I am interested for the term used when instances of two consecutive vowels sounds are in different syllables, such as:

thrOUGHOUt, abbrevIAtion, immedIAte, barrIER, cOExist, promiscUIty, crEAte, pallIAtive, amIAble etc

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    You mean diphthong ?: a vowel sound in which the tongue changes position to produce the sound of two vowels
    – user 66974
    Feb 25, 2018 at 14:22
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    I suspect it may simply come down to the cOIncidence of a syllable that ends in a vowel followed by one that begins with a vowel.
    – Spencer
    Feb 25, 2018 at 14:26
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    If you transcribed your examples to IPA-based phonemes, you would find that the real (i.e, spoken) vowels were all either /i/ or /u/, or their corresponding semivowels /y/ or /w/, followed by some other vowel. This is a phonological construction called a "glide" that links two successive vowels. It's different from a glottal stop like "uh-oh" (although some classify glottal stop as a glide for this reason). But most vowel sequences in English start with tense vowels, and all of those come with final glides. Feb 25, 2018 at 15:01

2 Answers 2


This is called hiatus: two consecutive vowel sounds in separate syllables; as opposed to diphthong, two consecutive vowel sounds in the same syllable. In hiatus, the vowel sounds need not be different, though it is rare for language to actually distinguish between two hiatus of the same vowel, and a long vowel: e.g., [e.e] vs. [ee]

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    With two consecutive but otherwise identical vowels in hiatus across syllabic boundaries, many English speakers unconsciously apply various sorts of largely optional sandhi effects for dissimilation. They may alter one of the two duplicate vowels or else separate with a very brief glottal stop [ʔ] or a linking glide like [j] or [w], or even [ɹ] when [ə.ə] occurs. So the east [ðiʔˈist], [ðiˈjist]; too oozy [tʰuʔˈu.zɪ], [tʰuˈwu.zɪ]; anti-immigrant [ˌæn.tɪʔˌɪ.mə.gɹənt], [ˌæn.tɪˌjɪm.ə.gɹənt]; idea of [ʌɪ̯ˈdi.əʔ.əv], [ʌɪ̯ˈdi.əɹ.əv], [ʌɪ̯ˈdiə̯.ɹəv], [ʌɪ̯ˈdi.jəv].
    – tchrist
    Feb 25, 2018 at 15:11
  • Thank you for this answer. Nice that hiatus contains a hiatus. Have not so far been able to find a list of haituses occurring in English anyone know of such a list - I am not looking for every word just every type of sound with examples. Feb 25, 2018 at 15:32
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    @atomised That list won’t help you: any arbitrary vowels can occur in hiatus, so you’re asking for hundreds of pairings.
    – tchrist
    Feb 25, 2018 at 15:34
  • @atomised for English examples read the The New Yorker. For some reason their style guide requires a diaeresis on the second of two vowels that are in hiatus.
    – user31341
    Feb 25, 2018 at 22:23
  • @jlovegren They explain why here. I have a hunch that the importance of the French language during the 1700s led careful writers of English to use their diæ̈reses in words like naïve, coälesce, reëlect, coöperate, antiïmmigrant, noöne, reïnvest and all the rest in the Romance style dominant in that day. You still see it aplenty in the 1800s but by the 1900s it’s the exception not the rule, and in the 2000s it’s considered an oddity. Yet not even The New Yorker has figured out how to write diæ̈resis. :)
    – tchrist
    Feb 25, 2018 at 22:34

As jlovegren mentioned, two sucessive vowels in separate syllables are said to be "in hiatus". Sometimes there is variation between pronunciations with two vowels in hiatus and pronunciations with diphthongs.

The 7 English vowels that can be closing diphthongs

In English, many vowel phonemes have a tendency to be pronounced as "closing diphthongs": at the end of the vowel, the tongue gets "closer" to the roof of the mouth. Speaking generally, there are 7 such sounds. (Of course, you can get a different number if you use a different analysis, or if you try to account for regional splits (usually with very little contrastive load) that exist, such as the aɪ/əɪ split that exists for some North American speakers with "Canadian Raising" or the əʊ/ɔʊ split that exists for some British English speakers because of the effects of /l/ coloring a preceding vowel.)

