在句子中起名詞作用的句子叫名詞性從句 (Noun Clauses）。 名詞性從句的功能相當於名詞詞組, 它在複合句中能擔任主語、賓語、表語、同位語、介詞賓語等，因此根據它在句中不同的語法功能，名詞性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。
一、引導名詞性從句的連接詞
引導名詞性從句的連接詞可分為三類：
連詞：that（無任何詞意）whether,if（均表示“是否”表明從句內容的不確定性）as if ,as though（均表示“好像”，“似乎”）以上在從句中均不充當任何成分
連接代詞：what, whatever, who, whoever, whom,whose, whichever,whomever
連接副詞：when, where, how, why,how many,how much,how often
不可省略的連詞：
1. 介詞後的連詞
2. 引導主語從句和同位語從句的連詞不可省略。
That she was chosen made us very happy. We heard the news that our team had won.
比較：whether與if 均為"是否"的意思。 但在下列情況下，只可用whether：
1. whether引導主語從句並在句首2. 引導表語從句 3. whether從句作介詞賓語4. 從句後有"or not"
Whether he will come is not clear.
大部分連接詞引導的主語從句都可以置於句末，用 it充當形式主語。
It is not important who will go. It is still unknown which team will win the match.
二. 主語從句
1、作句子主語的從句叫主語從句。主語從句通常由從屬連詞that，whether，if和連接代詞what，who，which，whatever，whoever以及連接副詞how，when，where，why等詞引導。that在句中無詞義，只起連接作用；連接代詞和連接副詞在句中既保留自己的疑問含義、又起連接作用，在從句中充當從句的成分。例如：
What he wants to tell us is not clear. 他要跟我們說什麼，還不清楚。
Who will win the match is still unknown. 誰能贏得這場比賽還不得而知。
It is known to us how he became a writer. 我們都知道他是如何成為一名作家的。
Where the English evening will be held has not yet been announced. 英語晚會將在哪裡舉行，還沒有宣佈。
有時為避免句子頭重腳輕，常用形式主語it代替主語從句作形式主語放於句首，而把主語從句置於句末。主語從句後的謂語動詞一般用單數形式。常用句型如下：
（1） It + be + 名詞 + that從句（2）It + be + 形容詞 + that從句（3）It + be + 動詞的過去分詞 + that從句（4）It + 不及物動詞 + that 從句
另注意在主語從句中用來表示驚奇、不相信、惋惜、理應如此等語氣時，謂語動詞要用虛擬語氣“(should) +do”，常用的句型有：It is necessary (important, natural, strange, etc.) that … It is suggested (requested, proposed, desired, etc.) that…
2、第一部分：常規主語從句，即句子在複合句中充當一個主語
主語從句的時態：不受主句的時態影響和限制。
（1）That he finished writing the composition in such a short time surprised us all.
（2）Whether we will go for an outing tomorrow remains unknown.
（3）Who will be our monitor hasn't been decided yet.
（4） Whom we must study for is a question of great importance.
（5）What caused the accident remains unknown.
（6）Whatever you did is right.
（7）Who the watch belongs to was lost is unknown.
（8）What we need is time.
（9）What we need are good doctors.
小結:（1)引導主語從句連詞有that,whether,who,what,whatever等（2)連詞位於句首不能省略（3)主語從句大多數情況下視為三單,但也有例外,如例9
第二部分：為了防止句子頭重腳輕，通常把形式主語it放在主語位置，真正主語擱置於句末
（1）It is certain that he will win the match.
（2）It is true that he has made a very important discovery in chemistry.
（3）It is very likely that they will hold a meeting.
（4）It is strange that he should do that.
（5）It is important that we all should attend the meeting.
（6）It is strange that the man should have stuck to his silly ideas.
（7）It is a pity that we won't be able to go to the south to spend our summer vacation.
（8）It is still a mystery what caused the accident.
（9）It is said that he has gone to shanghai.(=He is said to have gone to shanghai)
（10）It is known to all that the gun powder was first invented by the Chinese.
