所謂外在主義係指由認識主體嘅外部去尋找解釋同刻畫知識條件嘅理論。外在主義認為，令到A有理由相信B係因為B有客觀存在嘅外部因素。葛梯爾反例都有一個特點：令到A有理由相信B嘅原因客觀上都唔係真正令到B為真嘅原因。例如，喺第二個反例入面，令到史密斯認為“瓊斯有一輛福特車，或者布朗喺巴塞羅那”係真事嘅原因係因為佢有理由相信“瓊斯有一輛福特車”。但事實上令到呢句說話成真嘅原因係“布朗喺巴塞羅那”。如果呢兩個原因係相關嘅，就可以避免呢種情況。所以阿爾文·戈德爾曼（ ）就提出：
The so-called externalism refers to the theory that seeks to explain and characterize the conditions of knowledge from the outside of the subject of knowledge. Externalism holds that A has reason to believe that B is because B has objectively existing external factors. Gettier's counter-examples all have one characteristic: the reason that gives A reason to believe B is not objectively the reason that makes B true. For example, in the second counter-example, if Smith thinks that Lin Jones has a Ford, perhaps the reason Brown is real in Barcelona is because he has reason to believe that Lin Jones has a Ford wheel. But in fact, what made this statement true was Lin Brown's presence in Barcelona. This can be avoided if these two reasons are related. So Alvin · Godelman () proposed: