用来修饰名词、代词、句子等，在句中的作用相当于形容词，故称为形容词性从句。 形容词性从句--定语从句 用来修饰名词、代词、句子等，在句中的作用相当于形容词，故称为形容词性从句。

定语从句分为限制性定语从句和非限制性定语从句。 限制性定语从句对被修饰词起到限制、修饰的作用，一般不可缺少。 非限制性定语从句起补充、附带说明作用，缺少也不会影响全句的理解。 e.g. She said she had finished her work, which I doubted very much. I’ve got some personal affairs that I have to deal with.

定语从句常用关系词 关系代词：who, whom, whose, that, which, as等（在句中作主、表、宾、定等成分） 关系副词：where(on which), when(in which), why(for which)（在句中作状语） 关联词：that（引导表示方式、时间的定语从句）

e.g. In this earthquake, the number of people who lost homes reached as many as 250,000. I have many good friends to whom I am going to send postcards. You’re the only person whose advice he might listen to. The river which runs through the center of the city brings us a lot of pleasure. He has given us as much advice as he can. Potato can be grown in places where it is too cold to grow rice. I don’t like the way (that) you treat us.

定语从句引导词的选择 取决于先行词（被修饰词）在定语从句中的位置、成分。 e.g. The people whom\who\that you met in the campus are from Australia.（作宾语） This was the time when\at which she left for Beijing. The place which he often visits is always full of artists.

使用要点 1. 关系代词在从句中作主语时，不能省略。 e.g. The classroom that is on the fourth floor is poorly equipped. 2. 关系代词在从句中作宾语且前面没有介词时，常可省略。 e.g. This is the girl with whom he works. 3. 关系副词在定语从句中不可省略。 e.g. I have come to explain the reason why I was absent from the meeting.

4. 只用that，不用which的情况： 当先行词有序数词或形容词最高级修饰时； 当先行词前有the only, the very, the last等词修饰时； 当先行词为anything, nothing, something, everything, all, little, much等不定代词修饰时； 当先行词前有all, every, no, some, any, little, much, few等词修饰时； It is 句型中的引导定语从句时。

5. 只用which，不用that的情况： 引导非限制性定语从句时； 引导词前有介词时； 一个句子中若有两个定语从句，一个用that引导，另一个用which引导； e.g. He bought a book that could give him much knowledge and which could help him to kill the time. 6. 当those作为先行词指人时，通常只能用who引导；

as 从句的先行词是the same, such, 或被他们所修饰；多用于表示肯定意义的从句中，不用于表否定意义的从句中。 e.g. Many of the sports are the same as they were when they started. The result was not such as he expected. It was raining hard, which(as) was unexpected. 8. 介词+关系代词要根据 谓语动词的固定搭配 e.g. This is the evidence with which the case is connected. 先行词 e.g. I’ll never forget the day on which\when I joined the party.

c. 句子表达的意思 e.g. The boss in whose department Mr King worked got sacked. d. 在非限制性定语从句中，名词\代词+of+which\whom表示整体与部分的关系 e.g. The workers, some of whom stayed for four years, came from different countries. e. 介词的位置一般放在关系代词之前，有时也可放在从句中原来的位置上。 e.g. We did it in the same way in which he did\which he did in.

9. That 作为关联词可以当作关系副词用 e.g. This is the house in which Louis XIII lived. This is the house that Louis XIII lived. This is the house where Louis XIII lived. This is house which Louis XIII lived in. This is the house Louis XIII lived in.　

定语从句的使用需注意： My brother who is very clever studies chemistry all by himself. 使用定语从句勿滥！可以使用单个形容词，或较短的非谓语动词结构的，尽量使用简略些的方式。使句子读起来更顺口！