（11）It is suggested that the work should be done with great care.
（12）It seems that he has seen the film.(=He seems to have seen the film)
（13）It happened that the two cheats were there. (=The two cheats happened to be there)
小結:（1)以that 引出的主語從句,常以形式主語it引導. It is +形容詞/名詞/某些動詞ed + that 從句.（2) 在有些that從句中要用虛擬語氣 (should+do/should+have done)例句4,5,6,11.
3、主語從句的用法
主語從句是在複合句中充當主語的從句，通常放在主句謂語動詞之前或由形式主語it代替，而本身放在句子末尾。
1. It 作形式主語和it引導強調句的比較
It 作形式主語代替主語從句，主要是為了平衡句子結構，主語從句的連接詞沒有變化。而it引導的強調句則是對句子某一部分進行強調，無論強調的是什麼成分，都可用連詞that。被強調部分指人是也可用who/whom。例如： It is a pity that you didn’t go to see the film.
2. 用it 作形式主語的結構
(1) It is ＋名詞＋從句
It is a fact that … 事實是… It is an honor that …非常榮幸
It is common knowledge that …是常識
(2) it is ＋形容詞＋從句
It is natural that… 很自然… It is strange that… 奇怪的是…
(3) it ＋不及物動詞＋從句
It seems that… 似乎… It happened that… 碰巧…
(4) it is＋過去分詞＋從句
It is reported that… 據報道… It has been proved that… 已證實…
3. 主語從句不可位於句首的五種情況
(1) if 引導的主語從句不可居於複合句句首。
(2) It is said , (reported) …結構中的主語從句不可提前。例如：
It is said that President Jingo will visit our school next week.
(3) It happens…, It occurs… 結構中的主語從句不可提前。例如：
It occurred to him that he failed in the examination.
(4) It doesn’t matter how/whether …結構中的主語從句不可提前。例如：
It doesn’t matter whether he is wrong or not.
(5) 含主語從句的複合句是疑問句時，主語從句不可提前。例如：
Is it likely that it will rain in the evening?
4. What 與that 在引導主語從句時的區別
What 引導主語從句時在從句中充當句子成分，如主語．賓語．表語，而that 則不然。例如： What you said yesterday is right.
三、賓語從句
名詞句用作賓語的從句叫賓語從句。引導賓語從句的關聯詞與引導主語從句表語從句的關聯詞大致一樣，在句中可以作謂語動詞或介詞及非謂語動詞的賓語。
1. 由連接詞that引導的賓語從句
由連接詞that引導賓語從句時，that在句中不擔任任何成分，在口語或非正式的文體中常被省去，但如從句是並列句時,第二個分句前的that不可省。例如：
He has told me that he will go to Shanghai tomorrow. 他已經告訴我他明天要去上海。
We must never think (that) we are good in everything while others are good in nothing. 我們決不能認為自己什麼都好，別人什麼都不好。
注意：在demand、order、suggest、decide、insist, desire, request, command等表示要求、命令、建議、決定等意義的動詞後，賓語從句常用“（should）+ 動詞原形”。例如：
I insist that she (should) do her work alone. 我堅持要她自己工作。
The commander ordered that troops (should) set off at once. 司令員命令部隊馬上出發。
2. 用who，whom, which, whose, what, when, where, why, how, whoever, whatever, whichever等關聯詞引導的賓語從句相當於特殊疑問句，應注意句子語序要用陳述語序。例如：I want to know what he has told you. 我想知道他告訴了你什麼。
She always thinks of how she can work well. 她總是在想怎樣能把工作做好。
She will give whoever needs help a warm support. 凡需要幫助的人，她都會給予熱情的支持。
3. 用whether或if引導的賓語從句，其主語和謂語的順序也不能顛倒，仍保持陳述句語序。此外，whether與if 在作“是否”的意思講時在下列情況下一般只能用whether，不用if：
a. 引導主語從句並在句首時；b. 引導表語從句時；c . 引導從句作介詞賓語時；d. 從句後有“or not”時；e. 後接動詞不定式時。例如：
