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(yǔ)、賓語(yǔ)、表語(yǔ)、介詞的賓語(yǔ)以及同位語(yǔ)。

1. 主語(yǔ)從句主語(yǔ)從句可以由連詞that，wh-疑問(wèn)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(yǔ)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(yǔ)或非正式文體中，that常可省略，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(wèn)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(wèn)句中，wh-疑問(wèn)詞所引導(dǎo)的從句不能位于句首，如：Is it known where she went？

⑶主語(yǔ)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(yǔ)從句

⑴賓語(yǔ)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(yǔ)法作用，就要使用連接詞what等來(lái)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(yǔ)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(yǔ)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(wèn)句，賓語(yǔ)從句也必須保持陳述句的語(yǔ)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(yǔ)從句一般不能由that來(lái)引出，只限于except，in，but，besides，save等五個(gè)介詞的賓語(yǔ)從句，其它介詞后面不能跟由that引出的賓語(yǔ)從句，而只能跟由what，how，whether等引出的賓語(yǔ)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(yǔ)從句表語(yǔ)從句通常由that引出，當(dāng)然how，why，where，when等也可以引出表語(yǔ)從句。常見的表語(yǔ)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(yǔ)從句同位語(yǔ)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(yǔ)從句起進(jìn)一步解釋說(shuō)明先行詞的作用，通常由that引導(dǎo)。同位語(yǔ)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(wèn)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(yǔ)和that引導(dǎo)的定語(yǔ)從句的區(qū)別：that在同位語(yǔ)從句中只起引導(dǎo)從句的作用，本身并無(wú)意義，也不在句子中擔(dān)當(dāng)任何成分；而定語(yǔ)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(yǔ)從句，that不作句子成分。）

He is the best speaker that addressed the meeting.（定語(yǔ)從句，that在從句中作賓語(yǔ)，指代的先行詞是主句中的主語(yǔ)。）

定語(yǔ)從句定語(yǔ)從句是在句子中起形容詞作用的主謂結(jié)構(gòu)，通常修飾它前面的名詞或代詞，即它的先行詞。定語(yǔ)從句是由關(guān)系代詞和關(guān)系副詞引導(dǎo)的。

1.關(guān)系代詞引導(dǎo)的定語(yǔ)從句

⑴引導(dǎo)定語(yǔ)從句的關(guān)系代詞有：who，whom，whose，which，that.

⑵關(guān)系代詞在從句作主語(yǔ)、賓語(yǔ)、定語(yǔ)和表語(yǔ)的作用；當(dāng)作賓語(yǔ)時(shí)，關(guān)系代詞常�？墒÷�。如：

This is the girl （whom） you‘ve been looking for.

⑶當(dāng)定語(yǔ)從句所修飾的先行詞是人或人格化的動(dòng)物時(shí)，引導(dǎo)詞用who，whom或whose；

如果先行詞是無(wú)生命的東西，用關(guān)系代詞which；而that可用于以上兩種情況。

The man who robbed you has been arrested.

That is the book which cost me twenty dollars.

Which還可以指嬰兒、動(dòng)物和表示單數(shù)意義的集合名詞，如：

The baby （which） the nurse brought in was Mary‘s child.

⑷關(guān)系代詞that和which的語(yǔ)法區(qū)別當(dāng)先行詞的前面有形容詞的最高級(jí)修飾時(shí)，通常用that而不用which.如：

The final match is one of the most exciting football games that I have ever seen.當(dāng)定語(yǔ)從句所修飾的先行詞的前面有all，any，little，only，much等修飾時(shí)，或者這些先行詞本身就是all，one，little，much，nothing等不定代詞時(shí)，通常用that而不用which. I am interested in all that you have told me. It seems that is the only thing that we can do now.

當(dāng)定語(yǔ)從句作介詞的賓語(yǔ)時(shí)，只能使用which而不用that. The world in which we live is in constant motion and in constant change.當(dāng)定語(yǔ)從句是與代詞、數(shù)詞或名詞詞組連用引導(dǎo)非限定性定語(yǔ)從句時(shí)，只能使用which而不用that. I bought a dozen eggs，five of which broke when I dropped the box at my door.

當(dāng)先行詞的前面有the only （first，last，same，next，very）等詞修飾時(shí)，通常用that而不用which. This is the very movie that I want to see.當(dāng)被用來(lái)指代整個(gè)句子，引導(dǎo)非限定性定語(yǔ)從句時(shí)，只能使用which而不是that. Things then improved，which surprises me. Her brother snatched the letter away，at which she was furious.

2. 關(guān)系副詞引導(dǎo)的定語(yǔ)從句

⑴引導(dǎo)定語(yǔ)從句的關(guān)系副詞有：when，where，why，how等。

⑵關(guān)系副詞when，where，why在從句中作狀語(yǔ)時(shí)，可用“介詞 which”來(lái)替代。如：

The reason why （= for which） he is in hospital hasn‘t been known yet.

