Collins Cobuild

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.

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Unit 97
Purpose and reason clauses
Main points
Purpose clauses are introduced by conjunctions such as ‘so’, ‘so as
to’, ‘so that’, ‘in order to’ or ‘in order that’.
Reason  clauses  are  introduced  by  conjunctions  such  as  ‘as’,
‘because’, or ‘in case’.
A purpose or reason clause needs a main clause to make a complete
sentence.
A purpose clause usually comes after a main clause. A reason clause
can come before or after a main clause.
1
 You  use  a  purpose  clause  when  you  are  saying  what  someone’s
intention  is  when  they  do  something.  The  most  common  type  of
purpose clause is a ‘to’-infinitive clause.
The children sleep together to keep warm.
They locked the door to stop us from getting in.
Instead of using an ordinary ‘to’-infinitive, you often use ‘in order to’
or ‘so as to’ with an infinitive.
He gave up his job in order to stay at home.
I keep the window open, so as to let fresh air in.

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To make a purpose clause negative, you have to use ‘in order not to’ or
‘so as not to’ with an infinitive.
I would have to give myself something to do in order not to be bored.
They went on foot, so as not to be heard.
Another way of making purpose clauses negative is by using ‘to avoid’
with an ‘-ing’ form or a noun group.
I had to turn away to avoid letting him see my smile.
They drove through town to avoid the motorway.
2
Another type of purpose clause begins with ‘in order that’, ‘so’, or ‘so
that’. These clauses usually contain a modal.
When  the  main  clause  refers  to  the  present,  you  usually  use  ‘can’,
‘may’, ‘will’, or ‘shall’ in the purpose clause.
Any holes should be fenced so that people can’t fall down them.
I have drawn a diagram so that my explanation will be clearer.
When  the  main  clause  refers  to  the  past,  you  usually  use  ‘could’,
‘might’, ‘should’, or ‘would’ in the purpose clause.
She said she wanted tea ready at six so she could be out by eight.
Someone lifted Philip onto his shoulder so that he might see the
procession.
You  use  ‘in  order  that’,  ‘so’,  and  ‘so  that’,  when  the  subject  of  the
purpose  clause  is  different  from  the  subject  of  the  main  clause.  For
example, you say ‘I’ve underlined it so that it will be easier.’ You do
not say ‘I’ve underlined it to be easier’.
3
 You  can  also  talk  about  the  purpose  of  an  action  by  using  a
prepositional phrase introduced by ‘for’.
She went out for a run.
They said they did it for fun.

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I usually check, just for safety’s sake.
4
You use a reason clause when you want to explain why someone does
something or why it happens. When you are simply giving the reason
for something, you use ‘because’, ‘since’, or ‘as’.
I couldn’t see Helen’s expression, because her head was turned.
Since it was Saturday, he stayed in bed.
As he had been up since 4 am, he was very tired.
You  can  also  use  ‘why’  and  a  reported  question  to  talk  about  the
reason for an action.
See Unit
75
.
I asked him why he had come.
5
 When  you  are  talking  about  a  possible  situation  which  explains  the
reason why someone does something, you use ‘in case’ or ‘just in case’.
I’ve got the key in case we want to go inside.
I am here just in case anything unusual happens.
WARNING: You do not use a future tense after ‘in case’. You do not
say ‘I’ll stay behind in case she’ll arrive later’.

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