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名词性从句，语法书把它讲得繁琐而复杂。尤其是各种各样的引导词，什么从属连词啊，连接代词啊，连接副词啊，等等，英语初学者往往记不住甚至混淆不清。其实，只要我们把它们进行归类、对比，就发现名词性从句有规律可循。
顾名思义，名词性从句就是具有名词作用的从句。因为它在句中可以作主语、宾语、表语和同位语，所以又分为：主语从句，宾语从句，表语从句和同位语从句四种。其实，我们换个角度来看，名词性从句一点也不复杂。
名词性从句，我们先不考虑它们用何种引导词来引导。我们只考虑，这些句子如果是简单句的话，它们是些什么样的句子?原来就是我们学过的陈述句、一般疑问句和特殊疑问句啊。因此我们要记住：陈述句用that引导，一般疑问句用whether引导，特殊疑问句用特殊疑问词(即wh-word)引导。这样，基本问题就解决了。下面我们用3组例句进行讲解，每组例句都分别包含一个主语从句，宾语从句，表语从句和同位语从句，这样归纳看起来是很有意思的。
(一)that引导的各种名词性从句
1.That our team had won the matchmade us excited.
2. The headmaster saidthat our team had won the match.
3. The fact wasthat our team had won the match.
4. The headmaster announced the newsthat our team had won the match.
【特别提示】
在本组句子中，每句都含有that our team had won the match. 它在句1中作了句子的主语，是主语从句。在句2中作了said的宾语，是宾语从句。在句3中作了was的表语，是表语从句。在句4中作了news的同位语，是同位语从句。
1. that 引导的各种名词从句，都是陈述一个事实，没有疑问的含义。而且，that 只起引导作用，本身没有实际意义。
2. that 引导的主语从句，由于句子较长放在句首显得头重脚轻。为了使句子更加匀称，往往用it形式主语引导。例如：
It is clear that you have made a big mistake in your experiment.
It is a wonder that the wounded soldier is still alive.
3. that 引导的名词从句，在宾语从句中可以省略，但引导主语从句、表语从句和同位语从句时不可省略。偶尔引导表语从句时，口语中可以省略。例如：The truth is (that) I never been there.
4. 由于that 引导的各种名词从句，都是陈述一个事实。所以，无论是主语从句还是宾语从句、表语从句、同位语从句，其主句中并没有悬而未决，带有疑问的意思。因此，宾语从句经常和say, think, wish, hope, expect, suppose, see, believe, agree, explain, order, command, suggest, propose, insist, demand, require, declare, announce, know, hear, feel, imagine, notice, prefer, find, report, find out, regret, remember, forget, learn, decide, discover等词连用。同位语从句经常和fact, news, hope, truth, idea, suggestion, thought, promise, order, story, problem, belief, word, message, information, proof, announcement, desire, answer, proposal, advice, condition等名词连用。
(二)特殊疑问词引导的各种名词性从句
1.Who will attend the meetinghas not been decided.
2. No one knowswho will attend the meeting.
3. My question iswho will attend the meeting.
4. The questionwho will attend the meetingremains to be discussed.
【特别提示】
在本组句子中，每句都含有who will attend the meeting. 它在句1中作了句子的主语，是主语从句。在句2中作了knows的宾语，是宾语从句。在句3中作了is的表语，是表语从句。在句4中作了question的同位语，是同位语从句。
1. 英语中有一种wh-word，也叫特殊疑问词，因为这些引导词都含有wh两个字母。它们是 who, whom, whose, whoever, what, whatever, which, when, where, how, why, 这些词均可引导四种名词性从句，并且这些引导词仍然具有疑问的含义。
2. 主语从句可以用形式主语it替代，而把主语从句置于句子的最后。如：
It has not been decided who will take the place of the manager.
It is still a question when we shall have our sports meet.
