answer:Huh? I don’t remember that ever being a rule. Saying ‘An H’ is correct because it’s pronounced “aych”, hence it begins in a vowel sound and so is preceded by ‘an’. Most words that start with H actually start with the h sound, and thus are preceded by ‘a’, since it’s a consonant sound. As far as I’ve ever known (which, disclaimer, only goes back two decades), it’s only ever been that ‘a’ precedes a consonant sound, and ‘an’ precedes a vowel sound.