A diphthong is a glide from one vowel sound to another within a single syllable (e.g., the phoneme /aɪ/ in the words I, my  or try). This is different from a monophtong, where there is just one vowel sound (/æ/ in man or sand).

Unlike Spanish, in English diphthongs are normally considered just one phoneme, not the combination of two. Here are the eight English diphthongs:

 

Table 1

ɪə here, near, deer, weird

ʊə endure, tour, pure, poor

eɪ make, brain, play, eight, great, they

əʊ go, low, bode, boat, toe, so, shoulder

ɔɪ boy, toy, noise, voice

eə there, air, share, rare, pear, bear

aɪ time, type, my, lie, buy, eye, high, height,

aʊ how, loud, mouse, about, cow, allow,

 

Diphthongs are one of the greatest sources of mispronunciation for Spanish speakers. The main difficulty is that English letters can be pronounced in several ways, so sometimes it’s difficult to know which is the correct one. An i  can be said as /ɪ/ or /aɪ/, an o as /ɒ/ or /əʊ/, etc. We must also remember that vowels are often pronounced /ə/ when they are unstressed. This uncertainty leads to very common mistakes. Let’s see some examples of words which are often mispronounced by Spanish speakers.

                                  Right                                                                          Wrong

since                        /sɪns/                                                                      /sains/*

abroad                   /əˈbrɔːd/                                                              /aˈbroud/*

afraid                     /əˈfreɪd/                                                               /aˈfred/*

said                         /sed/                                                                       /seɪd/*

both                        /bəʊθ/                                                                    /boθ/*

old                            /əʊld/                                                                     /old/*

comfortable       /ˈkʌmftəbl/                                                         /komforˈteibol/*

Ian                           /ˈiːən/                                                                     /ˈaian/*

image                      /ˈɪmɪʤ/                                                                /iˈmeiʤ/*

famous                  /ˈfeɪməs/                                                              /ˈfamous/*

 

 
However, the glides included in Table 1 don’t exhaust the subject of diphthongs, not in the sense we, Spanish speakers, understand them in any case (there seem to be differences in the criteria we use to classify very similar phenomena).

There are English words such as music /ˈmjuːzɪk/, new /nju:/, one /wʌn/, win /wɪn/ or when  /wen/ that we would immediately think of as diphthongs. But if they are not diphthongs in English, what are they, then? These words include sounds which are called semiconsonants or even semivowels sometimes (/j/ and /w/, explained here and here), which are very similar to vowels but not exactly the same, and that’s why they are left out of the table. However, to have the whole picture in mind, it is advisable to be aware of their existence and to know how they are considered in English.

 

And here are a couple of examples of diphthongs pronounced by native speakers:

 Well, I thought I’d given loads away. I think I’m full of sort of heartfelt personal details about my joys and pains (David Mitchell, BBC4)

 There’re jokes about the aging process (John Wilson, BBC4).

 

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There are no absolute rules that will always allow us to know if a vowel is pronounced as a monophthong or as a diphthong, but fortunately we can use a couple of very useful guidelines. Let’s see them.

 

 

Now, if you want to further refine your pronunciation of diphthongs, here are five interesting points to take into account.

 

 

 

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