同位语从句和定语从句的混淆点是：这两种从句都可以被that引导，而且先行词都是名词。那么怎么区别呢?首先：先行词虽然都是名词，但是名词在定语从句中做先行词的范围要比同位语从句广泛很多。同位语从句的先行词是表示信息、观点、主张、事实等(如：idea, view, thought, order, suggestion, news, truth, hope, promise, answer, belief, condition, doubt, fear, problem, proof, question)等抽象的名词，而定语从句的范围不仅仅是这些名词，换言之，如果是表示具体意义的先行词，那么后面的从句是定语从句。

　　并且，连接词在从句中的作用也不一样。连接词在同位语从句不做成分，因为同位语从句本身的作用是对前面的名词进行解释说明的补充作用;连接词在定语从句中做成分。换言之，如果连接词如果在从句中做成分，则从句是同位语从句，如果连接词不在从句中做成分，则从句是定语从句。

　　另外，what, how, whether等不能用引导定语从句，但可用于引导同位从句。

　　接下来，就来看定语从句和同位语在考研英语翻译的应用。

　　首先，与that引导定语从句相比，that引导的同位语从句相对要少。来看一下同位语从句的考察，划线部分为同位语从句，加粗的字体为先行词。

　　2004- (64) Being interested in the relationship of language and thought, Whorf developed the idea that the structure of language determines the structure of habitual thought in a society.

　　2007- (48) But the idea that the journalist must understand the law more profoundly than an ordinary citizen rests on an understanding of the established conventions and special responsibilities of the news media.

　　2008- (48) On the other hand, he did not accept as well founded the charge made by some of his critics that, while he was a good observer, he had no power of reasoning.

　　2010-(46) Scientists jumped to the rescue with some distinctly shaky evidence to the effect that insects would eat us up if birds failed to control them.