Page 62 - English Grammar in Use

Unit
25 when I do and when I’ve done if and when

A Study this example:
Amy is on a train. She’s calling a friend. ‘I’ll call you again later when I arrive’ is a sentence
with two parts:
I’ll call you again later when I arrive. the main part: I’ll call you again later
and when … : when I arrive
The time is future (‘later’), but Amy says:
… when I arrive (not when I will arrive)
We say
when I do something (not will do)
when something happens (not will happen)

Some more examples:
We’ll go out when it stops raining. (not when it will stop)
When you are here again, you must come and see us. (not When you will be)
Don’t forget to lock the door when you go out. (not will go)

The same thing happens after while / before / aft er / as soon as / until:
What are you going to do while I’m away? (not while I will be)
Before you go, there’s something I want to ask you.
Wait here until I come back. or … till I come back.

B You can also use the present perfect (have done) after when / aft er / until / as soon as:
Can I have the newspaper when you’ve finished with it?
Don’t say anything while Ian is here. Wait until he has gone.
We use the present perfect to show that one thing is complete before the other. The two things do not
happen together:
When I’ve phoned Kate, we can go out.

(= first I’ll phone Kate and after that we can go out)
Do not use the present perfect if the two things happen together:
When I phone Kate, I’ll ask her about the party. (not when I’ve phoned)
It is often possible to use either the present simple or the present perfect:

I’ll come as soon as I finish. or I’ll come as soon as I’ve finished.
You’ll feel better aft er you have or You’ll feel better aft er you’ve had
something to eat. something to eat.

C if and when
Aft er if, we normally use the present (if I do / if I see etc.) for the future:
I’ll be angry if it happens again. (not if it will happen)
Hurry up! If we don’t hurry, we’ll be late.
We use if (not when) for things that will possibly happen (or not happen):
If it is raining this evening, I won’t go out. (not when it is raining)
Don’t worry if I’m late tonight. (not when I’m late)
If they don’t come soon, I’m not going to wait for them.
We use when for things which are sure to happen. Compare:
I might go out later. (it’s possible) If I go out, I’ll get some bread.
I’m going out later. (for sure) When I go out, I’ll get some bread.

50 if ➜ Units 38–40 even if / even when ➜ Unit 112D unless → Unit 115