不定式作主语，表示具体的、一次性的或将来的动作；在很多情况下，人们通常用it作为形式上的主语，而把不定式移到谓语之后，使句子结构显得平稳一些。

To know something about English is one thing; to know English is quite another.懂一点英语是一回事；完全掌握英语是另一回事。

It is impossible to learn a foreign language without making painstaking efforts.想不下苦功就能学会一门外语是不可能的。

基本用法：

1．不定式作主语通常位于句首

To love and to be loved is the greatest happiness one can get. 爱和被爱是一个人能得到的最大幸福。

To get up early is necessary. 早起是必要的。

To read without reflecting is like eating without digesting. 读书不思考，犹如吃饭不消化。

2．it作形式主语代替不定式的几种形式

把it放在句首作形式主语，而把真正的主语——动词不定式(短语)放在后面。

It‘s not easy to work out the problem. 算出这道题不容易。

It is interesting to play with snow in winter. 冬季里玩雪是很有趣的。

It作形式主语时有三种情况：

(1)常用形容词作它的表语。作真正主语的不定式通常有逻辑主语，一般用for短语来表示，即It is/was ＋adj.＋for sb to do sth(其中sb就是to do的逻辑主语)。

It’s important for us to keep the water clean. 保持水质清洁对我们来说是很重要的。

[注意] 在“It is/was＋adj.＋for/of sb to do sth”结构中，若形容词侧重于评价人物的特性、特征，则构成不定式复合结构的介词应用of，此时形容词常为kind，nice，foolish等词，且sb与形容词之间可构成逻辑上的系表关系；若形容词侧重于描写不定式动作的特征、特点，则构成不定式复合结构的介词应用for。

It’s very kind of you to say so. 你这样说真是太好了。(可以说：You are very kind.)

(2)有时也接名词作表语。

It must be great fun to fly to the moon in a spaceship. 乘宇宙飞船飞往月球一定很有趣。

(3)It作形式主语时，还常用于“It takes/took/will take sb some time to do sth”句型中。

It took me more than an hour to do my homework yesterday. 昨天我做作业用了一个多小时。

It will take us a long time to walk there. 步行去那儿要花费我们很长时间。

3．“疑问词＋动词不定式(短语)”结构

动词不定式(短语)可与疑问词when, where, how, what, which, who等组合，在句中作主语。

Where to hold the meeting is still unknown. 会议地点还未知。

How to solve the problem has not been decided yet. 如何解决这个问题还未决定。

不定式作表语

动词不定式(短语)作表语相当于名词作表语。它和主语处在同等地位，所指的或是和主语一样的东西，或是主语产生的结果。常常可以将主、表交换位置，句子的意义不变。

基本用法：

1．主语是以aim, suggestion, duty, hope, idea, intention, plan, purpose, the way to do sth等为中心的名词词组时，或者以what引导的名词性分句表示时，一般用动词不定式作表语说明主语的内容。

My idea is to climb the mountain from the north. 我的想法是从北面爬这座山。

Our plan is to make better use of these materials. 我们的计划是更好地利用这些材料。

What I would suggest is to ask your father for his opinion on this matter. 我的建议是就这件事征求你父亲的意见。

The best way to encourage your kids to enjoy meals is to involve them in the planning and preparing. 鼓励孩子享受美食的最好方法是让他们参与计划和准备(美食)。

2．表示目的。

The next step is to make sure that you know exactly what is required. 下一步你要真正弄清楚需要的是什么。

The immediate goal is to bring the COVID­19 under control for all countries.对所有国家来说，当前的首要目标是控制新冠病毒。

3．用于被动语态，相当于can/could, should, ought to, must，具有情态意义。

The regulations are to be observed. 规章制度必须遵守。 (must)

You are to be rewarded. 你应受奖励。(should)

It’s nowhere to be found. 哪儿也找不到它。(can’t)

4．表示“同意、安排、命令、决定、劝告、愿望、意愿、禁止”等。

They are to marry next week.他们将在下周结婚。(安排)

You must be patient and persistent if you are to succeed. 要想成功，就必须有耐心，有毅力。(愿望)

5．动词不定式(短语)作表语时，可用主动形式表示被动意义。

Who is to blame for the fire？谁该对此次火灾负责？(be to blame结构常考)

