1. CLAUSES OF PURPOSE You use a purpose clause when you want to explain the reason for a person's action. The most common type of purpose clause is a to-infinitive clause. Example: Sarah went to the computer lab to print out her research report. This can only be used if the subject of the main verb is the same as the subject of the infinitive clause.

2. In formal writing, in order to and so as to are often used when the subjects are the same. Example: Sarah went to the computer lab to print out her research report. Sarah went to the computer lab in order to print out her research report. Sarah went to the computer lab so as to print out her research report.

3. So (informal), so that and in order that are used with a subordinate clause. The subjects in both clauses can be the same or different. These conjunctions are usually followed by a modal verb. Examples: I gave Ann my telephone number so she could contact me. I hurried up so that I would not be late. Today I will make dinner in order that you can rest.

4. SO THAT/IN ORDER THAT+SUBJECT+ CAN/WILL+VERB= FUTURE Ex: I’ve come here so that we can talk. I will give her a key so that/in order that she can get into the flat at any time. SO THAT/IN ORDER THAT+SUBJECT+ COULD/WOULD+VERB= PAST Ex: He spoke quietly so that nobody could hear him. I left the note on the pillow so that/in order that he could find it.