动词不定式作主语时，句子的谓语动词常用单数，其位置有以下两种： (1)把不定式置于句首。如：
To get there by bike will take us half an hour.
(2)用it作形式主语，把真正的主语不定式置于句后，常用于下列句式中。如： ①It＋be＋名词＋to do
It's our duty to take good care of the old.
②It takes sb+some time+to do 花费某人多长时间干某事 How long did it take you to finish the work?
③It＋be＋形容词＋for sb＋to do
It is difficult for us to finish writing the composition in a quarter of an hour. ④It＋be＋形容词＋of sb＋to do
It is stupid of you to write down everything the teachersays. ⑤It seems(appears)＋形容词＋to do It seemed impossible to save money.
在句型③中，常用表示客观情况的形容词，如：
difficult,easy,hard,important,impossible,necessary 等；在句型④中，常用
careless,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise等 表示赞扬或批评的词。在不定式前的sb，可看作其逻辑主语。这一句式有时相当于Sb is＋形容词＋to do句式 ，如：It'skind of you to help me with my English.=You are kind to helpme with my English. (3)举例
1） It's easy (for me) to do that.我做这事太容易了
easy, difficult, hard, important, possible, impossible, comfortable, necessary, better; the first, the next, the last, the best, too much, too little, not enough It's so nice to hear your voice. 听到你的声音真高兴。
It's necessary for you to lock the car when you do not use it. 当你不用车的时候，锁车是有必要的。
2) It's very kind of him to help us. 他帮助我们，他真好。
Kind, nice, stupid, rude, clever, foolish, thoughtful, thoughtless, brave, considerate(考虑周到的), silly, selfish(自私的) 例句:
It was silly of us to believe him. 我们真愚蠢，竟然相信了他。
It seemed selfish of him not to give them anything. 他不给他们任何东西，这显得太自私了。
注意：1) 其他系动词如，look，appear等也可用于此句型
2) 不定式作为句子成分时，动词用单数形式。
3) 当不定式作主语的句子中又有一个不定式作表语时，不能用It is„ to„的句型 (对)To see is to believe. 百闻不如一见。 (错)It is to believe to see.
二、作宾语
1) 以下动词后，只能跟不定式作宾语
afford （付得起），agree（同意），aim(力求做到), appear（显得），arrange（安排），ask（要求），attempt （试图），care（想要），choose（决定），claim（声称），consent（准许），decide（决定），demand（要求），determine（决心），expect（期待），fail（未履行），help（帮助），hesitate（犹豫），hope（希望），learn（学会），manage（设法），neglect（疏忽），offer（主动提出），plan（计划），prepare（准备），pretend（假装），promise（答应），prove（证明），refuse（拒绝），seem（觉得好像），swear（发誓），tend（往往会），threaten（预示），undertake（承诺），volunteer（自愿做），want（想要），wish（希望） 举例：
The driver failed to see the other car in time. 司机没能及时看见另一辆车。
I happen to know the answer to your question. 我碰巧知道你那道问题的答案。 2） 动词+疑问词+ 不定式
decide, know, consider forget, learn, remember, show, understand, see, wonder, hear, find out, explain, tell
Please show us how to do that. 请演示给我们如何去做。
There are so many kinds of tape-recorders on sale that I can't make up my mind which to buy.有这么多的录音机，我都拿不定主意买哪一种。 注意:疑问词带不定式在句中作成分时，谓语动词用单数。 The question is how to put it into practice. 问题是怎样把它付诸实施。
3)当复合宾语中的宾语是不定式时，先用形式宾语it代替不定式，把不定式置于补语之后，即：主语＋动 词＋it＋补语＋to do句式。如：
We think it quite important for us to learn a foreignlanguage well. He feels it his duty to help the poor.
I find it difficult to learn English well. 三、作补语
1) 动词+宾语+不定式(to do)
advise allow believe cause challenge declare encourage forbid force find instruct invite order permit persuade remind request require select send suppose tell train urge 例句：
a. Father will not allow us to play on the street.
父亲不让我们在街上玩耍。
b. We believe him to be guilty. 我们相信他是有罪的。 Find 的特殊用法：
Find 后可用分词做宾补，或先加形式宾语，再加形容词，最后加带to 的动词不定式。find后也可带一个从句。此类动词还有get，have。
I found him lying on the ground. I found it important to learn.
