I’m not surprised when people ask me about this rule. Many believe that if a word begins with a vowel, then you use an, and if it begins with a consonant, you use an a. Unfortunately, it’s not that simple. It is the English language, after all…

My favorite thing about this rule is that it’s based on sound, not the written letters/word. If you’re confused about this rule, say the phrase aloud and you’ll usually hear which word (article) is correct.

Article: the, a, an – precedes a noun and tells you a noun will follow

Noun: a person, place, thing, or idea

Vowel: In the alphabet, the letters a, e, i, o, u, and sometimes y

Consonant: not a vowel (all the other letters)

The Rules

An – Use an if the noun following makes a vowel sound.

An apple, effort, octopus, honor

As you can see with honor, the h is there, but it is silent. If you say honor, you’ll hear the aw sound, which sounds like a vowel.

A – Use a if the noun following makes a consonant sound.

A fish, dog, rope, song

The exception (because there’s always an exception): the long u (pronounced yoo) sound.

A U-turn, unicorn, user

The best test is to think it aloud, so you hear the sound the noun makes. It’s all based on phonetics, and you’ll know whether it sounds and feels right or wrong.

For fun, say the following aloud and you’ll hear how wrong these sound and feel: an phone, an ladder, a ant, a ending.

If you have any tips or questions, feel free to comment below!

Sources: https://owl.english.purdue.edu/owl/resource/591/01/

Grammar Blue Book