不定式的定义和分类
不定式的定义

不定式的全称是“动词不定式”，是一种非限定动词，有不定式符号to+动词原形构成。不定式具有动词的特征，同时也有名词、形容词和副词的特征。

我们说不定式是一种非限定动词是因为它不受到主语的人称和数的限制。虽说不定式有“一般态”“进行态”“完成态”的变化，不过它不受“现在、过去、将来”的时间限制。

我们说不定式具有动词的特征是因为：它可以有自己的宾语，可以受副词的修饰等。

我们说不定式具有名词的特征是因为：它可以作主语和宾语。

我们说不定式具有形容词的特征是因为：它可以作定语。

我们说不定式具有副词的特征是因为：它可以作状语。

不定式的分类

不定式可以分为两种 "带to的不定式" 和 "不带to的不定式"。
不定式的功能
不定式的句法功能

不定式在句子中可以作 主语、宾语、宾补、表语、定语和状语：

一、不定式作 主语

To learn a foreign language is not easy.学外语不容易。

Is it necessary to complete the design before National Day?

有必要在国庆节之前完成这个设计吗？

二、不定式作宾语

I forgot to turn the oven on.我忘记打开炉子。

三、不定式作宾补

Will you help me plant this tree, please? 请您帮我种这棵树好吗？

四、不定式作定语

He has a lot of questions to ask.他有许多问题要问。

五、不定式作表语

Disney’s greatest wish was to be a famous artist.

迪斯尼最大的愿望就是成为一个著名的艺术家。

六、不定式作状语

She searched the top of the hill and stopped to rest on a big rock by the side of the path.她搜查了山顶上，然后在路边的一块大石头上停下来休息。
不定式做主语一

句型（1） 不定式短语 + 谓语动词

句型（2） It's + 形容词 + for/of 逻辑主语 + 不定式短语

句型（3） It's + 名词 + for 逻辑主语 + 不定式短语

在这一条目中，只讲述句型（1），例外两个结构在以下条目中讲述。

To know oneself is difficult.了解自己很困难。

在英语句子的表述中倾向主语短小一些，谓语部分长一些，以保持句子的结构平衡。故上句可以改写如下：

It's difficult to know oneself.

To go to school on foot every day takes me half an hour.

It takes me half an hour to go to school on foot every day.

我每天步行上学花费半个小时。

To read this book through will require time and patience.

It will require time and patience to read this book through.

读完这本书需要时间与耐心。
不定式做主语二

It's+ 形容词 +for/of 逻辑主语 + 不定式短语

It's kind of you to think so much of us.难为你这样替我们着想。

It's very nice of you to be so considerate.你太好了想得这么周到。

It's unwise of them to turn down the proposal.他们拒绝采纳这个建议是不明智的。

It's bad for your health to sit up to late at night.晚上睡得太晚对你的健康有害。

It's not easy for you to get him to change his mind.你要说服他改变主意是不容易的。

It's impossible for him to give up smoking.要他戒烟是不可能的。

适合这个结构的形容词有以下这些：

一、倾向用"of"

Kind, good, nice, wise, unwise, clever, silly, wrong, right, foolish, stupid,

Careless, considerate, rude, naughty, impolite

二、倾向用"for"

Costly, illegal, immoral, unfair, unhealthy, unjust, unlawful, unreasonable,

不定式做主语三

It's+ 形容词 +for/of 逻辑主语 + 不定式短语

of和for的判断

It's+ 形容词 +of 逻辑主语 + 不定式短语的句子可以做如下改写：

It's kind of you to think so much of us.

You are kind to think so much of us.

难为你这样替我们着想。

It's+ 形容词 +for 逻辑主语 + 不定式短语不能做如上改写。

我们可以通过尝试改写，来确定选择"of"还是"for"。

不定式做主语四

It's + 名词 + for 逻辑主语 + 不定式短语

It is a great honour for us to be present at this rally.

我们来参加这个大会是很荣幸的。

It will be a mistake for us not to help him.我们不帮助他们将是一个错误。

适用这种句型的有以下这些名词：

Pleasure, pity, mistake, honour
不定式做宾语

有些动词常用动词不定式作宾语

We agreed to meet here but so far she hasn't turned up yet.

