In addition to single vowel sounds, we regularly create sounds that consist of a combination of two vowel sounds, known as diphthongs. When we produce I o A E Figure 3.3 34 The Study of Language diphthongs, our vocal organs move from one vocalic position [a] to another [ɪ] as we produce the sound [aɪ], as in Hi or Bye. The movement in this diphthong is from low towards high front. Alternatively, we can use movement from low towards high back, combining [a] and [ʊ] to produce the sound [aʊ], which is the diphthong repeated in the traditional speech training exercise [haʊ naʊ braʊn kaʊ]. In some descriptions, the movement is interpreted as involving a glide such as [j] or [w], so that the diphthongs we are representing as [aɪ] and [aʊ] may sometimes be seen as [aj] or [aw].

While the vowels [e], [a] and [o] are used as single sounds in other languages, and in some other varieties of English, they are only typically used as the first sounds of diphthongs in American English. The accompanying diagram provides a rough idea of how diphthongs are produced and is followed by a list of the sounds, with examples to illustrate some of the variation in the spelling of these sounds.