The Real Rule for 'A' vs. 'An'

Monday, October 212 min read

Remember back in grammar school when the teacher taught you about the difference between “a” and “an”? They probably said something along the lines of: When you have a word that starts with a vowel, you use “an.” When you have a word that starts with a consonant, you use “a.”

For example, you have "a" peacock and "an" oyster. And you probably followed that rule for a long time, until you realized that sometimes it doesn’t sound quite right. For every rule, there is an exception. So how do these indefinite articles really work?

Determining Vowel Sounds

Your teacher had the right idea, but it wasn’t complete. Instead of looking for the vowel at the beginning of the word, you should listen for the pronunciation of a vowel sound. If the word begins with a consonant sound, you use “a.” If a word begins with a vowel sound, you use “an.”

You might already be following this rule naturally when you speak, but it can get tricky when you’re writing and you start to question your choices.

"University" is a good example. You would say, “I went to a university,” not “I went to an university.” Even though the word starts with a vowel, the first syllable in university is pronounced as “yun,” which makes it a consonant sound.

But the letter "u" doesn't always produce a consonant sound. If you wanted to remind your partner to take "an" umbrella when there’s a forecast of rain, you pronounce the “uhm” as a vowel sound.

“O” is another good vowel to pay attention to. Sometimes words that begin with the letter “o” have a consonant sound like a “wah” at the beginning. Say it out loud to yourself: “I went down a one-way road” not “I went down an one-way road.” Now try “octopus.” If you say, “I saw an octopus sliding down a one-way road,” you can see both at work. Octopus has an “aw” vowel sound at its beginning.

When a Consonant Becomes a Vowel

Consider the letter “h.” Is it “a history” or “an history”? The key is knowing where the emphasis is placed in the pronunciation. With the word "history," the accent is on “his,” which creates a consonant sound ("a" HIS-tory).

But with “historic,” the emphasis is on the second syllable, turning this variation into a vowel sound. So we’d say, “an hisTORic event.”

If you’re using British English or American English, the two don’t always agree on pronunciation. "Herb" is a good example. In American English, we say “an herb,” because we don’t pronounce the “h” sound. British English does, and they put “a herb” on their salad.

Watch Out for Acronyms  

What do you do with acronyms and abbreviations? Don’t fret; it’s easy-peasy. Just stop and listen to the sounds. If you pronounce a letter, and it begins with a vowel sound, you want to make sure that you use “an.”  


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The consonants that have vowel sounds are: "f," "h," "l," "m," "n," "r," "s," and "x." Can you come up with a fun mnemonic to remember these? If not, don't worry — just listen to the pronunciation.

Photo credit: Bogdan Dada/ Unsplash

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