作主语 不定式直接置于句首 , 或采用先行词 , 将不定式后置 .

1. 不定式 作主语 不定式直接置于句首,或采用先行词,将不定式后置. To hesitate is a pity.To be here is a great pleasure.It is a pity to hesitate.It’s a great pleasure to be here.

2. 后置不定式结构也适用于谓语动词不是连系动词的句子。后置不定式结构也适用于谓语动词不是连系动词的句子。 • It made me happy to find Mary there. • Wouldn’t it be a pity to spoil your drawing? • How exciting it was to fight a shark! • 不定式结构作主语通常表示具体动作,间或也可表示抽象动作,这一点与-ing 分词结构作主语恰恰相反。 • 用作主语的不定式结构的逻辑主语通常可以在特定上下文或情景中看出,也可以由”for+名词词组”.间或也可用for+ there to be表示。 • It is important for us to have a good grasp of English.

3. It is a great pleasure for us to be here this evening . • It’s a pity for there to be any disagreement in the family.（在这种结构中，there后面的不定式只能是to be） • 不定式结构作主语 不定式在联系动词后作主语补语有两种情况：一种情况，主语和主语补语都是不定式，其含义一是条件，一是结果。 • To see is to believe. To decide is to act. 另外一种情况，主语是以aim, ambition, duty, hope, idea, intention, mistake, plan, purpose, suggestion 等为中心的名词词组，或以what 引导的名词性分句，后面的不定式说明其内容。

4. My idea is to climb the mountain from the north. • What I would suggest is to start work at once. • 不定式结作主语补语时常带to，但在某些句型中可省略to，条件是主语部分必须具有一个动作动词do。 • All I did was empty the bottle. • The worst you can do is become very drowsy. • The only thing I can do now is go on by myself. • What I really wanted to do was drive all night.(也有人指出在由what引导的主语分句中，如果谓语词部分的do是完成体形式，后面的补语也可以用-ed，如果do是进行体形式，则补语必须用-ing 分词。) • What he’s done is :spoil the whole thing . to spoil the whole thing . spoilt the whole thing . • What he’s doing is spoiling the whole thing . • All she seems to do is gossip with her neighbors.

5. 不定式结构作动宾 ，能用带to不定式作宾语的有两种；一种是直接跟有带to不定式，另一种是跟有疑问词+带to不定式结构。 • 第一种常见的词有；afford, agree, aim, apply, arrange, ask, choose, claim, decide, decline, demand, desire, determine, expect, hope, learn, • long, manage, offer, pretend, promise, refuse, • seek, swear, threaten, want, wish ,etc. • He agreed to smoke no more cigarettes. • She applies to work only at weekends.

6. afford通常与 can,此同时can’t或它们的过去时形式连用。如： • We can afford to pay for it. • We can’t afford to go away for a holiday this summer. • 第二种常见的词有decide, find out, forget, inquire, know, learn, remember, see, settle, think, consider, understand, wonder, to be curious to know, etc.疑问词可以是what, where, who (m), when, how, whether, which, etc. (why除外)。 如：

7. I don’t know what to do./where to go/who(m )to ask/how to get there • She didn’t know which one to buy. • We must find out what to do next. • 有些双宾语及物动词，也能用疑问词+带to不定式结构作直接宾语。 • Please inform me where to get the ticket. • I showed them how to do it. • 此外，如果作宾语用的带不定式结构有自己的补语，就得用先行词代表它，把不定式置放到补语后。如： • Do you consider it wise to interfere?

8. He deemed it his duty to help. • I count it a great honour to serve the people. • 不定式结构一般不可以作介宾。只有在含有否定意义的带有介词except的结构中才能这样用。如： • In informal English “may” is rarely used except to express possibility. • He will do anything for you except lend you money. • 当but用作except解释时，其后也可跟不定式结构. • They could do nothing but wait for the doctors to arrive. • 不定式结构作宾补 • 1） see, hear, feel, watch, notice, observe等表示感觉的动词。不定式结构都不带to • I heard her sing.

9. The policeman observed the man open the window. • I felt something crawl up my arm. • 2)have, let, make, advise, cause, allow, ask, beg, drive, encourage, expect, forbid, force, get, intend, invite, permit, persuade, remind, trust, urge, want, warn,etc.表示“致使”等意义的动词。除了have ,let, make以外，都带to不定式结构作宾语补语。如： • What would you have me do? • You made me laugh. • I can’t get her to talk. • The notice warned us not to go into the fields.

10. 3) consider, declare, find, (=consider), prove, think, know, believe, discover, feel(=think), imagine, judge, suppose, understand等表示心理状态的动词。如： • We consider him to be a good teacher.We thought her to be quite a clever girl. • We found him to be dishonest. • We judge/believe/know him to be reliable. • 在consider, declare, find ，prove, think, etc.动词后的往往可以省略。但是，如果不定式是完成体形式，就不能省。如： • We consider him (to be) foolish. • We consider him to have been foolish.

