英语语法——不定式2
B. 用法：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…
(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 requires courage / patience / hard work… to do…
*注意: probable 和 possible 均可作表语，但possible可以用不定式作真实主语， 而probable不能用不定式作真实主语。
It is probable for him to come to the meeting.(错）
It is possible for him to come to the meeting.
It is possible / probable that he will come to the meeting.
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。
eg My idea is to climb the mountain from the north.
Your mistake was not to write that letter.
What I would suggest is to start work at once.
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.
*注意:某些及物动词可用-ing也可用动词不定式作宾语但意义不同的有
stop go on remember forget
regret try mean can’t help
be used to
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 want you to be his assistant. I saw her cross the street.
[注1] 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?
但如果句子是被动语态，则to不可省略。
He was made to clean the windows as a punishment.
Someone was heard to come up the stairs.
[注2] 1.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.
2.在美式英语或非正式文体中，help后用作宾补的不定式均不带to。
3.help后可以直接用带to或不带to的不定式作宾语。
They helped (to) carry the furniture upstairs.
[注3]look at及listen to后用作宾补的不定式不带to（这主要是美式英语）。
We have been listening to the radio tell a long story.
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.
To get the best results, use clean water.
To be elected monitor of our class, he gave money to us.
* 放在句末时， to do 表示目的， 不可有“，”若有用doing 表示伴随的目的
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.
例外 e g He opened the door for the children to come in.
They sent a man to mend the window.
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.
八．同位语
Is this your purpose, to avoid being punished?
九．独立成分
To tell you the truth, I don’t like you. They arrived here at 11:55 a.m., to be exact.
类似的有：to be frank坦率地说，to hear him talk听他说话的口气，to cut a long story short 长话短说，等等。
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