從句按其在主句中的句法功能可分為三類,即名詞性從句、形容詞性從句(即定語從句)和副詞性從句(即狀語從句).引導從句的詞稱作關聯(lián)句.
名詞性從句包括主語從句、表語從句、賓語從句和同位語從句.引導這些名詞性從句的關聯(lián)詞包括:
從屬連詞that,if,whether;
連接代詞who,whoever,whom,whomever,which,whichever,what,whatever,whose;
連接副詞where,when,why,how.
其中,從屬連詞只起連接作用,在從句中不充當任何句法成分,而連接代詞和連接副詞既起連接作用,在從句中又充當一定的成分.
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?
你聽說瑪麗要和湯姆結(jié)婚的消息了嗎?(that引導同位語從句)
[提示]
1.在含有主語從句的復合句中,為保持句子平衡,常用it作形式主語,而將真正的主語從句置于句末.
It's well known that water is indispensable to life.
2.為保持句子平衡,that引導的賓語從句也常用it代替,而將真正的賓語從句置于主句句末.這常常出現(xiàn)在主句有形容詞或分詞作賓語補足語的情況下.
He made it quite clear that he preferred to live here.
3.從屬連詞whether和if都作“是否…”解,但if不可引導主語從句和表語從句.whether可與or(not)連用,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引導名詞性從句的區(qū)別:that在從句中不充當成分,而what在從句中充當一定的成分,如主語、表語、賓語等.that可省略,what則不可省.
He always means what he says.
She suggested (that) he do it at once.
5.同位語從句大多由從屬連詞that引導,常跟在下列名詞后面,如fact,idea,opinion,news,hope,belief等,that不可省,一般用來解釋說明這些名詞的具體含義和內(nèi)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.
如何判斷各類從句呢?
答：
1．分析句子結(jié)構(gòu)以區(qū)分從句的種類.遇到一個復合句,首先要分析其句子結(jié)構(gòu),看從句在整個句子中起什么作用,那么它就是什么從句.
2． 分析引導詞的句法作用以區(qū)別從句的種類.that這個詞既可引導同位語從句,又可引導定語從句,這種兩種從句從形式和結(jié)構(gòu)上看特別相似,如何區(qū)分呢?區(qū)分that引導的是同位語從句還是定語從句的方法是,看that在從句中是否充當句子成分,若that在從句中不充當任何成分,則為同位語從句；若that在從句中充當主語或賓語,則為定語從句.
3． 根據(jù)被修飾詞來判斷從句的種類.定語從句常常修飾一些具有實際意義的名詞,如：the film；the student；the book；a house等等.而同位語從句常常修飾一些表示抽象概念的名詞,如fact、idea、promise、truth等,用來說明這些名詞所表示的具體內(nèi)容.狀語從句在句子中常用來修飾謂語動詞.
4．根據(jù)從句前詞的詞性來判斷從句的種類.賓語從句分兩種：動詞的賓語從句、介詞的賓語從句.賓語從句前肯定是動詞或介詞.定語從句是用來修飾名詞或代詞的,所以其前一定是一個名詞或代詞.
5．根據(jù)上下文意義和結(jié)構(gòu)形式上區(qū)分從句的種類.如so that即可引導目的狀語從句,又可引導結(jié)果狀語從句,如何區(qū)分呢?主要從以下兩點來區(qū)分.①根據(jù)上下文意義判斷.“以便……”表示目的,是目的狀語從句,“以致于……”,“結(jié)果……”表示結(jié)果,是結(jié)果狀語從句.②從結(jié)構(gòu)形式上來分辨.so that前有逗號,為結(jié)果狀語從句,反之,則為目的狀語從句.有時,so that前無逗號,這里要看從句中有無can、could、may、might、will、would、should 等情態(tài)動詞,如果有,則多是目的狀語從句,若沒有,則多是結(jié)果狀語從句.