摘要：关系从句是英语语法中最重要的语法之一，也是各类考试中必考知识点。
关键词：从句;先行词;代词;副词
一、概述
关系从句也叫定语从句，可分为：限制性关系从句和非限制性关系从句。
（1）限制性关系从句一般都直接置于其修饰的先行词之后，前面不加逗号，一般由下列关系代词引导：
（2）非限制性关系从句，用来对前面某一先行词进行补充说明，或对前面整句话进行评述（后者只能用which来引导），前面须加逗号，一般由下列关系代词引导：
（3）先行词是时间、地点、原因，且在从句中作状语时，分别用关系副词when，where，why引导。when和where可以用“介词+which”替换;why的先行词只能是reason，why可用“for which”代替。
Eg：
①She remembered the day when （=on which） Paul had first walked into her office.
②We then moved to Pairs，where （=in which）we lived for six years.
③This is the reason why （=for which） you should leave.
二、限制性定语从句
（一）只能用that，不用which 引导定语从句的特殊情况
（1）当先行词是all，everything，nothing，something，anything，little，none， few 等不定代词时。
（2）当先行词被序数词或形容词最高级修饰时。
（3）当先行词被no，every，some，any，only，very，much等限定修饰时。
（4）当先行词既有人又有物时。
（5）当先行词为主句的表语或关系代词为从句的表语时。
（6）There be 句型中，当先行词为物时。
（7）当先行词前面有who，which，what等特殊代词时。
Eg：
①All that we need is the support from you.
②The first lesson that I learned will never be forgotten.
③He is the only person that I want to see.
④The passengers and parcels that filled the car were mixed.
⑤Our school is no longer the school that it used to be.
⑥There is a room in the building that is still free.
⑦Who is the lady that is waiting at the school gate？
（二）只能用which，不能用that導定语从句的特殊情况
（1）which 可以引导非限制性定语从句，that 则不能。
（2）which之前可以接介词，that 则不能。
（3）当先行词本身为that时。
Eg：
①He changed his mind，which made me very angry.
②The questions were all on opera， about which I know nothing.
③Whats that which flashed in the shky just now.
（三）准关系代词as，than，but
as，than，but这几个连接词可以像关系词一样，前面有名词作先行词;但它们后面的定语从句却不像典型的定语从句。所以这些既像连接词又像关系词的词，称其为准关系代词。准关系代词只有as，than，but，用法如下：
（1）as 主要用在“such （+n）+as”（和….同样的），“the same（+n）+as”（像….这样的），the same as，such as，as…as 等结构中：
Eg：
①She has as much money as is required.
②I havent much money but you can use such as I have.
③The town is not the same country as it used to be.
④We do the same work as they do.
（2）than 作为准关系代词出现在more....than，less...than，fewer...than等结构中，这时than前面要有名词：
Eg：
①I have more money than is needed.
②Barbara seems to lake a keener interest in piano music than has ever been shown.
（3）But是具有否定意义的准关系代词代替人或物，在意义上等同于“that/which/who..not”，but前面的主句要有另一个否定意义。
Eg：
①There is no one but is concerned about his future.
②There is nothing but she can do.
三、非限制性定语从句
（一）两种定语从句关系词的区别
（1）非限制性定语从句中的关系词不可省略。
（2）whom在非限制性定语从句中作宾语时不可用who来代替。
（3）非限制性定语从句的先行词也可为整个主句，此时非限制性定语从句。
常由which引导，还可用in which case，at which point，on which occasion等（从句谓语动，词要用第三人称单数）。
Eg：
①A young man had a new girl friend，whom he wanted to impress.
②The son didnt pass the exam，which disappointed him.
③I may have to work late， in which case Ill telephone you.
（二）as与which 引导的非限制性定语从句的区别：
（1）as 只指代整个主句，而which即可指代整个主句也可指代句中的一部分。
（2）as 引导从句时表示“正如”，无具体内容，which引导从句时表示具体的内容。
（3）as 引导的从句位置很灵活，可在主句前面、中间和后面，而which 从句只能放在主句之后。
Eg：
①Air，as is well-known，contains some kinds of gas.
②The night has turned cold，as is usual around here.
③He changed his mind at the last moment，which make me angry.
④I called him by the wrong name，for which mistake I apologized.
四、定語从句与同位语从句的区别
二者形式相似，均位于名词或代词后，区别为：
（1）前者相当于形容词，对先行词加以限制或修饰;后者相当于名词，对名词性成分加以补充说明，是具体内容的体现。
（2）前者的关系词要代替先行词在从句中作句子适当的句子成分，有时可省略;后者的引导词不在从句中充当句子成分，但不可省略。
（3）前者不能用whether，how 等连词引导，后者可以。
Eg：
①The fact that he had not said anything surprised everybody.（同位语）
②The fact that you are talking about is important.（定语从句）
参考文献：
[1]伍乐其.专四语法与语汇[M].北京：世界图书出版公司，2015.
作者简介：
南玉祥（1979-），男，甘肃天水人，讲师，主要从事翻译和英语语用学研究工作。
