定义 / 说明
非限定性定语从句用于补充附加信息，所修饰的人/物本身已经被确定。它不回答“是哪一个”，只提供额外细节。因此书写时要用逗号隔开，口语中也有停顿。它不同于限定性定语从句（后者用于界定对象，因此不用逗号）。这种从句在描写和说明性写作中很常见。
关键规则
- 非限定性从句常用 who, which, whose，有时用 where。
- 若从句在句中间，两侧都要加逗号。
- 标准英语中非限定性从句不用 that。
- 该从句提供附加信息，不是核心识别信息。
- 去掉从句后，主句基本意义通常仍成立。
例句
- My brother, who lives abroad, is visiting. - 我哥哥（住在国外）正在来访。
- The car, which I bought used, is reliable. - 那辆车（我买的是二手）很可靠。
- Our office, which is near the river, closes at six. - 我们办公室（在河边）六点下班。
- Anna, whose father is a doctor, studies law. - Anna（她父亲是医生）学法律。
- The hotel, where we stayed last year, has reopened. - 我们去年住过的那家酒店重新开业了。
常见错误
- ❌ My brother, that lives abroad, is visiting. -> ✅ My brother, who lives abroad, is visiting.
- ❌ The car which I bought used is reliable. -> ✅ The car, which I bought used, is reliable.
- ❌ Anna, who father is a doctor, studies law. -> ✅ Anna, whose father is a doctor, studies law.