The house is to let.该房屋出租。

Something is still to find out.有些东西还有待查明。

二、动词不定式(短语)作表语省略to的情况

动词不定式(短语)作表语时，一般情况下不定式符号to不能省略，但在以下几种情况下可省略不定式符号to：

1．all作主句主语，其后的定语从句中含有实义动词do的某种形式时，省略to。

All we need to do is live each day with hope. 我们需要做的就是带着希望过好每一天。

2．what引导的从句作主语，从句中含有实义动词do的某种形式时，省略to。

What I want to do is take a holiday right away. 我想马上就去度假。

3．(主句)主语被 only, first, one, last或形容词最高级修饰，且其后作定语的从句或短语中含有实义动词do的某种形式时，省略to。

In the evening the only thing he did was read the newspaper.晚上他唯一做的就是看报纸。

动词不定式(短语)作表语和v.­ing(短语)作表语的区别

1．动词不定式(短语)和v.­ing(短语)作表语时，要注意与句子的主语在形式上保持一致，即若句子的主语为v.­ing(短语)，则表语也应使用v.­ing(短语)；若主语为动词不定式(短语)，则表语也应使用动词不定式(短语)。

To see is to believe. ＝Seeing is believing.眼见为实。

2．动词不定式(短语)和v.­ing(短语)作表语时可换用，但以下情况除外：

(1)当动词所表达的是某一特定的行为，尤其是将来的行为或有待于实现的行为时，通常用动词不定式(短语)作表语。

Her best wish is to put her new ideas into practice. 她最大的愿望是将自己的新想法付诸实践。

(2)若动词所表达的并不强调动作，而是表示主语的内容，则通常用v.­ing(短语)作表语。

My favourite sport is swimming. 我最喜欢的运动是游泳。

What I hate most is being laughed at. 我最痛恨的就是被嘲笑。

[即时训练]单句语法填空

(1)My job is __________ (look)after the old in the nursing home.

(2)My job now is __________ (take) care of my injured brother at home.

(3)My hobby is __________ (listen) to country music.

KEYS：looking, to take, listening

Mindmap解析

习题-Exercises

1、单句语法填空

(1)____________ (teach) you the uses of the infinitive is my job today.

(2)____________ (look) after the safety of the community is his responsibility.

(3)____________ (solve) this annoying problem is really out of the question.

(4)How ___________ (cure) this kind of illness is still unknown.

(5)Whether ___________ (do) it or not has not been decided.

(6)How ___________ (deal) with such a person isn’t known yet.

(7) I’ve had many dreams since I was a child. Now my dream is __________ (open) a café.

(8) The UN set up the World Food Programme, one of whose purposes is __________ (relieve) worldwide starvation.

(9) One way to begin is __________ (answer) your own excuses.

(10) What he hoped was __________ (admit) to Peking University.

(11) His aim is __________ (find) out a cure for the lung cancer one day.

2、补全句子

(1)__________________________________your umbrella in the train. 你真是粗心，把伞忘在了火车上。

(2) _________________________________what happened that day. 想起那天发生的事情，我被惊到了。

(3)__________________________________ her own children. 母亲担心她的孩子这是很自然的。

(4)All we have to do is ____________________. 我们要做的就是按下按钮。

(5)The only thing I can do is ______________________. 我唯一能做的就是陪伴你。

KEYS：

1、(1)-(5)To teach, To look, To solve, to cure, to do,
(6)-(11)to deal, to open, to relieve, to answer, to be admitted, to find

2、(1)It was careless of you to leave
(2)It shocked me to think of
(3)It is natural for a mother to worry about
(4)push the button
(5)keep you company

非谓语-不定式to do-作主语和表语最先出现在Clarissa Study。

不定式由“to＋动词原形”构成，有时to可以省略，其否定形式是“not to do”。不定式没有人称和数的变化，但有时态、语态的变化。不定式不能作谓语，但可以作主语、宾语、状语、表语、定语和补语，本章节主要讲解不定式作定语和状语的用法。

动词不定式的形式

1.不定式的一般式：表示不定式的动作与谓语动词同时（几乎同时）发生或在谓语动词之后发生。

I hope to see you next week. 我希望下周能见到你。

I’d like to be told what’s going on. 我希望被告知正在发生什么。

2.不定式的进行式：表示不定式的动作与谓语动词同时发生且正在进行。

I happened to be watching TV when she called. 她打电话来时，我恰巧正在看电视。

3.不定式的完成式：表示不定式的动作发生在谓语动词之前。

They seem to have cleaned the house. 他们似乎已经打扫过这座房子了。

The factory is reported to have been burnt down. 据报道这家工厂已经被烧毁了。

4.不定式的被动语态：不定式的逻辑主语是不定式所表示的动作的承受者而非发出者。

She felt puzzled to be asked such a question. 被问了这样一个问题，她很疑惑。

不定式作定语

1.不定式作定语，置于被修饰词之后，常表示未发生、将来的动作。

I have many letters to write. 我有许多信要写。

The car to be bought is for his sister. 要买的这辆车是给他姐姐的。

2.在序数词、形容词最高级、顺序词（the last，the next等）、the only、等修饰的名词/代词后用不定式作后置定语。(动词不定式与被修饰词之间有逻辑上的主谓关系)

