名詞性從句在復(fù)合句中的作用相當(dāng)于名詞，可作主語、賓語、表語和同位語。因此，名詞性從句可分為主語從句、賓語從句、表語從句和同位語從句。

1、主語從句

主語從句在復(fù)合句中作句子的主語。引導(dǎo)主語從句的詞有連詞that, whether；連接代詞who, which, what, whoever, whichever, whatever等；連接副詞when, where, why, how, how much, how many, how far等。

1. 連詞that在主語從句中不作任何成分，只起連接作用，無意義，不能省略。

2. 連詞whether在主語從句中不作任何成分，只起連接作用，意為“是否”。

3. 連接代詞who, which, what, whoever, whichever, whatever等在主語從句中常作主語、賓語、表語，起連接作用，有意義。what在主語從句中可作主語、賓語、表語或補(bǔ)足語。

4. 連接副詞when, where, why, how, how much, how many, how far等引導(dǎo)主語從句時(shí)，常作時(shí)間、地點(diǎn)、原因、方式等狀語，起連接作用，有意義。

5. 當(dāng)主語從句太長，為了平衡句子結(jié)構(gòu)，常用it作形式主語放在句首，而將that引導(dǎo)的主語從句放在句子的末尾。此類常見的句型結(jié)構(gòu)有：

1) it+be+形容詞+that從句：It’s strange that she knows nothing about it.

2) it+be+名詞+that從句：It’s a wonder that he is still alive.

3) it+be動詞+that從句：Is it that the gentleman is not your uncle?

4) it+動詞(+賓語/狀語)+that從句：It never occurred to me that perhaps she was lying.

5) it+動詞的被動語態(tài)+that從句：It’s said that there has been an earthquake in Japan.

在口語中that有時(shí)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作形式主語放在句首，而將從屬連詞、連接代/副詞引導(dǎo)的主語從句放在句子的末尾的常見句型結(jié)構(gòu)有：

1) it+be+形容詞+從句：It’s uncertain whether the game will be held.

2) it+be+名詞+從句：It’s a puzzle how life began.

3) it+動詞(+賓語/狀語)+從句：It doesn’t matter much where we live.

4) it+動詞的被動語態(tài)+從句：It is not decided who will perform it.

2、賓語從句

在復(fù)合句中作句子的賓語的從句被稱為賓語從句。引導(dǎo)賓語從句的詞有連詞that, whether, if；連接代詞who, whose, what, which, whoever, whatever, whichever等；連接副詞when, where, why, how等。

1. 如果賓語從句后還有賓語補(bǔ)足語，則用it作形式賓語，而將賓語從句后置，該賓語從句可用任何詞引導(dǎo)。常用的句型有：

1) ...make it possible/easy/difficult... that... 使……可能/容易/難……

2) ...find/feel/think it necessary/important... that... 發(fā)覺/認(rèn)為……必要/重要

3) ...make it clear that... 說清楚……

4) ...make it a rule that... 使……成為習(xí)慣……

5) ...take it for granted that... 認(rèn)為……是理所當(dāng)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... 務(wù)必……，一定注意到……

2. 賓語從句的否定轉(zhuǎn)移：當(dāng)主句謂語動詞是think, believe, imagine, suppose, expect等，且主語是第一人稱I/we時(shí)，習(xí)慣上將否定詞not轉(zhuǎn)移到主句中，形式上否定主句謂語，而實(shí)際上否定的是從句謂語。

3、表語從句

在復(fù)合句中作句子的表語的從句被稱為表語從句。引導(dǎo)表語從句的詞有連詞that, whether, as if；連接代詞who, which, what, whoever, whatever, whichever等；連接副詞when, where, why, how等。

1. 表語從句要用陳述語序。例如：The question is when he can arrive at the hotel.

2. 在有表語從句的復(fù)合句中，主句時(shí)態(tài)和從句時(shí)態(tài)可以不一致。例如：The question is who will travel with me to Beijing tomorrow.

3. 連詞that在表語從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、同位語從句

在主從復(fù)合句中，用作同位語的從句，稱為同位語從句。它一般跟在某些名詞的后面，用以說明或解釋前面的名詞，引導(dǎo)同位語從句的詞有連詞that, whether；連接代詞what, who；連接副詞when, where, why, how...等都引導(dǎo)同位語從句。

1. 連詞that引導(dǎo)同位語從句時(shí)，從句為一個(gè)句意完整的陳述句。that不能省略，沒有具體的意思，不充當(dāng)任何句子成分，只起連接作用。

2. 用連詞that引導(dǎo)的同位語從句解釋或說明的名詞有：fact, news, belief, doubt, hope, idea, conclusion, message, proof, feeling, possibility, thought, promise, impression, report, opinion, order等。

3. 同位語從句有時(shí)和前面的名詞分開。例如：The story goes that he often beats his children.