Whether there is life on the moon is an interesting question. 月球上有沒有生命是個有趣的問題。 The question is whether she should have a low opinion of the test?現在的問題是她是否應該有一個低意見的測試？ Everything depends on whether we have enough money. 一切要看我們是否有足夠的錢。 I wonder whether he will come or not. 我想知道他來還是不來。 Can you tell me whether to go or to stay? 你能否告訴我是去還是留？
4. 注意賓語從句中的時態呼應，當主句動詞是現在時，從句根據自身的句子情況，而使用不同時態。例如：
he studies English every day. （從句用一般現在時）
he studied English last term. （從句用一般過去時）
I know (that) he will study English next year. （從句用一般將來時）
he has studied English since 1998. （從句用現在完成時）
當主句動詞是過去時態（could, would除外），從句則要用相應的過去時態，如一般過去時，過去進行時，過去將來時等；當從句表示的是客觀真理，科學原理，自然現象，則從句仍用現在時態。例如：The teacher told us that Tom had left us for America．
5. think, believe, imagine, suppose等等動詞引起的否定性賓語從句中，要把上述主句中的動詞變為否定式。即將從句中的否定形式移到主句中。例如：
We don’t think you are here. 我們認為你不在這。
I don’t believe he will do so. 我相信他不會這樣做。
6.時態：1.主句用一般現在時，從句可用任意時態。2.主句用過去時，從句用過去某個時態。
3.主句用過去時，從句是客觀真理時，只用一般現在時。
7.賓語從句的連接詞
從屬連詞：連接賓語從句的從屬連詞主要有that,if,whether.that引導表示陳述句的賓語從句,而if和whether引導表示“是否”的賓語從句.
He told me that he would go to the college the next year他告訴我他明年上大學.
I don’t know if there will be a bus any more.我不知道是否還會有公交車.
Nobody knew whether he could pass the exam.沒人知道他是否會通過考試.
連接代詞：連接代詞主要有who, whom ,whose ,what ,whoever ,whomever ,whosever, whatever, whichever等.連接代詞一般指疑問,但what, whatever除了指疑問外,也可以指陳述.
Do you know who has won Red Alert game? 你知道是誰贏得了紅色警報的遊戲？
The book will show you what the best CEOs should know.
這本書會告訴你最好的執行總裁該瞭解些什麼.
Have you determined whichever you should buy,a Motorola or Nokia cell phone?
你決定好是買諾基亞還是摩托羅拉的電話了嗎?
連接副詞：連接副詞主要有when,where,why,how,whenever,wherever,however等.
He didn’t tell me when we should meet again.他沒有告訴我什麼時候我們能再見面.
Could you please tell me how you use the new panel?你能告訴我怎麼用這個新的操作盤嗎?
None of us knows where these new parts can be bought.
沒有人知道這些的新的零件能在哪裡買到.
8.動詞的賓語從句
大多數動詞都可以帶賓語從句
We all expect that they will win , for members of their team are stronger.
我們都預料他們會贏,因為他們的隊員更強壯.
He told us that they would help us though the whole work.
他告訴我們在整個工作中,他都會幫忙的.
部分“動詞+副詞”結構也可以帶賓語從句
I have found out that all the tickets for the concert have been sold out.
我發現這場音樂會的所有票都賣光了.
Can you work out how much we will spend during the trip?
你能計算出這次旅行我們將花費多少錢嗎?
動詞短語也可以帶賓語從句
常見的這些詞有:make sure確保 make up one’s mind下決心 keep in mind牢記
Make sure that there are no mistakes in your papers before you turn them in.
在上交試卷前確保沒有任何錯誤.
可運用形式賓語it代替的賓語從句
①動詞find,feel,consider,make,believe等後面有賓語補足語的時候,則需要用it做形式賓語而將that賓語從句後置.
I think it necessary that we take plenty of hot water every day .我認為每天多喝開水是有必要的.