She was the first woman to win the gold medal in the Olympic Games. 她是第一个在奥运会上获得金牌的女性。

Lily was the only one to stay for the whole speech. Lily是唯一一个整场讲座留下来的人。

The youngest person to enter this university was just fourteen. 进入到这所大学年纪最小的人只有十四岁。

3.不定代词（something，anything等）习惯上用不定式作定语。例如：

Though we have made great progress, there is still much to be improved. 虽然我们取得了很大的进步，但仍有许多地方需要改进。

Have you got anything to cure my bad cold. 你有治疗我重感冒的东西吗？

4.在某些由动词、形容词派生的名词，由于他们的词根配不定式（如decide to do; be able to do; plan to do)，因而这些名词后也常接不定式作定语，常见的有∶decision、ability、plan、promise、plan、offer、warming、attempt，willingness，tendency等等。

Does he have the ability to do the job? 他有做这份工作的能力吗？

I don’t trust his promise to come for a visit. 我不相信他来这参观的承诺。

She said she had no plans to go there. 她说她没有去那里的打算。

5.用于说明某些名词的内容，这类词有：chance，opportunity，reason，courage，way等。例如：

We have a good reason to believe that he is lying.我们有很好的理由相信他在说谎。

You must have the courage to say “No”.你必须要有说“不”的勇气。

注意：

1、作定语的不定式如果是不及物动词，或不定式所修饰的名词或代词是不定式动作的地点、工具等，不定式后面需有相应的介词。

I am looking for a room to live in. 我正在找一间房子住。

Can I borrow a pen to write with? 我可以借一只可以写字的笔吗？

2、不定式作定语需要后置。

3、作定语的不定式与被修饰的名词或代词存在着三种主要的逻辑关系，即被修饰的名词和代词是不定式的逻辑主语(逻辑上的主谓关系)或逻辑宾语(逻辑上的动宾关系)或修饰性关系(同位关系)。

①动宾关系：

I have a lot of work to do(要做)．

Give me a piece of paper to write on(写).

②主谓关系：

Women and children were the first to get into the lifeboat(登上救生艇)．

③修饰性关系：不定式前的名词是它修饰的对象，它所修饰的词多为抽象名词，如：need, time, way, right, chance, courage, reason, wish, movement…

There is no need for him to come.

He has no time to read the book.

[提示]　为动宾关系的不定式，必须是及物动词或不及物动词加介词；如果不定式所修饰的词是way或place，介词可省略。

It is a comfortable sofa to sit on.

He has no way to go.

This is the best place to work

不定式作状语

不定式由“to+动词原形”构成，其否定形式是“not to do”。

不定式可以在句子中作状语，通常可用来表示目的、结果、原因等，其逻辑主语就是句子的主语。

 1.不定式作目的状语

They came here to seek a new life.他们来这里寻求一种新生活。

 He started early in order not to be late.为了不迟到，他早早就动身了。

不定式前可加in order或者so as构成以下两个句式做目的状语，功能同“to do”

（1）in order to+动词原形（可置于句首或句尾），意为“为了”。例如：

（2）so as to+动词原形（只能至于句末，不能置于句首）意为“为了”。例如：

John went to California in order to make a fortune.

2. 不定式作结果状语（通常出现在句尾,常用于固定搭配中：only to do; too…to do；so…as to do; such…as to do; …enough to do）

（1）表示出人意料或者不太好的结果时，用only to do.

 I hurried to the station, only to find the train had left.我匆匆赶到车站，结果发现火车已经开走了。

（2）“too …to …”结构常表示”太……而不能……”

