'For' and 'to'
Alex from Spain writes:
  Very often I confuse the uses of to and for when I want to express the idea of purpose. When should I use for and when must I use to?
 
 
Roger Woodham replies:
 
 
for + noun or to + infinitive
 
 To talk about the purpose of an action, we use a for + noun construction or a to + infinitive structure. Compare the following:
 
We stopped off at the Goose for a drink and then we carried on to embassy for dinner.
 
I'm going to Brussels next week for an interview. I hope to work for the UN.
 
Do you want to have a drink at the Goose before we go on to dine with the ambassador?
 
I've come to Dublin to attend a seminar and to meet the new members of the faculty. But now I'm leaving for Rome.
 
for + -ing
 
 To talk about the purpose of something, we use a for + -ing construction:
 
- These double-strength paracetamols are good for getting rid of headaches.
- Are they suitable for backache too?
 
- What are these two knives used for?
- This one is for cutting bread and that one is just for slicing meat.
 
What…for?
 
 Note that What…for? can be used in questions to talk about the purpose of both actions and things:
 
- You pinched me! What did you do that for?
- I wanted to see if you were awake
 
- What are these two buttons for?
- The blue one is for gaining access to the main menu and the green one is for quitting teletext.
 
giving reasons and explaining behaviour
 
 Note that the same constructions, for + noun and for + -ing, are used with thank, apologise and be / feel sorry: With be / feel sorry a to + infinitive structure is also possible. Compare the following:
 
Thanks for the lift. Thank you for driving me home.
 
South Western trains would like to apologise for the late arrival of this train and for the inconvenience this may cause you.
 
He really should apologise for spitting in his face. That sort of behaviour is unacceptable, even on a football field.
 
I'm sorry to have taken so long with this report.
I'm sorry for taking so long with this report.
 
- I feel sorry for the cleaners.
- I feel sorry for them too. They've got the thankless task of cleaning up all this mess.
 

 
Note also the way in which the for + -ing construction is used to explain the reasons for the following actions:
 
He was rewarded for handing in the purse.
 
He was criticised for not coming forward as a witness to the accident.
 
He was fined heavily for speeding on the motorway.
 
He was sent to prison for falsifying the accounts.
 
in order (not) to / so as (not) to + infinitive
 
 Note that to + infinitive is one of the most common ways of expressing purpose. When we want to be explicit or sound more formal we can also use in order to or so as to. This structures are especially common before negative infinitives, in order not to and so as not to:
 
To get a better job I decided to take a computer course.
In order to get a better job I decided to take a computer course.
 
I left home early in order not to be late for the appointment.
I left the house early so as not be late for the job interview.
 
 
    
What are these pills for?