主语从句
主语从句，即在複合句中充当主语成分的句子，例如"That he finished writing the composition in such a short time surprised us all"，他在很短的时间内写完作文让我们都很惊讶，此複合句主要描述的是某事让我们惊讶，某事就是该複合句的主语，因此“That he finished writing the composition in such a short time”便是该複合句的主语从句。
引导主语从句的连词主要有：
从属连词：that whether
连线代词：who whoever whom whose what whatever which whichever
连线副词：when where how why
基本介绍
- 中文名：主语从句
- 外文名：Subject Clause
- 解释：複合句中充当主语成分的句子
- 从属连词：that whether
主语从句
定义
在複合句中充当主语成分的从句叫做主语从句。
第一部分
常规主语从句，即句子在複合句中充当一个主语
主语从句的时态不受主句时态的影响和限制
（1）That he finished writing the composition in such a short time surprised us all.
他在如此短的时间内写完作文使我们十分惊讶。
（2）Whether we will go for an outing tomorrow remains unknown.
我们明天是否会去郊游仍旧未知。
（3）Who will be our monitor hasn't been decided yet.
现在还没有决定谁会成为我们的班长。
（4）Whom we must study for is a question of great importance.
“我们为谁而学习”是个很重要的问题。
（5）What caused the accident remains unknown.
事故的起因是未知的。
（6）Whatever you did is right.
你做的任何事都是正确的。
（7）Whom the watch belongs to is unknown.
手錶的归属是未知的。
（8）What we need is time.
我们需要的是时间。
（9）What we need are good doctors.
我们需要的是好的医生。
名词性从句的时态规则：
1）、主句谓语动词是现在或将来时，从句谓语动词可以用任何需要的时态。
I wonder what he is doing now.
I wonder what he is doing now.
我想知道他现在在乾什幺。
Do you know when and where he was born?
Do you know when and where he was born?
你知道他在何时何地出身吗？
I'll write to tell him where I 'll meet him.
I'll write to tell him where I 'll meet him.
我将写信告诉他我将在哪里与他碰面。
2）、主句谓语动词是过去时，从句谓语动词一般需用过去时。
（1）从句与主句的谓语动作同时发生，从句用一般过去时或过去进行时。
I thought that he studied hard.
I thought that he studied hard.
我认为他学习很努力。
He told me his son was watching TV.
He told me his son was watching TV.
他告诉我他的儿子在看电视。
（2）从句谓语动作在主句谓语动作之后，从句用过去将来时。
He said he would spend his holidays in Qingdao.
He said he would spend his holidays in Qingdao.
他告诉我他将在青岛度假。
（3）从句谓语动作在主句谓语动作之前，从句用过去完成时。
They told me they had waited for me half an hour.
They told me they had waited for me half an hour.
他们告诉我他们已经等了我半小时了。
（4）从句如果有表示过去某一具体时间的状语，仍用过去时。
She told me her brother died in 1945.
She told me her brother died in 1945.
她告诉我她的哥哥（弟弟）死于1945年。
3)从句时态不受下列客观的条件影响。
（1）从句说明的是不受时间限制的事实或真理（客观真理）。
The teacher told us that the earth turns from west to east.
老师告诉我们地球自西向东转。
He said Asia is the largest continent.
He said Asia is the largest continent.
他说亚洲是最大的大陆。
It was true that water freezes at thirty-two degrees Fahrenheit.
水在的确是在32华氏度结冻的。
（2）当从句表示的是反覆出现的时态不变。
（2）当从句表示的是反覆出现的时态不变。
She told me that she gets up at six o'clock every morning.
她告诉我她每天早晨6点起床。
He asked me when the train usually starts.
He asked me when the train usually starts.
他向我询问火车通常何时出发。
（3）当从句的谓语动作仍在继续时，或者表示现在仍在的状态时，时态不变。
（3）当从句的谓语动作仍在继续时，或者表示现在仍在的状态时，时态不变。
He said that the workers in that factory are trying to fulfill the task in time.
他说那家公司的员工正在全力及时完成任务。
She told me the other day that she is only 10.
她告诉我那天她只有10岁。
（4）当从句的动作状态还未发生，要用一般式表示。强调与现在的联繫。
He said he will wait for me this evening.
他说他今晚将等待我。
She told me the other day that she is only 10.
