名詞性從句是在句子中起名詞作用的主謂結(jié)構(gòu)，它可以在主從復(fù)合句中作主語、賓語、表語、介詞的賓語以及同位語。
1. 主語從句來源：www.examda.com
主語從句可以由連詞that，wh-疑問詞或名詞性關(guān)系詞引導(dǎo)。
⑴由連詞that引導(dǎo)：從句可以位于句首，但常常用形式主語it替代，從句本身則放在主句后面，如：
That he will come to the party is certain. It happened that the harvest was bad that year. Is it true that she has never been there？
通常在口語或非正式文體中，that?？墒÷?，但必須是在用先行詞it的情況下，如：
It‘s a pity （that） you are leaving.
⑵由wh-疑問詞引導(dǎo)：從句既可以前置，又可以借助于先行詞it后置。如：
Who cleaned the meeting room is unknown. It‘s still a question when we shall have our sports meet. It is uncertain whether he will come.注意：在疑問句中，wh-疑問詞所引導(dǎo)的從句不能位于句首，如：
Is it known where she went？
⑶主語從句也可由名詞性關(guān)系詞引導(dǎo)，這類從句只能位于句首，如：
Where she went was Los Angeles. What will be，will be. Whomever you invite will be welcome.
2. 賓語從句來源：www.examda.com
⑴賓語從句可用that引導(dǎo)，這時(shí)that僅起連接作用，不充當(dāng)從句中的成分。如果連接詞要在從句中起語法作用，就要使用連接詞what等來引導(dǎo)從句。
I believe that he is honest. We fully understood what he meant.
⑵有些形容詞的后面也可跟賓語從句。這類形容詞有：certain，afraid，aware，sorry，sure，worried等。如：
I‘m afraid that you are wrong on this point. I am aware that you have been exceptionally kind to me.
⑶賓語從句也可以用how，when，who，which，where，why等詞引出，此時(shí)即使主句是一個(gè)疑問句，賓語從句也必須保持陳述句的語序。如：
Go and ask why he was late yesterday. Can you tell me where the hospital is？
⑷跟在介詞后面的賓語從句一般不能由that來引出，只限于except，in，but，besides，save等五個(gè)介詞的賓語從句，其它介詞后面不能跟由that引出的賓語從句，而只能跟由what，how，whether等引出的賓語從句。
You are wrong in that you took effect for cause. I would go with you，except that I have to work that day. They were arguing about what was to be done. I‘m thinking of whom I should ask for help.
3. 表語從句來源：www.examda.com
表語從句通常由that引出，當(dāng)然how，why，where，when等也可以引出表語從句。常見的表語從句有下面兩種句型：
⑴“The reason…that”：表示“原因是……”。如：
The reason for leaving was that it was too cold.
⑵“It （This，That） is because…”：表示“這是因?yàn)椤?，“這是由于……緣故”。如：
This is because iron contains more carbon than steel.
4. 同位語從句來源：www.examda.com
同位語從句表示與之同位的名詞中心詞的實(shí)際內(nèi)容。
⑴同位語從句起進(jìn)一步解釋說明先行詞的作用，通常由that引導(dǎo)。同位語從句的先行詞通常是一些抽象名詞，如：appeal，idea，truth，fact，theory，belief，plan，hope，proposal，rumor，suggestion等。
There is truth in the old saying that necessity is the mother of invention.
⑵由wh-疑問詞引導(dǎo)，如：
I have no idea when he will come. It is difficult to answer your question why I did it.
⑶由名詞性關(guān)系詞引導(dǎo)，如：
Fame and fortune—what others sought after with zest—was all rubbish to him.
