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.
不定式還可以表原因：
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.
不定式還可以放在名詞或代詞后表示它們可以怎么使用或處置：
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 等動詞后面也可以跟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... 比較：
I'm going to Spain for a holiday.
I'm going to Spain to learn Spanish.
for 之后用名詞，to 之后用動詞
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.
可以說...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... 都可用來表示一般目的：
This knife is only for cutting bread. (to cut bread)
What... for? 用在疑問句中表示目的
What is this switch for? ? ?What did you do that for?
有時必須用 so that 來表示目的诅愚，so that 后面不能跟動詞不定式
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.
