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动词不定式概述
定义：动词不定式是非谓语动词的一种，它没有人称和数的变化，在句子中不能独立作谓语，但它仍保持动词的特点，既可以有自己的宾语和状语。
e.g. He wants his students to read the book aloud.
1. 不定式的构成 （以动词do为例）
主动形式
一般式 to do
完成式 to have done
进行式 to be doing
2. 不定式的意义
不定式的一般式(to do )
一般式表示的动作或状态，发生在谓语动词表示的动作或状态的同时或之后。
My wish is to become a doctor.
He seemed to be tired.
She stopped to have a rest.
如果谓语表示的动作(情况)发生时，不定式表示动作正在进行，这时候不定式就要用进行式。
（to be doing）。
They are said to be building another bridge across the street.
They seemed to be talking about something important.
如果不定式所表示的动作或状态发生在谓语动词所表示动作或状态之前，就用完成式 (to have done) ；若是在此基础上的被动含义，就用完成被动式( to have been done)。
He is said to have written a novel about the Long March.
He thought it a pity not to have invited us.
不定式在句中所做成分
动词不定式具有名词、形容词和副词的特征。因此在句中可以做主语、表语、宾语、宾语补足语、定语和状语。
一、不定式做主语：
1. 不定式做主语一般表示具体的某次动作。动名词doing 表示习惯的，经常的动作。
e.g. To finish the building in a month is difficult.
To do such things is foolish.
To see is to believe. (对等)
注：1) 不定式作主语时，谓语用单数。
2) 当主语较长，谓语较短时，常用it做形式主语，而将不定式放到谓语的后面。
it做形式主语，不定式放在谓语动词之后常用于下列结构中：
(1) It is/was +adj.+of sb. to do…
It’s nice of him to help me out.
(2) It is +adj.+for sb.+to do…
It is easy / difficult / hard / foolish / unwise / right / wrong / unnecessary…
(3) it is +a +名词+ to do...
It is a pity / a pleasure / a pleasant thing / one’s duty / an honor / a shame /
a crime / no easy job… to do…
It takes (sb.) some time / courage / patience …to do…
It took them two weeks to finish the design.
二、不定式做表语
主语是以aim /duty/ hope/ idea/ intention /plan/ job/ suggestion/ wish/ purpose/ task 等为中心词的名词词组或以 what 引导的名词性从句表示，后面的不定式说明其内容，不定式作表语常表示将来或现在的动作或状态。
e.g. My idea is to climb the mountain from the north.
Your mistake was not to write that letter.
三、动词不定式作宾语
以不定式结构为宾语的动词有：
ask, agree, care, choose, demand, decide, expect, fail, help, hope, learn, manage, offer,
plan, prepare, pretend, promise, refuse, want, wish等只能用动词不定式作宾语。
口诀（接不定式作宾语的动词）
想要学习 早打算（ want learn plan）
快准备 有希望（ prepare hope wish expect）
同意否 供选择（agree offer choose）
决定了 已答应（decide be determined promise）
尽力去 着手做（manage undertake）
别拒绝 别假装（refuse pretend）
失败不是属于你（fail）
e.g. Tom refused to lend me his pen.
We hope to get there before dark.
The girl decided to do it herself.
四、动词不定式做定语
1. 不定式作定语需要后置。
2. 作定语的不定式与被修饰的名词或代词存在着两种主要的逻辑关系，即被修饰的名词和代词是不定
式的逻辑主语（逻辑上的主谓关系）或逻辑宾语（逻辑上的动宾关系）。
1）不定式前的名词是它的逻辑主语。
He is the doctor to do the operation.
2) 不定式和它所修饰的名词是逻辑上的动宾关系。
I have a lot of things to do.
3）不定式前的名词是它修饰的对象。
This is the right time to start.
注意：如果不定式所修饰的词是way 或 place，介词可省略。
He has no way to go (by). This is the best place to work (at).
五、宾语补足语
He wanted you to be his assistant. I saw her cross the street.
如果谓语动词为感官动词或使役动词，则作宾补的不定式不可带to，这些动词有see, hear, feel,
watch, notice; have, make, let等。
I felt my blood run cold. What made you think like that?
谓语动词help后可接带to或不带to的不定式作宾补。用不带to的不定式表示帮助者直接参与动作；用带to的不定式表示主语没有直接参与动作。
They helped me carry the boxes.
This kind of soap will help you to wash the clothes more easily.
六、表语补足语
当不定式与主语存在逻辑上动宾关系的时候，用主动表被动。
That is hard to say.
The chair is comfortable to sit in.
七、不定式做状语
不定式做状语修饰动词、形容词、副词等，表示目的、原因、结果、 条件等。
1. 表目的
e.g. To learn a foreign language well, you must try your best. (主语一致)
He came here to attend an important meeting.
He came here in order to see Charlie.
I turned the radio down so as not to disturb him.
注：表示目的的不定式可以置于句首，这也是区别于其他功能的标志之一。
● 但是，置于句首表示目的的不定式可以是to, in order to ，但却不可以是so as to。
● To draw maps properly, you need a special pen.
In order to draw maps properly, you need a special pen.
* 放在句末时， to do 表示目的。
e.g. He bowed to us to thank us for helping him find the way.
He worked day and night, hoping to finish the work beforehand.
注：1. 不定式结构表示目的时，通常句子的主语就是它的逻辑主语 (主语一致) 。
e.g. He bought a bicycle to go to town more quickly.
He went home to see his mother.
2. 表结果
不定式结构表示结果更常见于下列句型
① so…as to…
Would you be so kind as to lend me your bicycle / tell me the time?
