Unit 9 When and If sentences

1. Study this example:

A: What time will you phone me tonight?
B: I’ll phone you when I get home from work.

‘I’ll phone you when I get home from work’ is a sentence with two parts: ‘I’ll phone you’ (the main part) and ‘when I get hom from work’ (the when part). The sentence is future (tonight) but you cannot use will or going to in the when part of sentence. Instead we use a present tense, usually present simple (I do)

I’ll send you a postcard when I’m on holiday.
When the rain stops, we’ll go out.

The same thing happens after:
While - after - before - until/till - as soon as

Can you look after the children while I’m out?
Before you leave, you must visit the museum.
Wait here until I come back.

2. You can also use the present perfect (I have done) after when/after/until etc. to show that the firs action will be finish the second:

I’ll come as soon as I finish. Or I’ll come as soon as I’ve finished
You’ll feel better after you have something to eat. Or you’ll feel better after you’ve had something to eat.

3. After if we also use the present simple (I do) for the future.

It’s raining. We’ll get wet if we go out.
Hurry up! If we don’t hurry, we’ll be late.

Be careful not to confuse when and if.
Use when for things which are sure to happen:
I’m going shopping this afternoon. When I go shopping, I’ll buy some food.

Use if (not when) for things which will possibly happen:
I might go shopping this afternoon. If I go shopping, I’ll buy some food.
If it rain this evening, I won’t go out.
Don’t worry if I’m late tonight.
If he doesn’t come soon, I’m not going to wait.

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