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.

2010- (48) Time was when biologists somewhat overworked the evidence that these creatures preserve the health of game by killing the physically weak, or that they prey only on “worthless” species.

2011-(46) Allen’s contribution was to take an assumption we all share—that because we are not robots we therefore control our thoughts—and reveal its erroneous nature.

(46) But even as the number of English speakers expands further there are signs that the global predominance of the language may fade within the foreseeable future.

1997-(74) Arguing from the view that humans are different from animals in every relevant respect, extremists of this kind think that animals lie outside the area of moral choice.

再次，我们来看一下that引导的定语从句，举两个例子：

2001-(71) There will be television chat shows hosted by robots, and cars with pollution monitors that will disable them when they offend.

Pearson has pieced together the work of hundreds of researchers around the world to produce a unique millennium technology calendar that gives the latest dates when we can expect hundreds of key breakthroughs and discoveries to take place.

对于同位语从句，同位语的先行词不是定语成分，而是被定语所修饰的名词，翻译方法可以是“先行词+是+同位语从句”。而定语从句的翻译可以把先行词带入到连接词的位置，按着英文原文的顺序进行翻译就可以。