名詞性從句相當(dāng)于名詞，一個(gè)從句在整個(gè)句子中充當(dāng)名詞的作用，它可以作為主句的主語、表語、賓語和同位語。
名詞性從句主要分為四種：主語從句，表語從句，賓語從句，同位語從句。
1. Who will win the match is unknown.
2. I want to know what he has told you.
3. The fact is that he had won the game.
4. The news that we won the game is exciting.
賓語從句在復(fù)合句中做及物動(dòng)詞的賓語，或用作介詞和某些表示心理活動(dòng)的形容詞后作賓語，或是用it 作為形式賓語代表賓語從句。
例:1. I think that it will be of no use.
2. It depends on whether the boss will agree to you or not.
賓語從句的連接詞：
that,（常用且一般可省略）who, what, whether/if（是否）which, whoever, whatever ，when, where, how, why.
(連接詞的選擇要看從句的具體意思需要)
例：1. I know that you are a teacher.
2. I wonder if/ whether you are Mr Li.
3. Do you know what I will do next?
4. I can guess which team will win.
5. I don’t know when he will come.
6. I don’t know where he has gone.
7. They don’t know how they should help me.
8. Please give the book to whoever likes it.
Attention:
①★賓語從句的語序一定是正常的語序，即陳述句的語序，先主語后謂語。
I don’t know who are you. (X)
I don’t know who you are. (∨)
②★從句的時(shí)態(tài)需跟主句相配合。主句為一般現(xiàn)在時(shí)，從句可根據(jù)需要選擇各種時(shí)態(tài)；
主句為一般過去時(shí)時(shí)，從句通常用過去的時(shí)態(tài)。
③★介詞后的賓語從句，引導(dǎo)詞一般不用which，if，that，但可用what（常用， 常常是充當(dāng)從句的主語，賓語或表語），how, whether等引導(dǎo)。
④★that在所有的名詞性從句中都不充當(dāng)成分，在賓語從句中that可以省略。
1.Whose watch was lost is unknown.
2.What we need is time.
3.Whom we must study for is a question of great importance.
4.Whether we will go for an outing remains unknown.
5.That he finished writing the composition surprised us all.
1.主語從句的連接詞：
1）從屬連詞（從句中不充當(dāng)成分，只起連接作用）：that，whether等.
that 引導(dǎo)主語從句只起引導(dǎo)作用，本身無意義，在主語從句中不充當(dāng)任何成分，但不能省略。注意: 已確定的事由that引導(dǎo);沒決定的事由whether引導(dǎo).
That he will come is certain.
Whether it will please them is not easy to say.
2)連接代詞（在從句中充當(dāng)主語，賓語，或表語）who ，what ，which, whatever, whichever, whoever
What seems easy to some people seems difficult to others.
Which side will win is not clear.
Whoever comes is welcome.
Whatever I have is yours.
3)連接副詞 when（從句中作時(shí)間狀語） where （從句中作地點(diǎn)狀語）
how （從句中作方式狀語） why（從句中作原因狀語）
Why he did it remains a mystery.
When they will start is not known yet.
How he became a great scientist is known to us all.
2. 主語從句后置!
為了避免主語冗長(zhǎng),句子頭重腳輕,經(jīng)常用it作形式主語,主語從句放在后面作真正的主語.
如： 1）. That we shall be late is certain.
-- It’s certain that we shall be late.
2）. That the earth is round is known to all.
-- It’s known to all that the earth is round.
用it作形式主語的that從句有以下幾種不同的搭配：
1.It + be + 形容詞 ＋ that從句
2.It + be + -ed分詞 ＋ that從句
3. 主語從句需注意的問題
1）.“if” 通常不能引導(dǎo)主語從句，要用“whether”引導(dǎo)。
2）.主語從句中用陳述句語序
3）.主語從句的 “that” 一般不能省。That price will go up is certain.
4）.主語從句后謂語動(dòng)詞用第三人稱單數(shù)
That they haven’t phoned is strange.
5）.主語從句在句首時(shí)，必須由連接詞引導(dǎo)，不能省略這些連接詞；但是如果用it做形式主語，而把主語從句放在句末時(shí)，從屬連詞that可以省略。
6）.如果主語從句放在句首，不能用if引導(dǎo)，但是如果用it 做形式主語，而把主語從句放在句末時(shí)，也可以用if引導(dǎo).
誤：If Mary really heard him is really doubtful.
正：It was doubtful if Mary really heard him.
7）.用于It is important / natural / necessary /
impossible that...句型中, 主語從句謂語動(dòng)詞用“（should） + 動(dòng)詞原形”的形式, should可以省略。
例： It is imporant we (should) believe him.
8）. 在it + be + suggested/ advised/ required/ ordered/ requested/ insisted that…句型中
從句謂語動(dòng)詞也用“（should） + 動(dòng)詞原形”的形式.
例： It is suggested that we (should) go there by bus.
9）. what 與that 在引導(dǎo)主語從句時(shí)的區(qū)別
what 引導(dǎo)主語從句時(shí)在句時(shí)在從句中充當(dāng)句子成分，如主語．賓語．表語，而that 則不然。例如：
A： What you said yesterday is right.
What在此引導(dǎo)主語從句,又做said的賓語
B： That she is still alive is a consolation。
That 只起連接作用,不做成分
1.定義：放在be動(dòng)詞和系動(dòng)詞后的從句。
The question is who will do it.