There are three "true diphthongs" in Standard English where the tongue starts out in a very different place from where it ends up:

  • /aɪ/ (the vowel sound of buy; sometimes written /aj/, /ɑj/, /ai/, or in non-IPA transcription /ay/),

  • /aʊ/ (the vowel sound of now; sometimes written /aw/),

  • /ɔɪ/ (the vowel sound of boy; sometimes written /oɪ/, /oj/, or in non-IPA transcription /oy/).

There are also four vowel phonemes that are often pronounced as closing diphthongs where the tongue doesn't move as far, and the extent of diphthongization varies between accents and depending on the context. These are sometimes called "tense" vowels (the exact meaning of this term unfortunately seems to vary between authors):

  • /i/ (as in see; also written /iː/; sometimes written /ij/ or /ɪj/ or in non-IPA transcriptions /iy/),

  • /u/ (as in glue; also written /uː/; sometimes written /uw/ or /ʉw/),

  • /eɪ/ (as in day; sometimes written /e/, /ɛɪ/, /ei/, /ej/, /ɛj/, or in non-IPA transcriptions /ey/),

  • /oʊ/ (as in toe; also written as /o/ (for American English) or /əʊ/ (for British English); sometimes written as /ou/, /ow/ or /əw/).

The glide phonemes /j/ (the "y" sound in "yellow") and /w/ are articulated in a similar manner to the end of a closing diphthong, so many speakers find that in a sequence of a closing diphthong followed by another vowel, it sounds like there is a /j/ or /w/ sound in between the vowels (as mentioned in a comment by John Lawler).

Vowels that can be used as the first of two vowels in hiatus

As far as I know, in English, the first of two vowels in hiatus can never be /ɛ/, /æ/, /ʌ/, or /ɒ/ (the vowels of pet, cat, cut, and British English pot, respectively).

Vowels in hiatus with stress on the first

When the first vowel is stressed, I think there are at most 9 options for it:

  • any of the 3 "true diphthongs": /aɪ/, /aʊ/, /ɔɪ/ (as in quiet, allowance, annoyance)

  • any of the 4 "tense" (closing-diphthongized) high or mid vowels: /i/, /u/, /eɪ/, /oʊ/ (as in European, acuity, chaos, stoic).

  • in a number of accents, the first of two vowels in hiatus may be one of the 2 non-front non-closing-diphthong vowels /ɑ/, /ɔ/. However, in certain British English accents, sequences of /ɑ/ or /ɔ/ + another vowel may be separated by epenthetic /r/ in at least some contexts: for example, drawing is commonly pronounced as "droring". I'm not sure if it's common in British English to pronounce baaing as a homophone of barring. In some North American accents, such as mine, there is only one vowel phoneme corresponding to the /ɑ/, /ɔ/ of other accents.

As far as I know, the second vowel has no real restrictions based on the identity of the first, although some combinations are more or less common (and it seems likely that there are some gaps: I just doubt that the pattern of gaps can be described in any simple way). Also, when the first vowel is stressed, the second vowel is often unstressed, which means it may be subject to vowel reduction.

The phonetic process of "smoothing" may result in the use of a single vowel in place of a stressed vowel followed by an unstressed vowel in hiatus in certain contexts. The rules for this vary significantly between varieties; one example from my dialect is that I usually pronounce "Graham" as /græm/ (in broad phonetic transcription, [greə̯m]) rather than as /greɪəm/.

Vowels in hiatus without stress on the first, or with stress on the second

When the first vowel is unstressed, it's a bit harder to give a comprehensive list of all options. It could be:

  • one of the 2 neutralized high vowels /i~ɪ/ or /u~ʊ/ (as in median, gradual). In traditional British "Received Pronunciation", these sounds were identified with the "lax" vowel phonemes /ɪ/ and /ʊ/; however, in contemporary British English, they are often identified with the "tense" vowel phonemes /iː/ and /uː/, and in American English, it is typical for these to be transcribed as "tense" vowels. As with the stressed tense vowels, the transition between /i~ɪ/ or /u~ʊ/ and the following vowel often sounds similar to a glide phoneme (/j/ or /w/).

