Triphthongs

A triphthong is a type of vowel sound in which three adjacent vowel qualities occur within the nucleus of a single syllable. It is more complex than a monophthong, which has one vowel quality, and more extended than a diphthong, which moves from one vowel quality to another. In many languages, a triphthong is realized as a rapid sequence of three vowel sounds rather than as three separate syllables.

Articulation typically involves a glide through three vowel qualities in one syllable. The sequence often moves from a starting vowel to a middle vowel and then to a final vowel, frequently ending in a mid-central vowel such as a schwa. The exact articulation can vary by dialect and language, and some analyses describe what looks like a triphthong as a diphthong plus an adjacent vowel or as two syllables rather than a single nucleus.

In English, several sequences are commonly discussed as triphthongs, such as /aɪə/ in words like fire or liar, /eɪə/ in layer, and /aʊə/ in hour or our. The status of these sequences can be debated: in some dialects they are treated as three perceptual segments within one syllable, while in others they are analyzed as a diphthong followed by a schwa or as two separate syllables.

Across languages, triphthongs can be phonemic in some systems or arise from historical vowel changes in others. They are relatively less common than monophthongs and diphthongs and are typically described using phonetic detail for articulation and phonological analysis for their role in syllable structure.