Why are the vowel sounds in English words such as âoutâ and âiceâ called diphthongs?
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phonetics
Diagram depicting the location of human vocal organs and possible places of articulation used for speech.
In phonetics, the vowel sounds in words like "out" and "ice" are classified as diphthongs because they are gliding vowels.12
Unlike "pure" vowelsâalso known as monophthongsâwhich maintain a steady state during articulation, a diphthong involves a continuous transition from one vocal tract position to another. Although they function as single speech sounds, they are typically represented in phonetic transcription using a pair of characters to indicate the initial and final configurations of the vocal tract. For instance, the vowels in "out" and "ice" are represented as [au] and [ai], respectively, reflecting this movement between two distinct articulatory points.12