Main points
* You use time clauses to say when something happens.
* Time clauses can refer to the past, present, or future.
* Time clauses are introduced by words such as `after’, `when’, or `while’.
* A time clause needs a main clause to make a complete sentence. The time clause can come before or after the main clause.
1 You use time clauses to say when something happens. The verb in the time clause can be in a present or a past tense.
I look after the children while she goes to London.
I haven’t given him a thing to eat since he arrived.
WARNING: You never use a future tense in a time clause. You use one of the present tenses instead.
Let me stay here till Jeannie comes to bed.
I’ll do it when I’ve finished writing this letter.
2 When you want to say that two events happen at the same time, you use a time clause with `as’, `when’, or `while’.
We arrived as they were leaving.
Sometimes the two events happen together for a period of time.
She wept bitterly as she told her story.
Sometimes one event interrupts another event.
He was having his dinner when the telephone rang.
John will arrive while we are watching the film.
Note that you often use a continuous tense for the interrupted action. See Unit 60.
3 When you want to say that one event happens before or after another event, you use a time clause with `after’, `as soon as’, `before’, or `when’.
As soon as we get tickets, we’ll send them to you.
Can I see you before you go, Helen?
When he had finished reading, he looked up.
Note that you use the past perfect to indicate an event that happened before another event in the past.
4 When you want to mention a situation which started in the past and continued until a later time, you use a time clause with `since’ or `ever since’. You use a past simple or a past perfect in the time clause, and a past perfect in the main clause.
He hadn’t cried since he was a boy of ten.
Janine had been busy ever since she had heard the news.
I’d wanted to come ever since I was a child.
If the situation started in the past and still continues now, you use a past simple in the time clause, and a present perfect in the main clause.
I’ve been in politics since I was at university.
Ever since you arrived you’ve been causing trouble.
Note that after impersonal `it’ and a time expression, if the main clause is in the present tense, you use `since’ with a past simple.
It is two weeks now since I wrote to you.
If the main clause is in the past tense, you use `since’ with a past perfect.
It was nearly seven years since I ‘d seen Toby.
For `since’ as a preposition, see Unit 40.
5 When you want to talk about when a situation ends, you use a time clause with `till’ or `until’ and a present or past tense.
We’ll support them till they find work.
I stayed there talking to them until I saw Sam.
She waited until he had gone.
6 When you want to say that something happens before or at a particular time, you use a time clause with `by the time’ or `by which time’.
By the time I went to bed, I was exhausted.
He came back later, by which time they had gone.
7 In written or formal English, if the subject of the main clause and the time clause are the same, you sometimes omit the subject in the time clause and use a participle as the verb.
I read the book before going to see the film.
The car was stolen while parked in a London street.
