高中英语主语从句 知识点讲解

主语从句

在从句中充当主语的复合句，主语即为主句动作的发出者或状态的持有者。有两种形式：直接放句首；it 为形式主语，真正的主语在句子后（为了避免头重脚轻）。主语从句时态不受主句的限制。

（一）连接词引导的主语从句

主语从句在复合句中作主句的主语,引导主语从句的词有从属连词that, whether以及连接代词who, what, which, whoever, whatever, whichever和连接副词when, where, why, how等.

连接词引导的从句

That light travels in straight line is known to all.我们都知道光是以直线传播的。

Whether he will join us is still a question.他是否会加入我们仍是个问题。

连接代词引导的从句

Who will be sent there has not been decided.大家还没有决定谁会被送过来。（主语）

What you need is more practice. 你需要更多的练习。(宾语)

Whatever we do is to serve the people.我们无论做什么都是为了服务人民。（宾语）

Which is the best is not clear.我们不清楚哪个最好。(主语)

连接副词引导的从句

Where he has gone is a question.我们不知道他去哪儿了。（地点状）

How he can earn a living in London remains a big problem. 如何在伦敦谋生仍是个大问题。（方式状）

When we shall have our sports meet is a mystery. 什么时候会开运动会仍是个迷。（时间状）

注意：在主语从句中，为了避免头重脚轻的问题，常用it为形式主语，真正的主语在句子后。（上述的例子转换）

（二）总结it为形式主语的结构：

1)It is + adj. / n. +从句

It is a pity/shame that...遗憾的是……

It is possible that...很可能……

It is unlikely that...不可能……

2)It +不及物动词+从句

It seems/appears that...似乎……

It happened that...碰巧……

3)It + be +过去分词+从句

It is said that...据说……

It is known to all that...众所周知……

It is reported that...据报道……

It is believed that...据信……;人们相信……

It is suggested that...有人建议……

It must be pointed out that...必须指出……

It has been proved that...已证明…….例如:

It is believed that at least a score of buildings were damaged or destroyed.据信,至少有二十座楼房遭到破坏或彻底毁掉.

It is suggested that the meeting should be put off.有人建议会议延期召开.

It's reported that three people were killed in the accident and five were hurt badly.据报道,事故中三人丧生,五人重伤.

It is known to all that Taiwan is an inseparable part of China.众所周知,台湾是中国不可分割的一部分.

（三）学习主语从句应该注意的几个问题

1)引导词that与what

what既有引导主语从句的作用,同时又在从句中作句子成分(主语、宾语、表语等).这时what相当于all that/everything that...,常译成"所……的(东西、事情、话等.)";而that只起连接作用,本身无实际意义,在从句中也不担当任何句子成分.但that引导的主语从句放在句首时,不能省略that.例如:

What is done can't be undone. (谚语)已成定局,无可挽回.

What we can't get seems better than what we have.我们得不到的东西似乎比已得到的要好.

That we should work out a plan to deal with the present serious situation is important.我们应该制定一项计划来应付目前严峻的形势,这一点非常重要.

That a new teacher will come to teach us geography is true.一位新老师将来教我们地理,这是真的.

2)引导词if和whether

if和whether引导动词后的宾语从句时一般可通用,但介词后的宾语从句、主语从句(放在句首时)、表语从句

常由whether引导.例如:

Whether she will go home or not is unknown.她是否回家还不得而知.

Whether we shall raise ducks or geese remains to be decided.我们是养鸭还是养鹅仍没决定.

=It remains to be decided whether/if we shall raise ducks or geese.

但我们不能说If we shall raise ducks or geese remains to be decided.

3)其它引导词

连接代词who, which, whom, whose有各自的意义,起连接作用,并在从句中充当语、宾语、表语、定语等;连接副词when,where, why, how等有各自的意义,起连接作用,并在从句中充当状语.

（四）语气

在It is necessary / natural / important / strange...+ that-clause这类句型里,that所引导的主语从句中谓语动词用"should +原形",表虚似语气.例如:

It is necessary that the problem should be settled at once.这个问题必须马上解决.

It's strange that he should have gone away without telling us.他竟然没向我们说一声就走了,真是奇怪.

（五）以it作形式主语的主语从句与强调句型的区别

"It be + adj./n. + that-clause"与强调句型均有It be...that...之类的语言标志

,但不同的是:①前者中的that从句是主语从句.若删掉其中的It be和that,则剩余部分不论结构还是语意都不能成为一个句子;但若将后者中的It be和that去掉,则剩余部分的结构和语意仍能构成一个完整的句子.

②强调句型译为汉语时可加上"正是……"或"就是……"之类的字眼,而主语从句则不可以.请比较下面两个句子:

It is surprising that Mary should have won first place.令人惊奇的是玛莉竟然获得了第一名.

It is Mary that has won first place.正是玛莉得了第一名.

补充强调句：it引导的强调句与it做形式主语的复合句不可混淆。it引导的强调句是对句子某一成分强调，对主语为人强调用who，that都可，对其他只用that，（去掉it is that 句子仍完整）

I met John in the street yesterday. 我昨天在街上看见了John.

It was I that (who) met John in the street yesterday. 是我昨天在街上看到了John。(强调主语)

It was John that I met in the street yesterday. 我昨天在街上看到的是John。（强调宾语）

It was in the street that I met John yesterday. 我昨天看到John在街上。（强调地点状）

It was yesterday that I met John in the street.昨天，我在街上遇见了John。（强调时间状）