Indefinite Articles: a and an

A and an signal that the noun is indefinite, referring to any member of a group. These indefinite articles are used with singular nouns when the noun is general; the corresponding indefinite quantity word some is used for plural general nouns.

The rule is:

• a + singular noun beginning with a consonant: a boy
• an + singular noun beginning with a vowel: an elephant
• a + singular noun beginning with a consonant sound: a user (sounds like 'yoo-zer,' i.e. begins with a consonant 'y' sound, so 'a' is used)
• some + plural noun: some girls  or 0 girls (no article).

If the noun follows another word, like an adjective, the choice between a and an depends on the first sound of the that word;

• a broken egg
• an unusual problem
• a European country (sounds like 'yer-o-pi-an,' i.e. begins with consonant 'y' sound)

Note also that in English, the indefinite articles are used to indicate membership in a profession, nation, or religion.

• I am a teacher.
• Brian is an Irishman.
• Seiko is a practicing Buddhist.