When I was little I used to listen to the album Through Children’s Eyes by The Limeliters as often as I could get my dad to put it on his Hi-Fi. I haven’t heard it in over 45 years but I’m sure if I put it on today I’d still know every note by heart. It was recorded live with an audience of children in Berkeley in 1962. In one of the songs (probably B-A Bay) they said the vowels were “A, E, I, O, U and sometimes Y and W”. That’s the only place I’ve ever heard W could be considered a vowel. Has anyone else heard of W being considered a vowel?
The vowels sounds [j] and [w] are semivowels, a subset of approximants where there is some constriction of the airway, but not enough to make a full consonant sound.
In English Y sometimes sounds like [j] , like ‘yes’. And W sometimes sounds like [w], like ‘west’.
English has 5 to 7 vowel letters, but has 16ish vowel sounds (depending on how you count and which dialect). My favorite vowel sound is schwa (like the last vowel in ‘comma’ , which can be represented by the letters a, e, i, o, u, y, or be unwritten.
For contrast, Spanish has 5 vowel characters and 5 vowel sounds.