非谓语动词
在句中充当除谓语以外的句子成分的动词形式叫做非谓语动词。非谓语动词分为三种形式：不定式、动名词和分词（分词包括现在分词和过去分词）
不定式
一、不定式的作用
1、作主语不定式作主语时，谓语用单数。往往用it 作形式主语，把不定式放在谓语后面。
通常表示某次具体的行为，如：
It took us two hours to finish the job. To learn English well is not easy. It is not easy to learn English.
It’s difficult for sb. to do sth It’s important for sb. to do sth
It’s kind(good/ friendly/polite/careless 粗心的/rude 粗鲁的/cruel 残酷的/clever 机灵的/foolish /brave)of sb.to do sth It is very kind of you to help us.
注意：（1）其他系动词如look, appear等也可用于此句型。
（2）当不定式作主语的句子中又有一个不定式作表语时，不能用It is …to…的句型。这样的句子，不能用动名词作表语，试比较：It is to negate my own idea to believe him.（错）To teach is to learn.R Teaching is to learn. F To believe him is to negate my own idea .（对）
（3）It is+ adj. of / for sb. to do sth. 结构中，当不定式的逻辑主语和前面的形容词可以构成系表结构时1）for sb. 用于easy, hard, difficult, interesting, impossible 表示客观形式的形容词
It’s very hard for him to study two languages.
2) of sb. good, kind, nice, clever ,foolish, right.表示主观形式的形容词
It’s very kind of you to help me.
2、作宾语
（1）动词+不定式。如：
注：下列动词通常用不定式作宾语：want, try, hope, wish, need, forget, know, promise, refuse, help, decide, begin, start, learn, agree, choose, get，afford 提供，给予, aim 打算, arrange , ask , bother, care , choose , demand 要求，需要, desire渴望，期望, determine 决定，确定,Elect 选择，选举, endeavor尽力, hope, fail, long 渴望，happen, mean，manage, offer, plan, pretend, refuse , tend照管，护理, undertake承担，担任, expect ，hate, intend想要，打算, prepare, order, cause引起，促成, beg , agree.等
He managed to escape from the fire.
I find it hard to get along with him.（it 作形式宾语）
The driver failed to see the other car in time.司机没能及时看见另一辆车
（2）动词+疑问词+to , “特殊疑问句+不定式”相当于名词，作宾语。如：
Decide, know, consider, forget, learn. remember, show, wonder, find out, tell, inquire ,explain 等
I don’t know what to do next/ how to do it next.
I can’t decide when to go there.
There are so many kinds of tape-recorders on sale that I can’t make up mind which to buy.
注意：不定式短语作宾语时，如果还带有宾语补足语，往往把不定式短语放在宾语补足语之后，用it 作形式宾语。如：I find it necessary to learn a foreign language.
3、作宾语补足语
（1）动词+宾语+不定式（to do ）。如：
He warned me to be careful. I want you to speak to Tom. What makes you think so?（不带to的不定式）注：可以用动词不定式做宾补的动词有
主语＋ask / want / tell / get / force / expect / advise / invite / order / allow / require / like / would like / help / wish / warn / prefer / encourage / prefer / beg / hate / persuade/ cause / wait for / call on / permit / forbid + sb. to do sth.
主语＋cause / challenge / command / compel / drive驱使/ enable / forbid / impel / induce
/ instruct / make / let / have / persuade / request / send / train / urge + sb. to do sth.
The doctor advised him to stay in bed for another few days.
We wish him to remain and accept the post. 留下来接收这个职位
The officer ordered his men to fire.(开火)
Consider 用动词be 以外的不定式做宾补时，一般要求用不定式的完成式。
He is generally considered to have invented the first computer.
（2）表见解、看法的动词结构可为：动词+宾语+ to be 的不定式结构。如：
主语＋think / judge / suppose / believe / consider / imagine / feel / find / declare声称
Appoint / guess / fancy设想/ guess/ judge/ know+ sb.+ to be / to have done
We consider Tom to be one of the best students in our class.
The book is believed to be useful.（被动语态）
We know him to be a fool. 笨蛋
We believe him to be guilty. 有罪的
主语＋call on / upon / depend on / wait for / ask for + sb. +to do sth.