I found that to learn English is important. 典型例题:
The next morning she found the man ___ in bed，dead. A. lying B. lie C. lay D. laying
答案：A.find的宾语后面，用分词或分词短语，起宾语补足语作用。现在分词表达主动，也表达正在进行，过去分词表达被动。
2) to + be 的不定式结构，作补语的动词。
Acknowledge, believe, consider, think, declare(声称), discover, feel find, guess, judge, imagine, know, prove, see(理解), show, suppose, take(以为), understand
We consider Tom to be one of the best students in our class. 我们认为汤姆是班上最好的学生之一。 典型例题
Charles Babbage is generally considered ___ the first computer. A. to invent B. inventing C. to have invented D. having invented
答案：A. 由consider to dosth. 排除B、D。. 此句只说明发明这一个事实，不定式后用原形即可。而C为现在完成时，发明为点动词一般不用完成时，且此处也不强调对现在的影响，因此不选C。
3) to be +形容词
Seem, appear, be said, be supposed, be believed, be thought, be known, be reported, hope, wish, desire, want, plan, expect, mean„ The book is believed to be uninteresting. 人们认为这本书没什么意思。 4) there be+不定式
believe, expect, intend, like, love, mean, prefer, want, wish, undrstand We didn't expect there to be so many people there.我们没料到会有那么多人在哪里。
有些动词需用as 短语做补语，如regard, think believe, take, consider. We regard Tom as our best teacher. 我们认为汤姆是我们最好的老师。 Mary took him as her father . 玛丽把他当作自己的父亲。 四、作状语
1）目的状语
To„ only to (仅仅为了), in order to, so as to, so(such)„ as to„ (如此„„以便„„)
He ran so fast as to catch the first bus. 他飞快地跑以便赶上第一班车。 I come here only to say good-bye to you. 我来仅仅是向你告别。 2）作结果状语，表事先没有预料到的，要放在句子后面。 What have I said to make you angry.
He searched the room only to find nothing. 3) 表原因
I'm glad to see you. 典型例题
The chair looks rather hard, but in fact it is very comfortable to ___. A. sit B. sit on C. be seat D. be sat on
答案：B. 如果不定式为不及物动词，其后应有必要的介词。当动词与介词连用时，常位于\"形容词+动词不定式\"结构的末尾。 五、作定语
⒈不定式作定语
不定式在句中作定语，置于被修饰的名词或代词之后。如： ①The next train to arrive is from Washington.
②Do you have anything to be taken to your sister? ③Do you have anything to say on the question?
④Would you please give me some paper to write on? ⑤My wish to visit France has come true at last. 不定式短语作定语和被修饰词之间表示以下关系： (1)表示将来的动作（例①）。
(2)与被修饰词之间有动宾关系，如是不及物动词，则需加介词（例④）。
(3)与被修饰词之间有动宾关系，同时与句中其它词之间又有逻辑上的主谓关系时，尽管有被动含义，却仍 用主动语态（例③）；如只有动宾关系，而无逻辑上的主谓关系，则需用被动语态（例②）。
(4)不定式作定语时，一般可转换为定语从句，例①to arrive=that will arrive。
[省to 的动词不定式]
介绍
1） 情态动词 ( 除ought 外，ought to意思是\"应该\"，是情态动词，只有一种形式，后边接动词不定式，to不能省略。ought to没有人称和数的变化，后接动词原形可以表示现在、将来或过去将来，由时间状语或上下文决定。例如： They ought to come tomorrow.他们明天应当来)： 2） 使役动词 let, have, make：
3） 感官动词 see, watch, look at, notice , observe, hear, listen to, smell, feel, find 等后作宾补，省略to。
注意：在被动语态中则to 不能省掉。 在使役动词中get除外(get sb. to sth.) I saw him dance.
=He was seen to dance.
The boss made them work the whole night. =They were made to work the whole night. 4） 表示个人意愿或倾向的would rather，had better，might(just) as well：rather than置于句首时。
Rather than ride on a crowded bus,he always prefers to ride a bike. 5） Why„ / why not„：
6） help 可带to，也可不带to, help sb (to) do sth：
7） but和except：but前是动词do时，后面出现的动词用不带to的动词不定式。 8） 由and, or和than连接的两个不定式，第二个to 可以省去： 9） 通常在discover, imagine, suppose, think, understand等词后，可以省去to be：
He is supposed (to be) nice. 他应该是个好人。
10）but作介词，后接不定式结构时，前面谓语动词部分若含有do的形式时，but后的不定式要省去to，否则要带to。
He wants to do nothing but go out.