I feel it a pity that I haven’t been to the get-together. 我沒去聚會,感覺非常遺憾.
I have made it a rule that I keep diaries. 我每天寫日記成了習慣.
We all find it important that we (should) make a quick decision about this mater.
我們都認為對這件事馬上做出決定很重要.
②有些動詞帶賓語從句時需要在賓語與從句前加it
這類動詞主要有:hate, take , owe, have, see to.
I hate it when they with their mouths full of food.我討厭他們滿嘴食物時說話.
He will have it that our plan is really practical.他會認為我們的計劃確實可行.
We take it that you will agree with us.我們認為你會同意我們的.
When you start the engine, you must see to it that car is in neutral.
開啟發動機時, 一定要使汽車的離合器處於空擋位置.
③若賓語從句是wh-類,則不可用it代替
We all consider what you said to be unbelievable.我們都認為你所說的是不可信的.
We discovered what we had learned to be valuable.我們發現我們所學到的東西都是有用的.
9.介詞的賓語從句
用wh-類的介詞賓語從句
We are talking about whether we admit students into our club.
我們正在討論是否讓學生加入我們的俱樂部.
The new book is about how Shenzhou 6 manned spaceship was sent up into space.
這本新書是關於神州6號載人航天飛船是如何升入太空的.
用that,if引導的介詞賓語從句
有時候except,but,besides三個介詞後可見到that引導的賓語從句
I know nothing about my new neighbor except that he used to work with a company.
對於我的新鄰居我只知道他曾在一家公司上班,其他一無所知.
10.形容詞的賓語從句
常用來引導賓語從句的形容詞有: sure,certain,glad,please,happy,sorry,afraid,satisfied,surprised
I am sure I will pass the exam.我確信我會通過考試.
I am sorry that I have troubled you so long.很抱歉我這麼長時間在打擾你.
He is glad that Li Ming went to see him when he was ill.
他很高興在他生病的時候李明能去看望他.
11.if,whether在賓語從句中的區別
① if和whether在作“是否”解時,引導賓語從句常放在動詞know,ask,care,wonder,find out等之後,介詞後一般不用if② 少數動詞,如:leave,put,discuss,doubt後的賓語從句常用whether.③ whether後可以加or not,但是if不可以.④ 在不定式前只能用whether.（如：I can’t decide whether to stay. 我不能決定是否留下。）⑤ 避免歧異時,我們常用whether而不用if.
12.哪些賓語從句不可以省略引導詞that
1.當that作learn,suggest,explain,agree,wonder,prove,mean,state,feel,hold等動詞的賓語時;2.當賓語從句較長時;3.當主語狀語置於主句尾,賓語從句之前時;4.當主語謂語動詞(包括非謂語動詞)與賓語從句之間有插入語時;5.當一個動詞帶有兩個或兩個以上賓語從句時,此時第一個that可以省略,第二個that不可以省略;6.當賓語從句中的主語是this,that或this,that做主語的定語時;7.當賓語從句是雙賓語中的直接賓語時;當賓語從句的主語是非謂語動詞或主語從句時;8.當主語中的謂語動詞是固定詞組時;9.當賓語從句有it做其先行詞時;10.在直接引語中,轉述分句把賓語從句隔開時.
13.賓語從句的否定轉移
主句的謂語動詞是think,believe,imagine,suppose,consider,espect,fancy,guess等,並且主句的主語是第一人稱而且為一般現在時,從句的否定詞一般要轉移到主句上來,其反義疑問句一般與賓語從句一致.
I don’t think he will come to my party.而不能說成I think he won’t come to my party.
我認為他不會來我的舞會.
I don’t believe that man is killed by Jim,is he?
我認為那個人不是Jim所殺的,是不是?
如果賓語從句中有某個含有否定意義的形容詞或副詞,其反義疑問句要用肯定形式.
We find that he never listens to the teacher carefully,does he?
我們發現他從來不仔細聽老師講課,是不是?
14.賓語從句的時態和語序
當主句為現在時或將來時,賓語從句的時態一般不受主句的時態所影響.
當主句為過去時
①從句用一般過去時或過去進行時表示與主句謂語動詞動作同時發生
I only knew he was studying in a western country,but I didn’t know what country he was in.
我只知道他當時在西方的一個國家讀書,可不知道是哪個國家.
He asked me if I was reading the story The Old Man and the Sea when he was in.
他問我他進來的時候我是否正在讀<>.
②從句過去完成時表示該動作發生在主句謂語動作之前
He told me that he had told Mary about the meeting already.
他告訴我他已經把有關會議的事情告訴的了Mary.
③從句謂語用過去將來時表示該動作發生在主句謂語動作之後
The reporter asked if the government would take necessary measures to put down the to-do.
記者問政府是否會採取必要的措施鎮壓騷亂.
如果從句是一個客觀真理,那麼從句的時態不根據主句的時態而變化
The teacher said that the moon goes around the earth yesterday.
老師昨天說月亮繞著地球轉.
當賓語從句的引導詞是who,which,what,when,where,how,why等表疑問時,不能按正常語序安排,經常將這類引導詞置於句首
Who do you think the public might choose as their favorite singer this year?
你認為今年公眾會選誰為他們最喜歡的歌手.
四、表語從句
1、在句中作表語的從句叫表語從句。引導表語從句的關聯詞與引導主語從句的關聯詞大致一樣，表語從句位於連繫動詞後，有時用as if引導。其基本結構為：主語 + 系動詞 + that從句。例如：
The fact is that we have lost the game. 事實是我們已經輸了這場比賽。
That’s just what I want. 這正是我想要的。
This is where our problem lies. 這就是我們的問題所在。
That is why he didn’t come to the meeting. 那就是他為什麼不到會的原因。
It looks as if it is going to rain. 看上去天要下雨了。
需要注意的，當主語是reason時，表語從句要用that引導而不是because。例如：
The reason why he was late was that he missed the train by one minute this morning .
【注意】whether 可引導表語從句，但與之同義的if卻通常不用於引導表語從句。
2、簡介
定義：A 表語從句就是用一個句子作為表語。說明主語是什麼或者怎麼[1]樣，由名詞、形容詞或相當於名詞或形容詞的詞或短語充當，和連繫動詞一起構成謂語。
The problem is puzzling. 這問題令人困惑
主語 連繫動詞 形容詞作表語
The problem is when we can get a pay rise. 問題是什麼時候我們可以得到加薪.
主語 連繫動詞 一個句子作表語---表語從句
B 連接表語從句的連接詞有：that, what, who, when, where, which, why, whether,how.
He has become a teacher. 他已經成為一名教師。
He has become what he wanted to be ten years ago. 他已經成為了他10年前想成為的。
She has remained there for an hour. 她曾在那裡停留了一個小時。
She has remained where I stood yesterday for an hour.她一直在我昨天站的地方站了一個小時。
His suggestion is good. 他的建議是好的。
His suggestion is that we should stay calm. 他的建議是，我們應該保持冷靜。
The question is confusing. 這個問題令人困惑.
The question is when he can arrive at the hotel. 問題是，他什麼時候可以到達酒店。
who will travel with me to Beijing tomorrow.誰與我明天將前往北京。
why he cried yesterday. 昨天他為什麼哭。
how I can persuade her to join us in the party. 我怎麼能說服她加入我們的派對。
whether the enemy is marching towards us. 是否敵人正向我們行進.
注意：
A 表語從句一定要用陳述語序。
False: The question is when can he arrive at the hotel.
Right: The question is when he can arrive at the hotel.
B 不可以用if，而用whether 連接表語從句(as if 例外）。
引導賓語從句時可以互換if/whether 位於介詞後要用whether
位於句首時要用whether
引導表語從句，主語從句，同位語從句時要用whether
False: The question is if the enemy is marching towards us.
Right: The question is whether the enemy is marching towards us.