⑷注意同位語和that引導(dǎo)的定語從句的區(qū)別：that在同位語從句中只起引導(dǎo)從句的作用，本身并無意義，也不在句子中擔(dān)當(dāng)任何成分；而定語從句的that既引導(dǎo)從句又充當(dāng)句子成分。
The news that he intended to come gave us much pleasure.（同位語從句，that不作句子分。）
He is the best speaker that addressed the meeting.（定語從句，that在從句中作賓語，指代的先行詞是主句中的主語。）
1. 主語從句來源：www.examda.com
主語從句可以由連詞that，wh-疑問詞或名詞性關(guān)系詞引導(dǎo)。
⑴由連詞that引導(dǎo)：從句可以位于句首，但常常用形式主語it替代，從句本身則放在主句后面，如：
That he will come to the party is certain. It happened that the harvest was bad that year. Is it true that she has never been there？
通常在口語或非正式文體中，that?？墒÷?，但必須是在用先行詞it的情況下，如：
It‘s a pity （that） you are leaving.
⑵由wh-疑問詞引導(dǎo)：從句既可以前置，又可以借助于先行詞it后置。如：
Who cleaned the meeting room is unknown. It‘s still a question when we shall have our sports meet. It is uncertain whether he will come.注意：在疑問句中，wh-疑問詞所引導(dǎo)的從句不能位于句首，如：
Is it known where she went？
⑶主語從句也可由名詞性關(guān)系詞引導(dǎo)，這類從句只能位于句首，如：
Where she went was Los Angeles. What will be，will be. Whomever you invite will be welcome.
2. 賓語從句來源：www.examda.com
⑴賓語從句可用that引導(dǎo)，這時(shí)that僅起連接作用，不充當(dāng)從句中的成分。如果連接詞要在從句中起語法作用，就要使用連接詞what等來引導(dǎo)從句。
I believe that he is honest. We fully understood what he meant.
⑵有些形容詞的后面也可跟賓語從句。這類形容詞有：certain，afraid，aware，sorry，sure，worried等。如：
I‘m afraid that you are wrong on this point. I am aware that you have been exceptionally kind to me.
⑶賓語從句也可以用how，when，who，which，where，why等詞引出，此時(shí)即使主句是一個(gè)疑問句，賓語從句也必須保持陳述句的語序。如：
Go and ask why he was late yesterday. Can you tell me where the hospital is？
⑷跟在介詞后面的賓語從句一般不能由that來引出，只限于except，in，but，besides，save等五個(gè)介詞的賓語從句，其它介詞后面不能跟由that引出的賓語從句，而只能跟由what，how，whether等引出的賓語從句。
You are wrong in that you took effect for cause. I would go with you，except that I have to work that day. They were arguing about what was to be done. I‘m thinking of whom I should ask for help.
3. 表語從句來源：www.examda.com
表語從句通常由that引出，當(dāng)然how，why，where，when等也可以引出表語從句。常見的表語從句有下面兩種句型：
⑴“The reason…that”：表示“原因是……”。如：
The reason for leaving was that it was too cold.
⑵“It （This，That） is because…”：表示“這是因?yàn)椤?，“這是由于……緣故”。如：
This is because iron contains more carbon than steel.
4. 同位語從句來源：www.examda.com
同位語從句表示與之同位的名詞中心詞的實(shí)際內(nèi)容。
⑴同位語從句起進(jìn)一步解釋說明先行詞的作用，通常由that引導(dǎo)。同位語從句的先行詞通常是一些抽象名詞，如：appeal，idea，truth，fact，theory，belief，plan，hope，proposal，rumor，suggestion等。
There is truth in the old saying that necessity is the mother of invention.
⑵由wh-疑問詞引導(dǎo)，如：
I have no idea when he will come. It is difficult to answer your question why I did it.
⑶由名詞性關(guān)系詞引導(dǎo)，如：
Fame and fortune—what others sought after with zest—was all rubbish to him.
⑷注意同位語和that引導(dǎo)的定語從句的區(qū)別：that在同位語從句中只起引導(dǎo)從句的作用，本身并無意義，也不在句子中擔(dān)當(dāng)任何成分；而定語從句的that既引導(dǎo)從句又充當(dāng)句子成分。
The news that he intended to come gave us much pleasure.（同位語從句，that不作句子分。）
He is the best speaker that addressed the meeting.（定語從句，that在從句中作賓語，指代的先行詞是主句中的主語。）