动词不定式用法要点讲解
一、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
I自制冰淇淋
t'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 composition a quarter of an hour.
④It＋be＋形容词＋of sb＋to do
It is stupid of you to write down everything the teacher says.
⑤It ems(appears)＋形容词＋to do
It emed impossible to save money.
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,choo,decide,demand,expect,fail ,help,hope,lean,long
manage,offer,plan,prepare,pretend,promi,refu,wish等，这些词大部分可接th at引导的从句。如：
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。
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.
⒉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 handwriting 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：Thestudents are starting to work on the difficult maths probl重庆辣子鸡的做法
em.
③begin,continue,start与know,understand等状态动词连用时，如：I soon began to understand what was happening.
3．advi,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/us swimming in the lake.
Our teachers don't permit us to swim in the lake.
4．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：
We regret to tell you that all of you are not invited to attend the meeting.
They regretted ordering the books from abroad.
②mean to do 打算做某事 ;mean doing 意味着……
③try to do 设法尽力做某事; try doing 试着做某事
④stop to do 停下一件事去做另一件事（不定式作目的状语）; stop doing 停止做某事
⑤can't help doing 禁不住…; can’t to do不能帮助干……
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
⑦leave off to do 离开某地去干什么（目的状语）; leave doing停下某事
三、做表语
To be kind to the enemy is to be cruel to the people.
四、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：
Have you anything to be taken to your sister?
Would you plea give me some paper to write on?
不定式短语作定语和被修饰词之间表示以下关系：
(1)表示尚未发生的动作。
(2)与被修饰词之间有动宾关系，如是不及物动词，则需加介词。
(3)与被修饰词之间有逻辑上的主位关系。
(4)不定式作定语时，一般可转换为定语从句。
五、不定式作补足语
⒈作宾语补足语
一些及物动词除要求按宾语外，有时还需要有宾语补足语，说明宾语的行为、状态、特征，这时意思才相对完整。
(1)常要求不定式作宾补的动词有：allow,ask,advi,beg,cau,drive（强迫），encourage,expect,forbid,force,get,would like(love,hate), order,permit,persuade,teach,tell,want,warn,wish等。如：
I expect you to understand the whole passage clearly.
(2)部分动词后常接to be＋形容词、名词短语等形式，有时to be可省略，如： consider,imagine,judge ,prove,suppo等。
I consider him(to be)one of the best biology teachers .
但当不定式是完成式时，to不能省略，如：We consider him to have been foolish.
(3)感觉动词和使役动词后用作宾补的不定式须省略to。
①I didn't hear anyone say anything about it.
②They make the students do too much homework every day.
这种句式在变为被动语态时，to不能省略，如第②句：The students are made to do too much homework every day.
(4)部分短语动词后，常接不定式作宾补，如：
The Party calls on us to increa production and practi economy.
常这样用的短语动词有：ask for,care for,call on ,depend on,wait for,long for（渴望），prepare for等。
⒉作主语补足语
不定式作主语补足语，和主语构成一种逻辑上的主谓关系。如：
①He was not allowed to enter the classroom for being late.
②The young university student is considered to have great promi.
六、不定式作状语
⒈作目的状语
(1) I stayed there to e what would happen.
(2)有时为了强调，不定式前可加in order或so as。如：
Bob took down my telephone number so as(in order)not to forget it.
有时为强调目的状语可把in order to或不定式置于句首，但so as to不能这样用。在这种句式中不定式部分可转换为so that,in order that,成为目的状语从句，如：
I stayed there so that (in order that)I could e what would happen.
(3)在部分表示感情色彩的形容词、过去分词或动词之后可接不定式，如：astonished,glad,happy,laugh ,plead, sad,smile,sorry,surprid等。
①We are glad to hear the news.
②I was surprid to 睡前恐怖故事
e that a three-year-old baby could write so well.
