动词不定式的用法（二）
动词不定式的句法功能：动词不定式在句中可充当主语、表语、宾语、宾补、定语和状语等。
一、作主语：
不定式作主语时，通常表示一个具体的，特定的行为。其谓语动词用第三人称单数形式。动词不定式作主语可位于句首。例如：
To live means to create.
To do that sort of thing is stupid.
To learn a skill is very important for everyone in society.
但是当作主语的不定式是较长的短语是，我们通常使用it作形式主语，而将动词不定式置于句末。例如：
It is necessary for young students to learn a foreign language.
It was his job to repair bicycles(自行车)
常用it作形式主语，而用动词不定式作实际主语的常用句型有：
1. It is＋adj (＋for sb.／sth.) ＋ to do sth.表示“做某事对某人来说怎么样”。通常表明的是事情对人产生的影响或意义。比如“难易程度、重要性、可能性大小等”。
用于此句型的形容词有：easy, hard, difficult, possible, important, impossible, necessary, good, bad, exciting, interesting, surprising等。
例如：
It is interesting to play this game.
It is necessary for you to change your job.
How rude it was of the boy to jump the queue!
It is friendly of the family to try to make me feel at home in their house.
How silly it was of you to give up such a good chance！
2. It’s +adj.+of+sb.+不定式”表示“某人(做某事)怎么样”。 通常表示根据事实判断人的品行，特征。如：“聪明，愚笨，明智，错误等”。
注意：这一句型中常用描述不定式的逻辑主语的性格、品质的形容词，如good(好的)，kind(友善的)，nice(友好的)，polite(有礼貌的)，clever(聪明的)，foolish(愚蠢的)，lazy(懒惰的)，careful(细心的)，careless(粗心的)，wise(明智的)，right(正确的)，wrong(错误的)等。
用于此句型的名词有：pity, shame, pleasure, one’s duty, one’s job, fun, joy, good manners, bad manners等。例如：
It's our duty to take good care of the old.
What a pity it is for you to have missed such a wonderful film.
It is good manners for the young to give their seats to the old.
It's a shame for you to do such kind of thing.
例如：
It took us half an hour to ride to the town by bike.
二、作表语
主语和表语同为不定式时，通常主语表示条件，表语表示结果。
如：To see is to believe.
动词不定式作表语常用于以下结构：My wish/ job/ aim/ goal is+不定式以及The next step/ /important thing/problem/measure is +不定式等。例如：
My wish is to be a teacher.
My goal is to pass the college entrance examination(高考，大学入学考试).
The problem is how to get there.
The important thing in life is to have a great aim.(目标)
Your job is to type the papers in the office.
The next measure is to stop the river from being polluted.
☆另外：
A)当主语是一个由what引导的从句时，用作表语的不定式通常是说明what的具体内容的。 如：What I want is to go to the park tomorrow.
B)不定式作表语常常用来表示预定要发生的动作，或表示未来的可能性或假设。 如：His greatest wish is to see an end to the war.
All you have to do is (to) finish the job as quickly as possibly.
All I can do is just smile at him and say nothing.
注意：当主语中含有实义动词do的各种形式时，作表语的不定式通常省略“to”.
三、作宾语
许多动词都可和不定式搭配，即这些动词的用法决定了其后接带to的不定式作宾语。有些动词只能接“疑问词+不定式”作宾语。而句中的主语常常就是作宾语的不定式的逻辑主语。
常见的只能使用动词不定式作宾语的动词有：agree, choose, decide, hope, fail, wish, refuse, expect, manage, plan, intend, pretend, promise, offer, afford, demand, arrange等。
而常常接“疑问词+不定式”作宾语的动词有：decide,discover,forget,inquire（询问），know,learn,remember,see,settle,think,wonder.
例如：They decided to build a highway between these two cities.
She offered to help me when I was in trouble.
He promised not to tell anyone about it. I can't remember what to do.
I forgot how to operate the machine.
注意：当作宾语的不定式是较长的短语，常常用it作形式宾语，而把真正的不定式放到句末去。
常常这样用的动词有believe, think, consider, find,feel, make等动词。
可构成句型“动词+ it +adj. / n+to do sth.”句型，其中使用it作形式宾语，而将真正的
宾语动词不定式置于句末。例如：
I think it necessary for us to have a good rest after the long work.
