In English, the two indefinite articles are a and an. Like other articles, indefinite articles are invariable. You use one or the other, depending on the first letter of the word following the article, for pronunciation reasons. Use a when the next word starts with a consonant, or before words starting in u and eu when they sound like you. Use an when the next word starts with a vowel (a,e,i,o,u) or with a mute h.
- a boy
- an apple
- a car
- a helicopter
- an elephant
- a big elephant
- an itchy sweater
- an ugly duck
- a european
- a university
- a unit
- an hour
- an honor
The indefinite article is used to refer to something for the first time or to refer to a particular member of a group or class. Some use cases and examples are given below.
Use a to refer to something for the first time.
- Would you like a drink?
- I've finally got a good job.
- An elephant and a mouse fell in love.
Naming members of a group
Use a with names of jobs.
- John is a doctor.
- Mary is training to be an engineer.
- He wants to be a dancer.
Use a with nationalities and religions in the singular.
- John is an Englishman.
- Kate is a Catholic.
Use a with the names of days of the week when not referring to any particular day.
- I was born on a Thursday.
- Could I come over on a Saturday sometime?
Use a to refer to an example of something.
- The mouse had a tiny nose .
- The elephant had a long trunk .
- It was a very strange car .
Use a with singular nouns after the words 'what' and 'such'.
- What a shame !
- She's such a beautiful girl .
- What a lovely day !
Use a meaning 'one', referring to a single object or person, or a single unit of measure. In these sentences using "one" instead of the indefinite article is grammatically correct. It will add emphasis to the number, and contrast with other numbers.
- I'd like an orange and two lemons please.
- I'd like one orange and two lemons please.
- The burglar took a diamond necklace and some valuable paintings.
- I can think of a hundred reasons not to come.
- I need a kilogram of sugar.
- I need one kilogram of sugar.
- You can't run a mile in 5 minutes!