我们约定在这里见面，但是到现在她都还没露面。

He offered to help us.他提出要帮助我们。

Mary begged to go with us.玛丽恳求同我们一块去。

常用动词不定式作宾语的有如下动词：

Agree, ask, attempt, begin, care, choose, continue, Decide, desire, determine, expect, forget, hate, hope, Intend, learn, like, love, manage, mean, offer, prefer, Pretend, promise, refuse, start, try, undertake, want, and wish

主语 + 谓语动词 + it + 形容词/名词/代词 + 不定式

解释：这里的"it"是形式宾语，"形容词/名词/代词"是宾补，"不定式"是真实宾语。这里需要用"it"作为形式宾语的原因是不定式短语太长，而挪到后面去，以保持句子的平衡。

We think it wrong to tell a lie.我们认为说谎是不对的。

I felt it useless for us to say anything further.我觉得我们再说下去也没有用。

I made it a rule to get up early, take a cold bath, and then do some running.

我已经养成习惯，早早起床，洗个冷水澡，然后去跑步。

They found it impossible to get everything ready in time.

他们发现不可能把一切按时准备好。

I consider it better not to go.我认为还是不去为好。

形容词+不定式

主语 + be动词 + 形容词 + 不定式

这种句型中的主语通常是人，形容词多半是描述此人的态度或情感状况。

I'm glad to meet you.见到你很高兴。

He was angry to see nothing had been done.他看到什么事都没有做成而很生气。

She is eager to learn to speak English.他急切地要学说英语。

She was disappointed to know that you won't be able to come to her birthday party.她得知你不能来参加她的生日晚会而很失望。

以下是常用于词类句型的形容词：

afraid, anxious, ashamed, careful, content, delighted, desirous, determined, eager, fortune, glad, grieve, happy, hesitant, impatient, lucky, pleased, prepared, proud, ready, relieve, reluctant, simple, willing,

Amazed* astonished* disappointed* sad* shocked*sorry* stunned* surprised* upset*

带星号的形容词后面常接：

To see, to learn, to discover, to find out, to hear

专项练习

I asked him to _______ me a few minutes so that we could go over all the problems.
　　A. spend 　　B. spare 　　C. save 　　D. share

They won’t let their teacher _______ in that way.
　　A. to be treated　　　　 B. being treated
　　C. treated　　　　　　　 D. be treated

John, you must get your room ________ after breakfast.
　　A. to be cleaned　　　　 B. to clean
　　C. cleaning　　　　　　　D. cleaned

He reached the station _____ only _____ that the train had just left.
　　A. tired； learned　　　　　　B. tiring； learning
　　C. to tire； to learn　　　　 D. tired； to learn

--- Did that book give the information you needed?
　　　　--- Yes, but ______, we had to read it almost entirely.
　　A. for finding it　　　　 B. to find it
　　C. finding it 　　　　　　D. by finding it

She couldn’t decide which restaurant _______.
　　A. to have lunch　　　　 B. to eat
　　C. to eat at 　　　　　　D. eating at

This problem is said _____ three times.
　　A. to have been talked　　　　　 B. to have discussed
　　C. having been discussed　　　　 D. to have been talked about

Charles Babbage is generally considered ________ the first computer.
　　A. to invent　　　　　　　 B. inventing
　　C. to have invented　　　 D. having invented

He said he would rather not _______ it right now.
　　A. doing 　　B. to do 　　C. do 　　D. to be doing

Rather than _______ on a crowded bus, he always prefers _______ a bicycle.
　　A. ride； ride 　　　　　 B. riding； ride
　　C. ride； to ride　　　　 D. to ride； riding

答案+解析　　

答案

B D D D B C D C C C

解析:
spare sb. sth匀出、腾出……， 宾语为sb.； share分享，宾语为sth

let sb do, 此处用的是被动语态

get sth. done让某事被做

tired此处是过去分词， 表示主语的状态。only to learn…此处的不定式表结果

此处的to find it, 表示目的

to eat at the restaurant, 介词at不能丢

此处使用的是不定式的完成被动式。表示“曾经被讨论过三次”

被动语态后用不定式连接，根据句意用完成式

would rather not do sth. 宁愿不做某事

prefer to do sth. rather than do sth. 宁愿做……不愿做……