英语从句的种类及用法

从句按其在主句中的句法功能可分为三类,即名词性从句、形容词性从句(即定语从句)和副词性从句(即状语从句).引导从句的词称作关联句.
名词性从句包括主语从句、表语从句、宾语从句和同位语从句.引导这些名词性从句的关联词包括:
从属连词that,if,whether;
连接代词who,whoever,whom,whomever,which,whichever,what,whatever,whose;
连接副词where,when,why,how.
其中,从属连词只起连接作用,在从句中不充当任何句法成分,而连接代词和连接副词既起连接作用,在从句中又充当一定的成分.
That Owen should have married his cousin is not at all surprising.
The fact is that he didn't go to the dinner party.
I don't know if he will attend the meeting.
Have you heard the news that Mary is going to marry Tom?
你听说玛丽要和汤姆结婚的消息了吗?(that引导同位语从句)
[提示]
1.在含有主语从句的复合句中,为保持句子平衡,常用it作形式主语,而将真正的主语从句置于句末.
It's well known that water is indispensable to life.
2.为保持句子平衡,that引导的宾语从句也常用it代替,而将真正的宾语从句置于主句句末.这常常出现在主句有形容词或分词作宾语补足语的情况下.
He made it quite clear that he preferred to live here.
3.从属连词whether和if都作“是否…”解,但if不可引导主语从句和表语从句.whether可与or(not)连用,而if不可以.
I don't know whether (if) she is at home.
Whether she comes or not makes no difference.
4.that和what引导名词性从句的区别:that在从句中不充当成分,而what在从句中充当一定的成分,如主语、表语、宾语等.that可省略,what则不可省.
He always means what he says.
She suggested (that) he do it at once.
5.同位语从句大多由从属连词that引导,常跟在下列名词后面,如fact,idea,opinion,news,hope,belief等,that不可省,一般用来解释说明这些名词的具体含义和内容.
We are familiar with the idea that all matter consists of atoms.
The news that we are invited to the conference is very encouraging.
如何判断各类从句呢?
答：
1．分析句子结构以区分从句的种类.遇到一个复合句,首先要分析其句子结构,看从句在整个句子中起什么作用,那么它就是什么从句.
2． 分析引导词的句法作用以区别从句的种类.that这个词既可引导同位语从句,又可引导定语从句,这种两种从句从形式和结构上看特别相似,如何区分呢?区分that引导的是同位语从句还是定语从句的方法是,看that在从句中是否充当句子成分,若that在从句中不充当任何成分,则为同位语从句；若that在从句中充当主语或宾语,则为定语从句.
3． 根据被修饰词来判断从句的种类.定语从句常常修饰一些具有实际意义的名词,如：the film；the student；the book；a house等等.而同位语从句常常修饰一些表示抽象概念的名词,如fact、idea、promise、truth等,用来说明这些名词所表示的具体内容.状语从句在句子中常用来修饰谓语动词.
4．根据从句前词的词性来判断从句的种类.宾语从句分两种：动词的宾语从句、介词的宾语从句.宾语从句前肯定是动词或介词.定语从句是用来修饰名词或代词的,所以其前一定是一个名词或代词.
5．根据上下文意义和结构形式上区分从句的种类.如so that即可引导目的状语从句,又可引导结果状语从句,如何区分呢?主要从以下两点来区分.①根据上下文意义判断.“以便……”表示目的,是目的状语从句,“以致于……”,“结果……”表示结果,是结果状语从句.②从结构形式上来分辨.so that前有逗号,为结果状语从句,反之,则为目的状语从句.有时,so that前无逗号,这里要看从句中有无can、could、may、might、will、would、should 等情态动词,如果有,则多是目的状语从句,若没有,则多是结果状语从句.