The tripartite theory of knowledge analyses knowledge as justified true belief. According to this analysis, if something is true, and we believe it to be true, and we are justified in believing it to be true, then we know it.

The tripartite theory, though it has been around since Plato, and though it is still widely used by many philosophers as a working model of knowledge, is false. This was shown to the satisfaction of most philosophers by Edmond Gettier, who developed what are now known as “Gettier cases”.

Gettier cases are cases in which the tripartite theory’s three conditions for knowledge are satisfied, i.e. in which a person does have a justified true belief, but in which there is no knowledge. The existence of such cases shows that there is something more to knowledge than justified true belief, and so that the tripartite theory of knowledge is false.

Suppose that two students, Mark and Sam, have taken a test. Mark is a straight A student, while Sam consistently fails any work he is set. Mark has attended the lessons in preparation for the test, while Sam has been absent due to illness. Mark revised hard for the test, while Sam stayed out all night at a party. Mark wrote furiously for the full duration of the test, while Sam wrote a few lines and then walked out in disgust. Mark says that the test went well, while Sam says that he didn’t even understand the question.

Reflecting on the test, and on a book that he has recently been reading, Sam forms the following belief: the student that will get the highest grade on the test shares a name with the author of The Adventures of Huckleberry Finn.” Sam clearly has excellent evidence for this belief, he is justified in believing it; he has excellent evidence that Mark will get the highest grade on the test, and can see from the cover of his copy of “The Adventures of Huckleberry Finn that it was written by Mark Twain. Furthermore, the belief is true; the student that will get the highest grade on the test does indeed share a name with the author of “The Adventures of Huckleberry Finn.” According to the tripartite theory of knowledge, therefore, Sam knows that the student that will get the highest grade on the test shares a name with the author of “The Adventures of Huckleberry Finn.”

Sam, however, does not know this. Mark, despite his excellent grades in the past, perfect attendance, hours of revision, furious writing, and confidence, failed the test. He did not appreciate the subtlety of the question, and so missed its point entirely. Sam, on the other hand, despite his previous poor grades, frequent absences, late night partying, and pessimism concerning his performance, did understand the question. In the few lines that he wrote he managed to scrape a passing grade. Sam, therefore, rather than Mark, got the highest grade on the test.

Unknown to Sam, though, he does share a name with the author of “The Adventures of Huckleberry Finn.” Its author, who used the pseudonym Mark Twain, was in fact called Samuel Clemens. Sam, therefore, who is the student who will get the highest grade on the test, does share a name with the author of Huckleberry Finn.

Although Sam clearly did have a justified true belief, he equally clearly did not have knowledge. His justification for his belief, far from helping him to discern the truth, threatened to lead him astray. The truth of his belief had nothing to with his reasons for holding it; it was nothing more than good luck that the belief that he formed was true.

This example, and other Gettier cases like it, show that it is possible to have justified true belief without having knowledge; the tripartite theory of knowledge, which holds that justified true belief and knowledge are precisely the same thing, is therefore false.