a / an

In English, the two indefinite articles are a and an. You use one or the other, depending on the first sound of the word following the article, for pronunciation reasons. Use a when the next word starts with a consonant sound. Use an when the next word starts with a vowel sound.

Examples

• a boy
• an apple
• a car
• a helicopter
• an elephant
• a big elephant
• an itchy sweater
• an ugly duck
• a european
• an umbrella
• a university
• a unit
• a unicorn
• an hour
• an honor
• an SMS
• an MBA

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.

Examples

• 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.

Examples

• 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.

Examples

• 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.

Examples

• I was born on a Thursday.
• Could I come over on a Saturday sometime?

Use a to refer to an example of something.

Examples

• 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'.

Examples

• 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.

Examples

• 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.
  • The burglar took one diamond necklace and some valuable paintings.
• I can think of a hundred reasons not to come.
  • I can think of one 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!
  • You can't run one mile in 5 minutes!