It作形式主语常见用法

It作形式主语常见句型

有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下：1. It + be +名词+ that-从句

适用该句型的名词（词组）有: a pity，an honor，a good thing，a fact，a surprise，a question, a shame，a custom, a truth，our hope, no wonder, good/ bad manners等。如：

It is a pity that you missed the sports meeting last week. 你错过了上周的运动会太可惜了。

It is a fact that English is being accepted as an international language. 事实上英语已经被作为一种国际语言而接受了。

2. It + be +形容词+ that-从句

可用于此句型的形容词有：wonderful, true，good，right，wrong，（un）important，useless，surprising，disturbing，frightening，alarming，clear，unusual，lucky，certain, necessary等。如：

It is quite certain that he will be at the meeting.

他将出席会议是无疑的。

It is surprising that he came late to school this morning.

他今天早上迟到真令人惊讶。

It is important that we (should) study hard.

我们努力学习是很重要的。

注意：该句型中的形容词是（un）important, necessary等时，从句应为(should )+动词原形。

It is important that we (should) learn English well.

It is necessary that he (should) remember these words.

3. It ＋seem／appear／happen的适当形式＋that从句。

It seems that there is a big waste pipe coming down from the town.

It appeared that he was calm, but inside his heart was beating wildly with fear.

4. It + be + 过去分词+ 主语从句

可用于此句型的过去分词有：announced，believed，expected，hoped，decided，reported，said，shown等。如：

It is said that he has gone to shanghai. (=He is said to have gone to shanghai)

It is reported that 16 people were killed in the earthquake.

It is suggested that the work (should) be done with great care.

It is known to all that the gun powder was first invented the Chinese.

It is not decided who will give the operation to the patient.

5. It is time/ about time/ high time that ...

该句型中that 后的从句应该用虚拟语气，值得注意的是①常用过去时态表示虚拟．②有时也用should + 动词原形，should 不能省。常译为“是（正是）．．．的时侯．．．”。

It is time that children should go to bed.

= It is time that children went to bed.

6. It is the first (second ... ) time that ...

用完成时态。至于用什么完成时态，由主句的谓语动词的时态决定。如果是一般现在时，后面从句用现在完成时态；如果是一般过去时，后面从句则用过去完成时态。该结构中that 可以省去；it有时用this 替换．常译为“是第一（二）．．．次．．．”。

It is the first time I have been here.

= This is the first time I have been here.

7. It + be + adj./ n. (for sb. / of sb.) + to do sth.

该句型中的形容词通常是表示事物的特点或特征的如difficult，hard，easy，impossible，necessary，important等，此时用for；或表示人的性格特征或特点的如nice，good，bad，kind，silly，foolish，wise，clever，careless，rude，brave，cruel，careful，grateful等，这时要用of。如：

It is foolish of you to give up such a good chance.

It is necessary for college students to master at least a foreign language.