The Tricky Exceptions to the "A" vs. "An" Rule

Some grammar rules are as straightforward as can be — at first glance, at least. We’re taught in grade school to use “a” before words beginning with consonants and “an” before words that start with vowels. That means you could plant “a herb garden,” right? Then why does “an herb garden” sound slightly better to our American ears? It’s because this simple grade-school grammar rule is more complex than it seems.

What Are Indefinite Articles?

The English language has two types of articles: definite and indefinite. They identify whether a noun is specific or generic. “The” is a definite article — the only definite article in English, in fact — and it indicates that we are referring to a particular noun. For example, “John bought the car” refers to one very specific car.

“A” and “an” are indefinite articles, and they can refer to any person, place, or thing. For example, if “Tom will bake a cake,” it could be chocolate, vanilla, or lemon. We don’t know what Tom has planned, based on the language used.

When To Use "A" or "An"

If “the” is the only definite article in English, why are there two indefinite articles? The simple answer is that they’re used in different situations, namely in regard to the letters that follow in the next word. Use “a” if the word that follows begins with a consonant:

They’re adopting a cat.
Did you wear a raincoat?
I’m eating a strawberry pie.

Alternatively, use “an” if the following word begins with a vowel:

She needs an eye exam.
I gave him an umbrella.
Can you get an avocado from the store?

Using Indefinite Articles With Different Sounds

What we’ve discussed so far is pretty straightforward: Use “a” before words that start with consonants and “an” before words that begin with vowels. But it’s not just about the letters — it’s also about the sounds.

When certain vowels make a consonant sound at the beginning of a word, it’s appropriate to use the indefinite article “a” with that word. For example, pair “a” with words that start with “e” and make the “yoo” sound, such as “a euphemism” and “a eucalyptus tree.” “A university” and “a uniform” receive similar treatment. The same is true of “o” words that begin with a “w” sound.

She wanted a unicorn for her birthday.
France is a European country.
I handed them a one-dollar bill.

On the flip side, words with a silent “h” use “an” (as in the “herb” example from earlier). This includes “an honor” or “an hour.” The same is true of initialisms that start with the consonant letters “F,” “H,” “L,” “M,” “N,” “R,” “S,” and “X.” These all begin with a vowel sound, so they need to be paired with “an.”

The salad featured an heirloom tomato medley.
He signed an NFL contract.
It was an FBI investigation.

A Historic Exception

There’s some debate about whether “a historic” or “an historic” is correct. The choice usually comes down to pronunciation, but there’s also a bit of tradition at play with this word. In British English, the “h” is silent, so “an historic” would be correct. In American English, the “h” was pronounced after the 19th century, so it would be logical to use “a historic,” but the indefinite article “an” is still commonly used, especially with “historical.” The Oxford English Dictionary notes that around a quarter of the examples of “historical” are preceded with “an” rather than “a.”

Featured image credit: Credit: JHPhoto/ Alamy Stock Photo

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Lisa Galek

Freelance Writer

Lisa Galek is a freelance writer and editor based in Cleveland, Ohio. Her writing has appeared in Business Insider, Apartment Therapy, Scholastic Science World, and on, literally, thousands of American Greetings cards. The only thing she loves more than an Oxford comma — or an em dash — is her husband and three charming children.