当代英语通常用it 做形式主语定式和动名词置于谓语面特别主语较长时或些习惯用法
1） 谓语系表结构（be + 形容词 / 名词）时常定式置构成句型 it + be + 表语（形容词 / 名词）+ 定式
例 1 It is my duty to care for that patient.
照料位病人我职责（做主语定式to care for that patient 置it 形式主语）
例 2 It is not an easy thing to master a foreign language.
掌握门外语件容易事
例 3 It isn’t right to speak ill of someone behind his back.
别人背说坏对
2） 当谓语 takemakepaycost require feelneed 等动词时或者与情绪有关动词 delightamuseexciteannoyirritate 等时习惯上常用 it 做形式主语并定式置
例 1 It takes only ten minutes to get there.
儿只需十分钟
例 2 It pays to be honest.
诚实会吃亏
例 3 It feels good to stay away from the crowded city.
能远离拥挤城市感觉真错
例 4 It annoyed her to see someone spit on the ground.
看见有人随地吐痰让生气
3） 同定式样动名词也用于it + be + 表语 + 动名词句型二者区别参见10．2．2 1）论述下面两组句子没有多大差异
例 1 A） It is a waste of time to argue with him
B） It is a waste of time arguing with him.
和争辩浪费时间
例 2 A） It is worthwhile to discuss this again.
B） It is worthwhile discussing this again.
点值得讨论下
4） 表语（of）no usenot any usenot the slightest use no good not much goodfun等时常用动名词（用定式）做主语并置用 it 做形式主语
例 It’s no use crying over spilt milk.
覆水难收
5） 动名词还 there be 句型做主语（能用定式）常见形式 there is no + 动名词或 there is no / any + 名词 + 动名词
例 1 There is no denying the fact.
事实无否定
例 2 There isn’t any use trying again.
再试也没用