动词不定式具有名词、形容词和副词的特征,因此,在句中可以作主语、表语、宾语、宾语补足语、定语和状语。


一、常接不定式作宾语的动词有want,love,learn,agree,decide,hope,refuse等。例如:
I'm learning to skate on real ice. 我正在真正的冰上学滑冰。
[特别提醒]不定式短语作宾语时,如果还带有宾语补足语,通常用it作形式宾语,而把不定式短语放在宾语补足语之后。例如:
He found it very difficult to get to sleep.他发现入睡很困难。


二、动词不定式常用作目的状语。例如:
He came to give us a talk yesterday. 他昨天来给我们作了个报告。
Mrs Brown went to see her doctor. 布朗夫人去看她的医生了。


三、tell,ask,want,order,get,wish,warn,teach,invite等动词后常跟不定式作宾语的补足语,构成tell/ ask……sb to do sth(“告诉/请……某人做某事”)结构。例如:
Could you ask him to call me,please? 请你让他给我打个电话,好吗?
[特别提醒]使役动词let,make,have等,感官动词see,hear,feel,watch,notice,look at,listen to等,后常跟不带to的不定式作宾语补足语。例如:
A woman saw it happen when she was walking past. 一位妇女路过时看到(它掉下)了。
We often heard her sing in the next room. 我们经常听到她在隔壁唱歌。
注意:在被动语态句子中,不定式前必须加to.例如:
He was made to do it. 他被迫做这件事。
She was often heard to sing in the next room. 经常听到她在隔壁唱歌。


四、不定式短语作定语要放在被修饰的词语之后。例如:
I have a lot of work to do. 我有许多事情要做。


五、不定式短语作主语时,常用it作形式主语,真正的主语不定式短语放在后面。例如:
It is right to give up smoking. 戒烟是有益的。


六、作表语。例如:
To him,the first important thing was to save lives. 对他来说,最重要的事情就是拯救生命。
His wish is to become a scientist. 他的愿望是当一名科学家。


七、动词不定式用在疑问词how,when,where,what,which等之后,作宾语或宾语补足语。例如:
He taught us how to use a computer. 他教我们如何使用计算机。
I don't know where to go? 我不知道去哪里。