史上最标准的英语语法之主语从句

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第十二节主语从句

it 作形式主语的主语从句

有时为了考虑句子平衡,通常在主语从句处使用形式主语it,而将真正的主语从句移至句末。这分四种情况:

(1) 对于以连词that引导的主语从句,通常用形式主语it替代主语从句:

a. It is +名词+从句

It is a fact that… 事实是……;It is good news that … ……是好消息;

It is a question that … ……是个问题;It is common knowledge that … ……是常识类似的名词还有:a pity;a wonder;a good thing;no wonder;surprise等。

It is a mystery to me how it all happened.

It is common knowledge that the whale is not a fish.

It is no surprise that Bob should have won the game.

b. It is +形容词+从句

It is necessary that … 有必要……;It is clear that … 很清楚……;It is likely that … 很可能……;It is important that … 重要的是……

类似的形容词还有:strange; natural; obvious; true; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising; interesting; astonishing, etc.

It is doubtful whether she will be able to come.

It is essential that he should be here by the weekend.

It seems obvious that we can not go on like this.

It is necessary that you (should)master the computer.

需要注意的是这类主语从句中,谓语动词很多为“(should)+动词原形”,即要用虚拟语气。

c. It is +过去分词+从句

It is said that … 据说……;It is reported that … 据报道……;It has been proved that … 已证明……;It must be proved that… 必须指出……

类似的过去分词还有:known; estimated; expected; believed; thought; hoped; noted; discussed; required; decided; suggested; demanded; made clear; found out,etc.

例如:It is used to be thought that a new star must be due to a collision between two stars.

It has not been made clear when the new road is to be opened to traffic.

d. It seems不及物动词(happened / appears / doesn’t matter / makes no difference / occurred …)that …主语从句不可提前

It makes no difference whether he will attend the meeting or not.

It does not matter if I missed my train.

It happened that I saw him yesterday.

(2) 对于以连接代词(副词)引导的主语从句,可以使用形式主语代主语从句,也可直接在句首使用主语从句:

Whether they would support us was a problem.

他们是否会支持我们还是一个问题。

It was a problem whether they would support us.

他们是否会支持我们还是一个问题。

(3) 对关系代词型what引导的主语从句,通常直接将主语从句放在句首。如:What we need is money. 我们需要的是钱。

What I want to know is this. 我想知道的就是这一点。

有时也可将助用形式主语。如:It is clear enough what he meant. 他是什么意思很清楚。

(4) 如果句子是疑问句,则必须用带形式主语it的结构:

Is it true that he is the girl’s father? 他是那女孩的父亲,是真的吗?

How is it that you are late again? 你怎么又迟到了?

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