How many vowel sounds in a diphthong syllable?

Answer 1

There are two vowel sounds in a diphthong, although there may be only one vowel.

Two: the word "diphthong" comes from the Greek díphthongos, where di means two and phthongos means "sound" (another word that contains the Greek "di" is "dioxide", which means having two oxygen atoms).

Answer 2

There are typically two vowel sounds in a diphthong syllable, where the sound glides or slides from one vowel sound to another in a single syllable.