非限定关系子句
非限定关系子句会就句中论及的人事物额外补充信息，但这些信息并不会指明它谈的是何者。就拿这个例句来说：Gorillas, which are large and originate in Africa, can sometimes be found in zoos. 在这个句子中，我们谈的是「所有大猩猩」，而不是只有其中几只。非限定关系子句会多加补充有关一般大猩猩的信息，不会限定群体或单一只大猩猩。如果非限定关系子句从句中移除，剩下的句子文法上仍是正确的，整句话的意思不会有太大的改变，顶多少了些信息罢了。
非限定关系子句必定包含关系代名词和动词，有时也会包含动词的主词或受词，可有可无。非限定子句一般会用逗号或括号来与主要子句隔开。
举例
- John's mother, who lives in Scotland, has 6 grandchildren.
- My friend John, who went to the same school as me, has just written a best-selling novel.
- My grandmother, who is dead now, came from the North of England.
- We stopped at the museum, which we had never visited before.
- I've just come back from London, where John lives..
- Yesterday I met a woman named Susan, whose husband works in London.
关系代名词
以下的关系代名词是用在非限定关系子句，置于非限定子句的句首，而关系代名词指的是前面提到的名词。
| 人 | 事物 | 地方 | |
|---|---|---|---|
| 主格 | who | which | |
| 受格 | who/whom | which | where |
| 所有格 | whose |
非限定关系子句与限定关系子句的差别
在英语口头上，限定关系子句常用 that 来取代 who丶whom 和 which 等代名词。但在非限定关系子句中，就不能用 that 来取代其他关系代名词，也不能像限定关系子句一样省略关系代名词。在非限定关系子句中，关系代名词是不可或缺的，就算关系代名词是子句中的受格，也不能省略。非限定关系子句一般会用逗号来与主要子句隔开，而限定关系子句通常不用逗号分隔。
举例
- He gave me the letter, which was in a blue envelope.（非限定子句：信只有一封，而且是蓝色的；这时您必须用 which。）
- He gave me the letter which/that was in a blue envelope.（限定子句：信不只一封，而且颜色有很多种，而他给我的是蓝色的那封信。which 可以被 that 取代，并且不用加逗号。）
- He gave me the letter, which I read immediately.（非限定子句：信只有一封，而 which 是动词 read 的受词，但不能省略。）
- Stratford-on-Avon, which many people have written about, is Shakespeare's birthplace.（介词一般会放在关系子句的句尾。）
- Stratford-on-Avon, about which many people have written, is Shakespeare's birthplace.（书面用语上常会将介词放在代名词前。）
在非限定子句的引导词
在关系代名词前，可以用 all of 或 many of 来引导非限定子句。
| 人 | 物 | |
|---|---|---|
| all of, any of, some of, a few of, both of, each of, either of, half of, many of, most of, much of, none of, one of, two of 等 | whom | which |
举例
- There were a lot of people at the party, many of whom I had known for years.
- There are 14 girls in my class, a few of whom are my friends.
- He was carrying his belongings, many of which were broken.
- He had thousands of books, most of which he had read.
- He picked up a handful of stones, one of which was sharp.
用 which 来指整个主要子句的信息
在非限定关系子句上，句首 which 可以指前面句子的所有信息，而不是单指子句前面的那个词。
举例
- Chris did really well in his exams, which is quite a surprise.
- My friends were all hiding in my apartment, which isn't what I'd expected.
- She's studying to become a doctor, which is difficult.