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.

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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:

Here are a couple of example sentences:

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