11. 4)love, hate, like, prefer, want等表示情感状态的动词。 • I’d love them to come tonight • I’d like (for) you to come down here.(AmE) • 5) arrange for, ask for, long for prepare for, provide for, vote for, wait for, call upon, count on, rely on depend on,etc。如： • I will arrange for you to come.We wait for that to be done.You can’t rely on him to assist you • You can always depend upon John to be there when he is needed

12. 动词+宾语+不定式的被动态转换形式 • 上面五种动词，除了第四种，其它都可转为被动态。担有几点要注意： • 1）第一种动词（除notice, watch不用于被动态外）转为被动态时，后面不带to不定式转为带to不定式。 • We saw the car stop. • The car was seen to stop. • 2)第二种动词（除了have）转为被动态，其后常用带to不定式. • They made us wait outside. • We were made to wait for two hours. • 只有let跟有单音节不定式时属于例外. • The prisoners were let go. • 但常用be allowed to代替. • They won’t let us go. • We won’t be allowed to go.

13. 3)第三种to be省略与否，与主动结构相同. • We consider him (to be )very capable. • He is considered( to be )very capable. • We know him to be a good worker. • He is known to be a good worker.保(know的现在完成体否定形式为主动态时，后面接不带to的不定式。转为被动态时接带to的不定式。如： • I have never known him behave like this. • He has never been known to behave like that before. • 4)第五类动词，有些有被动态，有些没有。有些被动态体现在不定式结构上。如： • He was seldom called upon to speak at these gatherings.

14. He can be relied on to help us.(必须带can或could，否则不能转为被动态） • We asked/arranged/longed/waited for that to be done.(但类似I will arrange for you to come.这样的句子就无被动态。) • 不定式结构作名词修饰语，不定式与所修饰的名词中心词，有时有主谓或宾关系。如： • This is the best book on the subject to appear(=that has appeared) this year. • He has a large family to support(=that he must support). • 在处于动宾关系时，如果不定式是不及物动词，其后得加上一个所需的介词。 • I write with a pen. I use a pen to write with. • Is there anyone to talk to? • You have given me much to think about.

15. 不定式结构作状语表示目的，结果，原因，条件等。不定式结构作状语表示目的，结果，原因，条件等。 • I am saving up to buy a computer. • She stopped at home to help her mother. • Now, it’ll be cold up there, so we’d better take blankets to wrap ourselves in. • 另为了强调不定式结构表示目的，尤其在其前有否定词not时，通常在to之前加 in order /so as. • I’m attending college in order to learn. • He shouted and waved so as to be noticed. • 此外，表示目的的不定式可置于句首。在其前可加in order，但不能加so as.

16. 2)表示结果.如: • What have I done to deserve so much? • She went abroad never to return. • Would you be so kind as to lend me your bicycle? • Will you be so good as to tell him so? • His illness is not such as to cause anxiety. • He is such a fool as to think that his idle chatter can influence others. • That looks almost good enough to eat. • The ice is thick enough to walk on. • His eyesight is too poor to read such small letters.

17. That’s much too heavy for you to lift. • Notice: I shall be only too pleased to get home.(=I shall be very pleased to get home.) • You are too ready to find fault with others.(=You are very fond of finding fault with others.) • 有时,不定式结构还表示一个随后发生的动作，也表示结果。但通常是一个未料到的不愉快的结果。 • She woke early to find it was raining. • He got home to learn that his father was ill. • He got to the station only to be told the train had gone. • “Lifting a rock only to drop it on one’s feet” is a Chinese folk saying to describe the behaviour of certain fools.

18. 3)表示原因 不定式表示原因，与表示目的的形式相似。区别为第一表示目的可在其前加，第二，不定式表示的动作后于谓语动词的动作。 • She wept to hear the news. • She wept to obtain symathy. • I pretended to be happy to know him. • I pretended to be happy to stop my mother from worrying. • 不定式的体有进行体，完成体和完成进行体等形式。 • He is believed to be coming. • (=It is believed that he is coming.)

19. He is believed to have come. • (= It is believed that he has come.) • He is believed to have been working hard. • (=It is believed that he has working been hard.) • 但，不定式本身不表示“时”的特征，得借助于谓语动词。如： • He seems to be enjoying himself.= • It seems (that) he is enjoying himself. • He seemed to be enjoying himself.= • It seemed ()he was enjoying himself. • I am sorry to have missed him.= • I am sorry that I have missed him/missed him.

20. I was sorry to have missed him.= • I was sorry that I had missed him. • 表示目的，通常用不定式的一般形式。如： • He worked very hard in order to finish the work by five.而不用He worked very hard in order to have finished the work by five. • 在下列固定搭配中用不带to不定式 • We’ll have to make do with dry bread. • He made believe he was innocent. • He let go (of ) the rope. • I’ve often heard tell of such happenings. • I hear say that there will be an earthquake soon. • We can’t let things go hang.

21. Don’t let there be any noise. • Let there be no mistake about this. • Can I help (to) carry it for you? • 在had better, would rather, would sooner, might (just) as well, rather than之后也不用带to不定式。 • 不定式符号的省略问题。 • 当两个并列的带to不定式有and或or连接时，第二个不定式的符号可以省略。 • I intend to call on him and discuss this question again. • We were able to diagnose and begin treatment of 3,000,000 cases a month.

22. Christina hardly knew whether to laugh or cry. • She asked you to telephone or wire to her on Monday. • 如果两者有对比关系，第二个不定式的符号仍得要用。 • To be or not to be ,that is the question. • I haven’t decided to go home or to stay at school this summer. • 在不用连词的情况下，第二个不定式的符号也得保留。 • Please go to the seaside to swim ,to get suntanned. • Hw likes to stay with the peasants, to work in the fields with them. • 这样用时，第二个不定式前要用逗号，以与通常的表示目的的不定式相区别。