名词性从句的用法之主语从句

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 Clause)

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 indifferent 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 doesn’t matter too much.

（3）用连接代词引导的主语从句

在由连接代词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 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, 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 hasn’t 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 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.

As 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 didn’t go to see the film.

It doesn’t interest me whether you succeed or not.

It is in the morning 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