名词性从句
在复合句中起名词作用的从句叫做名词性从句。名词性从句相当于名词，可分别作主句的主语、表语、 宾语和同位语。因此，名词性从句可分为主语从句、表语从句 、宾语从句和同位语从句。
名词性从句的引导词：
| |
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| 连接词 |
that, if, whether |
不作成分 |
| 连接代词 |
who, whom, whoever, whose, what, whatever, which |
作成分（主语，宾语，表语） |
| 连接副词 |
when, where, why, how |
作状语 |
- 主语从句
作句子主语的从句叫主语从句。主语从句中，that 在句中无词义，只起连接作用；连接代词和连接副词在句中既保留自己的含义、又起连接作用，在从句中充当成分。
主语从句一般有三种结构：
- 主语从句+谓语
- It+be+形容词（名词词组、过去分词）+that 从句
（3）It +seem (happen，appear 等不及物动词)+that 从句
Eg : What he wants to tell us is not clear. 他要跟我们说什么，还不清楚。
It is known to us how he became a writer. 我们都知道他是如何成为一名作家的。
Where the English evening will be held has not yet been announced.
英语晚会将在哪里举行，还没有宣布。
【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：
Eg : It is necessary (important, natural, strange, etc.) that ...
It is a pity (a shame, no wonder, etc.) that ...
It is suggested (requested, proposed, desired, etc.) that ...
- 宾语从句
在句子中起宾语作用的句子叫宾语从句，宾语从句放在及物动词或介词之后作宾语。
Eg :He has told me that he will go to Shanghai tomorrow.
他已经告诉我他明天要去上海。
Eg: We must never think (that) we are good in everything while others are good in nothing.
我们决不能认为自己什么都好，别人什么都不好。
【注意】在 demand、order，suggest、decide、insist, desire, demand, request, command 等表示要求、命令、建议、决定等意义的动词后，宾语从句常用“（should）+ 动词原形”
Eg：I insist that she (should) do her work alone. 我坚持要她自己工作。
The commander ordered that troops (should) set off at once. 司令员命令部队马上出发。
- 表语从句
表语从句位于连系动词后,有时用 as if 引导。其基本结构为:主语 + 系动词 + that 从句
- be, look, remain, 等系动词后均可跟表语从句
Eg: My suggestion is that we should go shopping.
- as if 也可引导表语从句。
Eg: It looks as if it’s going to rain.
- the reason why … is that …结构
【注意】当主语是 reason 时，表语从句要用 that 引导而不是 because
Eg: The reason why he was late was that he missed the train by one minute this morning
- 同位语从句
同位语从句说明其前面的名词的具体内容。同位语从句通常由 that 引导常见的同位语从句的名词：
advice、demand、doubt、fact、hope、idea、information、message、news、order、problem、promise、question、request、suggestion、truth、wish、word
Eg：The news that we won the game is exciting.我们赢得这场比赛的消息令人激动。I have no idea when he will come back home. 我不知道他什么时候回来。
The thought came to him that Mary had probably fallen ill. 他想到可能玛丽生病了。
【注意】同位语从句和定语从句的区别：
that 引导定语从句:充当句子成分，在从句中作宾语时可以省略
that 引导同位语从句:不充当句子成分，一般不能省略,只起连接作用，没有实际意义。比较下面两个例句:
- I had no idea that you were here．（that 引导同位语从句，不能省略）
- Have you got the idea（that）this book gives you of life in ancient Greece？（that 引导定语从句，作宾语， 可以省略）