Right: It looked as if he had understood this question.
C 不像賓語從句，在有表語從句的複合句中，主句時態和從句時態可以不一致。
Right: The question is who will travel with me to Beijing tomorrow.
Right: The question is why he cried yesterday.
D that在表語從句中不可以省掉。
3、基本用法
表語從句只能置於主句之後，而主句的動詞只能是聯繫動詞。
名詞性從句在be等系動詞後作表語時被稱為表語從句， 例如： The problem is how we can get the things we need.問題是我們怎樣能弄到我們需要的東西。(how 在表語從句中充當方式狀語)// The scissors are not what I need. 這把剪刀不是我所需要的。(what 在表語從句中充當賓語)// What I told him was that I would find him a good play. 我告訴他的是我會給他找個好劇本。(what在主語從句中作直接賓語， that作為表語從句的引導詞在該表語從句中不充當句子成分， 不能省略)// That is what I want to tell you.那就是我想要對你講的。(what在表語從句中充當直接賓語)// That is why she failed to pass the exam. 那就是她考試不及格的原因。(why 在表語從句中充當原因狀語)
注意： “That is why...”是常用句型， 意為“這就是……的原因/因此……”， 其中why引導的名詞性從句在句中作表語， 該句型通常用於針對前面已經說明過的原因進行總結， 又如： That is why you see this old woman before you know, Jeanne. 珍妮， 這就是現在這個老太婆出現在你面前的原因。(前文提到Jeanne對老婦人顯得蒼老憔悴深感詫異， 說話人對她講述了其中的原因之後，用這一句來進行概括)。// That is why I came. 這就是我來的原因。
下面是兩個與“That is why...”形式相似的結構， 它們與“That is why...”結構之間的關係要能夠辨析清楚：
(1)“That is why...”與“That is the reason why...”同義， 只不過從語法結構上講， “That is the reason why...”中why引導的是—個定語從句， 將其中的the reason去掉則與“That is why...”結構一樣， 例如： That is (the reason) why I cannot agree. 這就是我不能同意的理由。
(2)“That is because...”句型中從屬連詞because引導的名詞性從句在此作表語， 這也是個常用句型， 意為“這就是為什麼……/因為……”。“That is because...”與“That is why...”之間的不同在於“That is because...”指原因或理由， “That is why...”則指由於各種原因所造成的後果， 例如： He did not see the film last night. That is because he had to help his little sister with her homework.昨天晚上他沒有去看電影， 那是因為他得幫助他的妹妹做作業。(第一句話說明結果， 第二句話說明原因)
He had seen the film before. That is why he did not see it last night.他以前曾看過那部電影， 因此他昨天晚上沒有去看。(第一句話說明原因， 第二句話說明結果)
五、同位語從句
1、同位語從句說明其前面的名詞的具體內容。同位語從句通常由that引導，可用於同位語從句的名詞有advice、demand、doubt、fact、hope、idea、information、message、news、order、problem、promise、question、request、suggestion、truth、wish、word等。例如：
The news that we won the game is exciting. 我們贏得這場比賽的消息令人激動。
I have no idea when he will come back home. 我不知道他什麼時候回來。
The thought came to him that Mary had probably fallen ill. 他想到可能瑪麗生病了。
同位語從句和定語從句的區別：
that作為關係代詞，可以引導定語從句，充當句子成分，在從句中作賓語時可以省略； that引導同位語從句時，起連詞的作用，沒有實際意義，不充當句子成分，一般不能省略。
試比較下面兩個例句:
I had no idea that you were here．（that引導同位語從句，不能省略）
Have you got the idea（that）this book gives you of life in ancient Greece？（that引導定語從句，作賓語，可以省略）
2、簡介
同位語部分是個句子,就是同位語從句,這種用法比較"固定",把關鍵的幾個詞背下來.
