由一个句子充当主语，就是主语从句。引导主语从句的有从属连词，连接代词和连接副词。
引导词：
一. 从属连词：that & whether
1. that引导
That he is still alive is a wonder.
他还活着，真是奇迹。
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。
*引导词that有时可以省略，有时则不能，若that引导的主语从句直接位于句首，则that不能省略，若that引导的主语从句位于句末，而在句首使用了形式主语it，则that可以省略：
That you didn’t go to the party was a pity.
It was a pity (that) you didn’t go to the party.
很遗憾你没去派对。
2. whether引导
Whether it will do us harm remains to be seen.
是否对我们有害还有待观望。
Whether they would support us was a problem.
他们是否会支持我们还是一个问题。
二. 连接代词：who, whoever, whom, whose, what, whatever, which,whichever
Whoever is top from wins the game when two matched players meet.
两强相争勇者胜。
Whichever you want is yours.
你要哪个哪个就是你的。
What we need is money.
我们需要的是钱。
Whom the watch belongs to is unknown.
我们不知道这个表是谁的。
Whatever you did is right.
无论你做什么都对。
三. 连接副词：when，where，how，why
When we arrive doesn’t matter.
什么时候到没有关系。
Where I spend my summer is no business of yours.
我在哪里过暑假不关你的事。
How this happended is not clear to anyone.
这件事怎样发生的，谁也不清楚。
有时为避免句子头重脚轻，常用it作形式主语，代替主语从句放在句首，而把主语从句置于句末。常用句型如下：
(1)It be 形容词 that 从句
(2) It be 名词 that 从句
(3) It be 动词的过去分词 that 从句
It was true that water freezes at thirty-two degreesFahrenheit.
水在的确是在32华氏度结冰的。
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。
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。
主语从句考点归纳：
一、连词that的省略问题
引导主语从句的连词that没有意义，不做成分， 有时可省，有时不能省，其原则是：若that引导的主语从句直接位于句首，则that不能省略；若that引导的主语从句位于句末，而在句首使用了形式主语it，则that可以省略：
That you didn’t go to the talk was a pity. 很遗憾你没去听报告。(that不可省)
It was a pity (that) you didn’t go to the talk. 很遗憾你没去听报告。(that可省)
二、引导主语从句，放在句首时，不能用if，只能用whether。
Whether we will hold a party in the open air tomorrow depends on the weather.
It depends on the weather Whether /if we will hold a party in the open air tomorrow.
三. 虚拟语气的考查
1. It is suggested / required / ordered / demanded that...句型中,动词为表示命令、建议、要求等意义的词。主语从句应使用虚拟语气,谓语动词用/"should 动词原形/",should可以省略。例如:
It is suggested that you (should) spend more time in studying English. 你应该花更多的时间学习英语。
2. It is important / natural / necessary / impossible that...句型中,主语从句应使用虚拟语气,谓语动词用"should 动词原形"的形式,should有时有感情色彩。
It is necessary that a college student should master at least a foreign language. 大学生掌握一问外语是必要的。
