This document discusses purpose and reason clauses. It explains that purpose clauses using "to" indicate someone's intention for an action. Purpose clauses can also use "in order" or "so as to" followed by an infinitive. Negative purpose clauses use "in order not to" or "so as not to". Purpose clauses with different subjects than the main clause use "in order that", "so", or "so that". Reason clauses explain why something happens or someone acts using "because", "since", or "as". Reason clauses can also use "why" and reported questions or "in case" to discuss possible reasons.

1. Purpose and Reason Clauses

2. Purpose and Reason Clauses
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.

3. Purpose and Reason Clauses
Instead of using an ordinary ‘to’-infinitive, you
often use ‘in order’ or ‘so as to’ with an
infinitive.
He was giving up his job in order to stay at
home.
I keep the window open, so as to let fresh air
in.

4. Purpose and Reason Clauses
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.

5. Purpose and Reason Clauses
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.

6. Purpose and Reason Clauses
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’, or ‘shall’ in the
purpose clause.

7. Purpose and Reason Clauses
Any hole should be fenced so that people
can’t fall down them.
I have drawn a diagram so that my
explanation will be clearer.

8. Purpose and Reason Clauses
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.

9. Purpose and Reason Clauses
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 under
underlined it to be easier’.

10. Purpose and Reason Clauses
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.
I usually check, just for safety’s sake.

11. Purpose and Reason Clauses
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’.

12. Purpose and Reason Clauses
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.

13. Purpose and Reason Clauses
You can also use ‘why’ and a reported
question to talk about the reason for an
action.
I asked him why he had come.

14. Purpose and Reason Clauses
When you are talking about a possible
situation which explains the reason why
someone does something, you use ‘in case’
or ‘just in case’.

15. Purpose and Reason Clauses
I’ve got the keys in case we want to go inside.
I’m here just in case something 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’.

16. Questions?
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