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

4 S + V + O + to V

不定词当受词补语的动词分为以下四类

1 表希望；期待

like 、want、 wish、 expect
I want you to tell the truth.
I didn’t expect her to be absent.

表许可

allow permit

please allow me to introduce my wife zss.
Mother did’t permit her to go to the movie alone.

表思考；认识等

think; believe; consider ; find ; recognize

We believe him to be honest
We believe that he is honest.

I thought the idea (to be practical).

表依赖 建议；要求命令等

tell ; advise ; order ; ask ; beg ; request; require; force ; persuade ;get ; cause ; teach
The doctor advised him to stop smoking .
I persuaded him to go with me .

5 S + V+ O + 原形不定词

感官动词之后

feel ; see ; watch ; look at ; notice ; observe ; hear ; listen to

I feel my heart beat violently.
I saw a boy put a chocolate in his pocket.

重点13

感官动词在被动语态中，要用to + v
The police officer watched the children cross the road.
The children was watched by the police officer to across the road.

使役动词之后

make
have
let
bid

The mother made the boy turn off the TV.

重点14

使役动词 get + to 不定词
I got him to repair the radio.

重点15

使役动词help + to 不定词/原形不定词
Can you help me put up the tent.

重点16

使役动词make 在被动语态中，要用to 不定词。

The teacher made the students try again.

The students were made by the teacher to try again.

6 S + V +it + C +to + 不定词

词句型的动词多位find, think, make 等。
She find it impossible to understand him.
I think it wrong to tell a lie.
I think it careless of you to loss your watch.

7 seem (happen ,appear, prove …)+ to 不定词

seem(appear ) to V ~ 似乎～

My dog seem to understand what I say.

happen (chance ) to V～ . 碰巧～

I happend to meet one of my friends at the station.
It happend that I met one of my friends at the station.

prove (turn out ) to ~. 结果是 ～ ，证明是～

The rumor proved (turned out ) to be ture.

It turned out that the rumor was ture.

come (get ) to~. 变得 ～

You will come to like this town.

8 be+ to + 不定词

表预订 —— 打算要做

The meeting is to be held on Wednesday.

表义务——必须，不得不

Rules are to be observed .

You are to start as early as possible .

表可能—— 能够

Not a cloud was to be seen in the sky.
Nobody was to be found on the street .

表命运—— 有～ 等命运

He was never to see his wife and family again.

表意图—— 想要；打算（intend to ）

表意图时，通常用if字句，而主要子句中以must,need ,necessary 等字，来表示必要。
If you are to succeed ,you must work harder.

9不定词的被动、进行、完成不定词

不定词的被动

to be pp
I lke to teach
i liketo be taugh.

不定词的进行

to be Ving
They seem to be waiting for me .

完成不定词

1 表示比叙述动词更早的时间。
The child seems to have been sick.
He seemed to have spent the money.

2 在can’t ,couldn’t 之后，表示否定推测。在must 之后表示肯定推测。
The couldn’t have been on strike.

3 在should ,ought to 之后，表示未能实现的事。
You should have seen it.
You ought to have kept the word.

4 在intend ,wish,would like 等动词之后。
表示没有实现的事
I intend to have a written to you.
I expected him to have helped me with the work.

10 特别注意的不定词用法

代不定词

为了避免相同的动词的重复，在句意非常明确的情形下，可以只用to而不用后面的动词。
You don’t have to eat it if you don’t want to.

分离不定词

修饰不定词的副词，有时可以放在to和原形动词之间，但not,never等常放在to之前。
I wish to utterly forget the past .
She made up her mind never to return.

独立不定词

是一种管用用法，用来修饰整个句子。
to spear strictly
to be frank
to begin with
to tell the turth
to be honest
to make matters worse
to be sure
to be brief
to say nothing of = not to speak of = not to mention
to say the least of it
strange to say
needless to say
so to speak
not to say

To begin with ,I’ll tell you about my character.
It’s very cold ,and to make matters worse ,It began to rain.
He can speak Franch and German. not to speak of English.

11 不定词的惯用表现

hadder better + 原形不定词

You had better leave it unsaid.

do nothing but + 原形不定词

he did nothing but eat all day.

choose /want/expect/desire + nothing but + to 不定词

She desires nothing but to live peacefully

can’t but / can’t help + 动名词/ can’t help but 原形不定词。

When I hear the news ,I could’t but cry,(I could’t help cring/ I could’t help but cry)

have only to 不定词

只要做～ 就行
You have only to follow his counsel.

used to 不定词

以前习惯～； 过去经常～
My father used to smoke ,but now he doesn’t

be used to doing

习惯～
I am used to staying up late at night.