I want to check my understanding of these 2 terms:

diphthong (concerned with sound; 1 sound; represented 2 letters; not long or short)
digraph (concerned with graphemes; 2 letters; can be long or short)

Is this accurate? If not what is the similarities/differences? And can a diphthong be represented by a digraph/ is it always represented by a digraph?

3 Answers 3


You are right about their being concerned with sound and graphemes, respectively.

A diphthong is concerned in particular with vowels. The term refers to a combination of two vowels characterized by a sort of glide from one vowel to the other. English is full of them, and particularly in English it is not true that a diphthong is always represented by two letters. Here are some examples:

a in "gate" /eɪ/

i in "bite" /aɪ/

o in "alone" /əʊ/ (BE) or /oʊ/ (AE)

ow in "cow" /aʊ/

A digraph is any two-letter representation of a single sound. Examples:

th in "another" /ð/ or in "thanks" /θ/

sh in "English" /ʃ/

oo in "root" /u/

The diphthong /aʊ/ in "cow" is represented as the digraph "ow". This is not unusal, but as you can see in the examples, not always the case.

  • All great responses. This one most correlated my thinking. Mar 29, 2013 at 2:08
  • I agree that diphthongs dont' have to be written with two letters. I don't agree with your examples. The "e" after the consonant is clearly a second letter: "gat", "bit" and "alon" would be pronounced with diphthongs. Two vowel letters separated by a consonant still totals two vowel letters (though two letters which I wouldn't call a digraph.) Mar 29, 2013 at 2:24
  • I think this misses a key point as the description it gives: 'combination of two vowels characterised by a sort of glide from one vowel to another'; can also apply to a non-dipthong sequence of two vowels. The main thing about diphthongs is that they are a sequence of two vowel qualities which are treated (in the language in which they are found) as a single vowel phone. Mar 29, 2013 at 7:12

A diphthong is a single vowel sound which is not a single 'pure' vowel quality, but is composed of a transition from one vowel target to another. Some examples (using RP English) are the vowel sounds in the following:

lied [laɪ̯d]

low [ləʊ̯w]

A digraph is a combination of two graphemes to represent a single sound. Thus the digraph <ph> is composed of two graphemes, <p> and <h>, but as <ph> it represents a distinct sound, the labiodental fricative [f]. Digraphs may be used to represent diphthongs.


Diphthongs are actually somewhat complicated in English.

There are phonemic diphthongs /ay aw oy/ (to use Kenyon and Knott's American phonemic system), as in buy bough boy, which are definitely phonemic, and in contrast with the vowels they transition between (/a o i u/).

Then there are phonetic diphthongs, which represent diphthongized allophones of single tense vowel phonemes, like [əʊ̯] in RP or [ow] in American English for the tense mid back rounded vowel phoneme /o/.

In American English, all tense vowel phonemes have diphthongized allophones -- front tense vowels /i e/ have a high front /i/ glide, and back tense vowels /u o/ have a high back rounded /u/ glide. There are no pure tense vowel phonemes for these diphthongs to contrast with, so they are normally not represented phonemically, viz:

/i/   [iy]     /u/ [uw]
/e/ [ey]     /o/ [ow]

This is such a common phenomemon that it's a feature of an American accent in other languages; speakers of American English are often unable to hear or produce the distinction between (for example) /e:/ and /ei/, or /o:/ and /ou/, when speaking European languages.

Edit: I find that I have already answered this question here.

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