He wants to believe anything but to take the medicine.
11）当两个或多个不定时短语由连词and，but或or连接时，后一个或几个不定式符号to常省略。但若表示对比、对照关系时，则不能省略。 He wants to move to France and marry the girl.
The purpose of new technologies is to make life easier,not to make it more difficult.
12）不定式做表语时，一般要带to，但若主语部分中含有do的各种形式时，符号to可省去。
We've missed the last bus.All we could do now is walk home. 典型例题
1) ---- I usually go there by train. ---- Why not ___ by boat for a change?
A. to try going B. trying to go C. to try and go D. try going 答案：D. why not 后面接不带to 的不定式，因此选D。
2） Paul doesn't have to be made ___. He always works hard. A. learn B. to learn C. learned D. learning
答案：B. make后接不带to 的动词不定式，当其用于被动时，to 不可省略。
[动词不定式的否定式]...not to do...
Tell him not to shut the window„
She pretended not to see me when I passed by. 我走过的时候，她假装没看见。 典型例题
1）Tell him ___ the window.
A. to shut not B. not to shut C. to not shut D. not shut
答案：B。 tell sb to do sth 的否定形式为tell sb not to do sth. 2) She pretended ___ me when I passed by. A. not to see B. not seeing C. to not see
D. having not seen
答案：A。 pretend 后应接不定式。其否定形式为pretend not to do sth.。 3）Mrs. Smith warned her daughter ___ after drinking. A. never to drive B. to never driver C. never driving D. never drive
答案：A。warn sb to do sth. 的否定形式为warn sb not to do sth. 此处用的是否定词never.
4) The boy wanted to ride his bicycle in the street，but his mother told him ____.
A. not to B. not to do C. not do it D. do not to
答案：A。not to 为not to do it 的省略形式。可以只用to这个词，而不必重复整个不定式词组。及物动词do后应有名词、代词等，否则不对，因此B，D不对。 5) The patient was warned ___ oily food after the operation. A. to eat no B. eating not C. not to eat D. not eating
答案：C。warn一词要求后用不定式，此处为不定式的被动，否定形式为be warned not to do。
[不定式的特殊句型]
4、不定式的特殊句型too…to…
1）too„to 太„以至于„ He is too excited to speak. 他太激动了，说不出话来。
---- Can I help you ? 需要我帮忙吗?
---- Well, I'm afraid the box is too heavy for you to carry it, but thank you all the same. 不用了。这箱子太重，恐怕你搬不动。谢谢您。
2) 如在too前有否定词，则整个句子用否定词表达肯定， too 后那个词表达一种委婉含义，意 为\"不太\"。
It's never too late to mend. (谚语)
改过不嫌晚。
[动词不定式的\"to\"与介词的\"to\"区别] to 有两种用法： 一为不定式+动词原形；
一为介词+名词/动名词, to 在下面的用法中是第二种，即to+ 名词/动名词： admit to承认，confess to承认，be accustomed to 习惯于，be used to 习惯于， stick to 坚持， turn to开始，着手于， devote oneself to 献身于， be devoted to 致力于， look forward to 盼望，pay attention to 注意 介词but,except,besides+to do(do)
在这种句型中，如介词前有动词do，后面应接不带to的不定式；如无do，则接to不定式，即带do不带to， 带to不带do。如：
The enemy soldiers had no choice but to give in.
On Sunday afternoon I had nothing to do but watch TV.
动名词
动名词作主语有如下几种常见情况： 1. 直接位于句首做主语。例如：
Swimming is a good sport in summer.