He is too weak to do the work.他身体太弱，不能做这项工作。

注意：

①但 too 之前如果有only 时，则不定式表肯定。因为only too表示”非常;很”之意。

I’ll be only too pleased to help them out with any questions.我非常乐意为他们答疑解惑。

②too后如果是 happy, glad, pleased, satisfied, ready之类的形容词时，不定式也表示肯定意义。

She was too happy to meet her friend in the street.在街上遇到她的好朋友她很高兴。

（3）so +adj./adv.+as (not) to do 或such +n.+as (not) to do句型，表示“如此……以至于……”。例如：

The house is so high and narrow as to resemble a tower.这个房子又高又狭窄，像一座塔。

I’m such a fool as to think that she is a warm-hearted woman.我真傻，竟以为她是个热心肠的女人。

（4）adj./adv. + enough to do，意为“足以去做……”。例如：

The rooms are all large enough to take a third bed.这些房间都很大，足够放下第三张床。

3. 不定式作原因状语（一般不置于句首）：不定式的动作先于谓语动词，但很少用完成式。大部分表达情感等的原因。有以下3种句型：

（1）主语+be+表情绪或感情的形容词+不定式，用于这一结构的形容词主要有：afraid，angry，anxious，glad，happy，sorry，amazed，delighted，disappointed，excited，shocked，surprised。例如：

I am glad to see you.见到你很高兴。

We were very excited to hear the news.我们听到这个消息很兴奋。

（2）主语+表示情感的不及物动词+不定式。例如：

I couldn’t but laugh to hear such a funny story.听到这样一个有趣的故事，我忍不住笑了。

He smiled to think of a clever plan.想到一个聪明的计划，他笑了。

（3）主语+be+说明人的品质或行为的形容词+不定式。例如：

The boy was rude to speak to the teacher like that.那个男孩对老师那样说话很无礼。

The boy was clever to solve the problem so quickly.这个男孩这么快就解决了这个问题，真聪明。

注意：

不定式短语还可作独立成分，位于句首、句中或句末作状语。常见的短语有: to be exact(确切地说), to

begin with (首先)，to do him justice(说句对他公道的话), to be sure(诚然)，to be honest(实话说)。

Mindmap解析

习题-Exercises

一、完成句子

1．Jessie有了一个可以玩的新玩具。Jessie got a new toy __________________．

2．她没有可以依赖的朋友。She has no friend  __________________．

3．为了通过大学入学考试，我们必须努力学习。

____________________________________，we must work hard.

4．公共汽车停下来以便接载乘客。The bus stopped __________________________________．

5．令我们吃惊的是，这座寺庙仍保持着最初的样子。

We were astonished _________________ still in its original condition.

6．我匆忙赶到机场，结果发现John已经走了。

I rushed to the airport _________________ that John had gone.

二、单句语法填空

1．He liked nothing but __________ (watch) TV.

2．__________ (find) out more about the computer course，visit this website.

3. He is always the first __________ (come) to school.

4．__________ (tell) the truth, I am not happy at the moment.

5．The meeting__________ (hold) tomorrow is important.

6．We didn’t expect there __________ (be) so many people.

7．I tried to persuade him __________ (agree) to your proposal.

8．They don’t allow these books __________ (take)out of the reading room.

9．They did all they could __________ (save) the child.

10．I am glad __________ (work) with you now.

三、短文语法填空

Recently in the US，more students prefer 1.________(leave) the campus and study in a foreign country for half 2.________ one year.

Some people may be 3.________(frighten)：communicating in a foreign language，leaving friends and adjusting to a new environment are very difficult for students 4.________(study) abroad.However，the experience students have abroad is often impossible to gain at their home universities.

“Globally，there is so much 5.________(do)．I’m hoping 6.________(go) somewhere and experience something I wouldn’t get at home，”a student who intended 7.________(study) abroad said.

It was said that the increase had something to do with the universities’ promise that they encourage students to study overseas.The universities have been 8.________(real) good about saying that students need 9.________(go) abroad.

For many American students，some of the most important lessons abroad are those 10.________(experience) outside the classroom. Students can have deep opinions.Even very small cultural difference can surprise the students.

KEYS:

一、完成句子

1． to play with．

2．to depend on．

3．To pass the college entrance examination，we must work hard.

4．The bus stopped in order to/so as to pick up passengers．

5．We were astonished to find the temple still in its original condition.

6． I rushed to the airport，only to find that John had gone.

二、单句语法填空

1．He liked nothing but to watch(watch) TV.

2．To find(find) out more about the computer course，visit this website.

3. He is always the first to come (come) to school.

4．To tell(tell) the truth, I am not happy at the moment.

5．The meeting to be held(hold) tomorrow is important.

6．We didn’t expect there to be(be) so many people.

7．I tried to persuade him to agree(agree) to your proposal.

8．They don’t allow these books to be taken (take)out of the reading room.

9．They did all they could to save(save) the child.

10．I am glad to be working(work) with you now.

三、短文语法填空

1.to leave　2.or　3.frightened　4.to study　5.to do　6.to go　7.to study　8.really　9.to go　10.experienced

非谓语-不定式to do-作定语和状语最先出现在Clarissa Study。