Indefinite article (a/an)

• With something we refer to for the first time.

Yve just had a great idea. I'll give you a call next week.

• With one of a group of things.

Shall we choose a book from this catalogue?

•Where we use an adjective to describe a noun.

Cairo is a very big city. It's a beautiful day.

• With someone's job.

Peter is a truck driver.

• With singular fractions, group numbers and large numbers.

one and a half kilos a dozen eggs a hundred envelopes

-Meaning per.

She earns $500 a week.

Definite article (the)

• With nouns we have mentioned previously.

There is a bedroom and a living room. The bedroom is quite large.

• With nouns we mention for the first time, but where it is clear which person or thing we are talking about.

Can you pass the marmalade?

• Where there is only one of something. It is clear which one we are talking about.

The moon is full tonight.

• With nouns followed by a descriptive phrase, which makes them definite.

This is the man I told you about.

•With national groups.

The British drink far too much tea.

• With classes of people.

The rich get richer and the poor get poorer.

• With individual items which represent a class.

The lion is fast disappearing.

• With names of musical instruments that we can play.

I can't play the piano but I can play the guitar.

• With some geographical names. In particular: oceans, seas, rivers, canals and regions.

The Thames flows into the North Sea. the Arctic

Also with plural countries, or where the country name contains a noun.

the Netherlands /the Republic of China

• With superlatives, ordinals, the same, the only.

This is the best. You are the first. This is the only one.

Zero article (no article)

• With uncountable nouns and plural countable nouns when we are talking generally.

Give peace a chance. Football is life. I hate wasps.

• With most continents, countries, states, islands, mountains, lakes, cities, parks, roads and streets, squares, bridges, palaces, castles, cathedrals, stations and airports.

We live in France. We took the train from Paddington Station to Bath.

• With company names, years, months, days and special times of the year.

She works for Lufthansa. I'll see you in January.

• With names of meals when we are talking generally.

It's time for lunch. (BUT The lunch I had at Cafe Sol was good value.)

•With unique jobs or roles (the definite article is also possible in these cases).

Jim is (the) chairman of the company.

• With prepositions of place with certain buildings, where the purpose of the building is more important than the place itself.

Sally is in prison. (She's a prisoner.)

Sally is in the prison. (She's a visitor to that specific building.)

Similar are: bed, church, class, court, hospital, school, university

• With means of transport when we are talking generally.

We went there by car. (BUT We went there in the car that Alex borrowed.)

Note that if we use in or on, we need an indefinite article.

We went there in a car / on a bus.