The English alphabet usually lists five vowel letters: A, E, I, O, and U.
Modern English uses 26 letters, conventionally divided into five vowel letters and 21 consonant letters, although the boundary is not perfectly simple. The five standard vowels can represent many different vowel sounds, depending on the word, spelling pattern, and dialect. For example, A sounds different in “cat,” “late,” and “father.”
Y is the common source of confusion. It acts as a consonant in “yes” but as a vowel in “myth” and “happy.” W can occasionally represent a vowel sound in a borrowed word such as “cwm,” but it is not normally included in the standard list. Also, vowel letters and vowel sounds are not the same: English spelling uses one letter or several letters, called digraphs, to represent sounds.