Collins Cobuild English Grammar (148 page)

If England had a hot climate
, the attitude would be different.
If I could afford it
I would buy a boat.

to talk about a situation when you do not know whether it exists or not

If he is right
it would be possible once more to manage the economy in the old way.
The interval seemed unnecessary,
unless it was to give them a break
.

to talk about a situation that may exist in the future.

If I leave my job
I’ll have no money to live on.
If I went back on the train
it’d be cheaper.
Don’t bring her
unless she’s ready
.

8.26
     Conditional clauses usually begin with
if
or
unless
.

You use
if
to say that a consequence of something happening or being the case would be that something else would happen or be the case.

If
you do that I shall be very pleased.
If
I asked for something I got it.
They will even clean your car
if
you ask them to.

When an
if
-clause is put first,
then
is sometimes put at the beginning of the main clause.

If
this is what was happening in the Sixties,
then
I’m glad I wasn’t around then.

Unless
means
except if
. For example,
You will fail your exams unless you work harder
means
You will fail your exams except if you work harder
.

There can be no new growth
unless
the ground is cleared.
Nobody gets anything
unless
they ask for it.

Clauses beginning with
unless
usually go after a main clause.

modals and imperatives

8.27
     When you are using a conditional clause, you often use a
modal
in the main clause.

You always use a modal in the main clause when you are talking about a situation that does not exist.

If you weren’t here, she
would
get rid of me in no time.
If anybody had asked me, I
could
have told them what happened.

Modals
are explained in paragraphs
5.92
to
5.256
.

Conditional clauses are often used with
imperative
structures.

If you dry your washing outdoors, wipe the line first.
If it’s four o’clock in the morning, don’t expect them to be pleased to see you.

Imperative structures
are explained in paragraphs
5.4
and
5.35
to
5.39
.

verb forms in conditional sentences

8.28
     There are special rules about which verb form to use in conditional sentences.

People often describe conditional structures in terms of three, or sometimes four (see zero conditional below), categories:

the
first conditional
, in which the verb in the main clause is
will
or
shall
and the verb in the conditional clause is in the
present simple
.

I’ll scream if you say that again.

the
second conditional
, in which the verb in the main clause is
would
or
should
and the verb in the conditional clause is in the
past simple
.

If I had more time, I would happily offer to help.

the
third conditional
, in which the verb in the main clause is
would have
or
should have
and the verb in the conditional clause is in the
past perfect
.

If I had tried a bit harder, I would have passed that exam.

the
zero conditional
, in which the verb in both clauses is in the
present simple
.

Water boils if you heat it to 100°C.

Many conditionals do follow these patterns. There are, however, various other normal patterns of tense in conditional clauses, which are set out in the following paragraphs.

talking about things that often happen

8.29
     When you are talking about something that often happens, you use the
present simple
or the
present progressive
in the conditional clause and in the main clause.

If a big dog
approaches
me, I
panic
.
He never
rings me up
unless he
wants
something.
If the baby’
s crying
, she probably
needs
feeding.
If an advertisement
conveys
information which is false or misleading, the advertiser
is committing
an offence.

talking about things that often happened in the past

8.30
     When you are talking about something that often happened in the past, you use the
past simple
or the
past progressive
in the conditional clause. In the main clause, you use the
past simple
or a
modal
.

They
sat
on the grass if it
was
fine.
If it
was raining
, we usually
stayed
indoors.
If anyone
came
, they’
d
say How are you?
If they
wanted
to go out, I
would
stay with the baby.
I
could not
fall asleep unless I
did
an hour of yoga.

possible situations

8.31
     When you are talking about a possible situation in the present, you usually use the
present simple
or the
present perfect
in the conditional clause. In the main clause you usually use a
modal
.

If anyone
doubts
this, they
should
look at the facts.
Unless you’
ve tried
it, you
can’t
imagine how pleasant it is.

If
-clauses of this kind are sometimes used when you are offering to do something, or giving permission for something to be done. You use a modal in the main clause, and the subordinate clause consists of
if
, a pronoun, and
want
,
like
, or
wish
.