：
4) there be+不定式
believe, expect, intend, like, love, mean, prefer, want, wish, understand
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。
注意
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。
3. 不定式作主语
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 you 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)
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。
It's for sb。和 It's of sb。
1) for sb. 常用于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：
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的句型一般用表示人物的性格，品德，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。
It's very nice of you to help me. 你来帮助我，你真是太好了。
for 与of 的辨别方法
用介词后面的代词作主语，用介词前边的形容词作表语，造个句子。如果道理上通顺用of，不通则用for。如：You are nice.(通顺，所以应用of)。He is hard.(人是困难的，不通，因此应用for。)
4. 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。
His dream is to be a doctor。
5. 不定式作定语
不定式做定语通常要放在被修饰的词后。例如：
I have a lot of work to do.
So he made some candles to give light。
6. 不定式作状语
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。
用作介词的to
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
省to 的动词不定式
1) 情态动词 ( 除ought 外，ought to)：
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。
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) would rather，had better：
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。举例：He wants to move to France and marry the girl. He wants to do nothing but go out. 比较：He wants to do nothing but go out. He wants to believe anything but to take the medicine。
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
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 seeingC. 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 driverC. 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 toB. not to doC. 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 eatD. 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。
3) 当too 前面有only, all, but时，意思是：非常… 等于very。
I'm only too pleased to be able to help you. 我非常高兴能帮助你。
He was but too eager to get home. 他非常想回家。
