动词不定式（todo）的用法
1. 不定式的用法------1.1 不定式作主语
不定式作主语，往往用it作形式主语，真正的主语不定式放至句子的后面。
例如：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 u it. 不用车的时候，锁车是有必要的。
It's very kind of you to help us. 他帮助我们，他真好。
It emed lfish of him not to give them anything. 他不给他们任何东西，这显得太自私了。
但是，用不定式作主语的句子中还有一个不定式作表语时，不能用It is… to…的句型。另外，这样的句子，不能用动名词作表语。例如：
（对）To teach is to learn.
（错）It is to learn to teach.
（错）To teach is learning.
（错）Teaching is to learn.
典型例题
The chair looks rather hard, but in fact it is very comfortable to ___.
A. sit B. sit on C. be at 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。
1.1.1 不定式做主语 It's for sb/It's of sb to do sth
这样的句子中，由于表语形容词性质的不同，导致了不定式逻辑主语标志用for或of的区别。
1）for sb. 句型中的形容词一般为表示事物的特征特点，表示客观形式的形容词，如easy, hard, difficult, interesting, impossible等：例如：
It's very hard for him to study two languages. 对他来说学两门外语是很难的。
2）of sb句型中的形容词一般为表示性格，品德，心智能力，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。例如：
It's very nice of you to help me. 你来帮助我，你真是太好了。
1.2 不定式作宾语
1） 有些及物动词用不定式作宾语，结构为动词+不定式。例如：
afford | aim | agree | arrange | ask | decide |
bother | care | choo | demand | desire | determine |
elect | endeavor | hope | fail | help | learn |
long 渴望 | mean | manage | offer | plan | pretend |
refu | tend | undertake | expect | hate | intend |
| | | | | |
例如：
The driver failed to e the other car in time. 司机没能及时看见另一辆车。
He offered to help me. 他表示愿意帮助我。
2）有些动词除了可以用不定式作宾语，还用不定式作补语，即有动词+宾语+不定式的结构。例如：
ask | choo | expect | help | beg | intend |
like/love | need | prefer | prepare | want | wish |
| | | | | |
例如：
I like to keep everything tidy. 我喜欢每件东西都保持整洁。
I like you to keep everything tidy. 我喜欢你使每件东西都保持整洁。
I want to speak to Tom. 我想和汤姆谈话。
I want you to speak to Tom. 我想让你和汤姆谈话。
3） 有些动词或动词词组可以用动词+疑问词+不定式的结构作宾语。例如：
decide | know | consider | forget | learn | remember |
show, | wonder | find out | tell | inquire | explain |
| | | | | |
例如：
Plea 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 don't know which to buy.
有这么多的录中国圣人
音机，我都拿不定主意买哪一种。
1.3 不定式作表语
不定式可放在be动词后面，形成表语。例如：
My work is to clean the room every day. 我的工作是每天清扫房间。
His dream is to be a doctor. 他的梦想是成为一名医生。
1.4 不定式作定语
不定式做定语通常要放在被修饰的词后，往往表示未发生的动作。例如：
I have a lot of work to do. 我有许多事要做。
There was nothing to bring home that morning. 那天早上（他回家时）两手空空。
1.5 不定式作状语
1）目的状语
常用结构为to do , only to do（仅仅为了）, in order to do, so as to do, so（such）… as to…（如此…以便…）。例如：
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，可以表示没有预料到的或事与愿违的结果，不定式要放在句子后面。
I awoke to find my truck gone. 我醒来发现箱子不见了。
He arched the room only to find nothing. 他搜索了房间，没发现什么。
3）表原因
I'm glad to e you. 见到你很高兴。
She wept to e the sight. 她一看到这情形就哭了。
4）表示理由和条件
He must be a fool to say so.
You will do well to speak more carefully.
1.6 不定式作补语
1） 有些有动词+宾语+不定式的结构。例如：
动词 | 宾语 | 不定式 |
He reminded | me | to buy some eggs. |
| | THAT-从句 |
He reminded | me | that I had to buy some eggs. |
| | |
advi | allow | cau | challenge | command | compel |
drive 驱使 | enable | encourage | forbid | force | impel |
induce | instruct | invite | like/love | order | permit |
make | let | have | want | get | warn |
persuade | request | nd | tell | train | urge |
| | | | | |
例如；
Father will not allow us to play on the street. 父亲不让我们在街上玩耍。
The officer ordered his men to fire. 长官命令士兵开火。
注意：有些动词如make，have，get，want等可用不定式作做宾补，也可用分词作怀念的人
宾补。现在分词表达主动，也表达正在进行，过去分词表达被动。
2) 有些有动词+宾语+不定式的结构，不定式的动词往往是be，不定式一般可以省去。例如：
consider | find | believe | think | declare（声称） | appoint |
guess | fancy（设想） | guess | judge | imagine | know |
| | | | | |
例如：
We believe him to be guilty. 我们相信他是有罪的。
We know him to be a fool. 我们知道他是个笨蛋。（to be 不能省去）
