主语从句
一、主语从句的引导词
主语从句通常由连词that和whether、连接代词或连接副词以及关系代词型what引导。
1. that引导
That he is still alive is a wonder. 他还活着，真是奇迹。
That we shall be late is certain. 我们要晚了，这是确定无疑的
That he should have ignored the working class was natural. 他忽视工人阶级是很自然的。That she is still alive is a consolation. 她还活着是使人感到宽慰的。
That she became an artist may have been due to her father’s influence. 她成为画家可能是受她父亲的影响。
That you are coming to London is the best news I have heard this long time. 你将来伦敦是好久以来我听到的最好消息。
That she was chosen made a tremendous stir in her village. 她被挑选上，在她村子里引起很大轰动。
2. whether引导
Whether it will do us harm remains to be seen. 是否对我们有害还要看一看。
Whether they would support us was a problem. 他们是否会支持我们还是一个问题。
3. 连接代词引导
Whoever is top from wins the game , when two matched players meet. 两强相争勇者胜。Whichever (of you) comes in first will receive a prize. 无论(你们)谁先到都可以得奖Whichever you want is yours. 你要哪个,哪个就是你的。
4. 连接副词引导
When we arrive doesn’t matter. 什么时候到没有关系。
How it was done was a mystery. 这是怎样做的是一个谜。
How this happened is not clear to anyone. 这件事怎样发生的，谁也不清楚。
How many people we are to invite is still a question. 邀请多少人还是一个问题。
Where I spend my summer is no business of yours. 我在哪里过暑假不关你的事。
5. 关系代词型what引导
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。
What’s done is done. 事已成定局。
What he says is not important. 他说的话并不重要。
What I am telling you is mere impressions. 我和你说的都不过是一些印象而已。
What make the river more beautiful are the lotus plants growing in the water. 为河水增色的是水里的荷花。
What you need is a good-sized canvas bag. 你需要的是一个比较大的帆布袋。
What I am afraid of is their taking him to Portugal. 我担心的是他们把他带到葡萄牙去。What struck me was that they have all suffered a lot. 给我很深印象的是他们都受过很多苦。
二、主语从句与形式主语it
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。这分三种情况：
(1) 对于以连词that引导的主语从句，通常用形式主语代主语从句：
It’s a pity that he didn’t come. 很遗憾他没来。
It is important that he should know about this. 他必须知道此事。
It’s vital that we be present. 我们出席是至关重要的
It was intended that you be the candidate. 大家的意图是让你当候选人。
It is important that this mission not fail. 这项使命不失败至关重要。
It is essential/indispensable that a meeting be convened this week. 本周开一次会非常重要。
It is appropriate that this tax be abolished. 废除这个税是恰当的。
It’s unfair that so many people should lose their jobs. 竟有这么多人失业这是不公平的。It’s amazing that she should have said nothing about it. 她竟未谈及此事令人惊讶。
It’s unthinkable that they should deny my request. 他们竟然拒绝我的请求，这是不可思议的。
That they should refuse to sign the petition required great courage. 他们拒绝在请愿书上签字这是需要很大勇气的。
3.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
It is a fact that … 事实是…It is an honor that …非常荣幸
It is common knowledge that …是常识
(2) It + be + 形容词 + that从句
It is natural that… 很自然…It is strange that… 奇怪的是…
（3）It + be + 动词的过去分词 + that从句
It is reported that… 据报道…It has been proved that… 已证实…
（4）It + 不及物动词 + that 从句
It seems that… 似乎…It happened that… 碰巧…
It is not known who he is.
It does not matter when he leaves.
It is a pity that he can’t attend the party.
It’s hard to say how much money is needed.
It is known to all that money can’t grow on the tree.
Has it been decided where the meeting is to be held?
三．注意：
1. 但主语从句如果是用连接代词what, whatever, whoever 等引导的，表示的是一个具体的东西或人，这种主语从句不能用引导词it 来替换。
What he said interested me greatly.
Whoever is tired may rest.
2. 另注意在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do”，常用的句型有：
It is necessary (important, natural, strange, etc.) that …
It is suggested (requested, proposed, desired, etc.) that…
3. 如果句中做主语的是一个从句，则谓语动词要用单数形式。
How close parents are to their children has a strong influences on the character of the children.
How and why he did the experiment is unknown to all.
4. If 不可以用来引导主语从句，要用whether
Whether he will write he book is not yet decided.
It is not yet decided whether/if he will write the book.
4. It 作形式主语和it引导强调句的比较
It 作形式主语代替主语从句，主要是为了平衡句子结构，主语从句的连接词没有变化。而it引导的强调句则是对句子某一部分进行强调，无论强调的是什么成分，都可用连词that。被强调部分指人是也可用who/whom。例如：
It is a pity that you didn’t go to see the film.
It doesn’t interest me whether you succeed or not.
It is in the morning that the murder took place.
It is John that broke the window.
5. 主语从句不可位于句首的五种情况
(1) if 引导的主语从句不可居于复合句句首。
(2) It is said , (reported) …结构中的主语从句不可提前。例如：
It is said that President Jingo will visit our school next week. (right)
That President Jiang will visit our school next week is said. (wrong)
(3) It happens…, It occurs… 结构中的主语从句不可提前。例如：
It occurred to him that he failed in the examination. (right)
That he failed in the examination occurred to him. (wrong)
(4) It doesn’t matter how/whether …结构中的主语从句不可提前。例如：
It doesn’t matter whether he is wrong or not. (right)
Whether he is wrong or not doesn’t matter. (wrong)
(5) 含主语从句的复合句是疑问句时，主语从句不可提前。例如：
Is it likely that it will rain in the evening? (right)
Is that will rain in the evening likely? (wrong)
4. What 与that 在引导主语从句时的区别
What 引导主语从句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如：
1) What you said yesterday is right.
2) That she is still alive is a consolation.