2023年高中英语语法名词性从句精讲之：四大从句用法大全主语从句主语从句的概念：如果一个句子在复合句中充当一个主语，那么这个句子就是主语从句。
主语从句通常由从属连词that，whether，if和连接代词what，who，which whatever，whoever以及连接副词how，when，where，why等词引导。
that在句中无词义，只起连接作用。
主语从句用法：1、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：如：That he is still alive is a wonder. 他还活着，真是奇迹。
When we arrive doesn't matter. 什么时候到没有关系。
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。
Whether they would support us was a problem. 他们是否会支持我们还是一个问题。
2、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：如：It's a pity that he didn't come. 很遗憾他没来。
(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：如：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，通常不用形式主语，总是主语从句放在句首：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。
(4)如果句子是疑问句，则必须用带形式主语it的结构：如：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？3、连词that的省略问题：引导主语从句的连词that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则可以省略：如：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)主语从句应注意的几个问题：1、that引导的主语从句既可放在句首，也可放在句尾，但在下列情况下that从句不可提前。
（1）在It is said/reported...that结构中：如：It is reported that a bank was robbed yesterday.（2）在I thappened/occurred...结构中：（3）含主语从句的复合句是疑问句时：如：Is it ture that you will give up the job?2、下面这种情况常用it作形式主语。
在It doesn't matter+what/whatever…结构中。
如：It doesn't matter what you say.3、由what引导的主语从句谓语动词单复数问题 what引导的主语从句一般按单数对待，但是，在实际使用中究竟按单数还是按复数对取决于其成分的含义。
如：What we need is more time.What were left behind were five empty bottles.宾语从句宾语从句的概念：置于动词、介词等词性后面起宾语作用的从句叫宾语从句。
宾语从句的语序必须是陈述语序。
谓语动词、介词、动词不定式，v.-ing形式后面都能带宾语从句。
有些形容词（afraid, sure, glad等）之后也可以带宾语从句。
宾语从句的用法：1、宾语从句的引导词：宾语从句通常由连词that和whether(if)、连接代词或连接副词以及关系代词型what引导：如：We believe that he is honest. 我们相信他是诚实的。
I don't know whether he'll arrive in time. 我不知道他是否能及时到。
I don't know who(m) you mean. 我不知道你指谁。
He asked why he had to go alone. 他问他为什么必须一个人去。
Please tell me which you like. 告诉我你喜欢哪一个。
She has got what she wanted. 她要的东西得到了。
注：有时介词后可接跟一个宾语从句(但介词后通常不接that 和if引导的宾语从句)：如：From what you say, he is right. 根据你所说的，他是对的。
有极个别介词(如but,except)可接that引导的宾语从句：如：She remembered nothing about him except that his hair was black. 她对他什么都不记得，只记得他的头发是黑的。
2、宾语从句与形式宾语it：当宾语从句后跟有宾语补足语时，通常在宾语从句处使用形式宾语it，而将真正的宾语从句移至句末：如：I think it best that you should stay here. 我认为你最好住这儿。
He hasn't made it known when he is going to get married. 他还没宣布他何时结婚。
3、连词that的省略问题：引导宾语从句的连词that通常可以省略：如：She said(that) she would come to the meeting. 她说过要来开会的。
I promise you(that) I will be there. 我答应你我会去。
注：有时为了强调，that引导的宾语从句可位于句首，此时that不可省略：如：That she is a good girl I know. 她是一个好姑娘，我是知道的。
4、宾语从句与否定转移当动词think, believe, suppose, expect, imagine后接一个表示否定意义的宾语从句时，其否定通常转移到主语：如：I don't suppose that it is true. 我认为那不是真的。
I don't imagine that he will come. 我想他不会使用宾语从句特别注意：一、宾语从句的语序：宾语从句的语序是陈述句语序即：连接代词/副词+主语+谓语+其他成分。
如：I don't know what they are looking for.Could you tell me when the train will leave?Can you imagine what kind of man he is?二、宾语从句的时态：主句是一般现在时，从句根据实际情况使用任何时态。
句：The headmaster hopes everything goes well.主句是过去时态，从句须用过去时态的某种形式。
句：She was sorry that she hadn't finished her work on time.当宾语从句表示的是一个客观真理或者事实时，即使主句是过去时，从句也用一般现在时态。
如：The teacher told his class that light travels faster than sound.三、宾语从句的特点：宾语从句可以作及物动词、介词及形容词的宾语。
宾语从句的语序一律用陈述句语序。
连接词that引导宾语从句在句中无词义，不充当句子成份，多数情况下可以省略。
whether和if都可引导宾语从句，但whether后可紧跟or not；whether从句可作介词的宾语。
如果从句太长，可以用形式宾语it.表语从句表语从句的概念：用作表语的从句叫作表语从句，它位于主句中的连系动词之后。
引导表语从句的词有从属连词that、whether、as though(if)；关系代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等；关系副词when, where, why, how, however, when。
表语从句用法：1、表语从句的引导词：引导表语从句的词有连词that, whether，连接代词和连接副词，关系代词型what，以及as if,as though,because等连词：如：The fact is that he doesn't really try. 事实是他没有做真正的努力。
The question is whether the film is worth seeing. 问题是这部电影是否值得看。
The problem is how we can find him. 问题是我们如何找到他。
That was when I was fifteen. 这是我15岁时发生的事。
It isn't as if you were going away for ever. 又不是你离开不回来了。
It is because I love you too much. 那是因为我太爱你了。
注：whether可此导表语从句，但与之同义的if 却通常不用于引导表语从句；because可引导表语从句，但与之同义的since, as, for等也不用于引导表语从句。
2、连词that的省略问题引导表语从句的that通常不省略，但在口语或非正式文体中有时也可省略：如：My idea is(that) we should do it right away. 我的意见是我们应该马上干。