动词不定式用法
一、动词不定式的基本形式是“不定式符号to+动词原形”，有时可以不带to。动词不定式没有人称和数的变化。在句中不能单独作谓语，但仍保留动词的特性，可以有自己的宾语、状语等。动词不定式同它的宾语和状语一起构成不定式短语。
例如：to sell flowers in the street 在街上卖花
to speak in the classroom 在教室里讲话
不定式省to有四种情况：
1、使役动词let, make, have等后接不定式。
例如：Let him go!
The boss made the child labors work the whole night.
2、would rather, had better后。
例如：You had better stay at home.
3、Why…/Why not…后。
例如：Why not have a good rest on Sunday?
4.感官动词see, watch, look at, hear, listen to, smell, feel, find，notice等后作宾语补足语，省to。例如：I saw him dance.
注意：这些情况在被动语态中，不可省to.
例如：The child labors were made to work the whole night.
二、动词不定式具有名词、形容词和副词的特征，可以作句子的主语、表语、宾语、宾语补足语、定语和状语。
1、用作主语
直接把动词不定式置于句首的情况不多，多数情况用it作形式主语，把真正的主语——动词不定式置于句末，特别是不定式短语较长时。动词不定式作主语，谓语动词用第三人称单数形式。带疑问词的不定式短语作主语常置于句首。
例如：The head teacher said it was necessary to talk with his mother.
How to make requests politely is important.
2、用作表语
动词不定式作表语，常用在be动词及seem, appear, happen等词之后，构成系表结构。说明主语的内容、性质、特征。
例如：The best way to improve your English is to join an English club.
She seem to be well-known.
3、用作宾语
○1. 用作宾语的动词不定式，常用在动词ask, choose, agree，expect, hope, decide, learn，prefer, know，wish, want, would like / love等及物动词之后，构成动宾短语。
例如：We decided to talk to some students about why they go there.
He prefers to eat white bread and rice.
I’d love to visit Mexico.
○2.动词feel, find, make, think, believe等，在语法上不能接受不定式作宾语，只有用it作形式宾语，从而把动词不定式后置。句子结构是：主语＋feel / find / make / ... it+adj. / n.+to do...。例如：I find it difficult to remember everything.
○3.既可接动词不定式又可接v-ing形式作宾语，意思差别不大的动词有begin, start, like, love 等。一般说来，动词不定式表一次、数次的具体动作的全过程，v-ing形式表习惯性的连续动作。但这种区别并不很严格，特别是美式英语，即使是习惯性的动作也可以用动词不定式。例如：Then I started to watch English-language TV.
I’m beginning to understand my Chinese roots, and who I am.
（begin用了进行时态，后面只接不定式作宾语，表示事情刚开始，还要继续下去。）
○4.后接动词不定式或v-ing形式作宾语，意思差别较大的动词有forget, remember等。后接不定式作宾语，表动作尚未发生；后接v-ing形式作宾语，表动作已经发生。stop to do停下来做另外一件事，to do是目的状语；stop doing停止做、不做当前这件事，doing是宾语。try to do尽力做，try doing试试看；go on to do接着做另外的事，go on doing继续做原来的事。例如：When I left home, I had forgotten to bring it with me.
I stopped using them last year.
○5后只接v-ing作宾语的一些常用特殊动词：give up, enjoy, practise, finish, mind等。
例如：Would you mind opening the window?
4、用作定语
用作定语的动词不定式一般都位于被修饰的名词之后。
例如：I have so much homework to do today.
I cant think of any good advice to give her.
通常chance, place, time, way等名词后接不定式作定语。另外在the first, the second, the last, the only等词后，也常用不定式作定语。
例如：He needs time to do homework.
You want to know the best way to get around the city.
5、用作补语
○1.常见动词不定式作宾语补足语的动词主要有：要求允许提议警告（ask, allow, permit, advise，warn），期望邀请鼓励（expect, suppose, invite, encourage），教导告诉想要（teach, tell, want），希望愿意（wish, would like / love）。
例如：I invited her to have dinner at my house.
Teenagers should be allowed to choose their own clothes.
○2.动词不定式作补语，在主动语态句里不带to，被动语态句里带to时多数动词是感官动词和使役动词，包括四“看”：look at, observe, see, watch，三“让”：have, let, make，二“听”：hear, listen to，一“感觉”：feel，一“注意”：notice。
例如：This picture makes me feel tense！
Of course we want to see Liu Yu achieve his dreams.
○3.help后接动词不定式作补语，to可带可不带。一般说来，带to表间接帮助，不带to表直接帮助。在被动语态句里，或者用不定式的否定式作补语时要带to。
例如：They can help you to compare two different products so that you can buy the one you really need.
Using e-mail English helps you write quickly.
○4.be said, be sure, hap pen, seem等后面可以接带to的动词不定式作主语的补语。
例如：He doesn’t seem to have many friends.
Be sure not to miss them if they come to a city near you.
6、用作状语
○1.目的状语，置于句首或句末，置于句首时常表示强调。为加强语气，常与in order或so as 组成短语。
例如：A group of young people got together to discuss this question.
In order to help him, we would do everything we can.
注意：置于句首时只用to do / in order to do。
○2.原因状语，多见于“sb.+be+adj.+to do...”结构句中。
例如：I was very sad to hear the news.
On Monday he told a radio interviewer that he had run out of money to buy old bikes.
○3.结果状语，多见于“too...to”，“enough to...”结构句中。
例如：Then I’m too tired to do well.
He is old enough to go to school .
○4.独立动词不定式多用作插入语，表示说话人的心理状态或对事情的看法。
例如：I’d like to stay healthy, but to be honest, I only eat food that tastes good.
T o begin with, she spoke too quickly, and I couldn’t understand every word.
7、动词不定式的复合结构
动词不定式的复合结构是“for / of sb. to do sth.”，for / of引出不定式动作的逻辑主语。这种结构在句子中可以作主语、宾语、表语、定语、状语等。不定式复合结构的介词用for还是of，主要决定于前面形容词的性质。一般说来，of前面的形容词是careful, clever, foolish, good, kind, nice, wise等，既说明人的特性，又说明不定式动作的特性。for前面的形容词是dangerous, difficult, easy, hard, heavy, important, interesting, necessary等，一般说明不定式动作的特性，不说明人的特性。前面如果是名词用for。
例如：(1)Its also probably a good idea for parents to allow teenagers to study in groups during the evening. (2) It’s kind of you to help me.
8、带疑问词的不定式短语
动词不定式前面可以带疑问代词what, which, who或疑问副词how, when, where, why等。这种结构起名词的作用，在句子里用作宾语、主语、表语等，或者单独使用。要注意的是，why后面的不定式不带to。
例如：I don’t know what to try next. （作宾语）Where to go is not decided yet.（作主语）
注意：单独使用时相当于一个特殊疑问句。
What to do next?(=What will we / you do next?)Why go there?(=Why do we / you go there?)
9、动词不定式的否定式
不定式的否定式是not / never to do...，不带to的不定式的否定式是not / never do...
例如：Sometimes they have disagreements, and decide not to talk to each other.
His parents tell him never to drive after drinking
