8月30日下午15:06--15：25
通常用不定式表目的：
'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.
不定式还可以表原因：
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.
不定式还可以放在名词或代词后表示它们可以怎么使用或处置：
It's difficult to find a place to park in the city center.
Would you like something to eat?
Have you got much work to do?
I get lonely if there's nobody to talk to.
money/time/chance/opportunity/energy/courage 等动词后面也可以跟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... 和 to... 比较：
I'm going to Spain for a holiday.
I'm going to Spain to learn Spanish.
for 之后用名词，to 之后用动词
What would you like for dinner?
What would you like to eat?
Let's go to the pool for a swim.
Let's go to the pool to have a swim.
可以说...for (somebody) to (do something)
There weren't any chairs for us to sit on, so we had to sit on the floor.
for -ing 和 to... 都可用来表示一般目的：
This knife is only for cutting bread. (to cut bread)
What... for? 用在疑问句中表示目的
What is this switch for? What did you do that for?
有时必须用 so that 来表示目的，so that 后面不能跟动词不定式
i) when the purpose is negative
I hurried so that I wouldn't be late.
Leave early so that you won't miss the bus.
ii) with can and 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.