同位语从句是名词性的,其前置词(先行词)在从句中不具句子成分功能;
定语从句是形容词性的,其被修饰的前置词在从句中有句子成分功能。
例:
同位语:We are talking about the same issue that Ebola has already come into this country as reported in the news.(从句为一个完整的句子,并不包括前置词 issue。)
定语从句:We are talking about the same news that reported the Ebola cases in the US.(前置词 news 在从句里的句子成分是主语。从句离开了前置词就不完整。)