一、在複合句中用作同位語的從句叫同位語從句。它一般跟在某些名詞後面，用以說明該名詞表示的具體內容。如：
I heard the news that our team had won．我聽到了我們隊獲勝的消息。
I had no idea that you were here．我不知道你在這裡。
二、可以跟同位語從句的名詞通常有news，idea，fact，promise，question，doubt，thought，hope，message，suggestion，words（消息），possibility等。如：
I’ve come from Mr wang with a message that he won’t be able to see you this afternoon． 我從王先生那裡來，他讓我告訴你他今天下午不能來看你了。
三、英語中引導同位語從句的詞通有連詞 that，whether，連接副詞 how,when,where等。（注：if,which 不能引導同位語從句。）如：
l have no idea when he will be back．我不知道他什麼時候回來。
He must answer the question whether he agrees to it or not.
他必須回答他是否同意這樣一個問題。
四、有時同位語從句可以不緊跟在說明的名詞後面，而被別的詞隔開。 如：
Several years later，word came that Napoleon himself was coming to inspect them．
幾年以後，有消息傳來說拿破崙要親自視 察他們。
The thought came to him that maybe the enemy had fled the city．
他突然想起可能敵人已經逃出城了。
六、名詞性that-從句
1）由從屬連詞that引導的從句叫做名詞性that-從句。 That只起連接主句和從句的作用，在從句中不擔任任何成分，本身也沒有詞義。名詞性that-從句在句中能充當主 語、賓語、表語、同位語和形容詞賓語，例如：
主語：That she is still alive is her luck. 他還活著全靠運氣。
賓語：John said that he was leaving for London on Wednesday. 約翰說他星期三要到倫敦去。
表語：The fact is that he has not been seen recently. 事實是近來誰也沒有見過他。
同位語：The fact that he has not been seen recently disturbs everyone in his office.
近來誰也沒有見過他，這一事實令辦公室所有的人不安。
形容詞賓語：I am glad that you are satisfied with your job.你對工作滿意我感到很高興。
2）That-從句作主語通常用it作先行詞，而將that-從句置於句末，例如：
It is quite clear that the whole project is doomed to failure. 很清楚，整個計劃註定要失敗。
It's a pity that you should have to leave. 你非走不可真是件憾事。
用it作形式主語的that-從句有以下四種不同的搭配關係：
a. It + be +形容詞+ that-從句
It is necessary that… 有必要…… It is important that… 重要的是……
It is obvious that… 很明顯……
b. It + be + -ed 分詞+ that-從句
It is believed that… 人們相信…… It is known to all that… 眾所周知……
It has been decided that… 已決定……
c. It + be +名詞+ that-從句
It is common knowledge that… ……是常識 It is a surprise that… 令人驚奇的是……
It is a fact that… 事實是……
d. It +不及物動詞+ that-從句
It appears that… 似乎…… It happens that… 碰巧……
It occurred to me that… 我突然想起……
七、名詞性wh-從句
1）由wh-詞引導的名詞從句叫做名詞性wh-從句。Wh-詞包括who, whom,. whose, whoever, what, whatever, which, whichever等連接代詞和where, when, how, why等連接副詞。Wh-從句的語法功能除了和that-從句一樣外，還可充當介詞賓語、賓語補語和間接賓語等，例如：
主語： How the book will sell depends on its author. 書銷售如何取決於作者本人。
直接賓語：In one's own home one can do what one likes. 在自己家裡可以隨心所欲。
間接賓語：The club will give whoever wins a prize. 俱樂部將給得勝者設獎。
表語： My question is who will take over president of the Foundation. 我的問題是誰將接任該基金會主席職位。
賓語補足語：She will name him whatever she wants to. 她高興給他起什麼名字就取什麼名字。
同位語： I have no idea when he will return. 我不知道他什麼時候回來。
形容詞賓語：I'm not sure why she refused their invitation. 我尚不能肯定她為什麼拒絕他們的邀請。
介詞賓語： That depends on where we shall go.