She felt it her duty to help the old woman.
I find it difficult to understand him.
※四、作介词宾语
动词不定式通常不能用作介词的宾语，但以下两点除外。
1
如：He gave me some advice on how to write a good composition(作文).
He talked with me about how to spend the frigid(极寒冷的) winter.
2)以下介词之后常常用不带to的不定式作宾语，特别是当句中的谓语动词为实义动词do的各种形式时，尤其如此。而谓语动词为其他动词时，也可用带to的不定式。
这类介词主要有：
I couldn't do anything but wait here.
The enemy(敌人投降).
敌人除了投降之外，别无选择。
除了让他生气外，这起不了任何作用。
如：His father could do nothing but wait for the doctor to arrive. We would do anything but confess(承认)our guilty.我们决不承认有罪。
She couldn't help but laugh at his clothes.她情不自禁地大笑他的着装。
I cannot but admire(钦佩) his courage.
I could not choose but love her.我不禁爱上了她。
作宾补
不定式作宾补时，其逻辑主语常常就是它前面的宾语。
1)可后接动词不定式作宾补的动词有：advise, allow, ask, beg, cause, challenge(挑战), convince(使信服), dare, drive(驱使), encourage, expect, forbid, force(强迫), hire, instruct(指导), invite, need, order, permit(允许), persuade, require, teach, tell, urge, hear, order, see, want, wish, worn(警告)等。例如：
I wish you to go to the meeting with me.
I persuaded him to give up smoking.
She asked me to stay here.
如：believe, consider, count, declare, deny, feel, find, guess, imagine, judge, know, prove, realize, suppose, think等动词后常常接to be型不定式作宾补。to be可以省略。例如：
He declared himself （to be） a college student. 他自称是名大学生。
The police proved him （to be ）a thief. 警察局证实他是小偷。
We consider him (to be ) diligent(勤奋的).
☆特别注意 hope, demand, suggest等动词不能后接动词不定式作宾补。例如：
【误】I hope my son to be back soon.
【正】I hope my son will be back soon.
【误】She suggests us to have a discussion about it.
【正】She advises us to have a discussion about it.
【正】She suggests that we (should) have a discussion about it.
3)在主动结构中，下列动词后作宾补的动词不定式应省略to：“五看”(see, watch, notice, observe, look at)“三使”(make, let, have)“两听”(hear, listen to)“一感觉”(feel)。例如：
His boss made/have/let him work all day long.
I heard him sing in her bedroom.
I saw him play basketball on the playground.
但是，改为被动结构后，应该还原省略的to。例如：
He was seen to break the window.
4)表示好恶的动词+宾语+带to的不定式
如：I like people to tell the truth.
She preferred me to do my job by myself.
I hate him to speak loudly in the classroom.
这类动词主要有：
5）Know和see的用法
当它们用于主动语态，特别是用于一般过去时或过去完成时，其后的宾语补足语常常可以省略。
如：I have never known him (to) tell a lie(谎言)
I have never known/seen it (to) snow in July before.
I never knew her complain.
我从没听她发过怨言。
注意：当know和see用于被动语态时，必须还原不定式符号to。
如：I have never seen that man (to) smile.
That man has never been seen to smile. 五、作定语
定语的不定式之间可能是逻辑主语，也可以是逻辑宾语的关系。例如：
Have you got anything to eat? (to eat修饰anything，位于其后)
Do you have anything to say/declare(宣布)？
What I want is to get something to do.
1)evidence, failure, means, measure, reason, refusal, promise, right,way, wish等。例如：
But she gave up the chance to go abroad.
You have no right to speak.
He has the ability to work out the math question.
I have the courage to invite her for dinner.
She has a great wish to to travel around the world.
2)常常用不定式修饰。
如： Do you have anything more to say?
We found a house to live in.
I need/want a piece of paper to write on.
3) 如：Mike is the person for me to turn to(求助于) in difficult time.
遇到困难，麦克是我可以向之求助的人。
This is the only point for us to pay attention to.
