모두 "~ 하기 위하여"라는 의미로 해석되는 표현에 사용됩니다. 이 경우 to ... 는 to 부정사의 부사적 용법에 해당하여 동사를 부사로 활용하게 해줍니다. for는 명사를 부사적으로 활용하게 해주며, so that은 문장의 절을 부사 구문으로 바꿔주는 역할을 합니다.
1. To ...
To는 행위의 목적을 설명하기 위하여 사용합니다:
"Why did you go out?" "To mail a letter."
A friend of mine called to invite me to a party.
We shouted to warn everybody of the danger.
To는 존재/소유/필요의 목적(이유)을 말하기 위해 사용합니다:
This fence is to keep people out of the yard.
The president has a team of bodyguards to protect him.
I need a few days to think about your proposal.
2. For ...와 to ...
for + 명사:
I'm going to Spain for a vacation.
What would you like for dinner?
Let's go to the café for coffee.
to + 동사:
I'm going to Spain to learn Spanish.
(not for learn, not for learning)
What would you like to eat? (not for eat)
Let's go to the café to have coffee.
"for somebody to do something" = somebody를 위하여 something을 하다:
There weren't any chairs for us to sit on, so we had to sit on the floor.
for -ing는 어떤 것의 일반적인 목적을 말하기 위해 사용할 수 있습니다. 이런 경우 to ... 를 사용해도 됩니다:
This knife is only for cutting bread. (or to cut bread)
목적을 묻기 위해 "What ... for?"를 사용합니다:
What is this switch for?
What did you do that for?
3. So that
"so that"은 주로 목적을 위해 사용합니다. So that (not to ...)
1) 목적이 부정적일 때 (so that ... won't/wouldn't):
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.
2) can 또는 could와 함께 쓰일 때 (so that ... can/could):
She's learning English so that she can study in Canada.
We moved to the city so that we could visit our friends more often.
3) 다른 사람에게 어떤 일을 하도록 할 때:
I gave her my address so that she could contact me.
He wore glasses and a fake beard so that nobody would recognize him.