Rules for When to Use 'A' vs. 'An'

Instructor: Charles Kinney, Jr.
The words 'a' and 'an' are used frequently in writing, but can be difficult to master. In this lesson, we will learn about the basic rules of when to use 'a' and 'an' and when there are exceptions to this rule.

What Are 'A' and 'An'?

The words 'a' and 'an' are indefinite articles. These are determiners. They help to identify (to determine) what we are talking about. Articles talk about things in general, or something specific. 'A' and 'an' can be difficult to learn, but there is a good rule to use based on the sound of the first letter coming right after them.

How Do We Use 'A' and 'An'?

In general, we use 'a' and 'an' before everything we can count (countable nouns), like a boat, an apple or an egg. They are not usually used before things we cannot count, like air or water (uncountable nouns), or anything more than one (plural nouns). 'A' or 'an' comes before a noun (a person, place or thing) and before an adjective (a word that describes a noun) in a noun phrase, like 'a blue boat' (article+adjective+noun=noun phrase 'a blue boat').

a house/a big house/three houses (houses is plural, so no 'a' or 'and')

a boat/a blue boat/six boats (boats is plural, so no 'a' or 'and')

We use 'a' and 'an':

- When referring to something for the first time: 'I see a house.'

- Meaning one of something: 'I have a dog.'

- Names of jobs: 'She is a doctor.'

- Nationalities: 'He is an American.'

That is something you do not see everyday: a penguin and a parrot in front of an igloo.

The Best Rule for 'A' and 'An'

The best rule when to use 'a' or 'an' is the sound of the letter that comes right after them.

For example, 'a' is used when the following word starts with a consonant: (b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, y, z).

'An' is used when the following word starts with a vowel: (a, e, i, o, u)

a an
a boat an egg
a cat an orange
a dog an ear
a big house an ugly hat
a tall tree an easy test



- Use 'a' when 'eu' makes the same sound as the 'y' in year: 'a European country.'

- Use 'a' when 'u' makes the same sound as the 'y' in you: 'a university.'

- Use 'a' when 'o' makes the same sound as 'w' in won: 'a one-horse town.'


- Use 'an' before a consonant sound that sounds like a vowel sound: 'an MP3' (M sounds like EM).

- Use 'an' when the 'h' is silent: 'an hour, an honest man.' Both 'a' and 'an' are used for the word herb: 'a herb' (UK, where the word is pronounced HURB) and 'an herb' (USA, where the word is pronounced URB).

- When using three-syllable words: You will see both 'an historic event' (USA) and 'a historic event' (UK). Americans sometimes use 'an' when a word starting with 'h' is three syllables or more, like 'HIS-TOR-IC' or 'HY-PO-THE-SIS'.

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