名词性从句的用法之主语从句

1、名词性从句从句有名词性从句、定语从句和状语从句三大类。名词性从句又可分为宾语从句、表语从句、主语从句及同位语从句，因为从句的在这个句子中的功用相当于名词；定语从句有称为形容词性从句，因为从句功能相当于形容词；而状语从句则称为副词性从句，因为从句功能相当于副词 。 什么是名词性从句?在英语的句子结构中，本来该由名词充当的主语、宾语、表语和同位语，由一个句子来充当,这个句子就叫名词性从句。宾语从句 ( The Object Clause)表语从句 ( The Predicative Clause)主语从句 ( The Subject Clause)同位语从句 ( The Appositive Cl

2、ause)主语从句一定义在句中充当主语的从句叫做主语从句。通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。He will come here on Wednesday is certain.他星期三来这里是肯定的。He will come here on Wednesday is not certain.他星期三是否来这里还不肯定的。二类型主语从句主要有四类：（1） 由连词that引导的主语从句:引导词that无含义/在句中不做成分/不可以省。例如：That you will win the medal seems unlikely. That you are so indi

3、fferent bothers me. That she survived the accident is a miracle.（2） 用连词 whether 引导的主语从句: whether有含义(是否)/在句中不做成分/不可以省。注意：引导主语从句，不能用if，只能用whether。例如：Whether we will hold a party in the open air tomorrow depends on the weather. Whether she is coming or not doesnt matter too much.（3） 用连接代词引导的主语从句 在由连接代词

4、who, whose, whom, which, what, whoever, whomever, whichever, whatever引导的名词性从句中，其连接代词在句中起名词性作用，担当一定成分.例如：What you need is more practice. What I want to know is this. Whatever we do is to serve the people.注：whatever / whoever的功用whatever, whoever在主语从句中不含疑问意义。它引导主语从句，并在从句中作主语、宾语、表语等。whatever = anything

5、that; whoever = anyone who。要注意和whatever, whoever引导的让步状语从句的区别。如： Whoever breaks the law should be punished. （主语从句）（ Anyone who breaks the law should be punished. ） Whoever breaks the law, he should be punished. （让步状语从句）（ No matter who breaks the law, he should be punished. ）（4）用连接副词when, where, why,

6、how引导的名词性从句(其连接副词有含义,在句中作状语。)例如:Where we should leave it is a problem.When they will come hasnt been made pubic.三注意事项1.it构成的主语从句由连词that引导的主语从句，在大多数情况下会放到句子的后面，而用代词it作形式主语。例如：That light travels in straight lines is known to all. =It is known to all that light travels in straight lines. When the plane

7、 is to take off has not been announced . = It has not been announced when the plane is to take off.但是，但当what引导的主语从句表示“的东西”时，一般不用it作形式主语。错:It is a book what he wants.对:What he wants is a book. 另外，需要注意的是，it作形式主语代替主语从句时，要注意和as引导的定语从句的区别。试比较： It was reported that the US was under the terrorist attack. A

8、s was reported, the US was under the terrorist attack. 2. it 作形式主语和it引导强调句的比较it 作形式主语代替主语从句，主要是为了平衡句子结构，主语从句的连接词没有变化。而it引导的强调句则是对句子某一部分进行强调，无论强调的是什么成分，都可用连词that。被强调部分指人是也可用who/whom。例如： It is a pity that you didnt go to see the film. It doesnt interest me whether you succeed or not. It is in the morn

9、ing that the murder took place.It is John that broke the window.3. 用it 作形式主语的结构<a> It is +名词+从句It is a fact that 事实是It is good news that 是好消息It is a question that 是个问题It is common knowledge that 是常识类似的名词还有：a pity；a wonder；a good thing； no wonder； surprise等。例如：It is a mystery to me how it all h

10、appened.It is common knowledge that the whale is not a fish.It is no surprise that Bob should have won the game.Its a pity that you missed the film. <b> It is +形容词+从句It is necessary that 有必要It is clear that 很清楚It is likely that 很可能It is important that 重要的是类似的形容词还有：strange; natural; obvious; tr

11、ue; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising; interesting; astonishing, etc.例如：It is doubtful whether she will be able to come. It was really astonishing that he refused to talk to you. It is essential that he should be here by the weekend. It se

12、ems obvious that we can not go on like this.It is necessary that you （should）master the computer. It is important that a student learn English well. Its clear that they badly need help. It is likely that a hurricane will arrive soon.需要注意的是，这类主语从句中，谓语动词很多为“（should）动词原形”，即要用虚拟语气。<c> It is +过去分词+

13、从句It is said that 据说It is reported that 据报道It has been proved that 已证明It must be proved that 必须指出类似的过去分词还有：known; estimated; expected; believed; thought; hoped; noted; discussed; required; decided; suggested; demanded; made clear; found out,etc.例如：It is thought that he is the best player. It is esti

14、mated that the vase is 2000 years old. It is used to be thought that a new star must be due to a collision between two stars. It has not been made clear when the new road is to be opened to traffic. It is said that he was killed in the earthquake. <d> It +动词+从句It seems （happened / appears / do

15、esnt matter / makes no difference / occurred ）that 如： It seems that they will win the game. It makes no difference whether he will attend the meeting or not. It does not matter if I missed my train.It happened that I saw him yesterday.4. What 与that 在引导主语从句时的区别 What 引导主语从句时在句时在从句中充当句子成分，如主语宾语表语，而that

16、 则不然。例如： 1) What you said yesterday is right. 2) That she is still alive is a consolation.牛刀小试1._ as much as one-fifth of all timber harvested is not used.A. The estimate    B. The estimated   &#

17、160;C. They are estimated   D. It is estimated that2._ some mammals came to live in the sea is not known.A. Which   B. Since    C. Although     D. How 3. _ we have&#

18、160;achieved is attributed to the guidance of our parents.A. Whoever   B. Whatever  C. However  D. That 4. _ wealthy does not necessarily mean that a man&#

19、160;is greedy.   A. For the reason that he is      B. Just because he is    C. The reason of being          &#

20、160;D. That he is 5. Although _ happened in this developed country sounds like science fiction,it could occur elsewhere in the world. A. which    B. what   C. h

21、ow     D. it6. _ she had forgotten to take her notebook. A. That occurred to her   B.She occurred that  C. To her that occurred   D.It occurred&#

22、160;to her that7. I am sure that _ she said is wrong. A. which    B. all    C. this    D. what8. We lost our way in the forest, and

23、0;_ made matters worse was that it was getting dark.   A. that    B. which    C. it    D. what9. _ or not is still uncertain.   A. Hes&

24、#160;coming    B. If he is coming     C. That coming     D. Whether hes coming10. Its _ hell be able to come.   A. doubt whether  

25、 B. doubtful     C. doubt it       D. doubtful whether 11. _ he is at work in the heart of the big city or at home in the quiet su

26、burb, Dicks life is tied to machines.A. Whether   B. Till    C. If    D. Unless12. _ he saw both surprised and frightened him.   A. That 

27、60;        B. When            C. What         D. Which13. _ is  warm sunshine.  A. What do we&#

28、160;all need.  B. What all we need  C. What we need        D. What we all need14. _ is a pity that he should feel so upset.   

29、;A. What    B. That    C. He    D. It15. _ a spoonful of soil can tell us so much about the structure and early history of the moon. A. Remarkable       B. Quite remarkably    C. It is remarkable that  D.