The rule for using “a” and “an” is actually more complicated than you may have been taught.
A lot of people learned the rule that you put “a” before words that start with consonants and “an” before words that start with vowels, but it’s actually more complicated than that. For example, here’s Matthew with a question:
I’ve been wondering if it is actually “a hour” or “an hour.” “An hour” sounds more correct, but “a hour” reads more correct to me. I’m just curious what it should be.
The rule is that you use “a” before words that start with a consonant sound and “an” before words that start with a vowel sound. See More . . .