2. 用 it 作形式主语，把动名词(真实主语)置于句尾作后置主语。 动名词做主语时，不太常用 it 作先行主语，多见于名词之后。例如： It is no use telling him not to worry. 3. 用于“There be”结构中。例如：
There is no saying when he'll come.很难说他何时回来。 4. 用于布告形式的省略结构中。例如：
No smoking ( =No smoking is allowed (here) ). （禁止吸烟） No parking. （禁止停车）
5在“It is no use...”，“It is no good...”，“It is fun...”，“It is a waste of time...”等句型中，通常用动名词作真实主语： 二、作宾语
（1）作动词的宾语
某些动词后出现非限定性动词时只能用动名词作宾语，不能用不定式。常见的此类动词有：admit,appreciate,excuse,stand,advise, allow, permit, avoid, consider, enjoy, finish, give up, cannot help, imagine, include, keep,understand, keep on, mind, report,risk,miss, put off, delay, practise, resist, suggest, depend on, think about, set about, succeed in, worry about, burst out, insist on, feel like,be used to, get
used to, devote„to„, look forward to, pay attention to, get down to,escape 等。如：
They went on walking and never stopped talking. 他们继续走，说个不停。
I found it pleasant walking along the seashore.
在海滩上走真是乐事。 Mark often attempts to escape being fined whenever he breaks traffic regulations. 每当马克违反交通规则时，他常常企图逃避罚款的处分。 （2）作介词的宾语
We are thinking of making a new plan for the next term. 我们正考虑为下学期制定新的计划。
Shall we have a rest or get down to doing our work? 我们休息呢还是开始干活？ （3）作形容词的宾语
The music is well worth listening to more than once. 这种曲子很值得多听几遍。 We are busy preparing for the coming sports meet. 我们正为马上到来的运动会忙
着做准备。
动名词的逻辑主语
带有逻辑主语的动名词称为动名词的复合结构。当动名词的逻辑主语与句子的主语不一致时，要在动名词之前加上物主代词或名词所有格，这便构成了动名词的复合结构。其中物主代词（名词所有格）是逻辑上的主语，动名词是逻辑上的谓语。动名词复合结构在句中可作主语、宾语、表语等，分别相当于一个主语从句、宾语从句、表语从句。如：
Her coming to help encouraged all of us. 他来帮忙鼓舞了我们所有人。 (=That she came to help encouraged all of us.)
Jane’s being careless caused so much trouble. 简的粗心惹来了不少麻烦。 (=That Jane was careless caused so much trouble.)
What’s troubling them is their not having enough food. 烦扰他们的是食物不足。 (=What’s troubling them is that they have not enough food.)
在口语中，如果动名词复合结构作宾语，其中的物主代词常用人称代词宾格，名词所有格常用名词普通格来代替，但在句首作主语时不能这样来代替。如：
Would you mind my/me using your computer? 用下你的电脑介意吗？
The father insisted on his son’s/his son going to college. 爸爸坚决要求儿子上大学。
Mary’s (不可用Mary) being ill made her mother upset. 玛丽病了，使她妈妈很着急。
His (不可用Him)smoking made his family angry. 他抽烟使他一家人非常生
常见题型
1） 动名词做主语时，谓语动词为单数
2） 在动名词和不定式中，作为介词的宾语是动名词
3） 动名词的否定直接在其前加否定词，通过代词的宾格或所有格形式给出逻辑主语 例：
I would appreciate_______ back this afternoon.
A．you to call B．you call C．you calling D．you’re calling（Key：C；换成your
calling也对）
4） 有些词后只能接动名词 admit; advise;allow;appreciate; avoid; celebrate; consider; delay; deny; enjoy; escape; excuse; explain; feel like; finish; forgive; can’t help; imagine; keep; mention; mind; miss; practice; prevent; recall; report; resist; risk; suggest; understand...
5） 另外还有一些接-ing形式的常用说法
it’s no good; it’s no/little/hardly any/ use; it’s not/hardly/scarcely use; it’s worthwhile; spend money/time; there’s no; there’s no point in; there’s nothing worse than; what’s the use/point...
6） 有些词后面加不定式和动名词均可
remember, forget, try, stop, go on, continue,stop,regret,cease, mean后面均可用不定式和-ing形式，但意义截然不容。 例：
remember to do/doing：
①I remembered to post the letters.（指未来/过去未来将要做的动作）
②I remembered posting/having posted the letters.（我记得做过这个动作） forget与remember的用法类似。 regret的用法：
①I regret to inform you that„（我很遗憾地通知你„„）
②I regretted having left the firm after twenty years.（为了“二十年前的离开”而遗憾。）
try to（努力）与try +–ing（试验）：
①You really must try to overcome your shyness. ②Try practicing five hours a day.
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