动词不定式的用法

1.不定式定义:由to＋动词原形构成.
不定式是一种非限定性动词.而非限定动词是指那些在句中不能单独充当谓语的动词,可分为不定式,动名词,现在分词和过去分词.
2.用途：
在句中不能作谓语.它具有动词的性质,本身可以带宾语和状语.
【动词不定式】
1.定义：动词 + 不定式
2.用途：
动词不定式在句中可以作句子任何成分.动词不定式的被动形式除了一般形式外还有其完成式和进行式.
[编辑本段][动词不定式的时态、语态]
动词不定式可以作以上各种成分,但它毕竟是动词,所以有动词的属性
动词不定式及其短语还可以有自己的宾语、状语,虽然动词不定式在语法上没有表面上的直接主语,但它表达的意义是动作,这一动作一定由使动者发出.这一使动者我们称之为 逻辑主语,其形式如下：
主动形式 被动形式
一般式 （not） to make （not） to be made
完成式 （not） to have made （not） to have been made
进行式 （not） to be making
完成进行式 （not） to have been making
(1)语态
如果动词不定式的逻辑主语是这个不定式所表示的动作的承受者,不定式一般要用被动语态形式.如：
It's a great honour to be invited to Mary's birthday party.（不定式作主语）
It was impossible for lost time to be made up.（不定式作主语）
I wish to be sent to work in the country.（不定式作宾语）
Can you tell me which is the car to be repaired?（不定式作定语）
He went to the hospital to be examined.（不定式作状语）
在There be结构中,修饰主语的不定式可用被动,也可用主动.如：There are still many things to t ake care of (to be taken care of).但有时两种形式表达的意思不同,如：These is nothing to do now.( We have nothing to do now.) There is nothing to be done now.(We can do nothing now.)
(2)时态
1) 现在时：一般现在时表示的动词,有时与谓语动词表示的动作同时发生,有时发生在谓语动词的动作之后.
He seems to know this.
I hope to see you again.= I hope that I'll see you again.我希望再见到你.
2) 完成时：表示的动作发生在谓语动词表示的动作之前.
I'm sorry to have given you so much trouble.
He seems to have caught a cold.
3) 进行时：表示动作正在进行,与谓语动词表示的动作同时发生.
He seems to be eating something.
4) 完成进行时：
She is known to have been wreaking on the problem for many years.
[编辑本段][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 for London has not been decided yet.（不定式在句子中做主语）
②Mr.Smith didn't know whether to leave or stay there.（不定式在句子中做宾语）
③I asked Professor Xu how to learn English well.（不定式在句子中做间接宾语）
④The question was where to get the medicine needed.（不定式在句子中表语）
以上例句中疑问词＋不定式部分,均可转换为相应的从句形式.如：①When we shall leave…③…how I
could learn…
经常在这种结构中使用的动词有：consider,decide,discover,explain,find out,forget,hear,know,lea rn,observe,understand,wonder等.
[编辑本段][动词不定式的语法功能]
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
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