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初中英语必考语法知识点：不定式动词不定式是由“不定式符号to+动词原形”构成的一种非谓语动词结构。有些动词不定式不带to。动词不定式可以作句子的主语、表语、宾语、定语、补语、状语或单独使用。不定式保留动词的某些特性，可以有自己的宾语、状语等。动词不定式和它后面的宾语、状语等一起构成短语，叫作不定式短语。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。It is our duty to try our best to deal with these problems.尽最大努力处理这些问题是我们的责任。The head teacher said it was necessary to talk with his mother.校长说，和他妈妈谈一谈很有必要。How to learn English well is important.如何学好英语很重要。To see is to believe.眼见为实；百闻不如一见。2. 用作表语动词不定式作表语，常说明主语的内容、性质、特征。如：The best way is to join an English club.最好的办法是加入一个英语俱乐部。The first thing is to listen to the teacher carefully.首先是要认真听老师讲课。3. 用作宾语（1）可以接带to的动词不定式作宾语的动词主要有：要求选择同意(ask, choose, agree)；期望决定学习(expect, hope, decide, learn)；宁可假装知道(prefer, pretend, know)；希望想要愿意(wish, want, would like / love)。如：We decided to talk to some students about why they go there.我们决定和一些学生谈谈他们去那里的原因。He prefers to eat white bread and rice.他更喜欢吃白面包和白米饭。I‘d love to visitMexico.我想要去参观墨西哥。（2）动词feel, find, make, think等后面，可以用it作形式宾语代替真正的宾语—动词不定式，句子结构是...feel / find / make / ... it+adj. / n.+to do....如：I find it difficult to remember everything.我发现记住所有事情很难。（3）既可接动词不定式又可接v-ing形式作宾语，意思差别不太大的动词有begin, start, like, love等。一般说来，动词不定式表一次、数次的具体动作、将来动作或动作的全过程，v-ing形式表习惯性的连续动作。但是这种区别并不很严格，特别是美国英语，即使是习惯性的动作也可以用动词不定式。如：Then I started to watch TV.然后我开始看电视。I am beginning to understand my parents.我开始理解我的父母。I like to eat vegetables.我喜欢吃蔬菜。（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ving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。如：When I left home, I forgot to bring it with me.我离开家时，忘记带上它了。I stopped using them last year.去年，我停止使用它们。4. 用作定语（1）表将来时。The question to be discussed next meeting is a difficult one.下次会议要讨论的这个问题非常难。（2）当被修饰词是最高级或序数词或被其修饰时。He is always the first man to come to the office.他总是第一个来到办公室。He is the best man to do the job.他是做这项工作最好的人选。（3）被修饰词是抽象名词时。This is the best way to work out the maths problem.这是解决这道数学题最好的办法。I have a chance to travel to London.我又一个去伦敦旅行的机会。5. 用作宾语补足语（1）带to的动词不定式作宾语补足语的动词主要有：要求允许提议(ask, allow, , advise)；期望邀请鼓励(expect, , invite, encourage)；教导告诉想要(teach, tell, want)；等待希望愿意(wait for, wish, would like / love)。如：I’d invite her to have dinner at my house.我想要邀请她来我家吃晚饭。We should allow the children to choose their own clothes.我们应该允许孩子们选择自己的服装。（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。如：This picture makes me feel excited！这幅画使我感觉很兴奋。We saw Liu Yu play baseball last week.上周我们看到刘宇打棒球了。（3）help后接动词不定式作补语，to可带可不带。They can help you (to) learn English.他们帮助你学习英语。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。如：In order to catch the early bus, she got up very early.为了赶上早班车，她起得很早。A group of young people got together to discuss this question.一组年轻人聚在一起讨论这个问题。She came to this city to visit her daughter.她来到这个城市看望她的女儿。（2）原因状语，多见于“sb.+be+adj.+to do...”结构句中。如：I feel very lucky to have him.拥有他我感觉很幸运。（3）结果状语，多见于“too...to”，“enough to...”结构句中。如：I’m too tired to do it well.我太累了以至于做不好这件事。The room is big enough for three people to live in.这个房间三个人住足够大。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.”。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，说明人的特性。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，前面如果是名词用for。如：It’s a good idea for parents to allow children to study in groups during the evening.对父母来说，在晚上让孩子分组学习是个好主意。It’s wise of him to do it well.对他来说，把这件事做好很明智。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。如：（1）用作句子的成分。I don’t know what to try next. (作宾语)我不知道接下来要尝试什么。Where to go is not decided yet.(作主语)还没有决定去哪里。（2）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?接下来做什么？Why go there?=Why do we / you go there?为什么去那里？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...如：They decide not to talk to each other.他们决定不和彼此说话。His parents tell him never to play soccer in the street.他父母告诉他不要在街上踢足球。
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