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。
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。
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.
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.