不定式（短语）可用作表示目的（a）,原因(b),结果(c) 等的状语: a.Sever women came over to help her.
The children sleep together to keep warm.
b.I rejoice to hear that you are well.
We jumped with joy to hear that news.
c.She lived to be 100.
The curtain parted，to reveal a market scene.
不定式还可以用在某些句型中作状语:
a.in order (not) to 以便, 为了(以免):
She went to live in Spain in order to learn Spanish.
We keep the window shut in order not to let the flies in.
b.so as (not) to 以便(以免):
Go in quietly so as to make a pie.
c.so (such) as to 到这种程度以致:
Ruth wouldn’t be so careless as to forget to lock the door.
I’m not such a fool as to put it in writing.
d.be so kind (good) as to 可否劳驾．．．．．
Would you be so kind as to let my people know?
Would you be so good as to look after her?
e.be kind (good) enough to 劳驾:
Will you be kind enough to shut the door?
Please be good enough to close the door
f.too…to…太．．．不能
I’m too tired to stay up longer.
g.(not) enough to… (不)够…..来做某事
She was not strong enough to travel.
We were fortunate enough to get an empty car.
不定式有时需要用被动形式(a)或完成形式(b)，有时可用进行形式(c):
a.He returned after the war, only to be told that wife had left him.
b.I am sorry to have missed you.
c.Are you glad to be going back to school.
有时不定式前面有一个for引起的短语，表示它逻辑上的主语。
a.I’m quite willing for you to join us.
b.Is it ripe enough for us to eat?
有些不定式短语可用来修饰整个句子，可以称作句子状语。
T o be honest , I don’t quite like the dish.
【不定式作表语】
有时不定式在句中可用作表语，说明主语的具体内容或
目的。
a.The wall is to keep people out of the garden.
b.My only wish is to do what is best for you.
有时不定式表示一个动作：
a.The best thing she ever did was to buy that house.
b.What you have to do is (to) fill in the questionnaire.
有时可用被动形式作表语：
The house is to be let.
He’s only to be pitied.
不定式可以用作主语：
To err is human ，to forgive divine.
一.It + be +形容词+ 不定式:
It’s important to know your own limitations.
It was silly to believe him.
二.It +be + 形容词+ for 引起的短语+不定式:
It is not hard for one to do a bit of good.
It won’t be easy for Tom to find a new job.
三.It + be +形容词+ of 引起的短语+不定式:
It’s unfair of him to criticize me.
It was selfish of him not to contribute anything.
四.It + 名词+ 不定式:
It’s fun to be here.
It has been a privilege to work with you.
五.It + 动词(+宾语) + 不定式:
It took me a year to save up for a new coat.
It costs 150 a week to keep someone in prison.
It pleased him to think of his father.
六.It + be +介词短语汇+ 不定式:
It was quite beyond me to help them.
It is against my principles to work with them.
其它这类结构：
It makes me sick to think about it.
It would look rude to refuse their invitation.
在这类结构中,不定式有时需用进行形式或完成形式:
It’s a new experience for her to be travelling by plane.
What a mistake it is to have come here.
一.在不少动词可跟一个由名词(代词)+不定式构成的复合宾语:
He told her to wake him up.
My doctor advised me to see a neurologist.
