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定语从句有限制性和非限制性两种。

限定性定语从句与主句的关系很紧凑,对其先行词起限定、修饰的作用。如果将其去掉,会影响句子意思的完整性;有时甚至于引起费解、误解。

非限定性定语从句在形式上就与主句很松散,它与主句之间有一个逗点 , 隔开;它对其先行词没有限定、修饰的作用,只起补充、说明的作用。有时也用它来对全句或句中某个成分进行补充、说明。即使将其去掉,也不会影响句子意思。由于上述原因,非限定性定语从句在表达意思方面也有别于限定性定语从句。另外,非限定性定语从句在中文译文里,我们往往将其作为一个分句处理,而不把它作定语翻译。

1. 从句区别

  限定性定语从句 非限定性定语从句
能否省略 省略导致主句意思不完整 省略后主句意思仍然完整
能否用 that 引导词 不能
引导词能否省略 有时可以省略 不可以省略
是否需要逗号隔开 不需要 需要
修饰部分 只修饰先行词 可修饰先行词、部分主句或整个主句

2. 引导词

引导非限定性定语从句的关系词如下

  1. 引导非限定性定语从句的关系代词:as,which,who,whom
  2. 引导非限定性定语从句的关系副词主要有:when,where。

注意:that 不能作为关系代词有两种情况如下

  1. 非限定性定语从句
  2. 介词 + 关系代词

3. 注意事项

  1. 引导限制性定语从句时,关系代词 which 可以与 that 互换;但引导非限制性定语从句时,只能用 which。

    She heard a terrible noise that frightened her.

    She heard a terrible noise, which frightened her.

  2. 先行词为 reason 时,限制性定语可以用 why 或 for which 来引导;非限制性定语从句则只能用 for which 来引导。

    I had told them the reason why I didn’t attend the meeting.

    I had told them the reason, for which I didn’t attend the meeting.

  3. 引导限制性定语从句的关系代词在从句中担任宾语时可以被省略;但引导非限制性定语从句的关系代词即使作宾语也不能省略。

    He was eager to go to the hospital to see his stepmother, whom he loved and respected as his own mother.

  4. 引导限制性定语从句时并作从句宾语的关系代词 whom 可以用 who 来代替;但在非限制性定语从句中, whom 就不能用 who 替换。

    Do you know Tom, whom we talked about?

  5. 当非限制性定语从句修饰整个主句时,其关系代词可以用 as 和 which,但从句位于句首时不能用 which,只能用 as。

    as I expected, he didn’t believe me.

    Mary was late for school, as often happened.

  6. 由 “介词 + 关系代词” 引导非限制性定语从句,关系代词指代整个主句时,不能用 as,只能用 which,因为有介词关系。

    He bought the car for more than $20,000, which his father was angry.

  7. 关系代词 as 在限定性定语从句中后跟 “be 动词 + 过去分词” 的被动语态时,be 动词可省略。

    As (is) reported in the newspaper, some artistic treasures will be on show at the exhibition on the weekend.

  8. as 有 “正如 … 一样、按照、正像、因为” 的意思,所以常用于肯定句,而 which 则用于肯定,否定都可以。

    as you all know, I am the most handsome.

    I am the most handsome, which you can’t imagine.

  9. which 引导的非限定性定语从句是用来说明前面整个句子的情况或主句的某一部分。

    The sun heats the earth , which makes it possible for plants to grow.

  10. as 引导的定语从句可以放在句首、句中和句尾,which 引导的定语从句可置于句中或句尾。

    as you all know, I am the most handsome.

  11. 在非限定性定语从句中,关系词不能用 that 和 those(that 的复数形式)。