不定，表示不确定，动词不定式的含义就是，动词的形式不随着句子的人称、性、数、时态而定（即不随着句子的人称、性、数、时态而发生变化），始终保持那个形式。
动词不定式有下列几个常见形式：
一般式：to + 动词原形
不带to的形式：动词原形
否定式：not + to + 动词原形
疑问式：wh-疑问词 + to + 动词原形
被动式：to be + 动词的过去分词
完成式：to have + 动词的过去分词
进行式：to be + 动词的现在分词
不定式是历次大学英语四级考试必考的内容。不定式在句子中可做主语、宾语、表语、定语、状语和宾语补语。
1)不定式做主语一般表示具体的某次动作。
【例如】
To complete the 30�storied building in one year was quite a difficult task.
To do that implies taking responsibility.
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。
【例如】
It is important for modern young people to master at least two foreign languages.
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：
a) It is＋形容词(easy, important, difficult, foolish, inconvenient, unnecessary, right, wrong...)＋( for/of sb.)＋不定式
【例如】
It is essential to reserve a table in advance of Christmas Eve.
It is hard to put my hopessintoswords.
It is not easy to catch fish with your hands only.
It is important for us young people to learn English and master it.
b) It is＋名词(a pleasure, a pity, a pleasant thing, one's du�ty, an honor, a shame, a crime, no easy job...)＋不定式
It is a sheer waste of time to read that kind of trash.
It is a pity to have to go without her.
It is a glorious death to die for the people.
c) It takes (sb.) some time (hours, months, days, a lot of time, patience...)＋不定式
It takes me three hours to learn English each day.
It took them half the night to get home in the snow.
2)不定式作表语不定式作表语常表示将来的动作，主语常常是表示意向、打算、计划的词，如wish, idea, task, purpose, duty, job等。
【例如】
The most important thing for one's health is to have plenty of exercise.
My chief purpose has been to point out the difficulties of the matter.
The purpose of the organization is to greet all new comers to the city and to provide them with any necessary information.
What I wanted was to get the work done as quickly as possible.
3)不定式作宾语不定式常在下列动词后面作宾语：
afford,agree,apply,arrange,ask,attempt,beg,begin,care,choose,claim,consent,demand,decide,desire,determine,expect,fail,hope,hesitate,hate,intend,learn,like,manage,mean,neglect,offer,plan,prepare pretend,promise,refuse,resolve,seek,tend,threaten,want等。
【例如】
I like to go out for walks in the warm sunshine in spring.
My mother hates to move from place to place, for she feels tired.I decide to work hard and get doctor's degree.
The room is designed to be my study, but now it has to be used as a bedroom for the children.
She failed to finish the assignment in time, and she was worried about it.
There is a man at the reception desk who seems very angry and I think he means( )trouble. (CET-4 1997, 1)
A) making
B) to make
C) to have made
D)shavingsmade
mean后面一般加不定式，所以A和D可以排除。根据句意，他看起来非常生气，他想找麻烦，不定式的动作还没有实施，应用一般式，因此答案为B。不定式作宾语还常用在下面结构中；主语＋动词＋it＋形容词＋不定式。
【例如】
We found it impossible to get everything ready in time. I think it important to learn English well in college.使用这种句型的常见动词有：believe, consider, declare, feel, find, guess, imagine, prove, realize, suppose, think,等。
4)“wh�word＋不定式”结构不定式前加一个疑问代词(what, which, who, whom, whose)或疑问副词(where, when, how, why)，以及连词whether构成特殊的不定式短语，其作用相当于一个从句，这样的不定式短语常在某些动词后面作宾语。
常见的可以接这种不定式短语的动词有：
know, see, decide, tell,ask,consider,discover,explain,findout,forget,guess,hear,imagine,inquire,learn,observe,perceive,remember,think,understand,wonder等。
【例如】
I couldn't decide which book to choose. I can tell youswheresto get this book.They found it hard to decide whether to go swimming next Sunday or to visit Aunt Sally in New Year.“wh�word+不定式”结构除了作宾语外，还可以在句中作主语或者表语。
【例如】
When to start the program remains undecided. The question is how to put the plansintospractice.
