关系词在定语从句的构成里是至关重要的。我们甚至可以说,掌握不好关系词就无法做成定语从句,也无法理解文中带有定语从句部分的意思。因此,我们首先讨论一下关系词的有关问题。
定语从句中的关系词只有两类:关系代词和关系副词;没有连词。也就是说,定语从句中的所有关系词不但都有具体的意义而且都在从句中担任一定的成分。
1)关系代词:who , whom , whose , which , that 等
     who用于代替"表示人的意义"的先行词,并且在从句中作主语;在现代英语里,也可取代whom在从句中作动词的宾语。
例如:I have no idea about the man who wrote the article .我不认识写这篇文章的那个人。
        The little boy who is singing there can recite quiet a number of Chinese poems .
     whom 用于代替"表示人的意义"的先行词,并且在从句中作动词或介词的宾语。
 在现代英语里,如果whom在从句中作动词的宾语,它与who可以通用;但是如果whom在从句中作介词的宾语,那么就只能用whom而不能与who通用了。当然,如果在口语或非正式文体中,介词没有提前,也就没有这点要求了。
例如:Who is the girl whom ( who ) you talked to just now ? 刚才和你说话的那个女孩子是谁?
        Yesterday, I happened to meet , in the shopping center , the professor who ( whom ) I got to know at a party .
        昨天在购物中心,我碰巧遇见了那位我在一次聚会上认识的教授。 
        They are looking for the patient on whom doctors just performed an operation . 他们正在寻找那位医生刚刚给他做过手术的病人。
      (句中的关系代词whom代替the patient ,在从句中作介词on的宾语,而且介词on提到关系代词的前面,所以who 和whom就绝不可以通用了,此处只能用whom 。)
       Who is the girl to who (whom) you talked just now ? (错误)
(句中的关系代词whom(who)代替the girl ,在从句中作介词to的宾语,但是由于介词to已提到了关系代词的前面,who 和whom就绝不可以通用了,所以如果还继续使用who句子就错了。此处只能用whom 。)
whose 用于代替"表示人或物意义"的先行词,在从句中作定语,往往与它所修饰的名词一起构成一个名词短语在从句中担当成分。Whose常表达"某人的、某物的"之意。
例如:Do you know the name of that girl whose brother is your roommate ?你知道她的哥哥与你同寝室的那位女孩的名字吗?
        Water whose boiling point is at 100 degree Centigrade has no color, no flavor. 沸点在摄氏100度的水无色、无味。
which 用于代替"表示事物意义"的先行词,在从句中作主语、宾语。
例如:Views which are entirely new or foreign may also be hard to accept .那些全新的或是来自国外的观点或许也很难被接受。
         I've got a novel which you may like to read .我弄到一本你或许想看的小说。
         That was a fault which could not be forgiven . 那是不能饶恕的错误。
that 既用于代替"表示人的意义"的先行词,也用于代替"表示事物意义"的先行词;在从句中既可以作主语,也可以作谓语动词的宾语,但是不能作介词的宾语。在一定范围内,that = who / whom / which 。
例如:Views that (which ) are entirely new or foreign may also be hard to accept .那些全新的或是来自国外的观点或许也很难被接受。
         Salaried people that ( who) earn more than a few thousand dollars must pay a certain percentage of their salaries to the federal government .工薪在几千美元以上的人必须将工资中的一定百分比交付给联邦政府。
         Who is the girl to that you talked just now ? (错误)
要点提示:定语从句中作宾语的关系代词可以省略;如果关系代词在定语从句中作宾语可以省略。
例如:This is the book ( which ) you were looking for yesterday . 这就是你昨天找的那本书。
         I don't like the novel ( that ) you are reading .我不喜欢你看的这本小说。
         Who is the man ( whom ) you're talking about ? 你们谈论的那个人是谁?定语从句中,关系代词的单复数取决于先行词的单复数。
例如:Those who are in their forties are required to have a physical examination this afternoon .(先行词Those是复数,关系代词who也就看作是复数,所以从句的谓语动词就用了复数形式are了。)请那些年龄在四十几岁的人于今天下午去进行体检。
         This is the magazine which was sent to me by post .(先行词the magazine是单数,关系代词which也就看作是单数,所以从句的谓语动词就用了单数形式was sent) 这是通过邮局寄给我的杂志。