2.可接表語從句的連系動(dòng)詞有be（is, am, are, was, were）, look, seem, sound, appear，remain, become, get等。
China is no longer what she used to be.
The question remains whether they will be able to help us.
At that time, it seemed as if I couldn't think of the right word.
3.表語從句的引導(dǎo)詞
1）. 從屬連詞whether, as, as if / though引導(dǎo)的表語從句.if不能引導(dǎo)表語從句。
He looked just as he had looked ten years before.
It sounds as if someone is knocking at the door.
2）. because, why引導(dǎo)的表語從句
That’s because he didn’t understand me.
That’s why he got angry with me.
The reason why I was sad was that he didn't understand me. （…的原因是…）
3）. 連接代詞who, whom, whose, what, which, whoever, whatever, whichever連接副詞 where, when, how, why
The problem is whom we can get to replace her.
The question is how he did it.
That was what she did this morning on reaching the classroom.
This is where our problem lies.
4）. 從屬連詞that。that在表語從句中不充當(dāng)句子成分，沒有任何意義, 也不能省略。
The trouble is that I have lost his address.
4、使用虛擬語氣的表語從句
在表示“意愿，建議、勸告、命令”含義的名詞后的表語從句，謂語動(dòng)詞需用“should+動(dòng)詞原形” should可省略。
常見的這些名詞有：advice, suggestion, order, proposal, plan, idea等。
My suggestion is that we (should) start early tomorrow.
5、表語從句的應(yīng)注意的問題：
1）. That在表語從句中既不充當(dāng)成分，也沒有任何意義
The fact is that he hasn’t yet recover from illness.
2）. What 在表語從句中充當(dāng)主語、賓語/表語表示什么，什么樣子，/所……
的（人或事）.
A. The question is what caused the accident.
B. That mountain is no longer what it used to be
3）. Which 在引導(dǎo)表語從句時(shí),常充當(dāng)定語, 表語表示其中哪一個(gè)
I read about it in some book or another,but what I don’t know is which (book) it is.
4）. whether在表語從句中表“是否”,不充當(dāng)句子的成分。if 不能引導(dǎo)表語從句。
What the doctor really doubts is whether my mother will recover from the serious disease soon.
5）. 當(dāng)主句的主語為reason,或者是由why引導(dǎo)的從句時(shí),與它們相關(guān)的表語從句用
that來引導(dǎo)，而不能由because引導(dǎo); because 引導(dǎo)表語從句時(shí)只能用于It/That/This is /was because…那是因?yàn)椤?/p>
It/That/This is /was why…那就是為什么…
The reason ( why…) is/was that.. …的原因是…
1. 定義：同位語從句就是在復(fù)合句中作名詞的同位語的名詞性從句。
2.同位語從句的功能
同位語從句對(duì)名詞進(jìn)一步解釋，說明名詞的具體內(nèi)容，這些名詞一般是抽象名詞，常用名詞有fact, news, hope, truth, idea, suggestion, thought, question, order, problem, belief, doubt, fear, result, information, opinion, demand, wish，promise, possibility, message,等.
常用引導(dǎo)詞：that （常用不可省略）, who, when, where, why, how, whether等。
3.同位語從句的引導(dǎo)詞
1）. 由that引導(dǎo)，在從句中不充當(dāng)任何成分，只起引導(dǎo)作用，不可省略，也不能用which代替。如：
The fact that you have passed the exam is true.
1）don’t know (that) you have passed the exam.
2）.由whether 引導(dǎo)，“是否”，
注意：同位語從句中表示“是否” 的意思時(shí)，不能用if。
如：The problem whether we should visit her has been settled.(不能用if)
3）.由who, when, where, how 等引導(dǎo)
如：①I have no idea who will go with me.
② We haven’t solved the problem how we should go there.
③ We haven’t solved the problem where we are going to spend the weekend.
④we have no idea when we will begin our holiday.
1、兩種從句都可以譯成定語
2、兩種從句都可以用that引導(dǎo)
The news that our team has won the final match is encouraging.(同位語從句)
我們隊(duì)取得決賽勝利的消息令人鼓舞。
The news that you told us is really encouraging.(定語從句)
你告訴我們的消息真的令人鼓舞。
1、從句的作用不同：同位語從句用來進(jìn)一步說明前面名詞的內(nèi)容；定語從句用來修飾、限定前面的名詞。
The news that our team has won the final match is encouraging. （從句說明“消息”的內(nèi)容：我們隊(duì)取得了決賽勝利。）
The news that you told us is really encouraging.
（從句對(duì)“消息”加以限定：是你告訴我們的, 而非來自其他渠道。但消息是什么卻不得而知。）
2. 引導(dǎo)從句的關(guān)聯(lián)詞that的功能不同:
①在that引導(dǎo)同位語從句中，從句是個(gè)完整的句子, that只是一個(gè)連接詞, 不充當(dāng)任何成分; that不能省略，不能用which代替。
Dad made a promise that he would buy me CD player. (that 不充當(dāng)任何成分)
②在that引的定語從句中，從句不完整，缺少主語或賓語that是關(guān)系代詞, 既指代先行詞又在從句中充當(dāng)主語或賓語，充當(dāng)賓語時(shí)可以省略，可換成which.
Dad made a promise that excited all his children. (that指代promise, 又在從句中充當(dāng)主語.)
③定語從句不可用what, how, whether, 來引導(dǎo)，而同位語從句的關(guān)連詞除了that 外，還可根據(jù)詞義使用其它疑問代詞或疑問副詞，如who, when, where, how, whether等。
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