It's easy for me to imagine the difference, but hard for me to conceptualize it. I guess one involves two vowels and the other involves a consonant, right? Am I on the right track, or is there a more precise definition?

5 Answers 5


If a language has a sequence of two vocoids, and one of them is high, there will be nothing in the signal to tell you whether you are dealing with a vowel+glide sequence or a vowel+vowel sequence. Three common sources of supplementary information (in decreasing order of empirical weight) are:

1) Cases where there is a lexical contrast between the vowel+vowel and the vowel+glide sequence. In Vietnamese, for example, there are lexical contrasts where the relevant difference is /-ai/ vs. /-aj/, or /-ou/ vs. /-ow/.

2) Morpho-phonological alternations or selectional restrictions that are sensitive to a vowel-consonant distinction. Two examples are given in Dixon (2010:196--9).

3) Phonotactic considerations. Is a statement of the overall phonotactic patterns of the language simplified by choosing one analysis over the other?

There will also be cases where no evidence is available. In these cases it will have to be admitted that there are no language-internal grounds for classifying the pattern in question.

Dixion, R.M.W. (2010) Basic Linguistic Thoery, vol.1. OUP

  • This term vocoid is not very common so I added a link to a definition. Commented Dec 14, 2011 at 11:12

The simplest distinction is

  • a glide is a single phoneme that is somewhere in the middle of the continuum between consonant and vowel, but is non-syllabic (by itself).

  • a diphthong is a sequence of two vowels, where one of them is often articulated just like a glide. It is questionable whether this two-vowel combination is a single phoneme or two separate phonemes in sequence, but there are two 'things', one of which is glide-like and the other a full vowel.

I hesitate to call the glide-like phone in a diphthong a full fledged glide only out of tradition, even though they are seemingly identical articulations.

The primary difference then is that a diphthong includes a glide as one of two constituent parts.

  • 2
    But a diphthong is also a single phoneme, your wording might make some people think it's not. Commented Dec 14, 2011 at 9:20
  • @hippitrail: I had always considered the thing called a diphthong is comprised if two phonemes. Looking things up again it seems that I'm not wrong but that there is vagueness on that, sometimes it is considered by authorities as a single phoneme and sometimes as two,
    – Mitch
    Commented Dec 14, 2011 at 13:16
  • Hmm maybe that's a good question then. It probably ties into the old "difference between phonetics and phonology" question. I do know that in the case of English the diphthongs are counted as phonemes. It's what makes "hop" and "hope" minimal pairs, each is three phonemes long. Commented Dec 14, 2011 at 13:52
  • 1
    @hippietrail: yes, what a diphthong really is is worth a separate question. But whatever one calls things, my main statement still stands, that a diphthong includes a glide and necessarily something else, so that the two concepts are not identical.
    – Mitch
    Commented Dec 14, 2011 at 14:03
  • 2
    I wonder if English speakers tend to think of diphthongs as single phonemes out of influence from the writing system (in my language we represent diphthongs with two letters, and I tend to think of them as an intra-syllabic sequence of a glide and a vowel). Commented Sep 13, 2018 at 22:32

Rather than a "vowel + consonant", a glide is a semivowel (it's a synonym). I posted once about them on here, for the question "Are there semivowels besides /w/ and /j/ and which are most common?". You can read more in the links

A diphthong is obtained by the combination of two vowels occurring in the same syllable. This combination varies according to the language and the rules that belong to the language itself.

  • In Spanish for example, a diphthong is obtained by joining a closed vowel (i, u) with an open vowel (a, e, o).
  • In Italian it's obtained by joining the vowels (i, u) in unstressed position to other vowels in stressed position, or by joining the same vowels, (/i/ and /u/ together), where one of them — in this case — can be in the stressed position.

And so on... You can read about more languages by clicking on the link.

  • Your Spanish example is a little misleading. It's only true if the open vowel comes BEFORE the closed vowel: aire [ai.re], peine [pei.ne], Europa [eu.ro.pa]. If the open vowel comes AFTER the closed vowel, the closed vowel turns into a glide: Cecilia [se.sil.ja], hierro [je.ro], fue [fwe].
    – alcas
    Commented Dec 13, 2011 at 20:58
  • Uhm, according to the answer provided by @Mitch, a diphthong can include a vowel articulated like a glide (which means not an actual glide, am I right?) but it's still a diphthong, and this matches with everything I find when I search about Spanish diphthongs. If this is true, my examples are not misleading. If I'm missing something, please point me to that.
    – Alenanno
    Commented Dec 13, 2011 at 21:18

In The Sound Pattern of English, SPE, a feature +/- syllabic, attributed to work by C.-J. Bailey, is used to distinguish [+syll] sounds which make for a syllable from [-syll] sounds, which do not make for a syllable. Or at least this is my interpretation of SPE. "Make for a syllable" means that the number of [+syll] sounds in a form will always be the same as the number of syllables in the pronunciation of the form.

Then, using this feature, glides are distinguished as [-syll], and diphthongs are characterized as combinations of syllabic and non-syllabic sounds. Rising diphthongs are [-syll][+syll], and falling diphthongs are [+syll][-syll]. In this conception, the difference between glide and diphthong is phonetic, and concerns whether a form has a syllable or not. A diphthong has a syllabic sound, but a glide does not.

  • As you no doubt recall, SPE did not recognize the existence of a syllable; so I would say that's your own spin-off from SPE, not something that SPE implied. Note, then, that [bæg] has a combination of [+syl][-syl] and a combination (overlapping) of [-syl][+syl], but it has no diphthongs of glides, so your account needs some tuning up.
    – user6726
    Commented Sep 13, 2018 at 21:45
  • @user6726, For the definition of SPE's syllabic feature. I hereby refer readers to SPE. I didn't mean to be defining it.
    – Greg Lee
    Commented Sep 13, 2018 at 21:56

At most cases,the make up model of language is structured by the sounds pf pronunciation n tone articulated during either talking,speaking and or telling. Tge variety differs in speed

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