英语语法讲解之定语从句一、几个基本概念1.定义：用作定语的从句叫定语从句。
2.先行词：被定语从句所修饰的名词或代词。
3.位置：紧跟先行词(名词或代词)之后。
4.引导词：引导定语从句的词(包括关系代词和关系副词)。
﹙1﹚关系代词：that/who/which/whom/whose﹙2﹚关系副词：when/where/why﹙3﹚引导词的位置：位于定语从句之前(先行词之后)。
﹙4﹚引导词的功能(作用)：①连接先行词和定语从句。
②在定语从句中充当一定的成分(关系代词充当主语或宾语，关系副词充当状语)。
5.定语从句的类型：﹙1﹚限定性定语从句(主句和定语从句之间无逗号)。
①直接由引导词引导定语从句Eg.The man who you’re talking to is my friend.②由介词+关系代词(whom/which)引导Eg.The man to whom you’re talking is my friend.=I need a pen with which I can write a letter.=I need a piece of paper on which I can write a letter.=介词的选用可根据从句中的相关词组确定，该介词通常可以放在关系代词之前，也可放在相关动词之后。
例如：The man (who/whom/that) I talked about at the meeting is from Beijing University.=The man about whom I talked at the meeting is from Beijing University.The palace (which/that) I often pay a visit to was built in the 17th century.=The palace to which I often pay a visit was built in the 17th century.※﹙2﹚非限定性定语从句(主句和定语从句之间用逗号隔开)。
除why和that不能引导非限定性定语从句外，其余引导词都可以，用法同限定性定语从句一样。
但要注意以下区别。
①在形式上非限定性定语从句与主句有逗号隔开。
②非限定性定语从句的作用：它只是补充说明先行词的情况，翻译时可译成两个句子。
The engineer，whose leg was badly hurt，was quickly sent to hospital.(那位工程师被很快送往医院，其腿部受了重伤)The engineer whose leg was badly hurt was quickly sent to hospital.(那位腿部受了重伤的工程师被很快送往医院)③在非限定性定语从句中，任何引导词都不能省略(包括引导词在此定语从句中充当宾语在内)。
指人做主语时只能用who，做宾语时用whom；指物做主语，宾语都用which；关系副词用when或where，也不能省略。
④whose引导非限定性定语从句：The house，whose window faces south，is mine.=The house，the window of which faces south，is mine.=The house，of which the window faces south，is mine.二、定语从句中关系代词和关系副词的基本用法。
1.who/that 指人，主格，代替先行词，在定语从句中作主语，不能省略。
Eg.Do you know the gentleman who/that is sitting there？2.whom/who/that指人, 宾格，代替先行词，在定语从句中作宾语(动宾或介宾)。
①当作动宾(动词后的宾语)时，关系代词可省略。
Eg.Do you know the gentleman (whom/who/that) we met just now？②当作介宾(介词后接宾语)时：介词不提前时，关系代词可省略；介词提前时，关系代词不可省，即介词+whom(指人时介词后的关系代词只能用whom)。
Eg. The man (whom/who/that) I spoke with is my teacher.Eg. The man with whom I spoke is my teacher.(不能用who/that)注：固定的动词短语(动词+介词)如look for，take care of等不能把动词与介词拆开，既介词不能提至引导词前。
Eg. She is the right girl (who/whom/that) we are looking for.3.whose：指人或物，是所有格“…的”形式，可指代形容词性物主代词、名词性物主代词和名词所有格。
Whose+n.一起在定语从句中充当主语、宾语(动宾或介宾)即先行词的什么东西怎样了，whose不能省略。
I didn’t find the desk whose leg was broken. (主语)He is the student whose pencil I broke yesterday. (动宾)The boss in whose company I work is very kind. (介宾)4.which/that指物，代替先行词，在定语从句中作主语或宾语(动宾或介宾)。
①当作动宾时，关系代词可省略。
②当作介宾时：介词不提前时，关系代词可省略；介词提前时，关系代词不可省，即介词+which(指物时介词后的关系代词只能用which)。
The house which/that was destroyed in the earthquake is weak.The pen (which/that) you found yesterday is mine.The games (that/which) the young men competed in were difficult.The games in which the young men competed were difficult.注：介词+关系代词即介词+whom/which(先行词指人用whom，指物用which)。
5.when 关系副词：指时间。
在定语从句中作时间状语，不能省略。
此时的when还可用介词+which替换(此时先行词一定是表时间的名词)。
When = on whichI still remember the time when I joined the League.=I still remember the time on which I joined the League.=I still remember the time (which/that) I joined the League on.6.where 关系副词：指地点。
在定语从句中作地点状语，不能省略。
此时的when还可用介词+which替换(此时先行词一定是表地点的名词)。
Where = in whichI still remember the school where I joined the League.=I still remember the school in which I joined the League.=I still remember the school (which/that) I joined the League in.7. why 关系副词，指原因，在定语从句中作原因状语，先行词通常为reason，不能省略。
且why引导的定语从句只能是限定性定语从句。
Why = for whichI don’t know the reason why he was late yesterday.The reason why(for which) he was late is that he missed the bus.注：对关系副词when，where的认识。
①. 先行词是时间的名词，并非都用关系副词when引导定语从句。
I’ll never forget the time (which/that) I spent in Beijing.②. 先行词是地点的名词，并非都用关系副词where引导定语从句。
This is the factory (which/that) he visited yesterday.③. 当句型为It/This/That is(was) the first(second…last) time引起的句子时用that连接其后的句子。
此时的time是次数，不是时间。
It/This is the first time that we travel.It/This is the last time that I shall give you a lesson.注：当先行词为reason时，关系副词并非都用why.This is the reason (that/ which) he gave/ explained to us.【判断用关系代词还是关系副词】从句缺少的是主语、宾语还是状语是确定用关系代词还是关系副词的关键。
试比较：I will never forget the day (which/that) I spent in Hongkong.( spent是及物动词，后缺宾语，因此用关系代词或省略)I will never forget the day when/on which Hongkong returned to its motherland.( 从句主谓宾结构完整，缺状语，因此用关系副词或介词加关系代词)The reason (that/which)he ga ve for not coming to school yesterday isn’t believable.( gave是及物动词，后缺宾语，因此用关系代词或省略)The reason why he didn’t come to school yesterday isn’t believable.( 从句主谓宾结构完整，缺状语，因此用关系副词或介词加关系代词)三、值得注意的几个问题：1）关系代词只用that的情况。
1.当先行词被序数词或形容词的最高级修饰时。
This is the best film that has been shown this year.This is the first book (that) I borrow from the library.※He is the first student that/who came to school today.2.当先行词既有人又有物时。