她告诉我那天她只有10岁。
（4）当从句的动作状态还未发生，要用一般式表示。强调与现在的联繫。
He said he will wait for me this evening.
他说他今晚将等待我。
小结:
（1）引导主语从句连词有that,whether,who,what,whatever等
（2）连词位于句首不能省略
（3）主语从句大多数情况下视为第三人称单数，但也有例外，如例（9）
注意：当what引导的名词性分句作主语时，主谓一致问题极为複杂。着名学者周海中教授在论文《关于what-分句作主语的主谓一致问题》中就这一问题做了深入研究，并给出了10种的主谓一致关係。这些一致关係值得英语学习者和使用者特别注意。
第二部分
为了防止句子头重脚轻，通常把形式主语it放在句首位置，真正主语搁置于句末
（1）It is certain that he will win the match.
他一定会赢得这场比赛的。
（2）It is true that he has made a very important discovery in chemistry.
他的确在化学领域有了一个伟大的发现。
（3）It is very likely that they will hold a meeting.
他们很有可能会举行一场会议。
（4）It is strange that he should do that.
他竟然那样做是很奇怪的。
（5）It is important that we all should attend the meeting.
重要的是我们都应该参加会议。
（6）It is strange that the man should have stuck to his silly ideas.
真奇怪，这个人竟然坚持自己愚蠢的想法。
（7）It is a pity that we won't be able to go to the south to spend our summer vacation.
真遗憾我们不能去南方度过我们的暑假。
（8）It is still a mystery what caused the accident.
造成事故的原因仍旧是个秘密。
（9）It is said that he has gone to shanghai.(=He is said to have gone to shanghai)
据说他已经去上海了。
（10）It is known to all that the gun powder was first invented by the Chinese.
所有人都知道火药最初是由中国人发明的。
（11）It is suggested that the work should be done with great care.
建议工作应该被小心地被完成。
（12）It happened that the two cheats were there. (=The two cheats happened to be there)
两个骗子碰巧在那里。
两个骗子碰巧在那里。
小结:
（1）为避免头重脚轻，常以形式主语it引导从句。 It+形式主语谓语+从句。
（2）由于主语从句一般被认为是单数形式，形式主语的谓语动词、be动词+表语 均为单数第三人称形式或过去式.
用法
主语从句与宾语从句两者的用法和在句中的作用是不同的，下面从它们的各自用法来介绍。
一．主语从句
主语从句 定义：在句子中担当主语的是一个从句，这个从句就叫做主语从句。
主语从句是在複合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。
1. It 作形式主语和it引导强调句的比较
①主语从句常用it作形式主语，一般常用句型为：It is+{名词/形容词/过去分词}+主语从句例如：
It is still a question whether she will come or not.
It is strange that you should like him.
It is still unknown which team will win the match.
另外，还有一些比较多见的结构：
It turned out that……;
It has been proved that……;
It happened/occurred that……;
It is well-known that……等等
②而强调句则不同，它的结构是：It+be+被强调部分+that+从句
强调主语：It is the times that produce their heroes.时势造英雄
强调宾语：It is English that Prof.Lin teaches us.
强调状语：It was in shanghai that I saw the film.
判断是否是强调句有一个方法，就是将that以后的“句子的其余部分”拿出来单独看，看有没有缺成分，缺的是什幺成分，再把谓语动词后面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句完整的句子了，那就说明是强调句。
2. 用it 作形式主语的结构
(1) It is +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 is +形容词+that从句
It is natural that… 很自然……
It is strange that… 奇怪的是……
(3) it +不及物动词+that从句
It seems that… 似乎……
It happened that… 碰巧……
(4) it is+过去分词+that从句
It is reported that… 据报导……
It has been proved that… 已证实……
3.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複合句句首。
(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.
(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.
(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..
(5) 含主语从句的複合句是疑问句时，主语从句不可提前。例如：
Is it likely that it will rain in the evening?
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：
What you said yesterday is right.
二：宾语从句用以区分主语从句的几个特徵：
1、引导词：what\which\whose\when\whether\if\where
2语序：宾语从句必须是用陈述语句。（名词性从句都是陈述语序）
如：I think that you must work harder.
宾语从句的引导词、连线词的区别、否定转移等现象。
补充：从句的语序永远是陈述句。