名词性从句讲解.doc

名词性从句
　　在句子中起名词作用的句子叫名词性从句 (Noun Clauses）。 名词性从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。
一、引导名词性从句的连接词
　　引导名词性从句的连接词可分为三类：
　　连词：that（无任何词意）
　　whether,if（均表示“是否”表明从句内容的不确定性）
　　as if ,as though（均表示“好像”，“似乎”）
　　以上在从句中均不充当任何成分
　　连接代词：what, whatever, who, whoever, whom,
　　whose, which.whichever,whomever
　　连接副词：when, where, how, why
　　不可省略的连词：
　　引导主语从句和同位语从句的连词不可省略。
　　That she was chosen made us very happy.
　　We heard the news that our team had won.
　　比较：
　　whether与if 均为"是否"的意思。 但在下列情况下，whether 不能被if 取代：
　　1. whether引导主语从句并在句首
　　2. 引导表语从句
　　3. whether从句作介词宾语
　　4. 从句后有"or not"
　　Whether he will come is not clear.
　　大部分连接词引导的主语从句都可以置于句末，用 it充当形式主语。
　　It is not important who will go.
　　It is still unknown which team will win the match.
二. 主语从句
　　作句子主语的从句叫主语从句。that在句中无词义，只起连接作用；连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。例如：
　　What he wants to tell us is not clear.
　　Who will win the match is still unknown.
　　It is known to us how he became a writer.
Where the English evening will be held has not yet been announced.
有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下：
　　（1） It + be + 名词 + that从句
　　（2）It + be + 形容词 + that从句
　　（3）It + be + 动词的过去分词 + that从句
　　（4）It + 不及物动词 + that 从句
　　三、宾语从句
　　1. 由连接词that引导的宾语从句
　　由连接词that引导宾语从句时，that在句中不担任任何成分，在口语或非正式的文体中常被省去，但如从句是并列句时,第二个分句前的that不可省。例如：
We must never think (that) we are good in everything while others are good in nothing.
He told me (that) he had finished his homework and that he wanted to go home.
　　2. 用who，whom, which, whose, what, when, where, why, how, whoever, whatever, whichever等关联词引导的宾语从句相当于特殊疑问句，应注意句子语序要用陈述语序。例如：
　　I want to know what he has told you.
She always thinks of how she can work well.
She will give whoever needs help a warm support.
　　3.此外，whether与if 在作“是否”的意思讲时在下列情况下一般只能用whether，不用if：
　　a. 引导主语从句并在句首时；b. 引导表语从句时；c . 引导从句作介词宾语时；d. 后紧跟“or not”时；e. 后接动词不定式时。例如：
　　Whether there is life on the moon is an interesting question.
　　Everything depends on whether we have enough money.
We didn’t know whether or not she was ready.
Can you tell me whether to go or to stay?
　　4. 注意宾语从句中的时态呼应，当主句动词是现在时，从句根据自身的句子情况，而使用
　　不同时态。例如：
　　I know he studies English every day. （从句用一般现在时）
　　I know he studied English last term. （从句用一般过去时）
　　I know (that) he will study English next year. （从句用一般将来时）
　　I know he has studied English since 1998. （从句用现在完成时）
　　当主句动词是过去时态，从句则要用相应的过去时态，如一般过去时，过去进行时，过去将来时,过去完成时；当从句表示的是客观真理，科学原理，自然现象，则从句仍用现在时态。例如：
　　The teacher told us that Tom had left us for America．
　　5. think, believe, imagine, suppose等等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式。即将从句中的否定形式移到主句中。例如：
　　We don’t think you are here. 我们认为你不在这。
　　I don’t believe he will do so. 我相信他不会这样做。
四、表语从句
　　The fact is that we have lost the game.
　　That’s just what I want.
　　This is where our problem lies.
　　That is why he didn’t come to the meeting.
　　It looks as if it is going to rain.
　　需要注意的，当主语是reason时，表语从句要用that引导而不是because。例如：
　　The reason why he was late was that he missed the train by one minute this morning .
五. 同位语从句
　　同位语从句说明其前面的名词的具体内容。同位语从句通常由that引导，可用于同位语从句的名词有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.　
　　I have no idea when he will come back home.
　　The thought came to him that Mary had probably fallen ill.
　六、名词性that-从句
由从属连词that引导的从句。That只起连接主句和从句的作用，在从句中不担任任何成分，本身也没有词义。
John said that he was leaving for London on Wednesday.　
　　The fact is that he has not been seen recently.　
　　The fact that he has not been seen recently disturbs everyone in his office.