When choosing between “a” and “an,” many think the rule is to use “a” with words that start with consonants and “an” with words that start with vowels. While this is true in many instances, the more accurate rule is to use “a” with words that start with a consonant sound and “an” with words that start with a vowel sound.

The word “one” starts with a vowel, but the sound it makes is the consonant “w.” So, “a one man show” is correct.

Some letters sound like vowels in one word, but sound like consonants in other words. For instance, these words that begin with the letter “h” start with a consonant sound:

She is writing a haiku.
Lynn hopes to spot a hawk while hiking in the mountains.

But these words that begin with the letter “h” start with a vowel sound:

She might have trouble finding an herb for that recipe.
The award was an honor.

Acronyms can be tricky, too, but they conform to the same rule of sound:

She’s graduating with a B.A.
He’s going back to school for an M.F.A.