A brief guide to using ‘a’ and ‘an’

The broad rules many teach for indefinite articles—that ‘a’ should go before a consonant and ‘an’ before a vowel—aren’t entirely accurate.

Determining whether to use “a” versus “an” should not be confusing, but it is.

This week, I had a prolonged discussion with a co-worker about why “an MRI” is correct and “a MRI” is not.

It turns out that many of us were taught the wrong rules for use of the indefinite articles. I remember being told to use “an” when the word preceding it starts with a vowel and to use “a” when the word preceding it starts with a consonant.

The rules actually say to use “an” before any word beginning with a vowel sound and to use “a” before any word beginning with a consonant sound. No matter how the word is spelled, “a” comes before words with a consonant sound, including /y/,/h/, and /w/. Likewise, no matter how it’s spelled, “an” comes before a word with a vowel sound.

Take these examples:

  • a unicorn
  • a user experience study
  • an umbrella
  • an uprising
  • a hotel
  • a historical study
  • an heir
  • an honor

Here are a couple of example sentences:

“It was quite a sight to watch such a histrionic performance.”
“That is an ugly drawing of a ukulele.”

All of this gets tricky when it comes to abbreviations, symbols, or numbers. But the rule is the same; it depends on how the term is pronounced.

  • a URL
  • a AAA membership
  • an FAQ list
  • an MRI
  • an NCAA player
  • an @ sign
  • a #
  • an 800 number
  • a 90s party

Another example sentence:

“I need a URL in order to create an FAQ page.”

So remember: Cut the confusion and answer the question of “a” versus “an” by listening instead of looking.

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Ragan.com readers, any “a” versus “an” stories to share?

Laura Hale Brockway is medical writer based in Austin, Texas. She is also a regular contributor to PR Daily. Read more of her work at impertinentremarks.com.


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