PURPOSE, CAUSE AND REASON CLAUSES.

Purpose, Cause and Reason clauses (taken from http://losprimeroseningles.blogspot.com)

As the own name indicates, these clauses are used to express the purpose, why the action is done.

• I went to the market to buy some fruit

There are some possible forms to introduce purpose clauses:

• TO + infinitive / IN ORDER TO + infinitive (SO AS TO + infinitive)
• IN ORDER NOT TO + inifinitive / SO AS NOT TO + infinitive
• SO THAT + Subject + Verb

Look at these examples:

• I visited the doctor to lose weight
• I visited the doctor in order to lose weight
• I visited the doctor in order not to have health probles for losing weight
• I visited the doctor so that he could give me some advice to lose weight

Notice that FOR+ -ing form is also possible but the infinitve form is much more common. 

If you want to get a further explanation you can go to this link; click here

For practising, you can do these exercises:

• exercise 1         exercise 2

In unit 9A the book deals with purpose, cause and result clauses so you can go to this link to see a long explanation and an exercise at the end; click here

Remember there is a link between the three kinds of clauses and it depends on you and what you want to say to use one or another.

• I went to the pub to meet my friends
• I went to the pub because I wanted to meet my friends
• I wanted to see my friends so I went to the pub

To finish with, let's see the different forms and meanings of SO:

• SO + adjective: She's so nice
• SO MUCH + singular/uncountable nouns  and   SO MANY + plural: I don't have so much money but I have so many coins
• SO THAT+S+V: I bought some medicine so that she could have it
• SO .... THAT .... : She was so tired that she went to bed
• Some expressions: and SO on; I think/hope SO; Do you like it? SO,SO
• You can also go to this link; click here

To finish with, here you have this song to see the use of infinitive of purpose: what can I do to make you love me?