English alphabet
The letters A, E, I, O, and U are considered vowel letters, since (except when silent) they represent vowels; the remaining letters are considered consonant letters, since when not silent they generally represent consonants. However, Y commonly represents vowels as well as a consonant (e.g., "myth"), as very rarely does W (e.g., "cwm"). Conversely, U and I sometimes represent a consonant (e.g., "quiz" and "onion" respectively).