A vs an: the rule is about sound, not spelling

The rule: listen to the first sound

Purdue OWL states the principle clearly: the choice of article is based upon the phonetic (sound) quality of the first letter in a word, not on the orthographic (written) representation of the letter.

Scribbr describes the two forms as 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 (for example the sounds of s, t and v). QuillBot agrees: you use a before a word that starts with a consonant sound (for example b, f or t).

The reason is practical: an exists to make speech easier. Saying "a apple" forces your mouth to stop between two vowel sounds. An apple flows. So the rule follows the mouth, not the page.

The consonant letters and vowel letters are a guide only. What matters is whether the first sound is a vowel or a consonant.

Words that look like vowels but sound like consonants

Some words start with a vowel letter but begin with a consonant sound, usually a "y" sound or a "w" sound. Use a with these.

• a university (starts with "yoo")
• a uniform, a union, a unit, a user, a useful tool
• a European country (starts with "yoo")
• a one-day trip, a one-time offer (starts with "w", as in won)
• a unicorn, a universe

The test: say the word and notice whether your mouth starts with a y or w movement. If it does, it is a consonant sound, so use a.

Be careful with words that look similar but sound different:

• an umbrella (starts with the vowel sound "uh")
• an uncle, an umpire, an upgrade, an ugly mistake
• a union but an unusual idea

All of these start with the letter u. The sound decides: "yoo" is a consonant sound, "uh" is a vowel sound.

Our guide to English vowel sounds lists the vowel sounds with examples, which helps if you find it hard to hear the difference.

Words that look like consonants but sound like vowels

This group is where silent letters matter. Purdue OWL's rule: use "an" before a silent or unsounded "h". Because the "h" does not have any phonetic representation or audible sound, the sound that follows the article is a vowel; consequently, "an" is used.

Common silent-h words:

• an hour, an honest person, an honour (British spelling; an honor in American English), an heir
• an hourly rate, an honest mistake

Compare with words whose h is pronounced, which take a:

• a hotel, a house, a history lesson, a hospital, a hundred, a horse

This answers questions learners often ask:

• "Is it a honor or an honor?" It is an honor, because the h is silent.
• "Do I say a hotel or an hotel?" Say a hotel. You may see an hotel in older British writing, but modern standard usage is a hotel.
• "Is it a historic event or an historic event?" In modern usage, a historic event is standard, because the h is pronounced.

Another common sound-based group is the letter x at the start of some words, as in an X-ray (starts with the sound "ex"), and words like a xylophone (starts with a "z" sound).

Abbreviations and acronyms: a MRI or an MRI?

With abbreviations, use the sound of the first letter name as you say it.

• an MRI ("em-ar-eye" starts with "em", a vowel sound)
• an FBI agent ("ef-bee-eye")
• an SMS, an LED light, an HR manager, an X-ray, an NGO
• a UN meeting ("yoo-en", starts with a "y" consonant sound)
• a UFO, a USB drive, a UK visa
• a PhD, a CEO, a TV, a DVD

This answers the question "Do I say a MRI or an MRI?" It is an MRI, because M is pronounced "em".

Acronyms that you say as a word follow the sound of the word:

• a NASA mission ("NA-sa" starts with a consonant sound)
• a UNESCO site ("yoo-NES-ko")

If you are unsure, say the abbreviation aloud first. It is the sound you make, not the letter you write, that decides.

Numbers follow the same logic: an 8 o'clock meeting (starts with "ay" sound of eight), an 11-year-old ("eleven" starts with a vowel sound), a 10-minute break ("ten" starts with a consonant sound), a one-hour class, an 80 per cent discount.

What about an adjective before the noun?

The article agrees with the next word, not with the noun. If an adjective comes first, check the adjective's sound.

• an apple, but a red apple
• an hour, but a long hour
• a university, but an old university
• a good idea, but an excellent idea
• a unique chance, but an unusual chance

The same applies when an adverb comes in front: a really good idea, an extremely good idea.

This is a common mistake in speech and writing: choosing the article for the noun and forgetting the adjective.

• Wrong: She is an very kind person.
• Right: She is a very kind person.
• Wrong: It was a amazing view.
• Right: It was an amazing view.

For the pronunciation of the join between the article and the next word, see our guide to linking sounds. In natural speech, an links to the vowel that follows, so an apple sounds like "a-napple". This is why learners sometimes hear a n at the start of the noun, and write a napple.

How to say a and an

In normal speech, both a and an are weak: they are pronounced with a short "uh" sound (the schwa), not with the sound of the letter a in the alphabet.

• a sounds like "uh": "uh book", "uh table".
• an sounds like "un": "un apple", "un hour".

In careful or emphatic speech, you can say a as "ay", for example when you want to stress one thing: "I want A book, not the book." In normal sentences, use the weak form. Using the strong form all the time makes your speech sound slow and robotic.

Practice sentences (weak forms):

• "I need uh pen and un envelope."
• "She's un engineer at uh big company."
• "It takes un hour to get to uh university."

Say them out loud at normal speed. The articles should be so short that they almost disappear. Our guide to the schwa sound explains why this vowel is the most common sound in English.

Quick quiz: a or an?

Choose a or an. Answers are below the list.

1. ___ umbrella
2. ___ university
3. ___ hour
4. ___ hotel
5. ___ honest mistake
6. ___ MRI scan
7. ___ unique opportunity
8. ___ 8 o'clock meeting
9. ___ European city
10. ___ unusual question

Answers: 1. an. 2. a. 3. an. 4. a. 5. an. 6. an. 7. a. 8. an. 9. a. 10. an.

To lock the rule in, say each answer aloud as a short phrase, using the weak forms ("uh" and "un"). Then make five sentences about your day with a mix of a and an. For more help turning rules like this into natural speech, see our English speaking practice guide.