A. Study this example:
JOHN: I had a sandwich and an apple for lunch. The sandwich wasn’t very good but the apple was nice.
John says ‘a sandwich’, ‘an apple’ because this is the first time he talks about them.
John now says ‘the sandwich’, ‘the apple because Karen knows which sandwich and which apple he means – the sandwich and the apple he had for lunch.
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.
B. 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 the door. (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)
For a see also Units 70 and 72A.
C. 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.
* 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’)
D. 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?’ ‘Ll.20 a kilo.’
* She works eight hours a day, six days a week.