不定式和动名词作主语的几种情况分析

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 composition in a quarter of an hour.

常用表示客观情况的形容词,如:difficult, easy, hard, important, impossible, necessary 等。

④It+be+形容词+of sb +to do

It is stupid of you to write down everything the teacher says.

常用careless, clever, good, foolish, honest, kind, lazy, nice, right, silly, stupid, wise等 表示赞扬或批评的词。

⑤It seems(appears)+形容词+to do

It seemed impossible to save money.

在不定式前的sb,可看作其逻辑主语。

此类句式有时相当于Sb is+形容词+to do句式 。

例句：It's kind of you to help me with my English.=You are kind to help me with my English.

⒉动名词作主语

Learning without practice is no good.

动名词作主语时,也常用It句式.如:

①It's +no good(no use, fun, a pleasure, a waste of time)+doing…

It's no good reading in dim light.

It's no use sitting here waiting.

②It's+形容词+doing

It's dangerous swimming in the sea in windy days.

这样用的形容词有expensive, nice, tiring等,但important, necessary则不适用于这种结构,应用不定式 代替,如:It's important for you to keep fit.

③There is no + doing

There is no saying what will happen next.

在这一结构中,动名词后常带宾语,相当于'It's impossible to…'结构.

⒊动词不定式和动名词作主语的区别

①不定式作主语经常表示具体动作,常与特定的动作执行者联系在一起;而动名词作主语经常表示抽象动作,经常不与特定的动作执行者联系在一起.如:

It's no good eating too much fat.

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

②动名词结构作主语,可以用名词或代词属格形式作逻辑主语.如:

It's no use your pretending that you didn't know the rules.

不定式做主语，一般用it当形式主语，把作主语的不定式短语后置。

It took me only five minutes to finish the job.

③在疑问句中，句首总用-ing形式，而不用不定式。

Does our saying mean anything to him? 我们说这话，对他能起作用吗？

④动名词作主语时，通常用以表示一件已知的事或经验。

Climbing mountains is interesting．爬山很有趣。(经验)

⑤不定式短语通常用来表示一件未完成的事或目的。

Driving a car during the rush hour is tiring．在高峰时刻开车令人厌烦。(经验）