在句子中起名詞作用的句子叫名詞從句 (Noun Clauses）
名詞從句的功能相當於名詞詞組, 它在復合句中能擔任主語、賓語、表語、同位語等，因此根據它在句中不同的語法功能，名詞從句又可分別稱為主語從句、賓語從句、表語從句和同位語從句
壹主語從句 二表語從句 三賓語從句
四定語從句 五同位語從句 六狀語從句
壹主語從句：在主句種充當主語成分的從句叫主語從句，
引導主語從句的連詞有：從屬連詞；連接代詞；連接副詞
A 從屬連詞：that，whether。
從屬連詞；that，whether引導的主語從句在主語從句中不充當任何成分,只起連接詞的作用，通常不可以省略。分句置於句首時，that絕對不可以省略。如果是由It作形式主語，後面that可以省略.
1,有that 引導的主語從句如下：
1. That the driver could not control hiswar was obvious.
=It was obvious（that）the driver could notcontrol his car.
2. Thatshe was chosen made us very happy.
=it made us very happy that she was chosen
3. Thathe is still alive is sheer luck.他還活著全靠運氣。
=It issheer luck that she is still alive
4. Thatthe whole project is doomed to failure is quite clear
=It isquite clear that the whole project is doomed to failure.
很清楚，整個計劃註定要失敗。
5. Thatyou should have to leave is a pity
=It's apity that you should have to leave.
妳非走不可真是件憾事。
6. That he will refuse this piece of advice isimpossible.
=It is impossible that he will refuse this piece ofadvice
7. That they should like each other is natural
=It is natural that they should like each other
8. Thathe will not come to the meeting this evening is true
=It istrue that he will not come to the meeting this evening
9. Thathe will help others is a fact
10. That theearth turns around the sun is known to all.
=It is known to all that the earth turnsaround the sun.
11. That we can win is certain
=It is certain that we can win.
12. That you have made a mistake is a fact.
=It is a fact that you have made a mistake
13. It is ordered that we should leave at once.
14. That you don’t like him is none of my business.
用it作形式主語的that-從句有以下四種不同的搭配關系：
a. It +be +形容詞+ that-從句
It isnecessary that… 有必要……
It is important that… 重要的是……
It is obvious that… 很明顯……
It’s certain that… 肯定…
It is possible that... 很可能……
It is unlikely that... 不可能……
It is necessary \important \natural\... that…
It is possible that she will come back tomorrow.
It is obvious that this measure is effective.
b. It +be +V ed 分詞+ that-從句
It is known to all that… 從所周知……
It has been decided that… 已決定……
It is said that... 據說……
It is known to all that... 眾所周知……
It is reported that... 據報道……
It is believed that...據信……;人們相信……
It is suggested that + (should）do... 建議……
It must be admitted that…必須承認……
It cannot be denied that… 不可否認……
It must be pointed out that…需指出的是……
It was reported that 20 people were killed in the accident.
It was suggested that we shouldeat more vegetable and do more exercise
c. It + be +名詞+ that-從句
It is a pity/shame that... 遺憾的是……
It is a surprise that…令人驚奇的是…
It is common knowledge that… …是常識
It is common knowledge that… 是常識
It is a fact that… 事實是……
It was a pity that we lost the match.
It was a fact that he cheated in the exam.
d. It +不及物動詞+ that-分句
It appears that…似乎……
It happens that…碰巧……
It occurred to me that…我突然想起……
It occurred to methat I forgot to send this letter
It happened that I came into the office at that time.
It is important(necessary / advisable /desirable / imperative / true / strange / possible ...)that ...需要註意的是,這類主語從句中,謂語動詞很多為"(should)＋動詞原形",即要用虛擬語氣。例如:
It isnecessary that several nurses (should) stay.
幾個護士留在這兒是很有必要的。
It isimperative that everyone (should) learn from practice.
每個人都應該從實踐中學習。
It isreported (well-known / hoped / thought / expected / said / believed / decided /suggested / ordered ...)that ...例如:
It issaid that many people was killed in the earthquake.
據說很多人在這次地震中喪生了。
itseems(appears / doesn’t matter / makes no difference / ...)that ...
例如:
It makesno difference whether he will attend the meeting or not.
他是否會參加會議都無關緊要。
二表語從句 ：表語從句的定義：表語從句在復合句中作主句的表語。表語從句和主語指同壹內容，它對主語進行解釋、說明，使主語的內容具體化。
表語是用來說明主語的身份、性質、品性、特征和狀態的，表語常由名詞、代詞、數詞、動詞過去分詞、動詞的-ing形式、副詞、介詞短語、形容詞、不定式和從句等來充當。
Lyne is anexcellent student
Henry was anAmerican businessman
Henry met anAmerican businessman
The person stood in front of you just now is myheadmaster.
I didn’t know that it was you at that time.
The door remained closed.
Mary’s daily job is cleaning the house.
The house is not only large but also beautiful.
When I went to your house, you were out.
No one was in the dorm, when she arrived.
My job is to teach you English.
The reason why he came late was that his clockdidn’t work.
Position (位置)表語常位於系動詞（be等詞）之後，與主語***同構成主--系--表結構(Subject-Predicative structure) 的句子。
Linking Verbs (連系動詞)
除動詞be以外，還有壹些後面可接表語的特殊連系動詞，如：look, smell,taste, sound, feel, fall, come, go（變成…）, become, grow（漸漸地變化）, turn(變成，壹般用於顏色), appear, seem,get, keep, remain, stay等。
壹、表語從句定義：表語從句的定義：表語從句在復合句中作主句的表語。表語從句和主語指同壹內容，它對主語進行解釋、說明，使主語的內容具體化。
The question is who will do it.
表語從句放在連系動詞之後，充當復合句中的表語。
二、表語從句構成
（系動詞） +引導詞 +簡單句
His suggestion is that we should stay calm
That is why she was late.
三、引導表語從句的關聯詞
1從屬連詞that，whether；that 在表語從句中不充當任何句子成分，也沒有任何意義。
The trouble is that I have lost her address.
麻煩是我把她的地址弄丟了。
My question is whether he left ( or not ).
我的問題是他是否離開了。
The question is whether we should ask them for help.
The trouble is that he has never done the work before
The fact is that he hasn’t yetrecover from illness.
The reason why he has to go is thathis mother is ill in bed.
比較 that在定語從句中的用法。
Thereare some films thatI’d like to see.
She isthe only student thatknows French.
結論:that 在引導定語從句時,指事物,也可指人,
在從句中作主語或賓語,作賓語時常可省略。
2.從屬連詞as, as if / though引導的表語從句
由as if 引導表語從句時要註意語態.若從句表示與現在事實相反,謂動用be 動詞要用were
與過去事實相反用 had +過去分詞
Li Lei is now ina new jacket.
He looks as if he were an American boy.
The girl isgiving us a vivid description of the moon.
It seems as ifshe had been to the moon many times.
He looked just ashe had looked ten years before.
It sounds as ifsomeone is knocking at the door.
It looks as if it were going to rain.
whether在表語從句中表是否 ,但不充當句子的成分。if 不能引導表語從句.如:
What the doctor really doubts is whether my mother will recover fromthe serious disease soon
3because, why 引導的表語從句
(1) That’sbecause he didn’t understand me.
那是因為他不理解我。(強調原因）
(2) That’s why hegot angry with me
那正是他對我生氣的原因。（強調結果）
4.連接代詞who, whom, whose, whoever, what,
whatever, which,whichever 引導表語從句
(1) The problemis who we can get to replace her.
問題是我們能找到誰去替換她呢。
Guilin is not whatit used to be.
What she wants to know is whichdress she should buy.
The question is what caused the accident.
That mountain is not what itused to be .
