- "When the medial phase shows an audible change of quality, with the change consistently progressing toward a single target, as it were, then the sound is classified as a diphthong." (Laver 1994:146)
[ai] in English wine, [au] in English house.
From Greek di-phthongos 'two-sound'. The word is first attested in English in the 15th century.
- monophthong (a vowel whose quality does not change)
- triphthong (a vowel whose quality changes twice during its pronunciation)
- Laver, John. 1994. Principles of phonetics. Cambridge: Cambridge University Press.