  • either of the 2 "tense" (diphthongized) mid vowels: /eɪ/, /oʊ/ (aorta, oasis); however, unstressed /eɪ/ may be reduced for some speakers in some contexts to /i~ɪ/ (see my answer to Which English words feature reduction of diphthongs like /eɪ/ to /i/?) and unstressed /oʊ/ may be merged for some speakers (not sure if in perception or production, or both) in some contexts with /əw/: Merriam-Webster transcribes heroine as ending in "-ə-wən".

  • a "true" diphthong: I think only /aɪ/ is at all common (in words like biography), but /aʊ/ and /ɔɪ/ seem to be possible (as in however, Loyola, Toyota). That said, it seems possible that at least some speakers think of the words that appear to have /ɔɪ/ followed by a stressed vowel as actually having a phonemic glide /j/ (corresponding to the use of the letter "y" in the spelling); it's a bit hard to say. Also, I'm not sure if the first syllable of "however" is actually unstressed; now that I think about it, it seems like it might have secondary stress.

  • The reduced non-high vowel /ə/: this is fairly uncommon as the first of two vowels in hiatus, but it seems it may occur for some speakers in certain words spelled with a, such as Pasiphae and Danae.

  • One of the 2 non-reduced non-front non-closing-diphthongs /ɑ/, /ɔ/: These are pretty uncommon in unstressed syllables as they often reduce to /ə/ in this context. However, it seems possible that they occur unreduced for some speakers in certain loanwords or things like that (e.g. the name Raúl). There appears to be a tendency to merge /ɑ/ in an unstressed syllable followed by the high front vowel /i/ or the glide /j/ with the diphthong /aɪ/: an example is the word naive, from French naïf/naïve with hiatus (/naif/, /naiv(ə)/); English speakers may identify the vowel in the first syllable with either /aɪ/ or /ɑ/.

  • What Jon Lawler was saying is that all "tense" vocalic phonemes a;waus finish up with a little phonetic semi-vocalic off-glide, so phonemic /e/ is phonetic [eʲ], phonemic /i/ is phonetic [iʲ], phonemic /o/ is phonetic [oʷ], phonemic /u/ is phonetic [uʷ]. American textbooks don’t write that little off-glide because it’s merely a part of the phonology of the language, not a phonemic distinction. These are not phonemic diphthongs like /aɪ̯/, /aʊ̯/, and /oɪ̯/ are (sometimes written more simply as /aj/, /aw/, and /oj/). The simplest way to write hiatus phonemically is just /hajˈetəs/ that way.
    – tchrist
    Feb 25, 2018 at 22:07
  • @tchrist: As I said, there are different ways of analyzing the data and of transcribing the relevant sounds. John Wells wrote in a blog post (linking semivowels?): "The IPA symbols [ʲ, ʷ] are properly no more than diacritics, indicating palatalization and labialization respectively. [Cruttenden], though, is obviously using them to denote very short, transitional, non-phonemic glides."
    – herisson
    Feb 25, 2018 at 22:10
  • (cont.) "I suppose he is right in saying that these not-quite-segments may sometimes be “heard”, since experience shows that some naïve transcribers are convinced that they exist. Personally, I take the line that they are figments of our imagination: the supposed “[ʲ]” in my arms merely represents the point of maximum upward excursus of the tongue body as it moves from [a] through [ɪ] towards [ɑ]. How could one possibly detect the presence vs. absence of this entity on a spectrogram?"
    – herisson
    Feb 25, 2018 at 22:11
  • @tchrist: Of course, in British English the "goat" vowel is often realized phonetically as something like [əʊ], and my impression is that a number of speakers don't feel like this can be considered to be just a diphthongal surface representation of some underlying monophthongal vowel phoneme.
    – herisson
    Feb 25, 2018 at 22:14
  • I’d broadly transcribe the three-syllabled coalesce (once written coälesce to show the hiatus) as a simple /ˌko.əˈlɛs/ without spelling out the phonetic glide, but I feel strangely compelled to put a dot there to indicate the hiatus lest someone think I meant a two-syllabled non-rhotic word coreless /ˈkoə̯.lɛs/ or some such. But perhaps writing it explicitly with /ˌkowəˈlɛs/ gets around that, even if it is conflating phonetics and phonemics. Sigh.
    – tchrist
    Feb 25, 2018 at 22:17

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