A/ an and the

Compare a and the in these examples:

• A man and a woman were sitting opposite me. The man was American but I think the woman was British.

• When we were on holiday, we stayed at a hotel. Sometimes we had our evening meal at the hotel and sometimes we went to a restaurant.

We use the when we are thinking of one particular thing. Compare a/an and the:

• Tom sat down on a chair, (perhaps one of many chairs in the room)

but Tom sat down on the chair nearest. (a particular chair)

• Ann is looking for a job. (not a particular job)

but Did Ann get the job she applied for? (a particular job)

• Have you got a car? (not a particular car)

but I cleaned the car yesterday. (= my car)

We use the when it is clear in the situation which thing or person we mean. For example, in a room we talk about 'the light / the floor / the ceiling / the door / the carpet' etc.:

• Can you turn off the light, please? (= the light in this room)

• I took a taxi to the station. (= the station in that town)

• I’d like to speak to the manager, please. (= the manager of this shop etc.)

In the same way, we say (go to) the bank, the post office:

• I must go to the bank to get some money and then I'm going to the post office to get some stamps. (The speaker is usually thinking of a particular bank or post office.)

Also: the doctor, the dentist:

• Carol isn't very well. She's gone to the doctor. (= her usual doctor)

• I hate going to the dentist.
Compare a:

• Is there a bank near here?       

• My sister is a dentist.

Don't forget the:

•   Susan works in the city centre, (not 'in city centre')

• My brother is in the army, (not 'in army')

We say 'once a week / three times a day / £1.20 a kilo' etc.:

• How often do you go to the cinema?' About once a month.'

•   'How much are those potatoes?' £1.20 a kilo.'

Put in a/an or the