1.214 choosing 'a' or 'an'
You use 'a' when the following word begins with a consonant sound.
This includes some words that begin with a vowel in their written form, because the first sound is a 'y' sound, |P|/j/.
You use 'an' when the following word begins with a vowel sound.
This includes some words that begin with the letter 'h' in their written form, because the 'h' is not pronounced.
'A' is usually pronounced |P|/%e/. 'An' is usually pronounced |P|/%en/.