不定词有以下三种用法：
1 名词用法——可当主词、补语、受词
2 形容词用法——可当补语、也可以修饰名词
3 副词用法——修饰动词、副词、形容词及表示目的、理由、结果

1 名词用法

当主词

To please everyone at the same time is impossible
To protect environment is important.

重点1

不定词当主词时，可以使用假主词代替
It  is impossible to please everyone at the same time
It is important to protect the environment.

重点2

表明不定词意义上的主词时，在前加For
	It  is impossible  for me to please everyone at the same time
	It is important  for all of us to protect the environment.

重点3

It’s + 形容词（表人格性质）+ of 人 + to V …

1 It's dangerous for children to play on the streets.
2 It's very kind of you to see me off.
3 It was stupid of me to do such a thing.

重点4

不定词的否定形： not + to V

Not to depend on others is the best way to success

当补语

位于be动词之后
A doctor’s duty is to take care of sick people
His fault is to talk too much

当受词

we decide to put off the meeting.
my son needs to see a dentist

重点5

疑问词 + to V ——> 名词片语
How to reduce the costs is a big problem.
The problem is where to set up the tent.
I didn’t know whether to laugh or get angry

2 形容词用法

Amy was the only person to remember my birthday.
I didn’t have a chance to use English in Japan

重点6

（代）名词+ 不定词+ 介词 形式中
不定词前的名词为介词的受词
I have parents to take care of .
I want a knife to cut it with.

重点7

修饰名词的不定词可用关系代名词表示

I’m looking for someone to help me
I’m looking for someone who will help me

Do you have anything to write with.
Do you have anything that you can write with

3 副词用法

表目的

表 ”为了～“

1 he went to Germany to study music.
2 The window was open a few inches  to keep the air circulating.

表原因

跟在表示情感的形容词之后

I was shocked to see the scene.
We could not but laugh to see it.

表结果

有时会伴随only 、never ,有【失望】之意
We were separated never to see each other again.
The police hurried to the house only to find that it was empty.

表条件

用来修饰假设语气的主要句子。
To hear him talk on the phone ,you would take him for his brother.
I would give you anything to go to the concert.
I would give you anythin if you could go to the concert.

重点8

表 [难、易]形容词 + to V
Potery is hard to translate
The rule is easy to remember.

重点9

be动词 + 形容词 + 不定词 的惯用表现

be apt to 易于
we are apt to make mistakes.
be ready to 愿意，易于
be willing to 乐意
be eager to 渴望
be likely to 可能
be anxious to 着急

重点10

～ enough to V … ——> so ~ that + s + (can) …

1 She was kind enough to offer me her seat
2 I have an enough(a sufficient) income  to support you

重点11

too ～ to (太～ 而不能… ). ——> so ~ that + s + cannot …
The bed is too small for me to sleep in.
The bed is so small for me so that I can’t sleep in .

I am only to glad to help you
I am very glad to help you

only too + happy/glad /pleased
very happy /glad /pleased

He is not too pround to ask questions of others.
He is too wise not to see the reason.
He is so wise that he can’t but see the reason.

重点12

so ~ as to V (非常～以致于 ；到～到程度)
——>so ~ that + S …
1 He was so angry as to be unable to speak
He was so angry that he was unable to speak.

I am not so foolish as to trust him.
I am not such a fool as to trust him.