A good friend asked about the correct use of the indefinite articles “a” and “an.”
Here’s the answer.
Listen to the word that follows the a or an. If the word begins with a vowel sound, use an. If the word begins with a consonant sound, use a.
Notice we said “vowel sound” and “consonant sound.” Some words begin with a vowel, but have a consonant sound; some words begin with a consonant, but have a vowel sound.
Consider these examples:
So far, no problem.
a one-armed man (pronounced wun)
a union (pronounced yewn-yun)
Now we’ve got a problem. Notice how in these examples the words begin with vowels but have consonant sounds. And because they begin with consonant sounds, they draw the consonant article, a.
an heir (pronounced air)
an hour (pronounced our)
an honor (pronounced on-or)
The problems continue. Notice how in these examples the words begin with a consonant, but have vowel sounds. And because they begin with vowel sounds, they draw the vowel article, an.
And just when you thought you were comfortable, the sounds change on you.
a history (pronounced hiss-story)
Because history begins with a consonant sound (h), it draws the consonant article, a.
The principle applies to the word immediately after the article; sometimes a modifier jumps in between the article and its noun:
an elegant elephant
a charging elephant*
The principle applies to acronyms and abbreviations. They’ll draw an a or an an depending on how they’re pronounced. How they sound:
a NATO agreement
an NFL contract
NATO, for example, draws an a because of the consonant N sound (a NATO agreement).
NFL draws an an because of the vowel sound (an en-eff-ell player).
*How do you stop an elephant from charging? Go ahead. You know the answer. Oh, we love this stuff.