The most complex English sounds of the vowel type are the triphthongs. They can be rather difficult to pronounce, and very difficult to recognize. A triphthong is a glide from one vowel to another and then to a third, all produced rapidly and without interruption. For example, a careful pronunciation of the word 'hour' begins with a vowel quality similar to ɑ:, goes on to a glide towards the back close rounded area (for which we use the symbol ʊ), then ends with a mid-central vowel (schwa, ə). We use the symbol aʊə to represent the pronunciation of 'hour', but this is not always an accurate representation of the pronunciation.

The triphthongs can be looked on as being composed of the five closing diphthongs described in the last section, with O added on the end. Thus we get:

eɪ   +     ə =  eɪə

aɪ   +     ə =  aɪə

ɔɪ   +     ə =  ɔɪə

əʊ   +     ə =  əʊə

aʊ   +     ə =   aʊə

The principal cause of difficulty for the foreign learner is that in present-day English the extent of the vowel movement is very small, except in very careful pronunciation. Because of this, the middle of the three vowel qualities of the triphthong (i.e. the ɪ or ʊ part) can hardly be heard and the resulting sound is difficult to distinguish from some of the diphthongs and long vowels. To add to the difficulty, there is also the problem of whether a triphthong is felt to contain one or two syllables. Words such as 'fire' faɪə or 'hour' aʊə are probably felt by most English speakers (with BBC pronunciation) to consist of only one syllable, whereas 'player' pleɪə or 'slower' sləʊɔ are more likely to be heard as two syllables.

We will not go through a detailed description of each triphthong. This is partly because there is so much variation in the amount of vowel movement according to how slow and careful the pronunciation is, and also because the "careful" pronunciation can be found by looking at the description of the corresponding diphthong and adding ə to the end. However, to help identify these triphthongs, some example words are given here:

eɪə   'layer', 'player'

aɪə   'liar', 'fire'

ɔɪə    'loyal', 'royal'

əʊɔ   'lower', 'mower'

aʊə   'power', 'hour'