动词不定式具有名词、形容词和副词的作用,它可以作主语、宾语、宾补和状语.
(1)作主语
动词不定式作主语时,常用it作形式主语,而将真正的主语放在句末,It＋be＋形容词＋(for sb)＋动词不定式.
It's important (for us) to protect environment.
(对我们来说)保护环境是很重要的.
注：当在kind,good,nice,clever等表示人的品质的形容词后,不用for而用of.
It's very kind of_you_to_help_me.
你帮助我真是太好啦.
It's very clever of_you_to_do_like_that.
你那样做真是太聪明啦!
(2)作宾语
He wants to_go_out_with_her.
注：①一些谓语动词后只能用不定式作宾语,常见的这类词表示命令、打算或希望,如：would like,want,wish,hope,decide,plan,expect等.
Would you like to_see_a_film this evening?
你今晚想去看电影吗?
②在find,think后跟不定式作宾语时,常用it代替,而将真正的宾语放在句末.
I find it easy to_read_English_every_day.
我发现每天读英语很容易.
(3)宾语补足语
动词不定式作宾补时,它与宾语有逻辑上的主谓关系.
Lucy asked him to_turn_down_the_radio.
露西要他关小收音机.
(4)作定语
动词不定式作定语时,应放在名词之后,它与名词有逻辑上的动宾关系.
I have a lot of homework to_do.
我有许多家庭作业要做.
There is nothing to_worry_about.
没什么要担心的.
(5)作状语
Mrs Wang went to Shanghai to_see_her_daughter.(目的)
王太太去上海看她女儿.
We're glad to_meet_you here.(原因)
我们很高兴在这见到你.
He is too tired to_work_on.(结果)
他太累了而不能继续工作.
3．不定式的否定形式是在不定式前加not.
They told us not_to_play basketball too long.
他们告诉我们不要玩太长时间篮球.
You'd better not_go_to_bed late.
你最好不要睡觉太晚.
4．不定式常和疑问词what,which,when,where,how连用,相当于一个宾语从句.
The teacher is telling the students what_to_do.
老师正告诉同学们做什么.
He didn't know where_to_go.(where to go＝where he should go)
他不知道去哪里