The indefinite article – a, an

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1. When to use the indefinite articles – a, an

We use the indefinite articles with nouns that we can count:

  • a boy      three boys

We do not use them with plurals of countable nouns as a/an means one:

  • a three boys

We no not use them with nouns that we cannot count as we do not think of them as separate units:

  • knowledge       (not two knowledges)
  • furniture          (not a furniture)

We use the indefinite articles when the listener doesn’t know which specific thing we are talking about:

  • My sister has a German boyfriend.

The indefinite article a/an is the same for all genders.

  • a boy
  • an elephant
  • a chair

1.2 When to use a and when to use an

We use an if the following word starts with a spoken vowel.

the following word starts with a spoken consonantthe following word starts with a spoken vowel
  • a boy
  • a chair
  • a girl
  • an English boy
  • an apple
  • an old lady
The choice between a and an is based on pronunciation not spelling. Compare the following words:
The first sound we speak is /j/, so we use aa unitThe first sound we speak is /ʌ/, so we use anan uncle

2. Use of the indefinite article a/an

2.1. before phrases of time and measurements (per week/weekly)

  • We have German 2 times a week.
  • I go on holiday once a year.
  • Our car can do 120 miles an hour.
  • Oranges are €3 a kilo.

2.2. before phrases of jobs

  • My father is a dentist.

2.3. with a noun complement

  • She is a bad girl.

2.4. before phrases of nationality

  • Barack Obama is an American.

2.5. half/quite

  • We need half a kilo of coffee.
  • This is quite an interesting book.