UNIT 63. To. , for. and so that. (purpose)

A. We use to... to say why somebody does something (= the purpose of an action):

* 'Why did you go out?' 'To post a letter.'

* A friend of mine phoned to invite me to a party.

* We shouted to warn everybody of the danger.

We use to... to say why something exists or why somebody has/wants/needs something:

* This wall is to keep people out of the garden.

* The President has a team of bodyguards to protect him.

* I need a bottle opener to open this bottle.

B. We use to... to say what can be done or must be done with something:

* It's difficult to find a place to park in the city centre. (= a place where you can park)

* Would you like something to eat?

* Have you got much work to do? (= work that you must do)

* I get lonely if there's nobody to talk to.

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 practise your English?

* I need a few days to think about your proposal.

C. For... and to...

Compare:

* I'm going to Spain for a holiday.

but I'm going to Spain to learn Spanish. (not 'for learn Spanish', not 'for learning Spanish')

We use for + noun (for a holiday) but to + verb (to learn). Some more examples:

* What would you like for dinner?

but What would you like to eat? (not 'for eat')

* Let's go to the pool for a swim.

but Let's go to the pool to have a swim.

Note that you can say... for (somebody) to (do something):

* There weren't any chairs for us to sit on, so we had to sit on the floor.

You can use for ~ing to say what the general purpose of a thing is. To... is also possible:

* This knife is only for cutting bread. (or... to cut bread.)

You can use What... for? to ask about purpose:

* What is this switch for?

* What did you do that for?

D. So that

Sometimes you have to use so that for purpose. We use so that (not to...):

i) 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.

ii) with can and could (so that... can/could)

* She's learning English so that she can study in Canada.

* We moved to London so that we could visit our friends more often.

iii) when one person does something so that another person does something else:

* I gave her my address so that she could contact me.

* He wore glasses and a false beard so that nobody would recognize him.