不定式作主语

时间:09-27 18:44   浏览:
To +动词原形
Not to do

解释:具有动词的性质,作宾语,状语/具有名词的性质,作主语/具有形容词性质,作定语/具有副词的性质,作状语。除谓语不可作之外,其他都可。

一般式:to do
进行时:to be doing
完成时:to have done
完成进行时:to have been doing

to do:表示动作发生在谓语之后,I want to go home.与谓语动词几乎同时发生
to be doing :表示与谓语动词同时发生
to have done:发生在谓语动词之前 Someone was considered to have done something.
to have been doing :动作从过去开始一直持续到谓语动词这个动作的发生


(1)动词不定式作主语时,谓语动词常常用单数。例如: 

    To do morning exercises is useful for our health. 做早操有利于我们的健康。 
    To sweep the floor is my duty every day. 每天打扫地板是我的责任。

(2)如果动词不定式太长,常常用it作形式主语,而将真正的主语——动词不定式后置。例如: 
   It took me half an hour to walk there.我走到那儿花了半小时的时间。
   It’s important for us to learn English well.对我们来说,学好英语是重要的。


下面归类五种句型:

    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 composition in a quarter of an hour.

    ④It+be+形容词+of sb+to do
    It is stupid of you to write down everything (that) the teacher says.

    ⑤It seems(appears)+形容词+to do
    It seemed impossible to save money.

注意:
    在句型③中,常用表示客观情况的形容词,如:difficult,easy,hard,important,impossible,necessary 等;在句型④中,常用careless,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise等 表示赞扬或批评的词。在不定式前的sb,可看作其逻辑主语。这一句式有时相当于Sb is+形容词+to do句式。
如:
    It's kind of you to help me with my English.=You are kind to helpme with my English.

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