引导定语从句的关系代词who,which有时可与that互换使用。但在下面情况，一般只用that。 一、当先行词为不定代词anything, everything, nothing, any, little, one, few, much, all, none等时。如： a.There isn't much that I can do. b.He is one of the few that can work it out in five minutes. 二、当先行词是形容词最高级或被形容词最高级修饰时。如： a.The book is the best that I have read. b.This is the biggest laboratory that we have ever built in our university. 三、当先行词是序数词或其被序数词修饰时。如： a. It is the third one that I've bought. b.This is the first place that I've ever visited. 四、当先行词被the very, the only等词修饰时。如： a.Is this the very museum that you visited the other day? b.This is the only book that I need at present. 五、当先行词包含了人和事物两方面的含义时。如： They talked of things and persons that they remembered in the school. 六、当先行词被same修饰，且指“同一物品”时。如： She is wearing the same dress that she wore yesterday. 七、关系代词在定语从句中作表语时。如： a.This is no longer the place that it used to be. b.He is not the man that he was. 八、当主句是以who,which开头的特殊疑问句或先行词是who时。如： a.Which is the book that he bought yesterday? b.Who that you have ever seen can beat him in 定语从句是由关系代词和关系副词引导的从句，其作用是作定语修饰主句的某个名次性成分，定语从句分为限定性和非限定性从句两种。 一、 限定性定语从句 1. that即可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语则不能省略。而且，如果which在从句中作“不及物动词＋介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置 2. which作宾语时，根据先行词与定语从句之间的语义关系，先行词与which之间的介词不能丢 3. 代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括all, anything, much等，这时的that常被省略 4. who和whom引导的从句用来修饰人，分别作从句中的主语和宾语，whom作宾语时，要注意它可以作动词的宾语也可以作介词的宾语 5. where是关系副词，用来表示地点的定语从句 6. when引导定语从句表示时间（〔注〕值得一提的是，表示时间“time"一词的定语从句只用when引导，有时不用任何关系代词，当然也不用that引导） By the time you arrive in London, we will have stayed there for two weeks. I still remember the first time I met her. Each time he goes to besiness trip, he brings a lot of living necessities, such as towers, soap, toothbrush etc. 7. whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格 8 当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用there is来引导 二、非限定性定语从句：非限定性定语从句的作用是对所修饰的成分作进一步说明，通常和主句间用逗号隔开，将从句拿掉后其他部分仍可成立 1. which引导的非限定性定语从句来说明前面整个句子的情况或主句的某一部分 2. 在引导限定性定语从句时，that有时相当于in which, at which, for which或at which Attitudes towards daydreaming are changing in much the same way that(in which) attitudes towards night dreaming have changed. 人们对白日做梦的态度正在改变，这与人们对夜间做梦的看法的变化有非常相似之处 I like the music for the very reason that(for which) he dislike it. 我出于某种原因喜欢这种音乐，而他恰恰与我相反 We arrived the day that(on which) they left. 刚好我们到的那天他们走了。 3有时as也可用作关系代词 4在非限定性定语从句中，不能用that，而用who, whom代表人，用which代表事物. 一.定语从句及相关术语 1.定语从句：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。 2.关系词：引导定语从句的关联词成为关系词（关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等；关系副词有where, when, why等） 关系词常有3个作用：1，引导定语从句。2，代替先行词。3，在定语从句中担当一个成分。 二.关系代词引导的定语从句 1.who指人，在从句中做主语 The boys who are playing football are from Class One. 2. whom指人，在定语从句中充当宾语，常可省略 Mr. Liu is the person (whom) you talked about on the bus（注意：关系代词whom在口语和非正式语体中常用who代替，可省略） 3. which指物，在定语从句中做主语或者宾语，做宾语时可省略 Football is a game which is liked by most boys 4. that指人时，相当于who或者whom；指物时，相当于which。在宾语从句中做主语或者宾语，做宾语时可省略 The number of the people that/who come to visit the city each year rises one million. 5. whose通常指人，也可指物，在定语从句中做定语 He has a friend whose father is a doctor. 三.介词+关系代词引导的定语从句 关系代词在定语从句中做介词宾语时，从句常由介词+关系代词引导 The school (that/which) he once studied in is very famous 注意：1. 含有介词的动词短语一般不拆开使用，如：look for, look after, take care of等 1) This is the watch which/that I am looking for. (T) 2) This is the watch for which I am looking. (F) 2. 若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，不能用that；关系代词是所有格时用whose The man with whom you talked is my friend. (T) The man who/that you talked with is my friend. (F) 3. “介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词 (1) He loved his parents deeply, both of whom are very kind to him. 本文来源：https://www.wddqw.com/doc/a92b8d8fe309581b6bd97f19227916888486b983.html