want to do sth
动词不定式、动名词用法要点讲解
一、作主语
⒈不定式作主语
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 compositionin a quarter of an hour.
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 help me 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…
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.
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 start back on foot.
When our visit to the farm was over, we expected that we would start back on foot.
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, imagine,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.
You must give up smoking, for it does too much harm to your 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,hate,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.
②当谓语动词begin,continue,start等是进行式时，如：The students are starting to work on the difficult 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.
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