In epistemology, the Gettier Counterexamples are two scenarios proposed by Edumnd Gettier in his 1963 article titled “Is Justified True Belief Knowledge?”, which suppose to find fault in the previously-accepted definition of knowledge. The problem created by these counterexamples is therefore named the Gettier problem.

Since Plato formulated his tripartite definition of knowledge, philosophers have generally accepted that knowledge is justified true belief. Gettier's counterexamples are meant to be cases of justified true belief that one would be hesitant to call knowledge.

Case I: Smith's Job

In the first example, Gettier supposes that two people, Smith and Jones, have applied for a job. We suppose that Smith has a justified belief that Jones will get the job. The evidence for it is high enough that Smith justifiably believes it, “might be that the president of the company assured him that Jones would in the end be selected”¹

Smith also believes (and indeed, knows) that Jones has ten coins in his pocket, which is true and was demonstrated to him, possibly by Jones counting them himself. From this he believes the logical conseqence of these beliefs, that “the man who will get the job has ten coins in his pocket”¹.

It turns out that Smith was wrong, and that, for some unforseeable reason, it turns out that Smith gets the job, and Jones does not. It also turns out that Smith has ten coins in his pocket, though he didn't realize it. The question is, was Smith's belief that “the man who will get the job has ten coins in his pocket” knowledge?

Case II: Jones’ Ford

Smith has very strong evidence to believe that his friend, Jones owns a Ford. Gettier writes:

“Jones has at all times in the past within Smith's memory owned a car, and always a Ford, and that Jones has just offered Smith a ride while driving a Ford”¹

Suppose that Smith also knows someone named Brown, but he has no idea where Brown is. From this he forms several disjunctions, one of which is “Either Jones owns a Ford, or Brown is in Barcelona”. This is a justifiable thing to do, given the justifiable belief that Jones owns a Ford.

Suppose that, despite all of his evidence, Smith is wrong, and it turns out that Jones does not own a Ford. Perhaps he was borrowing a friend's car, or owned a Ford but has since sold it. In any case, Smith's belief that Jones owns a Ford is false. However, it turns out, by sheer coincidence, that Brown is, in fact, in Barcelona.

Surely, one would not claim that Brown knew the proposition “Either Jones owns a Ford, or Brown is in Barcelona”, since he had no idea where Brown was, and Jones does not own a Ford. He formed other false disjunctions the same way, believing also that “Either Jones owns a Ford, or Brown is in Boston” was equally true.

Structure of Gettier counterexamples

Both of Gettier's counterexamples essentially follow the same general form:

Smith justifiably believes that P.

P is false.

Smith correctly infers that if P is true, then Q is true.

So, Smith believes Q, justifiably.

Q is true, but not because of P.

So, Smith has a justified true belief that Q.

In these examples, and all true Gettier-style examples, the flaw arises from forming an inference based on a false premise, though there is sufficient evidence to believe that premise is true.

Responses to Gettier

There are three general sorts of responses to Gettier's counterexamples:

Adding a fourth condition to the justified-true-belief definition of knowledge to account for these situations.

Attempting to redefine knowledge in order to remove the independence of the conditions

Denying that Gettier's scenarios are counterexamples, by claiming that they do meet the justification requirement.