According to Diana Finch a diphthong is a

According to Diana Finch, a diphthong is a vowel sound where the tongue glides from one vowel position in the direction of another, within the same syllable.

Diphthongs are sounds which consist of a movement or glide from one vowel to another. A vowel which remains constant and does not glide is called a pure vowel.

The closing diphthongs have the characteristic that they all end with a glide towards a closer vowel. Because the second part of the diphthong is weak, they often do not reach a position that could be called close. The important thing is that a glide from a relatively more open towards a relatively more close vowel is produced.

As the tongue moves closer to the roof of the mouth there is at the same time a rounding movement of the lips. This movement is not a large one, again because the second part of the diphthong is weak.

�the distance the tongue travels from one place to another: narrow/ wide �the direction of the movement: closing/ centring �the prominence of the element: falling/ rising

* Classify diphthong n° 18.

�A TRIPHTHONG IS A GLIDE FROM ONE VOWEL TO ANOTHER AND THEN TO A THIRD, THIRD ALL PRODUCED RAPIDLY AND WITHOUT INTERRUPTION.

A third vocalic element /ə/ can be added to all diphthongs except the centring ones: eɪ+ ə /eɪə/ «layer» , «player» aɪ+ ə /aɪə/ «liar» , «fire» ɔɪ+ ə /ɔɪə/ «loyal» , «royal» əʊ+ ə /əʊə/ «lower» , «mower» aʊ+ ə /aʊə / «power» , «hour» The resulting sequence, however, is pronounced fully only occasionally, as when using either a slow, formal style of pronunciation, or when the word containing the vocalic sequence is given special emphasis.

Speakers of general RP, though tend to weaken and/or omit the second element (/ɪ/ or /ʊ/) in ordinary conversational style. This vowel reduction, a form of compression, is known as «levelling» . e. g. «fire» /faɪə/ /faə/