动词不定式作主语时，句子的谓语动词常用单数，其位置有以下两种：
(1)把不定式置于句首。如：
To get there by bike will take us half an hour.
(2)用it作形式主语，把真正的主语不定式置于句后，常用于下列句式中。如：
①It＋be＋名词＋to do
It's our duty to take good care of the old.
②It takes sb+some time+to do
How long did it take you to finish the work?
③It＋be＋形容词＋for sb＋to do
It is difficult for us to finish writing the positionin a quarter of an hour.
1 / 11
word ④It＋be＋形容词＋of sb＋to do
It is stupid of you to write down everything the teachersays.
⑤It seems(appears)＋形容词＋to do
It seemed impossible to save money.
在句型③中，常用表示客观情况的形容词，如：difficult,easy,hard,important,impossible,necessary 等；在句型④中，常用careless,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise等表示赞扬或批评的词。在不定式前的sb，可看作其逻辑主语。这一句式有时相当于Sb is＋形容词＋to do句式，如：It'skind of you to help me with my English.=You are kind to helpme with my English.
⒉动名词作主语
Learning without practice is no good.
动名词作主语时，也常用It句式。如：
①It's +no good(no use,fun,a pleasure,a waste of time)+doing…
2 / 11
word It's no good reading in dim light.
It's no use sitting here waiting.
②It's＋形容词＋doing
It's dangerous swimming in the sea in windy days.
这样用的形容词有expensive,nice,tiring等，但important,necessary则不适用于这种结构，应用不定式代替，如：It'simportant for you to keep fit.
③There is no+doing
There is no saying what will happen next.
在这一结构中，动名词后常带宾语，相当于\"It's impossible to…\"结构。
⒊动词不定式和动名词作主语的区别
①不定式作主语经常表示具体动作，常与特定的动作执行者联系在一起；而动名词作主语经常表示抽象动作，经常不与特定的动作执行者联系在一起。如：
It's no good eating too much fat.
3 / 11
word It's no good for you to eat so much fat.
②动名词结构作主语，可以用名词或代词属格形式作逻辑主语。如：
It's no use your pretending that you didn't know the rules.
二、作宾语
⒈不定式作宾语
①以下动词后，只能跟不定式作宾语。如：agree,ask,aim,arrange,choose,decide,demand,expect,fail ,help,hope,lean,long,
manage,offer,plan,prepare,pretend,promise,refuse,wish等，这些词大部分可接th at引导的从句。如：
I decided to ask for my money back.
I decided that I would ask for my money back.
When our visit to the farm was over,we expected to startback on foot.
When our visit to the farm was over, we expected that wewould start back on foot.
4 / 11
word ②当复合宾语中的宾语是不定式时，先用形式宾语it代替不定式，把不定式置于补语之后，即：主语＋动词＋it＋补语＋to do句式。如：
We think it quite important for us to learn a foreignlanguage well.
He feels it his duty to help the poor.
③介词but,except,besides+to do(do)
在这种句型中，如介词前有动词do，后面应接不带to的不定式；如无do，则接to不定式，即带do不带to，带to不带do。如：
The enemy soldiers had no choice but to give in.
On Sunday afternoon I had nothing to do but watch TV.
⒉动名词作宾语
①以下动词后，只能接动名词作宾语，如：admit,appreciate,consider,delay,enjoy,finish,keep,imag ine,mind,miss,practise,resist,risk,save,suggest,don't mind,give up,insist,on, put off等。如：
I suggest spending our summer vacation in a seaside town.
5 / 11
word You must give up smoking, for it does too much harm toyour health.
②动名词作介词的宾语
I should go to attend the birthday celebration instead of staying at home.
What about inviting Li Jun to make a speech?
动名词前的介词有时可以省略，如：have difficulty(in)doing,have no trouble(in)doing,lose no ti me(in)doing,prevent/stop…(from)doing,there is no use(in)doing等。
⒊部分动词后面，既可接动词不定式，也可接动名词作宾语，意义不变。如：begin,continue,start,hat e,like,love,need,require,want等。
在need,require,want后接-ing形式，表示被动意义，也可接不定式，但要用被动形式，如：Your handwr iting needs improving(tobe improved). hate,love,like接不定式表示特定的未来事件，接动名词表示目前正在进行的活动或一般的行为。
在下列情况下，一般要用不定式：
①hate,like,love前有would(should)时，如：I'd like to have a cup of coffee.
6 / 11
word ②当谓语动词begin,continue,start等是进行式时，如：Thestudents are starting to work on the di fficult maths problem.
③begin,continue,start与know,understand等状态动词连用时，如：I soon began to understand what
was happening.
⒋advise,allow,encourage,forbid,permit等动词后接动名词作宾语，或带不定式作宾语补足语。如：
Our teachers don't permit our swimming in the lake.
Our teachers don't permit us to swim in the lake.
⒌部分动词后接不定式或动名词时，意义差别较大，应根据句子语境选择使用。
①forget,remember,regret后接不定式，表示现在或未来的动作，接动名词表示动作已经发生。如：
Don't forget fo post the letter for me.
Have you forgotten meeting her in BeijingAirport?
Remember to close the windows before you leave.
7 / 11
word I remember writing him a letter a year ago.
We regret to tell you that all of you are not invited toattend the meeting.
They regretted ordering these books from abroad.
②mean to do 打算做某事
doing 意味着……
I meant to catch up with the early bus.
This means wasting a lot of money.
③try to do 设法尽力做某事
doing 试着做某事
You should try to overe your shortings.
Try working out the physics problem in another way.
④stop to do 停下一件事去做另一件事（不定式作目的状语）
8 / 11
word doing 停止做某事
On the way to the airport,I stopped to buy a paper.
You'd better stop arguing and do as you are told.
⑤can't help doing 禁不住……
to do不能帮助干……
They couldn't help jumping up at the news.
Sorry I have lots of work to do.So I can't help to make up the room for you.
⑥go on to do 做不同的事或不同内容的事
doing 继续不停地做某事，指同一动作的继续
He went on to talk about world situation.他接着又谈了世界形势。
We'll go on fighting so long as there is oppression inthe world.
⑦leave off to do 离开某地去干什么（目的状语）
9 / 11
word doing停下某事
It's time to leave off talking and to start acting.
They left off to go fishing.
三、做表语
不定式作表语表示具体动作或将来动作；动名词作表语表示抽象的一般行为。
①To be kind to the enemy is to be cruel to the people.
②My chief purpose is to point out the difficulties ofthe matter.
③What I would suggest is to put off the meeting.
当主语和表语都是不定式时，其含义一是条件，一是结果（例①）。当主语是aim,duty,hope,idea,mista ke,plan,purpose,suggestion等为中心词的名词词组（例②）时，或以what引导的名词性分句（例③），不定式说明主语的内容。
④Our work is serving the people.
⑤What he likes is taking a walk after supper.
10 / 11
word ⑥The story told by Mr.Wang is interesting.
④⑤句动名词作表语，与主语部分可以转换，如Serving thepeople is out work,而⑥句中是现在分词作表语，说明主语的性质、状态，现在分词具有形容词的各种特征，另外，动名词作表语还应与进行时态区别开来。
四、作定语
⒈不定式作定语
不定式在句中作定语，置于被修饰的名词或代词之后。如：
①The next train to arrive is from Washington.
②Have you anything to be taken to your sister?
③Do you have anything to say on the question?
④Would you please give me some paper to write on?
⑤My wish to visit France has e true at last.
11 / 11
因篇幅问题不能全部显示，请点此查看更多更全内容