I've mostly heard that its a ɯ sound. But I've also heard that its an 'endo-labial close back rounded vowel'. By 'endo-labial', I mean that its a rounded vowel that's pronounced without protruding the lips.

I would like to know what is the actual phoneme that the Roman letter 'u' signifies in Japanese.

One thing I should note, is I just watched the video for Freeze by Aural Vampire. In that, she's obviously pronouncing a 'u' sound (and by that, I mean the rounded close back vowel). Even looking at her lips she appears to be pronouncing a 'u' sound.

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    What do you mean by "actual phoneme"? Do you mean "what is the featural analysis of 'u' in Japanese? Or is this about the phonetics of the vowel?
    – user6726
    Sep 4, 2018 at 20:46
  • There are several dialects that use a rounded /u/, and even in compressed-lips dialects, speakers may round it depending on the circumstances. Notice also that trained singers may use special vocalic articulation, sometimes even taught explicitly, in order to better manipulate resonances for artistic purposes; for example, the lowered F3 of rounded lips is consciously employed as a "darkening" technique in singing methods. Sep 4, 2018 at 23:40

1 Answer 1


The labelling of phonemes is fairly arbitrary: we say English has an /d/ phoneme, for example, but it may not ever be realized as a true perfect IPA [d]. Reconstructed languages often have phonemes not named after any IPA symbol, such as Proto-Indo-European's /*ǵ/ (what would it even mean to put a high-tone mark on a velar plosive?) or Proto-Slavic's /*ъ/ (not even a Latin character). Some reconstructions (such as Alice Kober's early analysis of Linear B) have even just given each phoneme a number, to avoid committing to any ideas of what it might have sounded like.

So the phoneme in Japanese is usually written /u/ or /ɯ/, whichever the individual doing the analysis prefers. Neither is wrong: you could just as well call it "vowel number three" and write it /3/, and that wouldn't be wrong either. What's important is just that readers understand what phoneme you mean, and neither /u/ nor /ɯ/ (nor even /3/) is likely to be mistaken for any other phoneme.

Phonetically, the most consistent features of Japanese /u/ is that it's high and non-front. It sometimes moves as far forward as central [ɨ] after palatals, and might have the lips rounded, unrounded, or compressed ([ɯ̟ᵝ]). The version used in the prestige dialect of Tokyo in careful, formal speech tends to be more like [ɯ̟ᵝ], so we might well call the phoneme /ɯ̟ᵝ/, but that's just too annoying to write over and over.

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