3. 限定性定語(yǔ)從句和非限定性定語(yǔ)從句限定性定語(yǔ)從句與先行詞關(guān)系密切，用來(lái)描述主句所涉及的人或物的具體情況，與主句不可分割。這種從句在口語(yǔ)中前后沒(méi)有停頓，在文字中前后沒(méi)有逗號(hào)。

非限制性定語(yǔ)從句與先行詞之間的關(guān)系比較松散，為主句所描繪的人或物提供一些附加情況，并非絕對(duì)必要。這種從句在口語(yǔ)中有停頓，在文字中往往用逗號(hào)與主語(yǔ)隔開。

另外，非限定性定語(yǔ)從句可用which，who，whose，when，where等來(lái)引導(dǎo)，但不可以用that來(lái)引導(dǎo)。如：

The wine，which was in the cellar，was ruined.（非限定性）

The wine which （that） was in the cellar was all ruined.（限定性）

在限定性定語(yǔ)從句中，關(guān)系代詞有時(shí)可省略；但是在非限定性定語(yǔ)從句中，關(guān)系代詞不能省略。

狀語(yǔ)從句

在句子中起狀語(yǔ)作用的句子叫做狀語(yǔ)從句。狀語(yǔ)從句可以位于句首、句中或句末。位于句首時(shí)，從句末通常有逗號(hào)與主句隔開；位于句中時(shí)，從句的前后都必須有逗號(hào)；位于句末時(shí)，從句的前面可以不用逗號(hào)。狀語(yǔ)從句按意義可分為時(shí)間、地點(diǎn)、原因、條件、讓步、方式、比較、目的和結(jié)果等狀語(yǔ)從句。狀語(yǔ)從句由從屬連詞引導(dǎo)。

1.時(shí)間狀語(yǔ)從句引導(dǎo)時(shí)間狀語(yǔ)從句的連詞有：after，as，before，once，since，till，until，when，whenever，now （that），as soon as，as long as，no sooner…than等。有些名詞短語(yǔ)也可以引導(dǎo)狀語(yǔ)從句，如：

every time，the moment，the instant. When I saw her，she was watching closely at the photo on the wall. As the sun rose，the fog dispersed. The instant he received the letter，he started off at once. Every time he went to Beijing，he used to visit the Great Wall. as，when和while都可以表示主句中動(dòng)作發(fā)生的背景，也可以表示主句的動(dòng)作與從句的動(dòng)作同時(shí)發(fā)生，如：

As he stood there，he heard what they were talking about. I stood up and wanted to go out，when she came in. till和until在主句謂語(yǔ)為持續(xù)性動(dòng)詞的肯定式時(shí)，作“直到……為止”解，在主句謂語(yǔ)為瞬間動(dòng)詞的否定式時(shí)作“直到……才”解，如：

Let‘s wait till / until the rain stops. I did not begin work till / until he had gone. once，directly，the moment，the instant和as soon as都作“一…就”解，通�？梢曰�換，如：

Once you understand this，you will surely make rapid progress in your study.由副詞加從屬連詞no sooner…than，hardly / barely / scarcely…when等引導(dǎo)的時(shí)間狀語(yǔ)從句，如果no sooner，hardly，barely，scarcely前置句首，主語(yǔ)與謂語(yǔ)須用倒裝結(jié)構(gòu)。如：

Hardly had the film started when they came. No sooner had we reached the top of the hill than we all sat down to rest.

2. 地點(diǎn)狀語(yǔ)從句地點(diǎn)狀語(yǔ)從句通常由where，wherever引導(dǎo)，如：

Where there is a will，there is a way. She painted wherever she happened to be.從屬連詞還能與any，no，every等一起構(gòu)成復(fù)合句，引導(dǎo)地點(diǎn)狀語(yǔ)從句。如：

Everywhere you go，you will be warmly welcomed.

3. 方式狀語(yǔ)從句引導(dǎo)方式狀語(yǔ)從句的連詞有as，as if，as though等，從句通常位于主句之后，如：

He had never blushed as she blushed then.（as作“按照”或“像”解。）

as if和as though都做“好象”解，兩者可以互換，從句既可用陳述語(yǔ)氣（表示可能符合事實(shí)的情況），又可用虛擬語(yǔ)氣（表示與事實(shí)不符的情況），如：

I remember the whole thing as if it happened yesterday. His mother loves me as if / as though I were her daughter.

4. 條件狀語(yǔ)從句引導(dǎo)條件狀語(yǔ)從句的連詞有：if，unless，as / so long as，suppose （that），supposing （that），in case，when等。條件狀語(yǔ)從句可以分為真實(shí)條件狀語(yǔ)從句和非真實(shí)條件狀語(yǔ)從句。

⑴真實(shí)條件句真實(shí)條件句表示現(xiàn)實(shí)或可能的情況，由if引導(dǎo)，它的主句可以是陳述句，疑問(wèn)句或祈使句，可置于主句之前或之后。

If you heat ice，it melts. If it rained，I went by bus. unless引導(dǎo)的否定條件狀語(yǔ)從句，在意義上相當(dāng)于if…not，如：

Don‘t come unless I telephone. as / so long as，provided / providing （that）意為“只要、如果”，如：

You can borrow this pen as long as you can keep it well. in case在英國(guó)英語(yǔ)中表示目的，在美國(guó)英語(yǔ)中可表示條件，意為“如果、萬(wàn)一”，如：

In case the house burns down，we‘ll get the insurance money.

