名词性从句在复合句中的作用相当于名词，可作主语、宾语、表语和同位语。因此，名词性从句可分为主语从句、宾语从句、表语从句和同位语从句。
1、主语从句主语从句在复合句中作句子的主语。引导主语从句的词有连词that, whether；连接代词who, which, what, whoever, whichever, whatever等；连接副词when, where, why, how, how much, how many, how far等。
1. 连词that在主语从句中不作任何成分，只起连接作用，无意义，不能省略。
2. 连词whether在主语从句中不作任何成分，只起连接作用，意为“是否”。
3. 连接代词who, which, what, whoever, whichever, whatever等在主语从句中常作主语、宾语、表语，起连接作用，有意义。what在主语从句中可作主语、宾语、表语或补足语。
4. 连接副词when, where, why, how, how much, how many, how far等引导主语从句时，常作时间、地点、原因、方式等状语，起连接作用，有意义。
5. 当主语从句太长，为了平衡句子结构，常用it作形式主语放在句首，而将that引导的主语从句放在句子的末尾。此类常见的句型结构有：
1) it be 形容词 that从句：It’s strange that she knows nothing about it.
2) it be 名词 that从句：It’s a wonder that he is still alive.
3) it be动词 that从句：Is it that the gentleman is not your uncle?
4) it 动词( 宾语/状语) that从句：It never occurred to me that perhaps she was lying.
5) it 动词的被动语态 that从句：It’s said that there has been an earthquake in Japan.
在口语中that有时可以省略：
It was clear her words pleased him.
It’s not our fault this has happened.
It strikes me Jack is a good boy.
6. 用it作形式主语放在句首，而将从属连词、连接代/副词引导的主语从句放在句子的末尾的常见句型结构有：
1) it be 形容词 从句：It’s uncertain whether the game will be held.
2) it be 名词 从句：It’s a puzzle how life began.
3) it 动词( 宾语/状语) 从句：It doesn’t matter much where we live.
4) it 动词的被动语态 从句：It is not decided who will perform it.
2、宾语从句在复合句中作句子的宾语的从句被称为宾语从句。引导宾语从句的词有连词that, whether, if；连接代词who, whose, what, which, whoever, whatever, whichever等；连接副词when, where, why, how等。
1. 如果宾语从句后还有宾语补足语，则用it作形式宾语，而将宾语从句后置，该宾语从句可用任何词引导。常用的句型有：
1) ...make it possible/easy/difficult... that... 使……可能/容易/难……
2) ...find/feel/think it necessary/important... that... 发觉/认为……必要/重要
3) ...make it clear that... 说清楚……
4) ...make it a rule that... 使……成为习惯……
5) ...take it for granted that... 认为……是理所当然的
6) ...bring it to one’s attention that... 使……被某人注意到，使某人注意到……
7) ...see to it that... 务必……，一定注意到……
2. 宾语从句的否定转移：当主句谓语动词是think, believe, imagine, suppose, expect等，且主语是第一人称I/we时，习惯上将否定词not转移到主句中，形式上否定主句谓语，而实际上否定的是从句谓语。
3、表语从句在复合句中作句子的表语的从句被称为表语从句。引导表语从句的词有连词that, whether, as if；连接代词who, which, what, whoever, whatever, whichever等；连接副词when, where, why, how等。
1. 表语从句要用陈述语序。例如：The question is when he can arrive at the hotel.
2. 在有表语从句的复合句中，主句时态和从句时态可以不一致。例如：The question is who will travel with me to Beijing tomorrow.
3. 连词that在表语从句中一般不可以省掉。例如：What I told him was that I would find him a good play.
4、同位语从句在主从复合句中，用作同位语的从句，称为同位语从句。它一般跟在某些名词的后面，用以说明或解释前面的名词，引导同位语从句的词有连词that, whether；连接代词what, who；连接副词when, where, why, how...等都引导同位语从句。
1. 连词that引导同位语从句时，从句为一个句意完整的陈述句。that不能省略，没有具体的意思，不充当任何句子成分，只起连接作用。
2. 用连词that引导的同位语从句解释或说明的名词有：fact, news, belief, doubt, hope, idea, conclusion, message, proof, feeling, possibility, thought, promise, impression, report, opinion, order等。
3. 同位语从句有时和前面的名词分开。例如：The story goes that he often beats his children.
