When to Use A vs. An | Difference & Example Sentences

A and an are different forms of the same word, the indefinite article that often precedes a noun.

  • A is used before a noun that starts with a consonant sound (e.g., “s,” “t,” “v”).
  • An is used before a noun that starts with a vowel sound (e.g., “a,” “o,” “i”).

Note that the rule is not whether they start with a consonant or vowel, but whether they start with a consonant or vowel sound. This can help you decide which to use in difficult cases like words beginning in “u” or “h.”

Examples: A in a sentence Examples: An in a sentence
He had a dog when he was a child.

Oranges are a good source of Vitamin C.

She had an aneurysm when she was a child.

Many employees of the company owned an iPhone.

A usurper to the throne was imminent. Following an SOP is a good way to ensure everything goes smoothly.

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A or an before H

The rule of thumb for words beginning with “h” is to consider the way the word is pronounced. Words that have a silent “h” begin with a vowel sound, so they use “an.”

  • For words where the “h” sound is pronounced, such as hat, hotel, or hard, use “a.”
  • For words where the “h” is silent, such as honor, hour, or honest, use “an.”
Example: Words beginning with “h”
She wore a hat to keep out the sudden chill in the air.

They bought a house in May of last year.

He was thought to be an honest person, so his lies came as a surprise.

The meeting took an hour.

A or an before U

Similarly, for words beginning with “u,” consider the way the word sounds.

  • For words where the “u” sound is pronounced like “you,” such as user, usual, or utilized, use “a.”
  • For words where the “u” sound is pronounced like “uh,” such as unusual, understanding, or utter, use “an.”
Example: Words beginning with “u”
The email was about an urgent matter.

They came to an understanding about the cost of the repair.

It would have been helpful to have a user manual.

The invention of scissors proved a useful one.

Prevent plagiarism. Run a free check.

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A or an before acronyms

The same rule applies to acronyms—say the acronym aloud to sound out whether it begins with a consonant sound or a vowel sound.

Some acronyms (like “NASA” [nass-uh]) are usually pronounced as full words, others (like “TV” [tee-vee]) by saying the individual letters. But remember that even the spoken form of a consonant can begin with a vowel sound (e.g., [em] for M, [aitch] for H).

  • Acronyms beginning with a consonant sound use “a.”
  • Acronyms beginning with a vowel sound use “an.”
Example: Acronyms
A NATO [nay-toe] regiment landed amphibiously during the night.

The hospital acted swiftly to prevent a HIPAA [hip-uh] violation.

An MRI [em-arr-eye] machine uses magnets to take detailed scans of your organs.

It can be expensive to pay for an SAT [ess-ay-tee] prep course out of pocket.

Worksheet: A vs. an

Test your knowledge of the difference between “a” and “an” with these practice sentences. Fill in either “a” or “an” in each sentence.

  1. The trail ended at __ hut.
  2. I was not __ witness to anything, I promise!
  3. He accidentally ate  __ poisonous mushroom.
  4. The waiter brought us __ apple pie.
  5. __ HIV-positive diagnosis is typically treated with antiretroviral therapy.
  6. She has been in there for __ hour already.
  1. The trail ended at a hut.
    • Since “hut” begins with a hard “h” sound, you use “a.”
  1. I was not a witness to anything, I promise!
    • Since “witness” begins with a consonant sound, you use “a.”
  1. He accidentally ate a poisonous mushroom.
    • Since “poisonous” begins with a consonant sound, you use “a.”
  1. The waiter brought us an apple pie.
    • Since “apple” begins with a vowel sound, you use “an.”
  1. An HIV-positive diagnosis is typically treated with antiretroviral therapy.
    • Since the “h” in the acronym “HIV” is pronounced as [aitch], you use “an.”
  1. She has been in there for an hour already.
    • Since the “h” in “hour” is silent, you use “an.”

Other interesting language articles

If you want to know more about commonly confused words, definitions, and differences between US and UK spellings, make sure to check out some of our other language articles with explanations, examples, and quizzes.

Frequently asked questions

Is it “an historic” or “a historic”?

A and an are different forms of the indefinite article. Words where the “h” sound is pronounced, such as hat, hotel, or hard, use “a” instead of “an.” Since “historic” begins with a hard “h” sound, you use “a historic” instead of “an historic.”

  • A historic battle
  • A historical fossil
Is it “an unique” or “a unique”?

A and an are different forms of the indefinite article. Words where the “u” sound is pronounced like “you”, such as user, usual, or utilized use “a” instead of “an.” Since “unique” begins with this “you” sound, you use “a unique” instead of “an unique.”

  • A unique hair color
  • A unique situation
Is it “an hour” or “a hour”?

A and an are different forms of the indefinite article. Words where the “h” is silent, such as honor or honest, use “an” instead of “a.” Since the “h” in “hour” is silent, it is “an hour” instead of “a hour.”

  • An hour ago
  • An hourly wage
Is it “an honor” or “a honor”?

A and an are different forms of the indefinite article. Words where the “h” is silent, such as hour or honest, use “an” instead of “a.” Since the “h” in “honor” is silent, you use “an honor” instead of “a honor.”

  • It’s an honor
  • An honorable person

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Tegan George

Tegan is an American based in Amsterdam, with master's degrees in political science and education administration. While she is definitely a political scientist at heart, her experience working at universities led to a passion for making social science topics more approachable and exciting to students.