一般用ing形式,为动名词做主语,也有的用to do动词不定式做主语.对动词及物或不及物无太大要求.
例 (1).动名词作主语,常表示泛指意义的行为.Seeing is believing.Using the right hand to shake hands is a convention many countries.Talking mends no holes.空谈无济于事.(2).动名词在“It is no use/ no good/ fun/ a waste of time/ a good pleasure/ not any use/ useless/ worthwhile/need等词+dong”结构中作主语,it为形式主语
3.在there is no +v.—ing----结构中,常用动名词作主语.如There is no saying when he'll come.
动词不定式做主语
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
(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
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.
.