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.   

⒉ 动名词作主语

   Swimming id good for health..

⒊ 动词不定式和动名词作主语的区别     

  不定式作主语表示具体动作，动名词作主语表示抽象动作。如：

   It's no good eating too much fat.     

   It's no good for you to eat so much fat.     

 二、作宾语     

⒈ 不定式作宾语     

① 以下动词只能跟不定式作宾语。如：agree,ask,choose,decide,expect,fail ,help,hope,lean, lan,prepare,pretend,promise,refuse,wish

② 主语＋动词＋it＋补语＋to do句式。如：We think it important for us to learn a foreign language.

⒉ 动名词作宾语

① 以下动词只能接动名词作宾语，如：consider,enjoy,finish,keep,mind,practice,suggest,mind,give up, put off等。

② 动名词作介词的宾语

I should go out for a walk instead of staying at home. 

What about asking the teacher for help?     

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,start,hate,like,love,等。     

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。    

① forget,remember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。

② go on to do 做不同的事或不同内容的事     

   go on doing 继续不停地做某事，指同一动作的继续     

③ try to do 设法尽力做某事     

   try doing 试着做某事    

④ stop 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   

⑤ can't help doing 禁不住……     

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。     

 My job is to look after my pet dog.

 My job is studying hard.

四、作定语     

1. 不定式作定语，常置于被修饰的名词或代词之后。如： Do you have anything to say?     

2. 动名词作定语。  如：The reading room can hold 800people. 

五、不定式作补足语     

⒈ 作宾语补足语

  (1)不定式作宾补的动词有：allow,ask,advice,encourage,expect,force,would likelove,hate,teach,tell,want,wish等。

如：I want you to understand the whole passage clearly.    

 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： He was not allowed to enter the classroom for being late.  

六、不定式作状语     

⒈ 作目的状语  I stayed there to see what would happen.     

⒉ 作结果状语  We came home after our holiday to find our garden neat and tidy. 

                         The tree is short enough for us to catch up with it.     

                         I'm too tired to stay up longer. 

⒊ 不定式短语还可作独立成分，用于句首、句中或句末。

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（真的）等等。     

七、动词不定式、动名词的其它用法     

 疑问词＋不定式结构      疑问词who,what,which,when,where,whether,how后可接不定式构成不定式短语，在句中作主语、宾语、表语等。如：

①When to leave is not decided.     

②Mr. Smith didn't know when to leave.     

③I asked Professor Xu how to learn English well.