主语从句是一个重要的语法点

主语从句是一个重要的语法点，主语从句是中学阶段的重点语法项目,也是高考的热点之一。

为使同学们更好地掌握其用法,本文对主语从句语法做了一个详细的梳理，帮助大家梳理主语从句的语序，连接词的选用等内容，对于it构成的主语从句做了详细的解释。

以便帮助大家掌握这一重要知识点。

一.主语从句的语序
主语从句要求使用陈述句语序，而非一般疑问句语序。

如：
What surprised me most was that the little girl could play the violin so well.
使我感到惊讶的是这个小女孩的小提琴拉得太好了。

How he was successful is still a puzzle.
他是如何成功的仍然是个谜。

二. 连接词的选用
（1）that和what的选用
that和what都可引导主语从句。

what除起连接作用外，还在名词性从句中充当某些成分，可作从句的主语、宾语或表语。

而that在名词性从句中不充当任何成分，无词义，只起连接词作用。

如：
What he wants is a book.
他想要的是一本书。

That light travels in straight lines is known to all.
众所周知，光线沿直线运行。

（2）if和whether的选用
引导主语从句，不能用if，只能用whether。

如：
Whether we will hold a party in the open air tomorrow depends on the weather.
我们明天是否在户外开晚会要看天气而定。

（3）其它连接代词和副词的选用
根据主语从句的具体意义，正确的选择who, which, when, where, why, how 等连接词，这些连接词既有疑问含义，又起连接作用，同时在从句中充当各种成分。

如：
When we shall hold our sports meet is not decided.
我们何时举行运动会还没有决定。

Who broke the glass yesterday is not clear.
还不清楚昨天谁打破了玻璃。

Which car you will choose to buy makes no difference.
你决定买哪一辆车都不会有任何区别。

（4）whatever / whoever的功用
whatever, whoever在主语从句中不含疑问意义。

它引导主语从句，并在从句中作主语、宾语、表语等。

whatever = anything that; whoever = anyone who。

要注意和whatever, whoever引导的让步状语从句的区别。

如：
Whoever breaks the law should be punished.（主语从句）
（＝Anyone who breaks the law should be punished. ）
Whoever breaks the law, he should be punished. （让步状语从句）
（＝No matter who breaks the law, he should be punished. ）
三. it构成的主语从句
（1）由连词that引导的主语从句，在大多数情况下会放到句子的后面，而用代词it作形式主语。

如：
It is well-known that the earth moves around the sun.
众所周知，地球围绕太阳转。

另外，需要注意的是，it作形式主语代替主语从句时，要注意和as引导的定语从句的区别。

试比较：
It was reported that the US was under the terrorist attack.
（主语从句，有that，无逗号）
As was reported, the US was under the terrorist attack.
（定语从句，无that，有逗号）
上两句意为“据报道，美国遭到恐怖分子的袭击”。

（2）常见用it作形式主语的复合句结构
<a>It is a fact （a good idea / a pity / a shame / no wonder / good news…）that… 如：
It’s a pity that you missed the film.
你没有看那部电影真是太遗憾了。

<b> It is necessary （clear / true / strange/ important /wonderful / possible/ likely…）th
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。

如：
It is necessary that you （should）master the computer.
你很有必要掌握电脑。

It is important that a student learn English well.
学生学好英语很重要。

It’s clear that they badly need he lp.
很明显，他们急需援助。

It is likely that a hurricane will arrive soon.
飓风很可能马上就要到达了。

<c> It is reported （well-known / hoped / thought / expected /said
/believed/decided /suggested /ordered…）that…
如：
It is said that he was killed in the earthquake. 据说他在地震中丧生了。

<d> It seems （happened / appears / doesn’t matter / makes no difference / …）that …
如：
It seems that they will win the game.
看起来他们好像会赢得这场比赛。

It makes no difference whether he will attend the meeting or not.
他是否会参加会议都无关紧。

在句中作主语的从句叫主语从句(Subjective Clause).主语从句是一种重要的名词性从句,在高考试题中频频出现.那么高考对它考查的重点是什么?
I.由what等连词引导的从句
在主语从句中, what = the thing(s) that,它本身在从句中充当某个成分,或是主语,或是宾语,其含义为"所做/说/想的".
[考题点击]
1. _______ you have done might do harm to other people.(MET ' 87)
A. That
B. What
C. Whether
D. How
2. _______ he said at the meeting astonished everybody present.(NMET'93)
A. What
B. That
C. The fact
D. The matter
3. _______ we can't get seems better than _______ we have. (NMET ' 96)
A. What; what
B. What; that
C. That; that
D. That; what
II.由that引导的主语从句
that在主语从句中不充当具体的句子成分,也无实际词义,只起连接作用,而且当它在句首时,不能省略.
[考题点击]
4. It worried her a bit _______ her hair was turning grey. (MET 1992)
A. while
B. that
C. if
D. for
5. _______ you don't like him is none of my business. (上海1992)
A. What
B. Who
C. That
D. Whether
III.由whether或if引导的主语从句
whether与if皆可引导主语从句,但放在句首常用whether.
[考题点击]
6. _______ the 2000 Olympic Games will be held in Beijing is not known yet.(MET ' 92)
A. Whenever
B. If
C. Whether
D. That
7. _______ we'll go camping tomorrow depends on the weather.(NMET ' 96)
A. If
B. Whether
C. That
D. Where
IV.由whoever, whatever等引导的主语从句
whoever = the person who或anyone who.who也可以引导主语从句,但只表示"谁",如:Who will win is not important.
anyone与the person皆不能引导从句.
[考题点击]
8. _______ leaves the room last ought to turn off the lights. (MET ' 88)
A. Anyone
B. The person
C. Whoever
D. Who
9. It is generally considered unwise to get a child _______ he or she wants. (NMET ' 97)
A. however
B. whatever
C. whichever
D. whenever
V.由it作形式主语引起的主语从句
that从句作主语时,常用it作形式主语,而把that引导的主语从句放到句后.在下列情况下,一般使用形式主语it,将主语从句放在句尾.
1)谓语是seem, appear, be (im)possible, be a pity, be a wonder, be likely等.如:
It seemed certain that this would win the prize.
It appeared that he was right.
2)在It is known... ; It is said... ; It is hoped... ; It is believed...等句型中.如:
It is said that our school football team won.
3)主语从句也可以用it作形式主语,以wh-连接的句子作真实主语,放到句子后面.如:
It is still a question when we shall have our sports meet.
It doesn't matter what you say.
[考题点击]
10. Does _______ matter if he can't finish the job on time ?(MET ' 91)
A. this
B. that
C. he
D. it
11. _______ is a fact that English is being accepted as an international language.(NMET ' 95)
A. There
B. This
C. That
D. It
注意:1)有时在"It is necessary(important, suggested等)+ that从句"结构中, that从句常用"should +动词原形"形式来表示虚拟语气,其中should常可省去.
[考题点击]
12. It is necessary that a college student _______ at least a foreign language.(1993上海)
A. masters
B. should master
C. mastered
D. will master
2)在此结构中,要注意句子结构的变化.如NMET 2001年的一道高考题:
_______ is known to everybody, the moon travels round the earth once every month.
A. It
B. As
C. That
D. What
该题很多同学误选了A或C,其原因是没有注意到题中逗号的作用.其实,句中逗号已暗示了该句绝非主语从句,而是as引导的非限制性定语从句, as代表整个主句内容.
Key:1-5 BAABC 6-10 CBCBD 11-12 DB。