动词不定式和动名词的句法功能比较
一,作主语
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.
④It+be+形容词+of sb +to do
It is stupid of you to write down everything the teacher says.
⑤It seems(appears)+形容词+to do
It seemed impossible to save money.
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 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
参考资料：BAIDU