这就是我们需要给以关注的唯一一点。 4) 如：We must find a hotel to live in because it is getting dark.(live in a hotel)
Please give me a piece of paper to write on.(write on a piece of paper)
There are a lot of goods(商品)to choose from.(choose from the goods)
5)由only, first, last, next, only, second以及序数词或形容词最高级修饰的名词后，也常接不定式作定语。例如：
Who was the last one to leave the classroom last night?
She was the first girl to come to the party.
He is the only person to know the thing.
This is the best film to be played that year.
这是那年放映的最好的电影。
The cheapest products(商品，产品)to be bought is in that store.
如：There is nothing to worry about/to be worried about.
There is a lot of work to do/be done.
Is there anything to eat?
7)
如：The meeting to take place is very important for the company.
即将召开的会议对这个公司极其重要。
The person for you to talk with is the manager.
将和你谈话的人是经理。
六、作状语
动词不定式作状语，可表示目的、原因、结果或条件。
1)如：I must leave now to get there on time.我必须马上动身，以便按时到达那儿。 I am saying this to encourage you.
I store the food in the fridge to keep it fresh.
We went there to see our grandparents.
※A)注意：不定式表示目的时，常常在不定式前面加上in order或so as，构成in order to或so as to，以突出或强调目的。
如：Many people go to work on foot in order to /so as to lose weight.
I got up so early in order to catch the early bus.
He worked so hard so as to get high salary(薪水).
B)in order to 和so as to 的否定式是在to前面加not，构成in order not to 和so as not to. He studied in his bedroom so as not be disturbed.
C)in order to既可以放在句首表目的，亦可以放在句中，而so as to 只能放在句中。 In order to catch the early bus, I get up early every day.
=I get up early every day so as to catch the early bus.
2)
What have I done to offend you?
用so...as...和such...as...引导的结果状语：
He is not so stupid as to do that.他还没用蠢到去做那种事情。
He got up so early as to catch the first bus.
他起的如此早，以致他赶上了头班车。
She is such a beautiful girl as to be liked by people.
He is such a strong boy as to carry that heavy box.
由too...to引导的结果状语，意为“太。。。以致不能。。。”
She is too young to attend school.
The food is too hot to eat.
I am too tired to study any more.
注意：A)如果too 前有all,but,not,only等修饰时，too的意思是“非常、很”，这种情况下，即使too后面跟了不定式，也不含否定意义，不表示结果。
I am not too sad to see them leave.
看到他们离开了，我并不感到很悲伤。
I am not too happy to meet you.
见到你，我并不很高兴。
I am only too pleased to help you.
我十分乐意帮助你。
B)当too和以下形容词连用时，即使其后跟有不定式，也不表示否定，too意为“非常。” 这些形容词有：
Food is too apt to go bad in summer.
She is too eager to see you.她很渴望见到你。
The girl is too ready to cry.这个女孩动不动就哭。
由enough引导的结果状语。
注意：enough用来修饰名词时，可以放在名词前面或后面；但是用来修饰形容词或副词时，只能放在其后。
如：He made enough noise/noise enough to wake the dead.
他连死人都要吵醒了。
I don't know him well enough to ask for his help.
He was kind enough to help me.
他十分友善，帮助了我。
☆另外：不定式表示结果时，常常和only连用，暗示一种意外的结果。
如：He worked hard only to fail in the exam.
和努力学习，结果却没有及格。
He rushed to the station only to find the train had left.
He invited the girl for dance only to receive a polite refusal.
3)动词不定式用作原因状语，通常放在谓语之后，表示原因。该状语的时间常常略早于谓语动作发生的时间。
如：They jumped high to hear the news.听到这个消息，他们高兴的跳起来了。
I feel very happy to be praised by my teacher.
I am very sorry to hear that.（原因）
The boy was shocked to see his girlfriend walk hand in hand with another boy.
4)动词不定式用作条件状语。此时，不定式位于句首，句末皆可。
如：She will be glad to hear the news.
He would be stupid not accept her advice.
To look at him, you could not help laughing.
如果看看他，你就会禁不住笑起来。
5）不定式用作方式状语。此时，不定式前面常常有as if，as though，表示比喻关系。 如：He raised his hand as if to stop the car.
She opened her mouth as though to speak.
她张开嘴，好像要说话似的。