to talk about sb/sth that has not been mentioned before; to talk about sb/sth for the first time

I've just seen a car coming up the drive.

There's a spider in the bath.

to talk about one person, thing, etc., without saying which person, thing, etc. we mean

I'd like an orange. (= any orange, not a specific one)

I want a new computer. (= any computer, not a specific one)

to refer to people and things in general

Is a spider an insect? (= all spiders)

A teacher ought to be patient. (= all teachers)

to mean 'one', with some numbers and fractions

a hundred, a thousand, a third

to mean 'each' or 'per'

twice a week (= twice each week)

I get fifty pounds a day. (= each day)

He was driving at 110 miles an hour. (= per hour)

when we classify or define things or people (e.g. say what job sb does, what sth is used for, etc.)

He's a teacher.

A dictionary is a book that explains the meanings of words.

with adjectives followed by nouns, in descriptions

He was a tall young man.

It was a beautiful day.

before sb's name, when we don't know the person

There's a Mr Wilkins here to see you.

with some illnesses, especially ones that aren't serious

I've got a headache.

She's got a cold.

in certain phrases, especially ones that express an amount or quantity

a few, a little, a lot, a great deal

after what or such, for emphasis

What a day it's been!

He's such a fool!

Note that the choice of a or an depends on pronunciation, not on spelling: we use a before a consonant sound and an before a vowel sound.

Compare: a book - a computer - a professor - an orchestra - an email - an igloo


a euro - a university - a one-year-old child - an hour - an MP





to talk about sb/sth you have mentioned before

I've got a cat and a dog. The cat's name is Bob and the dog's name is Rosie.

to talk about sb/sth specific

We went to the café that's next to the post office. I want the red dress. (= not any dress)

to talk about sth that is unique

What time does the moon rise? (= There is only one moon.) London is the capital of Britain. (= Britain only has one capital.)

to refer to people, animals or things in general

The white tiger is an endangered species. (= all white tigers)

with inventions

Alexander Graham Bell invented the telephone.

with musical instruments

She plays the piano.

with superlatives

Which is the tallest building in the world?

with the names of certain countries

the United States, the United Kingdom, the Netherlands, the Lebanon, the Czech Republic

with the names of groups of islands

the Philippines, the Maldives

with the names of some mountain ranges

the Alps, the Pyrenees, the Himalayas with the names of oceans, seas, rivers, deserts and regions the Pacific, the Atlantic, the Aegean Sea, the North Sea, the Thames, the Mississippi, the Sahara Desert, the Gobi Desert

with the names of hotels, theatres, museums and newspapers

the Hilton, the Sheraton, the National Theatre, the Natural History Museum, the Times

with some important buildings

the White House, the Houses of Parliament

to refer to the media or types of entertainment

the cinema, the theatre, the radio, the press, the opera

with surnames, when we are referring to a whole family

the Jones, the Mitchells

with the names of groups

the Beatles, the Rolling Stones

with adjectives used as nouns to refer to a group of people

the sick, the injured, the rich, the young

with nationalities, to refer to a group of people

the Japanese, the Asians, the French

in dates

the fourteenth of July, March the twenty-fifth

in some phrases referring to our physical environment

the sea, the mountains, the countryside, the weather

to refer to a place or person that people visit regularly

the doctor, the dentist, the hairdresser

to refer to a part of sb's body

She hit him on the ear. (= his ear)

I punched him on the nose. (= his nose)





with plural countable nouns, to talk about sb/ sth in general

I buy magazines about computers.

I like music.

Dogs love bones.

with uncountable nouns, especially abstract nouns or nouns referring to substances

She hates dishonesty.

Many people are afraid of death.

Chocolate is bad for your teeth.

Gold is expensive.

with adjectives that are not followed by nouns

Her husband is tall. (But: She's married to a tall man.)

The film was excellent. (But: It was an excellent film.)

with the names of people

Sarah didn't come with us last night.

Mr Edwards will be with you in a moment.

with the names of countries, states, cities, towns, etc.

France, New York, London, Texas, Devon

with the names of continents

Asia, Europe, Africa

with the names of mountains and lakes

Mount Everest, Mount Olympus, Lake Geneva, Lake Ontario

with the names of streets, roads, squares and parks

Oxford Street, Fifth Avenue, Brighton Road, Trafalgar Square, Hyde Park

with the names of shops, banks and restaurants

Harrod's, Barclays Bank, McDonald's

with the names of airports or stations

Gatwick airport, Charing Cross Station

with the names of universities

Cambridge University, York University (But: The University of York)

with the names of churches or cathedrals

St Martin's Church, St Paul's Cathedral

with the names of magazines

People magazine, Hello magazine

with languages

She speaks German.

with games, sports and school subjects

I love chess.

How often do you play tennis?

Geography has always been my favourite subject.

with meals

Have you had lunch yet?

Dinner's ready.

with some diseases and illnesses

They haven't found a cure for cancer yet.

She has diabetes.

with ways of travelling/means of transport

travel by car/bus/train; go on foot

with some buildings and institutions, when we are referring to their main function or basic purpose

He was sent to prison.

She goes to school.


He's in hospital. (= He's a patient there.)

He went to the hospital to visit his friend. (= not as a patient)

She's at school. (= as a pupil)

My mum will be waiting for us outside the school. (= We are referring to the building, not its purpose.)

SIMILARY: bed / church / court / college / university

in some common phrases

at work, at home, in bed, watch TV, listen to music