⑵非真實(shí)條件句請(qǐng)參閱第十一章“虛擬語(yǔ)氣”。

5.讓步狀語(yǔ)從句引導(dǎo)讓步狀語(yǔ)從句的連詞有：although，though，even if，even though，if，for all that，when，while，whether…or，whatever，no matter what等。

although和though意義一樣，都作“雖然、即使”解，都表示讓步，一般情況下可互換使用，只是although語(yǔ)氣較重，大多置于句首。如：

They are generous though they are poor. Although he was Japanese，he spent most of his life in China. even if和even though都作“即使”解，兩者可以互換使用，如：

She insisted on her own opinion even though / even if he was wrong. if作“即使、雖然”解，也表示讓步，如：

If he is wrong，he is honest. whether…or作“不論……是否”或“不論……還是”解，如：

You don‘t have to worry me whether I am well or ill.為了強(qiáng)調(diào)讓步意義，在正式文體或文學(xué)作品中，常用as引導(dǎo)讓步從句，從句的補(bǔ)語(yǔ)或狀語(yǔ)置于句首。如：

Tall as he was，he couldn‘t reach the top of the shelf. Strong as you may be，you cannot lift it.詞尾為-ever的wh-詞可以與“no matter wh-詞”互換使用，作“無(wú)論……”解，后者常用于口語(yǔ)中，如：

Whoever / No matter who rings，tell him I‘m out. Wherever / No matter where he is，he will be thinking of you.由whenever，wherever，however引導(dǎo)的從句，也可以分別看作時(shí)間狀語(yǔ)從句、地點(diǎn)狀語(yǔ)從句和方式狀語(yǔ)從句。把它們當(dāng)作讓步狀語(yǔ)從句是因?yàn)樗鼈兂Ｓ衝o matter when （where，how）的含義。

6.原因狀語(yǔ)從句原因狀語(yǔ)從句通常由because，since，as，when now （that），seeing （that），considering （that）等引導(dǎo)。

because，since和as三者的區(qū)別如下：

because的語(yǔ)勢(shì)最強(qiáng)，其次是since，再次是as. because可以回答why引導(dǎo)的特殊問(wèn)句，而since和as不能。

because引導(dǎo)的從句可以被just，only，simply等副詞修飾，也可以用并列連詞構(gòu)成并列的because從句，而since和as則不能。如：

We pardoned him only because he was still young. for表示原因時(shí)，作“因?yàn)椤苯�，多用于正式文體，有時(shí)可以與because換用，但for從句只能置于主句之后。如：

She didn‘t go to school，for / because she was ill. now （that）和seeing （that）都作“既然”解，通常可與since或as換用，如：

Now （that） you have come，you may as well stay. Seeing （that） he is inexperienced，he is not fit for the work. 7. 結(jié)果狀語(yǔ)從句引導(dǎo)結(jié)果狀語(yǔ)從句的連詞有：so that，so…that，such that，such…that，that等。

當(dāng)從句前面有逗號(hào)時(shí)，so that中that可省略，如：

It was dark，so （that） we could see nothing in front of us.“So 形容詞 / 副詞 that”是引導(dǎo)結(jié)果狀語(yǔ)從句的常用結(jié)構(gòu)，如：

He talked so loud that he annoyed the speaker. He was so brilliant that he made a lot of inventions.“such （a）形容詞名詞 that”與“so…that”的意義相同，如：

It was such a hot day that people could not go out. He painted such beautiful pictures that the visitors were lost in admiration. that可以單獨(dú)引導(dǎo)結(jié)果狀語(yǔ)從句，如：

The question is of great importance that it cannot be neglected. 8. 目的狀語(yǔ)從句引導(dǎo)目的狀語(yǔ)從句的連詞有：in order that，so that，so，that，in case，for fear that，lest等。

in order that與so that的意義和用法基本相同，in order that多用于正式文體，常表示經(jīng)過(guò)認(rèn)真考慮的目的，如：

In order that he would have more space for painting，he bought a big house. You ought to write to him，in order that he won‘t feel we are hiding things from him. So和that可視為so that的省略形式，但不如so that常用，如：

Bring it closer so / that I may see it better. for fear that，in case和lest都表示否定的目的，相當(dāng)于so that…not或in order that…not，作“以免、以防”解。

He wrote the name down for fear that he should forget it . lest限于正式文體，它所引導(dǎo)的從句中的謂語(yǔ)動(dòng)詞多用should be型或be型虛擬形式，如：

He hid the box lest it （should） be stolen. in case引導(dǎo)的從句謂語(yǔ)既可以用虛擬形式，又可用陳述語(yǔ)氣，如：

Better take more clothes in case it is cold. She doesn‘t dare to go out in case she is recognized / （should） be recognized.