限制性定语从句和非限制性定语从句都是修饰名词和代词的一种从句，两者虽然性质相同，但在意义上和用法上有许多不同。

　　1.限制性定语从句是先行词在意义上不可缺少的定语，如果去掉，主句的意思就不完整或失去意义。这种定语从句和主句的关系十分密切，书写时不用逗号分开。例如：

　　I was the only person in my office who was invited. 我是办公室里唯一受到邀请的人。

　　He has found the hammer that he was looking for.他找到了他正在寻找的那把锤子。

　　2.非限制性定语从句同主句的关系不十分密切，只是对先行词作附加或补充的说明，不起限制的作用，如果省去，主句的意思仍然清楚完整。例如说“He has two brothers.”时，句意已经很明确了，但若要进一步说明“two brothers”的情况，可以在其后面加上 who live in Guilin 或 who can speak English 等非限制性定语从句。故非限制性定语从句仅仅是对意思已经相当明确的先行词加以补充说明，不起限制的作用。这类定语从句在书写时大多用逗号与主句分开。例如：

　　Last week I met John, who seemed to be very excited.上星期我见到了约翰，他好像很兴奋。

　　The project, which lasted two years, cost five million dollars. 这项工程历时两年，耗资五百万美元。

　　3.非限制性定语从句对所谈及的人或事物只提供进一步的说明或解释，它形式上是一个从句，但在功能上相当于一个分句，在意义上相当于一个状语，故可根据其句意改为并列句或状语从句。例如：

　　The meeting, which was held in the park, was attended by 1000 people. →The meeting was attended by 1000 people, and it was held in the park. 那次会议有一千人参加，它是在公园里举行的。

　　I don't like the boy, who is very lazy. →I don't like the boy, since he is very lazy. 我不喜欢这个男孩, (因为)他太懒惰了。

　　4.关系代词 who，whom，which 在限制性定语从句中作动词的宾语时往往可以省略，但在非限制性定语从句中不能省略。值得注意的是，关系代词 that 可引导限制性定语从句，但一般不可引导非限制性定语从句。例如：

　　I know the man (whom) you mean. 我认识你指的那个人。

　　I happened to meet Li Hong, whom I didn't recognize at once. 我碰巧遇到李红，但并没有马上认出她来。

　　These are the pictures (that / which) I took in Guilin.这些是我在桂林拍的照片。

　　These apple trees, which I planted three years ago, have not borne any fruit.这些苹果树是我三年前栽的，还没有结过果实。(不可将 which 改为 that)

　　5.限制性定语从句对先行词起限制的作用，非限制性定语从句对先行词起补充说明的作用，故两者的意义往往有别。例如：

　　His brother, who is eighteen years old, is a PLA man. 他的哥哥是个解放军战士，现今十八岁。(说明他只有一个哥哥)

　　His brother who is eighteen years old is a PLA man. 他那个十八岁的哥哥是位解放军。(说明他还有别的哥哥)

　　All the books there, which have beautiful pictures in them, were written by him.那里所有的书都是他写的, 书里附有漂亮的插图。(说明那里没有除他以外的人写的书)

　　All the books there which have beautiful pictures in them were written by him. 那里所有附插图的书都是他写的。(暗示没有附插图的书不是他写的)

　　小试牛刀：选择最佳答案。

　　1. Can you think of anyone _______ could look after him a bit for the next few days?

　　A. that B. which C. whom D. /

　　2. In Britain he had come across a painter _______ nobody else had heard of.

　　A. which B. where C. with whom D. /

　　3. Sunday is a holiday, _______ people do not go to work.

　　A. on which B. on when C. in which D. where

　　4. Yesterday was one of the coldest days _______ I have ever known.

　　A. which B. when C. who D. that

　　5. I am off to St. James Park,_______ I have to give a lecture on the Theatre.

　　A. when B. there C. where D. which

　　6. This I did at nine o'clock, and _______ I sat sometimes reading the paper.

　　A. after doing it B. after which C. after while D. when

　　7. She was very fond of speaking French, _______ indeed she spoke very well.

　　A. that B. where C. which D. /

　　8. She had two new cars, _______ was made in Japan.

　　A. one B. which C. and one of which D. and one of them

　　9. My new car, _______ I paid several thousand pounds _______ , is not running well.

　　A. which; for B. that; for C. which; / D. what; with

　　10. His son, _______ he had been devoted, was living abroad.

　　A. whom B. to whom C. to which D. that

　　Key: 1—5 ADADC 6—10 ACDAB

　　(文/王官敏 刘石才； 英语辅导报高一版 04~05学年度第7期；版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)