那取決於我們去哪兒。
2）Wh-從句作主語也常用先行詞it做形式主語，而將wh-從句置於句末，例如：
It is not yet decided who will do that job. 還沒決定誰做這項工作。
It remains unknown when they are going to get married. 他們何時結婚依然不明。
八、if, whether引導的名詞從句
1）yes-no型疑問從句
從屬連詞if, whether引導的名詞從句是由一般疑問句或選擇疑問轉化而來的，因此也分別被稱為yes-no型疑問句從句和選擇型疑問從句，其功能和wh-從句的功能相同， 例如：
主語：Whether the plan is feasible remains to be proved. 這一計劃是否可行還有等證實。
賓語：Let us know whether / if you can finish the article before Friday. 請讓我們知道你是否能在星期五以前把文章寫完。
表語：The point is whether we should lend him the money. 問題在於我們是否應該借錢給他。
同位語：They are investigating the question whether the man is trustworthy. 他們調查他是否值得信賴。
形容詞賓語： She's doubtful whether we shall be able to come. 她懷疑我們是否能夠前來。
介詞賓語： I worry about whether he can pass through the crisis of his illness. 我擔心他是否能度過疾病的危險期。
2）選擇性疑問從句
選擇性疑問從句由關聯詞if/whether…or或whether…or not構成，例如：
Please tell me whether / if they are Swedish or Danish. 請告訴我他們是瑞典人還是丹麥人。
I don't care whether you like the plan or not.我不在乎你是否喜歡該計劃。
if和whether的區別：
1、 在動詞不定式之前只能用whether 。如：
例8 I can’t decide whether to stay. 我不能決定是否留下。
2、 在whether …… or not 的固定搭配中。如：
例9 I want to know whether it’s good news or not . 我想知道是否是好消息。
3 、在介詞後，只能用whether。如：
例10 His father is worried about whether he lose his work . 他的父親擔心是否會失去工作。
4、賓語從句放在句首表示強調時，只能用whether 。如：
Whether this is true or not, I really don’t know. 這是否真的，我真的不知道。
（例11 Whether they can finish the work on time is still a problem . 他們是否能準時完成這項工作還是個問題。－－此例為主語從句，有誤，感謝指出）
5、用if會引起歧義時，只用whether。如：
例12 Could you tell me if you know the answer ?
這句話有兩種意思：“你能告訴我是否知道答案嗎？”或“如果你知道答案，請告訴我，好嗎？”。如用whether可避免歧義.
九、否定轉移
1) 將think, believe, suppose, expect, fancy, imagine等動詞後面賓語從句的否定詞轉移到主句中，即主句的謂語動詞用否定式，而從句的謂語動詞用肯定式。
I don't think I know you. 我想我並不認識你。
I don' t believe he will come. 我相信他不回來。
注意：若謂語動詞為hope,賓語從句中的否定詞不能轉移。
I hope you weren't ill. 我想你沒有生病吧。
2) 將seem, appear 等後的從句的否定轉移到前面。
It doesn't seem that they know where to go. 看來他們不知道往哪去。
It doesn't appear that we'll have a sunny day tomorrow. 看來我們明天不會碰上好天氣。
3) 有時將動名詞，介詞短語或整個從句的否定轉變為對謂語動詞的否定。
I don't remember having ever seen such a man.
我記得從未見過這樣一個人。 (not否定動名詞短語 having…)
It's not a place where anyone would expect to see strange characters on the street.
在這裡，人們不會想到在街上會碰上陌生的人。 (anyone 作主語，從句中的謂語動詞不能用否定形式。)
4) 有時狀語或狀語從句中否定可以轉移到謂語動詞前。
The ant is not gathering this for itself alone. (否定狀語) 螞蟻不只是為自己採食。
He was not ready to believe something just because Aristotle said so. (否定because狀語) 他並不因亞里斯多德說過如何如何，就輕信此事。
She had not been married many weeks when that man's younger brother saw her and was struck by her beauty. (否定狀語many weeks) 她結婚還不到幾個月，這個人的弟弟就看見她了，並對她的美貌著了迷。
閱讀更多 夢裡人生 的文章
