非限制性定语从句主句(句子的其他部分)关系不太紧密，对所修饰名词或代词的意思没有太大影响，把它们拿掉，句子依然很完整，它们可以说是附加上去的东西，而且通常都有逗号把它们和句子的其他部分分开。
例如：
This is the house which we bought last month. 这是我们上个月买的那幢房子。(限制性)
The house, which we bought last month, is very nice.这幢房子很漂亮，是我们上个月买的。(非限制性)
People who take physical exercise live longer. 进行体育锻炼的人活得长些。(若把从句去掉句子就失去意义)
His daughter, who is in Boston now, is coming home next week. 他女儿现在在波士顿，下星期回来。(若把从句去句子意义仍然完整)
非限定性定语从句与主句之间通常有逗号隔开，口语中使用时有停顿。
非限定性定语从句用于对先行词起补充说明作用，如果省略，句意仍然清楚、完整： People who take physical exercise live longer.
在翻译定语从句时把非限定性定语从句与主句分开：He is the man whose car was stolen. 他就是汽车被窃的那个人。
He is the man whose car was stolen. 他就是汽车被窃的那个人。
I’ve invited Jim, who lives in the next flat. 我邀请了吉姆，他就住在隔壁。
非限定性定语从句的先行词则可以是名词或代词，也可以是短语或句子
Peter drove too fast, which was dangerous. 彼得开车很快，这是很危险的。(which指drive too fast)
He changed his mind, which made me very angry. 他改变了主意，这使我很生气。(which指整个主句)
Mr. Smith, who is our boss, will leave for Japan next week. 我们的老板史密斯先生下周要去日本。(先行词为专有名词，要用非限制性定语从句修饰)
Her father, who has a lot of money, wishes her to study abroad. 她父亲很有钱，希望她出国学习。(先行词为表独一无二意义的普通名词，要用非限制性定语从句修饰)
非限定性定语从句练习题加详解
1. The place _______interested me most was the Children's Palace. A. Which B. where C. what D. in which
参考答案及解析： A.
A. which用作关系代词，在定语从句中作主语。
2. Do you know the man _______? A. whom I spoke B. to who spoke C. I spoke to D. that I spoke
参考答案及解析：C
C. "和谁讲话”要说speak to sb. 本题全句应为Do you know the man whom I spoke to.。whom是关系代词，作介词to的宾语，可以省略。
3. This is the hotel _______last month. A. which they stayed B. at that they stayed C. where they stayed at D. where they stayed
参考答案及解析：D
D. where是关系副词，表示地点，在定语从句中作地点状语。
4. Do you know the year ______the Chinese Communist Party was founded? A. which B. that C. when D. on which
参考答案及解析：C
C. when是关系副词，表示时间，在定语从句中作时间状语。
参考答案及解析：
5. That is the day ______I'll never forget. A. which B. on which C. in which D. when
参考答案及解析：A.
A. which是关系代词，在从句中作forget的宾语。其他几个答案都不能作宾语。
扩展：非限定性定语从句：as的用法
