一动词不定式：to + 动词原形
1.基本用法：可在句中作主、宾、表、定、状、补。
1）作主语
To get up early is a good habit.
It's so nice to hear your voice.(it 为形式主语)
It is important for us to learn English well.
It’s silly of you to do such a thing.
How to improve our English is still a problem.
2) 作宾语
We all hope to see you.
They found it hard to learn Chinese. （it 为形式宾语）
I do not know what to do next. （疑问词+ 不定式）
He asked me how to improve English.（疑问词 +不定式）
3）作表语
① 一般情况
My work is to clean the room every day.
His dream is to be a doctor.
The question is how to put it into practice. 问题是怎样把它付诸实施。
He seemed to have known the news.
② 如果主语是不定式，则表语也用不定式。例如：
To see is to believe.
Seeing is believing.
③ 作表语的不定式有时可省略符号to：这时主语部分必须含有动词do,而作表语的不定式则解释do 的精确意思。
All I did was (to) give him a little help.
What we want to do now is (to) have a rest.
4)作定语
① 不定式作定语时，被修饰的名词常为它的逻辑宾语。不定式与该名词存在逻辑上的动宾关系。
I have some clothes to wash.（后置定语）
He has something important to tell you.
如果不定式是不及物动词，后面应有必要的介词。
Give me a pen to write with.
I need a warm room to live in.
② 逻辑上的主谓关系。
He was the first teacher to come.
I need a box to hold my books.
Is there anyone to answer my question?
He was the last student to have left the classroom .( 不定式完成式)
③ 逻辑上的同位关系。
Everyone has the right to speak at the meeting
= Everyone has the right that he may/ can speak at the meeting.
Do keep your promise to write to me.
= Do keep your promise that you will write to me.
5)作状语
① 作目的状语
He will go to the station to meet his friend.
I often read China Daily in order to (或so as to ) improve my English.（in order to可放在句首； so as to 只能放在句中）。
I come here only to say good-bye to you.
② 作结果状语
I hurried to his house only to find he was out.
He is (not) old enough to join the army.
It’s too late to play basketball.
He was so angry as to be unable to speak.
③ 作原因状语
I was surprised to see him here.
They were pleased to hear the good news.
I am glad to meet you .
④ 在形容词后作状语
This question is easy to answer.
6）作补语
He wants his son to become a lawyer.
She encouraged me to try again.
They persuaded him to give up smoking.
They believe him to be writing a new book .他们认为他正在写一本新书。
He wanted the letter to be typed at once .
The letter was wanted to be typed at once.(主补)
注：有些动词后跟不带to 的不定式作宾语补足语。常见的有：
① 感官动词feel, hear ,see, watch, notice , observe
② 使役动词let, make, have
③ help ：help sb. do…… 或help sb. to do…… 两种说法均可。
I often hear him sing this song.
The boss made the workers work 12 hours a day.
当此类句子改为被动语态时，要补上to.
He is often heard to sing this song.
The workers were made to work 12 hours a day.
☆在 think, find, consider, discover等动词后常用to be +adj.结构作宾补，有时to be 可省略。
We all think/ consider/ find/ discover him (to be) kind and honest. 我们都认为/发现他既善良又诚实。
