Eli5: What makes a vowel a vowel?

Question

In English, at least as I learned it 40 years ago, the vowels are a, e, i, o , u, and sometimes y. I know that every word must have a vowel. But, what IS a vowel. Why is “a” a vowel and “b” is not?
Muchas gracias.

In: 7

Answer 1

in simple words, every english word contains atleest one of the letters (a, e, i, o, u) making them a different class to the rest of the letters and thus vowels. its how i learned lul