The first time you mention a thing/person or when the listener doesn’t know which thing we mean.
Eg: I saw an old woman in the garden.
Tom sat down on a chair (we don’t know which chair)
When you say what something/somebody is or what something/somebody is like.
Eg: She is a cute girl. (what she is like)
A dog is an animal. (what it is.)
When you say what somebody does. (with jobs...)
Eg: He is a fireman.
In exclamations with What...!
Eg: What a horrible day!
In expressions like three times a week.
When we talk about something we have already mentioned.
Eg.: I saw a strange man yesterday night. The man was very tall.
When there is only one thing of something.
Eg: The earth is the planet where we live.
When it’s clear what you are referring to. For example, in a room we talk about “the light/the floor/the ceiling/the door/etc.
Eg: Michael closed the window.
Where is the toilet, please?
Did Ann get the job she applied for? (the speakers know about it previously)
We use the with: the police/the fire-brigade/the army, etc.
We also say: the doctor, the dentist, etc.
We usually say the radio . Eg: We often listen to the radio .
With places in a town: the cinema, the theatre, the bank, the post office,etc.
Eg:I went to the cinema yesterday night.
Eg: She is the most beautiful in the world.
We use the with some adjectives (without a noun). The meaning is always plural, the rich=rich people in general.
Eg: Why doesn’t the government do more to help the unemployed ?
We use the with some nationalities. Eg: The French are famous for their food = the French people)
DON’T USE AN ARTICLE…
When you are speaking in general (with plural or uncountable nouns).
Eg: Lions are more dangerous than dogs.
Sugar is sweet.
With some phrases like at home/work, go home/to bed,
With institutions ( school, church,prison, etc.) we don’t use an article when you are thinking about the institution and the normal purpose it is used it for. If you are just thinking about the building, use a or the .
Eg: She is in prison (she is a prisoner)
They must rebuild the prison as it is too old. (the building)
Before meals, days and months .
Eg: I always have lunc h at 2 p.m.
But we say a meal. Eg: We had a meal in a restaurant.
Before next/last + day s,week,etc.
Eg: We are meeting next Mond ay.
Continents: Africa (not The Africa)—NO ARTICLE
Countries and states: France (not The France)—NO ARTICLE
**But we say the with names that include words like ‘republic’,’kingdom’,’states’.--ARTICLE
Eg:The United Kingdom, The United States
**We also use the with plural names-ARTICLE: The Netherlands, The Philippines.