② such (…) as to…
I’m not such a fool as to believe that.
③ adj./adv. + enough to…
The boy is old enough to go to school.
④ too … to …
His eyesight is too poor to read such small letters.
（5）only to find, only to be told出乎意料之外的结果
3. 原因不定式可以用于动词、形容词或-ed分词后表示原因。
He was too excited to get high marks.
常见的含有动词不定式的句式
一、It takes sb. some time （money）to do sth.
某人花费多少时间（金钱）做某事。
例如：
1. It often takes me half an hour to watch TV every evening.
每天晚上我常常用半小时看电视。
2. It took me ten yuan to buy the book last week.
上周我花了10元买那本书。
3. How long will it take them to finish the work?
完成那项工作需要花费他们多少时间？
在使用该句式要注意的是：sb. 如果代词表示用宾格；take随时态改变；句中的时间用段时间，对此提问用how long。
例：It takes us more than two hours to do our homework every day.
It took us more than two hours to do our homework yesterday.
It will take us more than two hours to do our homework tomorrow.
二、It’s time to do sth. 该做某事了
同义句为：
It’s time for sth. / doing sth.
例：
It’s time to go to school. 该上学了。
（It’s time for school.）
It’s time to get up. 该起床了。
（It’s time for getting up.）
此句可以扩展为：It’s time for sb. to do sth. 是某人做某事的时间了。
for sb. to do sth. 是动词不定式的复合结构。
例：It’s time for me to work.
到我工作的时间了。
三、主语＋be（not）+adj.+enough to do sth.
（某人、某物）足够（不能）做某事。
例：
The boy is old enough to go to school.
这个孩子到了上学年龄。
I’m tall enough to reach the top of the tree.
我足够高，高到能够到树顶。
*1. 此句是肯定句时，可以用主＋be＋so＋adj.＋that的句型（即so…, that…表示的结果状语从句）来替换。
The boy is so old that he can go to school.
I’m so tall that I can reach the top of the tree.
2. 此句是否定句式时，既可以用so…that…引导的结果状语从句来替换，还可以用too…to…句式替换。
例：
He is not old enough to go to work.
他太小不能去上班。
He is so young that he can’t go to work.
He is too young to go to work.
再如：
The box is not light enough for me to carry.
这个箱子太重我搬不动。
The box is too heavy for me to carry.
The box is so heavy that I can’t carry it.
四、sb. +be ready + to do sth. （某人乐意做某事）
He is always ready to help others.
（他总是乐于帮助别人）
I’m always ready to make new friends.
我总是乐于结交新朋友。
五、It’s +adj. + for / of sb. to do sth.
对某人来说做某事……
例：
It’s dangerous for children to play football in the street.
对孩子来说在街上踢足球是很危险的。
It’s good for us to take more exercise.
对我们来说多运动是有益的。
It’s very kind of you to say so.
你这样说真是太好了。
It’s very kind of you to help me.
你真好，愿意帮我。
该句式中，引导动词不定式的逻辑主语的介词用for还是of，主要取决于前面的形容词。如果形容词是描述动词不定式的行为者的性格、品质的。如：kind, good, nice, wrong, right, clever, careless, foolish等，应用of；如果形容词仅仅是描述事物，不是对动词不定式的行为者的品质进行评价的，就用for。常见这类形容词有difficult, easy, hard, important, dangerous等。
六、主+would like / love to do sth. ……喜欢（想做某事）
I’d like to go there with you.
我很想和你一起去那。
I’d love I like to help you study English.
我很愿意帮你学英语。
此句式还可以扩展为：
would like / love sb. to do sth.
“喜欢/想让某人做某事。”
I’d like you to stay here.
我想让你留在这。
I’d like them to help me.
我想让他们帮助我。
七、had better do sth. （……最好做……）
It’s very cold outside, you’d better put on your coat.
外面很冷，你最好穿上大衣。
…had better do 的否定式为…had better not do. （在better后加not即可）
例：
You’d better not speak when your mouth is full of food.
满嘴食物时你最好别讲话。
八、Why don’t you +动词原形+…？（Why not＋动词原形…？）你为什么不……？
这本书有点难，为什么不读些容易的？
This book is a bit hard, why not read something easier?
It’s warm here, why don’t you take off your coat?
这很暖和，你为什么不脱掉外衣？
There is a seat, why not sit down?
还有座位，怎么不坐下？
九、Would / Will / Could you please ＋动词原形＋…？
请你……好吗？（用来请求对方为自己做某件事）
Would you please bring some water with you?
请你带点水来好吗？
Will you please help her with her maths?
请你帮她学数学好吗？
十、…prefer …to do sth. rather than do sth. ……宁愿……也不愿……
I prefer to stay at home rather than go out.
我宁愿呆在家里，也不愿出去。
She prefers to be poor rather than get money in such a way.
她宁愿受穷也不愿以这种方式挣钱。
十一、It’s one’s turn to do sth. 该轮到谁做某事了。
one’s用形容词性物主代词或名词所有格来替换。
例：
It’s my turn to be on duty.
该轮到我值日了。
It’s Li Ping’s turn to clean the blackboard.
该轮到李平擦黑板了。
It’s our turn to do the cleaning.
该轮到我们做扫除了。
It’s Danny’s turn to give a talk.
该轮到Danny做报告了。
十二、主语＋be＋形容词＋to do sth. ……做某事如何。
例：
I’m sorry to hear that.
听到这事我很难过。
I’m glad to see you again.
再次见到你我很高兴。
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