3. 上述例句都使用了wh-word引导各种名词从句，由于wh-word具有疑问的含义，所以，无论是主语从句还是宾语从句、表语从句、同位语从句，其主句也都带有悬而未决的意思。例如：没有决定，问题是等等。因此主句中经常出现这一类词语：wonder, dont know, no idea, not decided, doubt, question, problem等。
(三)whether引导的各种名词性从句
1.Whether she will agree with medoesnt matter too much.
2. I wonderwhether she will agree with me.
3. What I want to know iswhether she will agree with me.
4. I have no ideawhether she will agree with me.
【特别提示】
在本组句子中，每句都含有whether she will agree with me. 它在句1中作了句子的主语，是主语从句。在句2中作了wonder的宾语，是宾语从句。在句3中作了is的表语，是表语从句。在句4中作了idea的同位语，是同位语从句。
1. whether 表示是否的含义，它引导的名词从句具有一般疑问句的特点。作主语时，我们也可用it作形式主语，代替whether从句。例如：It doesnt matter too much whether she will agree with me.
2. if 也有是否的含义，它可以引导宾语从句。例如：I wonder if the conclusion is true.但不能引导主语从句。例如，我们不可以说：If the conclusion is true hasnt been proved.
但若用it作形式主语，则后面可以接if 引导的主语从句，例如：It hasnt been proved if (whether) the conclusion is true. 此外，if 一般不能引导表语从句和同位语从句。
最后，需要补充的是：
1. because也可以引导表语从句，例如： It is just because the public dont know the truth. 这仅仅因为公众不知道事情的真相。
2. as if (as though)也引导表语从句，此类表语从句常跟在seem, appear, look, taste, sound, feel等词之后。
It looks as if it is going to rain.看来要下雨了。
It sounds as though you are from the south of the United States . 听起来你好像来自美国南部。
3. 介词后也可跟宾语从句，但不用that引导，一般常用wh-word引导。
I cant agree with what he said.我不同意他所说的话。
I worried about whether I hurt her feelings.我担心我是不是伤了她的感情。
4. 一些表示心理感情色彩的形容词，其后也可跟宾语从句，这时的宾语从句一般理解为主句的原因。这类形容词有sure,certain,glad,pleased,happy,afraid,surprised,satisfied,sorry等。
I am sure that we will make it in spite of the great trouble. 我确信不管困难多大，我们都会取得成功的。
下面是我编写的一个小故事，语篇中含有各种名词性从句，请找出来：
Our teacher wondered why Tom had not attended his lessons for a few days. It was said that he had asked for leave. What surprised the teacher most was that Tom was suffering a very serious disease.
His doctor suggested that he should be sent to the hospital for further medical treatment. Tom became relieved when the news that his disease was not deathful was announced last week. However, the problem that he later developed another rare heart disease bothered the doctors and his parents. Yesterday the doctors made the decision that Tom should be operated on in no time. The fact that Toms illness got worse disappointed his parents and all his friends. The doctors hold the belief that the operation might lead to many important scientific breakthroughs.
But then the question came to their minds whether the operation would be successful. Besides that, there was also a different opinion about the question whether Tom and his parents would agree to the operation. Finally, after several discussions, the doctors and Toms parents reached an agreement that the operation would be performed next day.
【参考答案】
1. why Tom had not attended his lessons for a few days (宾语从句)
2. that he had asked for leave(主语从句)
3. What surprised the teacher most(主语从句)
4. that Tom was suffering a very serious disease(表语从句)
5. that he should be sent to the hospital for further medical treatment(宾语从句)
6. that his disease was not deathful(同位语从句)
7. that he later developed a serious heart disease(同位语从句)
8. that Tom should be operated on in no time(同位语从句)
9. that Toms illness got worse(同位语从句)
10. that the operation might lead to many important scientific breakthroughs(同位语从句)
11. whether the operation would be fully successful(同位语从句)
12. whether Tom and his parents would agree to the operation(同位语从句)
13. that the operation would be performed next day(同位语从句)