We use to … to say why somebody does something (= the purpose of an action):
– “Why are you going out?” “To mail a letter.”
– A friend of mine called to invite me to a party.
– We shouted to warn everybody of the danger.
We use to … to say why something exits (= its purpose):
– This fence is to keep people out of the yard.
– The president has a team of bodyguards to protect him
We use to … to say what can be done or must be done with something:
– It’s hard to find a place to park downtown. (= a place where you can part)
– Would you like something to eat?
– Do you have much work to do? (= work that you must do)
– I get lonely if there’s nobody to talk to.
– I need something to open this bottle with.
Also money / time / chance / opportunity / energy / courage, etc., to (do something):
– They gave us some money to buy some food.
– Do you have much opportunity to practice your English?
– I need a few days to think about your proposal.
For … and to …
For + noun:
– I’m going to Spain for a vacation.
– What would you like for dinner?
– Let’s go to the pool for a swim.
to + verb:
– I’m going to Spain to learn Spanish. (not for lean, not for leaning)
– What would you like to eat?
– Let’s go to the pool to have a swim.
You can say “for (somebody) to (do something)”:
– These weren’t any chairs for us to sit on, so we ha to sit on the floor.
You can use for -ing or to … to talk about the general purpose of something, or what it is generally used for:
– Do you use this brush for washing the dishes? (or … to wash the dishes?)
You can use What … for? to ask about purpose:
– What is this switch for?
– What did you do that for?
Sometimes you have to use so that for purpose.
We use so that (not to …) especially
When the purpose is negative (so that … won’t/wouldn’t):
when the purpose is negative (so that … won’t/wouldn’t):
– I hurried so that I wouldn’t be late. (= because I didn’t want to be late)
– Leave early so that you won’t (or don’t) miss the bus.
with can and could (so that … can/could):
– She’s leaning English so that she can study in Canada.
– We moved to the city so that we could see our children more often.