名词性从句

名词性从句
名词性从句包括主语从句、表语从句、宾语从句、同位语从句。

其关联词有连接词that，if，whether；疑问代词who，what，which和疑问副词when，where，how，why等。

1.主语从句
主语从句在句中做主语。

它可以放在主句谓语动词之前，但多数情况由it作形式主语，而把主语从句放在主句之后。

例如：
Who did that is known to all.
It is interesting that you should like him.
2.表语从句
表语从句在句中作表语，位于主句中的系动词之后。

如：
The question is who can complete the difficult task.
表语从句不能用if引导，但可用as if引导。

例如：
He looked as if he was going to cry．
3.同位语从句
同位语从句跟在名词后面，进一步说明该名词的具体内容。

引导同位语从句的名词主要有fact，news，promise，idea，truth等。

连接词用that（不用which），及连接副词how，when，where，why等。

例如：
His delay is due to the fact that the car went wrong halfway．
The news that our team has won the match is true.
She asked the reason why there was a delay．
4.宾语从句
1.宾语从句在句中作及物动词或介词的宾语。

例如：
We can learn what we did not know．
He will talk to us about what he saw in the U.S.
如果主句的谓语动词是及物动词make，find，see，hear等，则把宾语从句置于宾语补足语之后，用it作为形式宾语。

如：
We find it necessary that we practise spoken-English every day．
另外，某些作表语的形容词，如sure，happy，glad, certain等之后也可带宾语从句。

如：
I am sure that he will succeed.
注意：
1)关联词只能用whether不能用if表示“是否”的情况如下：
a)在表语从句和同位语从句中。

例如：
The question is whether the film is worth seeing.
The news whether our team has won the match is unknown.
Answer my question whether you are coming.
b)在主语从句中，只有用it作形式主语时，whether和if都能引导主语从句，否则，也只能
用whether。

例如：
Whether we shall attend the meeting hasn't been decided yet.
It hasn't been decided whether (if) we shall attend the meeting.
c)在介词之后。

（介词往往可以省略）例如：
It all depends（on）whether they will support us．
d)后面直接跟动词不定式时。

例如：
He doesn't know whether to stay or not.
e)后面紧接or not时。

例如：
We didn't know whether or not she was ready．
f)引导让步状语从句，只能用whether。

例如：
Whether you like it or not，you must do it well.
g)用if会引起歧义时。

例如：
Please 1et me know if you like it.
2)关联词if，whether均可使用的情况如下：
a)引导宾语从句。

例如：
I wonder if（whether）the news is true or not．
b)在“be十形容词”之后。

例如：
He was not sure whether (if) it is right or wrong.
3)关联词只能用whether 或if，不能用that的情况如下：
若doubt一词作“怀疑”解接宾语从句时，主句为肯定句用whether或if，主句为否定句或疑问句用that。

例如：
I doubt whether he will come soon.
I do not doubt that he will come soon.
Do you doubt that he will come soon？
直接引语和间接引语。

引述别人的原话叫直接引语，用自己的话转述别人的话叫间接引语。

这两种引语都是宾语从句，但
直接引语放在引号内，不用连词连接；间接引语不用引号，通常用连接词连接于主句。

1)陈述句变为以that引导的宾语从句。

例如：
He said，“I'm very glad.”
He said that he was very glad.
2)一般疑问句变为if（whether）引导的宾语从句。

例如：
He said，“Can you come this afternoon, John？”
He asked whether John could come that afternoon.
3)特殊疑问句变为由who，what, when等疑问词引导的宾语从句。

例：
He said，“Where is Mr. Wang？”
He asked where Mr. Wang was.
一般现在时变为一般对去时；现在进行时变为过去进行时；一股将来时变为过去将来时；现在完成时变为过去完成时；一般过去时变为过去完成时；过去完成时仍为过去
完成时。

如果主句谓语动词为各种现在时或一般将来时，直接引语变为间接引语时，时态一律不变。

例如：
He says，”I cleaned the f1oor.”
He says he cleaned the floor.。