THE INFINITIVE OF PURPOSE

A to-infinitive can be used to express purpose:

       I'm studying English to find a better job.

       Mary went to the door to open it.

In order  and so as can be used before a to-infinitive for emphasis in more formal styles:

       

       The parties started negotiations so as to reach agreement as soon as    possible.        

       They had to fly to Japan in order to meet her parents.

The negative is always in order not + to-infinitive or so as not + to-infinitive:

       He tiptoed through the hall so as not to be heard.

        In order not to lose time, we must act at once.

The infinitive of purpose can only be used if the doer of the action expressed by the infinitive is the same as the subject of the main clause. If the subjects are different, we can use in order + that-clause or so +that-clause .

        Peter works hard so that his family has everything they need.
        My mother gave me a shopping list so that I wouldn't forget anything.

In order + that-clause is more formal and it is less common:

       Our company does everything in order that all complaints are dealt with effectively.


 When the verbs  come and go are used as infinitives or as imperatives, instead of to we use and:

              I must go and check the heater.
             Come and  talk to him.  
             Go and fetch a glass.