主语从句讲解

主语从句讲解

主语从句

主语从句定义:在句子中担当主语的是一个从句,这个从句就叫做主语从句。

主语从句是在复合句中充当主语的从句，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。

1.引导主语从句的关联词有三类：

(1)从属连词that，whether

That they were true sisters was clear from the facial resemblance between them.Whether he’ll come here isn’t clear.

(2)连接代词who, whom, whose, what, which, whoever, whatever, whichever，What she did is not yet known.

How this happened is not clear to anyone.

Whoever comes is welcome.

(3)连接副词where，when, how, why

2.主语从句是在复合句中充当主语的从句，其功同名词一样。为了避免头重脚轻，常用it作形式主语,而把真正主语放在句子末尾。

How the book will sell depends on its author.

That he is the best student in the class is obvious.

= It is obvious that he is the best student in the class.

注意：主语从句不可位于句首的五种情况

(1) if引导的主语从句不可居于复合句句首。

(2) It is said , (reported) …结构中的主语从句不可提前。

例如：It is said that President Jingo will visit our school next week.

(3) It happens…, It occurs…结构中的主语从句不可提前。

例如：It occurred to him that he failed in the examination.

(4) It doesn’t matter how/whether …结构中的主语从句不可提前。

例如：It doesn’t matter whether he is wrong or not.

(5)含主语从句的复合句是疑问句时，主语从句不可提前。

例如：Is it likely that it will rain in the evening?

3.主语从句用陈述语序。关联词位于句首不能省略。

How he became a great scientist is known to us all.

That he finished writing the composition in such a short time surprised us all.

4.主语从句中注意的事项：

1）在主语从句中，谓语动词一般用单数。

Whatever he says is of no importance.

Whoever says this is wrong.

但谓语动词用单数还是复数，不可一概而论，而要视句子的意义而定

What I need is money.

What I need are books.

2）what与that在引导主语从句时的区别

what引导主语从句时在从句中充当句子成分，如主语、宾语、表语，而that则不然。

What you said yesterday is right.

That she is still alive is a consolation.

3）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。

1. It作形式主语和it引导强调句的比较

①主语从句常用it作形式主语，一般常用句型为：It is+{名词/形容词/过去分词}+主语从句例如：

It is still a question whether she will come or not.

It is strange that you should like him.

It is still unknown which team will win the match.

②而强调句则不同，它的结构是：It+be+被强调部分+that+从句

强调主语：It is the times that produce their heroes.时势造英雄

强调宾语：It is English that Prof.Lin teaches us.

强调状语：It was in shanghai that I saw the film.

判断是否是强调句有一个方法，就是将that以后的“句子的其余部分”拿出来单独看，看有没有缺成分，缺的是什么成分，再把谓语动词后面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句完整的句子了，那就说明是强调句。

It is still a mystery what caused the accident.

It is a mystery that his death remained.

4) whether与if