Diphthongs

In simple vowels, or monophthongs, the tongue body has a relatively stable position throughout. But there are other vowels where the tongue body does not stay in one place, even in the most abstract diagrams with artificial slices. Complex vowels which are characterized by movement are called diphthongs.

To transcribe a diphthong, we need two symbols: the first indicating the starting position and the second indicating the finishing position or the direction of movement.

In the English diphthong [aj], the tongue body starts in the position for [a] -- between [æ] and [script-a]. Almost immediately, it begins moving upwards and forwards. Occasionally it gets as far as [i], but usually only as far as [I] or even lower. In a broader transcription, we can ignore the exact position of the end-point and simply use the glide [j] as a cover symbol.
Rogers 2.11

In the English diphthong [aw], the tongue body starts out in the same position (for most Canadian speakers) and moves upwards and backwards, towards [u], [U], or [o]. In a broader transcription, we can use the glide [w] as a cover symbol for the end-point. The lips become increasingly rounding throughout the diphthong.
Rogers 2.12

In the diphthong [Oj], the tongue body begins in the position for [O] and moves upwards and forwards. The lips become increasing less rounded throughout the diphthong.
Rogers 2.13

In most dialects of English, the vowels we have been transcribing [e] and [o] also involve an upwards movement of the tongue body. In narrower transcriptions of these dialects, they would be written [ej] and [ow]:
Rogers 2.14
A tendency to pronounce all tense mid vowels as diphthongs is one of the most noticeable accent features of English-speakers trying to speak other languages.

In many dialects, even the vowels we have been transcribing [i] and [u] have short upwards movements:
Rogers 2.15



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