1. 所阐述的语义功能存在差异
定语从句与同位语从句均具备修饰名词的语法功能。定语从句主要用于界定名词的属性特征、来源出处等概念信息；而同位语从句则着重于阐释名词所承载的具体内涵。
The fact that he presented constituted a compelling evidentiary basis.
他所呈现的事实构成了具有说服力的证据依据。(定语从句，明确fact的来源出处)
The fact that she maintained silence elicited astonishment among all listeners.
她保持沉默这一事实令所有在场者感到震惊。(同位语从句，揭示fact的具体内容)
2. 关联词在句法结构中的功能定位不同
充当定语从句引导词的that具有关系代词属性，其核心作用在于建立主句与从句的语法连接，并在从句中承担特定的句子成分；值得注意的是，当that在定语从句中充当宾语时存在省略现象，且在指代事物范畴时能够被which一词替换使用。
作为同位语从句引导词的that仅具备连接功能，不参与从句的句子成分构建，该关联词不可省略，也无法通过which进行替换。
The intelligence (that/ which) we obtained was disseminated throughout the region.
我们所获取的情报信息已传遍整个区域。(定语从句)
We articulated a desire that the Smith couple would undertake a visit to China in the subsequent year.
我们表达了一种期望，即史密斯夫妇在来年能够访问中国。(同位语从句)
3. 先行词的语法属性存在明显界限
同位语从句的修饰对象具有特定范围，通常涉及承载信息内容的名词，例如message、news、fact、hope、desire、problem、idea、suggestion、advice、question、order、belief、doubt、fear、truth、thought等特定名词类别；而定语从句的先行词则不受此类限制。
We are not conducting an investigation into the query regarding his credibility.
他是否具备可信度的问题并非我们正在调查的事项。(同位语从句)
After this period of transformation, he has evolved into a person who differs significantly from his former self.
经历这段转变之后，他已蜕变为一个与过去截然不同的人。(定语从句)
4. 区分定语从句与同位语从句的判定方法
凡是可以转换为”The fact/ news / idea / order / truth / thought is / was…结构且在语法层面与语义层面均保持逻辑通顺的从句，属于同位语从句；而定语从句则不具备这种转换能力。
The news that our team secured victory in the competition induced excitement among every participant.
我们队伍在比赛中取得胜利的消息使每位参与者都感到兴奋。(“The news is that our team secured victory…”这种表述方式是符合语法的。that引导的是同位语从句)
The news that the radio station transmitted this morning is entirely false.
今天早晨广播电台播报的消息完全是虚假的。(无法转换为”The news was that the radio station transmitted…”这种结构，that引导的是定语从句)
when、where、why等关联词引导定语从句时，其先行词通常表示时间、地点或原因的概念，且关联词在从句中充当状语成分；同位语从句中的when、where、why等关联词同样在从句中履行状语功能，但具有疑问性质，且其先行词并非时间、地点或原因类名词。
I will perpetually cherish the moment when I achieved recognition in the National Maths Competition.
我将永远铭记在全国数学竞赛中获奖的宝贵时刻。(定语从句)
We have yet to resolve the matter regarding the optimal time when we should initiate our journey.
我们尚未确定应该何时出发的最佳时机。(同位语从句)
I possess no comprehension as to the rationale why he experienced a delay.
我对他为何迟到的原因缺乏了解。(同位语从句)
Are you acquainted with the cause why he encountered a delay?
你是否知晓他迟到的原因？(定语从句)