Which term describes a phoneme formed of two vowel sounds joining in a glide, such as /au/?

• A. Monophthong
• B. Diphthong
• C. Phonotactics
• D. Prosody

Answer: (B)

A vowel sound that slides from one vocal quality to another within the same syllable is a diphthong. A diphthong is a single phoneme whose articulation starts with one vowel position and glides toward another, creating two distinct vowel qualities in one nucleus. In your example, the sounds move from /a/ toward /u/ during the articulation, forming a single, evolving vocalic sound rather than two separate, discrete vowels. This glide distinguishes diphthongs from monophthongs, which are pure, steady vowels with no moving quality. Phonotactics and prosody deal with sound sequences and rhythm/intonation, respectively, but neither describes a single vowel sound that changes quality like a diphthong does.