What he told you was what had been discussed at the meeting.
4連接副詞where, when, how
The question ishow he did it.問題是他如何做此事的。
That is where he was born. 那就是他出生的地方
That is whereLu Xun used to live.
That is whyhe didn’t pass the exam.
四. 使用虛擬語氣的表語從句(if不可以引導表語從句)
在表示建議、勸告、命令含義的名詞後的表語從句，謂語動詞需用"should+動詞原形" 表示，should可省略。常見的詞有：advice, suggestion, order, proposal, plan等。
My suggestion isthat we (should) start early tomorrow.
The question iswhether we will have our sports meet next week.
The reason why hefailed is that he was too careless.
The problem iswho we can get to take the place of John.
The question iswhen he can arrive at the hotel.
The question iswhether the enemy is marching towards us.
It looked as ifhe had understood this question.
The question iswho will travel with me to Beijingtomorrow.
The question iswhy he cried yesterday.
註意點1：if 不能引導表語從句
註意點2：主句主語為reason, 只能用that引導表語從句，不可用because.
註意點3：如果從句是特殊疑問句，用陳述句語序
A：表語從句壹定要用陳述語序
B 不可以用if，而用whether 連接表語從句(as if 例外）。
C 不像賓語從句，在有表語從句的復合句中，主句時態和從句時態可以不壹致。
三賓語從句：賓語從句在主從復合句中起賓語的作用，是壹種名詞性從句，既可作謂語動詞的賓語，也可作介詞、非謂語動詞（動詞不定式、動名詞、分詞.形容詞）的賓語根據引導賓語從句的不同連詞，賓語從句可分為三類。
1. 由that引導的賓語從句。that只有語法作用，沒有實在的意義，在口語
和非正式文體中可以省略。例如：
He said (that) he wanted to stay athome.
She doesn’t know (that) she isseriously ill.
I am sure (that) he will succeed.
2. 由連接代詞who, whom, whose, what, which和連接副詞when, where, why, how引導的賓語從句。這些連接代詞和連接副詞在賓語從句中充當某個成分。例如：
Do you know who (whom) they are waitingfoe?
He asked whose handwriting was thebest.
Can you tell me where the No.3 bus stopis?
I don’t know why the train is late.
3. 由if或whether引導的賓語從句。if和whether在句中的意思是“是否”。例如：
I want to know if (whether) he livesthere.
He asked me whether (if) I could helphim.
（二）賓語從句的語序
賓語從句的語序應為陳述句的語序。例如：
I hear (that) physics isn’t easy.
I think (that) you will like thisschool soon.
Can you tell me how I can get to zoo?
Please tell me when we’ll have themeeting.
（三）賓語從句的時態
1. 如果主句的時態是壹般現在時，賓語從句該用什麼時態就用什麼時態。
如： I don’t think (that) you are right.
Please tell us where he is.
Can you tell me how I can get to therailway station?
2. 如果主句的時態是壹般過去時，賓語從句只能用相應的過去時態（壹般過去時， 過去進行時， 過去將來時，過去完成時）。例如：
He asked what time it was.
He told me that he was preparing forthe sports meet.
He asked if you had written to Peter.
He said that he would go back to the U.S.soon.
3. 如果賓語從句所陳述的是客觀真理，其時態常用壹般現在時。例如：
Our teacher said that January is thefirst month of the year.
Scientists have proved that the earthturns around the sun.
4.當主句謂語動詞是think、believe、imagine等時，後面的賓語從句要表示否定意義時，要通過主句的否定式來實現，即否定主句中的動詞。 e.g. 我認為他明天不會來。
（wrong）I think he willnot come tomorrow.
（right）I don’t think hewill come tomorrow.
某些形容詞後面也可有賓語從句,這些形容詞有:sure、certain、glad、pleased、happy、afraid、surprised、satisfied等。 e.g. I’m sure you can learn English well.
希望能解決您的問題。