5)不定式作状语
a)不定式作状语表示目的。或用于so as和in order之后，来强调这种目的。
【例如】
To learn a foreign language well, you must make painstaking efforts.
Mother saved every cent she could spare to pay for my schooling.We must develop science and technology at high speed so as to raise scientific and cultural level of our country.
Insgroupsto get a high mark in Band 4, he did a lot of exercises both in grammar and reading comprehension.
b)不定式表示结果，特别是在so...as to, such...as to, only to...以及too...to等结构中的不定式表示结果。
【例如】
I rushed to the station as fast as I could, only to find the train already gone.
She left her hometown with her beloved man, never to return.No one is too old to learn.
Would you be so kind as to carry the luggage for me?
c)不定式常用来修饰形容词，构成下列词组：be able to, be afraid to, be apt to, be bound to, be certain to, be easy to, be eager to, be fit to, be likely to, be ready to, be sure to, be unable to, be unwilling to, be willing to等。
【例如】
Chinese team is bound to win the World Cup.
It is likely to rain today, for it is very cloudy.
I am willing to help you with your homework, for we are friends.
6)不定式作宾语补语不定式常跟在下列动词之后作宾语补语：ask, advise, allow, beg, cause, compel, command, enable, encourage, expect, feel, force, find, hear, have, inform, invite, let, make, mean, notice, order, permit, persuade, remind, require, request, teach, tell, urge, watch, warn, watch等。
【例如】
Because of the complexity of the modern equipments, most offices require secretaries to have specified training.
He asked you to call him at ten o'clock.
The note reminds me to be careful whatever I do.
I'd never allow my children to behave like that.
当不定式在let, make, have, hear, look at, listen to, feel, observe, watch, notice, perceive(感觉到)等动词后面作宾语补语时，不定式不带to.
【例如】
Whenever something is wrong with you, please do let me know.
I will have the students write a passage about Internet.
I saw my mother shed tears at the news that the neighbor girl got seriously hurt in a car accident.
It seemed so long before he heard the stone hit the water.
7)不定式作主补带有宾语及宾语补足语结构的动词变为被动语态时，原来的宾语变为主语，宾补则变为主补。加主补的动词主要有：assume, believe, know, report, say, suppose等。
【例如】
Mr. Brown is said to have left for Italy last week.(It is said that Mr. Brown left for Italy last week.)
Persons have been said to climb on roofs, solve mathematical problems, compose music, walk through windows and commit murder in their sleep.
He is reported to have won the 100�meter running race in the Olympic games.
8)不定式作定语
a)不定式作定语通常要放在其所修饰的名词或代词之后。
不定式常作下列的名词定语：attempt, ability, anything, chance, desire, determination, decision, effort, failure, intention, need, opportunity, plan, promise, pressure, right, tendency, time, way等。
【例如】
His efforts to carry out the plan were successful.I have no intention to go to the cinema with you.
There is no need to bother him with such trifles.
There is a tendency to writer quite long sentences in commercial correspondence.
The pressure( )causes Americans to be energetic, but it also put them under a constant emotional strain. (CET-4 1997,6)
A) to compete
B) competing
C) to be competed
D)shavingscompeted
pressure后面应接后置定语，表示竞争的压力。单个分词作定语一般置于名词前，故B和D可以排除。C为不定式的被动式，而竞争和压力之间没有被动关系，因此正确答案为A。
特别注意的是在不定式与其修饰的名词有动宾关系时，要根据句子的需要在不定式后加适当的介词，这个介词的选用取决于被修饰的名词或不定式本身的要求。
【例如】
She is a very nice person to work with.
This is an important issue to talk about.
b)由only, last, next,序数词或形容词最高级修饰的名词常用不定式作定语。
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