从表面看,限制性定语从句和主句之间没有“,”逗号. 非限制性定语从句 有 “,” 从功能上看,限制性定语从句 对先行词 进行识别 筛选. 非限制性定语从句 补充说明. 比如His brother who joined the army has returned home. 限制性定语从句who joined the army 对brother进行识别,筛选,他参军的那个兄弟. 言外之意是,他有2个或以上兄弟. His brother,who joined the army has returned home. 非限制性定语从句,对his brother 补充说明,他的兄弟,之前参军去了,现在回来了. 言外之意,他只有一个兄弟.
