A or An? Rules and Exceptions for Using Indefinite Articles

You probably know that “a” comes before a word starting with a consonant and “an” is used before a word starting with a vowel. But, what about those tricky words that don’t sound quite right when you follow the rule? Learn how to use a and an in certain instances, including hour and URL, with these example sentences.

A vs An Example A vs An Example

A and An: Indefinite Articles

Unlike other languages that use masculine and feminine articles, English uses three articles to identify nouns: a, an, and the. The is a definite article that refers to a specific item, while both a and an are indefinite articles for singular nouns. When the noun is plural, a or an can change to some. These are the only four indefinite articles in the English language.

When the next word begins with a consonant sound, you use a. Examples of sentences with a include:

  • I went to a restaurant. (The next sound is r-)
  • A man was driving too fast. (The next sound is m-)
  • A dog barked all night. (The next sound is d-)
  • Sharon decided to read a book. (The next sound is b-)
  • Joel drives a purple Audi. (The next sound is p-)

You can tell when to use an instead of a if the next sound is a vowel sound. For example:

  • I bought an umbrella just before the rain started. (The next sound is uh-)
  • The news reported an alligator attack. (The next sound is ah-)
  • Lily wanted an ice cream cone. (The next sound is eye-)
  • An eager child ran into the store. (The next sound is ee-)
  • The boy picked up an orange cup. (The next sound is oh-)

The rule is easy to follow in English. It’s simple and it’s easy to hear errors. “I bought a umbrella” doesn’t sound correct; neither does “I went to an restaurant.” But, some words make it harder to tell which article is appropriate.

Common Confusion

A misunderstanding of the rule is that you need to pay attention to the actual letter of the next word. In reality, it’s the sound of the word that you should follow when deciding to use a or an.

It’s tempting to call these words “exceptions,” but they follow the rule just as well as words that are spelled phonetically.

Words That Begin With H

It’s hard to tell whether you should use a or an before h words. The rule dictates that if the first syllable is not stressed, you can use an. Additionally, some words have the h sound at the beginning, while it is silent in other words. Check out these examples of different words that begin with h.

  • Hourglass
  • Horse
  • Honor
  • Heir
  • Hair

Even though they all begin with the consonant h, some of these words use the an article.

  • An hourglass (first sound is ow-)
  • A horse (first sound is h-)
  • An honor (first sound is aw-)
  • An heir (first sound is eh-)
  • A hair (first sound is h-)

A tricky word not listed above is historic. It’s a word that doesn’t sound quite right either way. That’s because the h is not silent, but the first syllable is also not stressed (hi-STOR-ic). Another word with French etymology, hotel, falls into the same trap. A is technically the correct article to use with both words, as in “a historic moment” and “a hotel.”


Words That Make a You- Sound

Some words that begin with vowels don’t actually start with a vowel sound. In these cases, their you- beginning sounds are actually consonant sounds, which then require the article a. Some of these words are:

  • A European trip
  • A ewe
  • A union
  • A URL
  • A unicorn
  • A eulogy

It’s natural to see the vowels when writing and automatically add an. But, trying saying each word out loud. You’ll find that an union doesn’t sound correct at all.

Words That Make a W- Sound

Another instance of consonant-sound words hiding as a vowel words are words that make a w- sound, but begin with the letter o. There are only two words in English that fit this description: once and one.

If you are writing about a one-legged bird or a once in a lifetime opportunity, use the article a.


Using the correct article when writing acronyms isn’t always easy. Just like in other words, you are listening for the initial sound, not necessarily the letter. Take a look at these examples of acronyms in which you pronounce each letter individually (also known as initialisms).

  • An MBA (first sound is em-)
  • A GRE (first sound is gee-)
  • An NFL coach (first sound is en-)
  • A DOJ employee (first sound is dee-)
  • An SOS signal (first sound is es-)

If you say the acronym as a single word, such as NATO or AIDS, refer to the first sound of the word: a NATO treaty and an AIDS treatment. It may seem complicated, but as long as it sounds right, you are probably on the right track.


More Resources on Parts of Speech

Now that you’ve mastered indefinite articles, make sure that the rest of your parts of speech are in order. These parts of speech examples are a great reminder for writing exercises. You can also learn the six spelling secrets that English teachers would love for you to know.