【定语从句】是英语语法中的一个重要概念,它用于修饰名词或代词,相当于形容词,起到描述或限定的作用。定语从句分为限制性和非限制性两种,前者与先行词关系紧密,不可省略,后者则起补充说明作用,可有可无。
1. **定从分类**
- 限制性定语从句:与先行词关系密切,不能省略,无逗号隔开,如"The girl who is wearing a blue necklace is Mary."。
- 非限制性定语从句:对先行词进行补充说明,可独立成句,用逗号隔开,如"The girl, who is also a student, is planting trees in the field."
2. **先行词**
- 先行词是被定语从句修饰的名词或代词,如"somebody", "those", 和"novel"。
3. **关系词**
- 关系代词:who, whom, whose, which, that,分别代表人、物、所属关系。
- who 主语;whom 宾语;whose 所有格;which 物;that 既可指人也可指物。
- 例如:"The boys who are playing football are from Class One."中,"who"是关系代词,代替"the boys"做主语。
4. **特殊用法**
- that 不用于非限制性定语从句和介词后,如:"The book that I bought yesterday"。
- which 通常用于非限制性定语从句,如:"This is the house, which was built in 1920."
- whose 用来表示所属关系,既可指人也可指物,如:"The girl whose hair is red is my sister."
5. **关系副词**
- when 时间状语;where 地点状语;why 原因状语。
- 可用介词+关系代词替代关系副词,如:"I'll never forget the day when (on which) we first met."
6. **特殊情况**
- as 有时可替代which,但出现在句首或否定句中时,只能用as。
- "such/so...as"结构中,as引导的定语从句通常不包含be动词。
- one of + 复数名词作先行词时,从句谓语动词根据"one"的单数性质确定,但如果有"only/very",则根据复数名词确定。
- all that 结构可用what替换,如:"All that she needs is love."可转化为"All she needs is love."
定语从句的掌握需要大量练习,通过顺口溜可以帮助记忆这些规则。学习定语从句能提升英语表达的准确性和复杂度,对于阅读和写作都有极大的帮助。在实际应用中,要灵活运用各种关系词和结构,确保句子清晰易懂。