Purpose and cause
For can be used to talk about people’s purposes in doing something. It is then followed by a noun.
- I went to the college for an interview with Professor Mark.
- We stopped at the pub for a drink.
For + -ing form
For can be used before an -ing form to express the purpose of a thing especially when the thing is the subject of the clause.
- An altimeter is used for measuring height above sea level.
When the clause has a person as subject, it is more common to use an infinitive to express the purpose of a thing.
- We use altimeters to measure height above sea level.
For + -ing can also be used to explain the behaviour that causes a particular reaction.
- They punished the child for lying.
- We are grateful to you for helping us out.