:51

The sound change /y/ > /i/ is more common than /y/ > /u/ partly since /y/ is acoustically closer to /i/ than /u/; the reason you feel the opposite is due to the peculiarities of English phonology. E.g. see:


Front, rounded NG [North German] vowels were assimilated primarily to back AE [American English] vowels, despite the fact that they were acoustically more similar to AE front vowels

Incidentally, as a speaker of a language that distinguishes /i/, /y/ and /u/, /y/ sounds so far apart from /u/, while I can kind of hear how people might associate /i/ and /y/ together.

  • 1
    What exactly is it you call “even more front” in Mandarin? That sentence isn’t very clear, but neither /u/ nor /y/ is significantly more front in Mandarin than their standard IPA values. And of course, historically speaking, Mandarin /y/ is by and large the outcome of erstwhile /u/ or /w/ in proximity to a /j/ – even if [y] and [i] do acoustically sound closer than [y] and [u]. Commented Apr 10 at 12:39
  • @JanusBahsJacquet I removed that from my answer as I'm not 100% sure, but it maybe sounds a tad different from how /y/ is usually pronounced in Finnish (which I speak)? Not by much certainly. Maybe it's Finnish that differs from the standard IPA symbol, although the Finnish vowel seems to sound the same as German (but not French) /y/ to me.
    – Someone211
    Commented Apr 10 at 12:44
  • @JanusBahsJacquet so I took a look at the vowel charts that are on Wikipedia which seem to confirm what I hear; Finnish and German /y/ are a little more central than Mandarin /y/ according to how the diagrams look at least.
    – Someone211
    Commented Apr 10 at 12:50
  • 3
    Yes, Finnish /y/ is slightly retracted, that’s true (short German /y/ is even more centralised in both height and frontness, phonetically closer to [ʏ]). The French or Danish /y/ is closer to the IPA value, and also more or less identical to the Mandarin one (as far as I can tell by pronouncing the closest thing to a minimal pair that I can think of: Danish i ly ‘sheltered’, French il a lu ‘he has read’ and Mandarin 一律 yílǜ ‘equally’). Commented Apr 10 at 13:17

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