oxford_guide_to_english_grammar

32 CONDITIONAL CLAUSES PAGE 334
Librarian: No, that's the class number. The number - the accession number -
you'll find if you open the book on the fly-leaf. It's usually about six numbers
at least. And if you'd give us that, the date that is stamped on the date label -
the last date stamped - and your name and address.
Reader: Uh-huh. If I do that, how do I know that it's all right? I mean, if you
want the book back, do you write to me?
Librarian: Yes, we would do that if you had written in, but of course, if you'd
telephoned or called in we could tell you then.
(from M. Underwood Listen to This!)
Conditions express different degrees of reality. For example, a condition can be
open or unreal.
Open: If you join the library, you can borrow books.
Unreal: If you'd arrived ten minutes later, we would have been closed.
An open condition expresses something which may be true or may become true.
(You may join the library). An unreal condition expresses something which is not
true or is imaginary. (You did not arrive later.)
NOTE
A condition can also be definitely true.
I'm tired. ~ Well, if you're tired, let's have a rest.
The meaning here is similar to You're tired, so let's have a rest.
2 We can use conditional sentences in a number of different ways: for example to
request, advise, criticize, suggest, offer, warn or threaten.
If you're going into town, could you post this letter for me?
If you need more information, you should see your careers teacher.
If you hadn't forgotten your passport, we wouldn't be in such a rush.
We can go for a walk if you like.
If I win the prize, I'll share it with you.
If you're walking along the cliff top, don't go too near the edge.
If you don't leave immediately, I'll call the police.
257 Verbs in conditional sentences
1 Introduction
a
We can use many different verb forms in conditional sentences. Here are some
real examples.
If you haven't got television, you can't watch it.
If you go to one of the agencies, they have a lot of temporary jobs.
If someone else has requested the book, you would have to give it back.
If you lived on the planet Mercury, you would have four birthdays in a single
Earth year.
In general we use verb forms in conditional sentences in the same way as in other
kinds of sentences. In open conditions we use the present to refer to the future (if
you go to one of the agencies). When we talk about something unreal we often use
the past (if you lived) and would (you would have four birthdays).
NOTE
When the condition is true, we use verb forms in the normal way.
Well, if your friends left half an hour ago, they aren't going to get to Cornwall by tea time.