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Gettier problem

The Gettier problem is a fundamental problem in epistemology and the philosophy of knowledge. It owes its name to a three-page paper published in 1963, by Edmund Gettier, called "Is Justified True Belief Knowledge?". In the paper, Gettier argues (most would say, proves) that knowledge is not the same as justified true belief.

The view that knowledge was justified true belief was widely held by philosophers, but Gettier showed that there were cases of justified true belief that did not appear to be knowledge. Thus, the Gettier problem shows that justified true belief is not a sufficient condition[?] for knowledge (in other words, something else is needed as well).

Table of contents

Gettier's actual examples

Gettier provides two actual examples of his problem, both of which rely on the fact that justification is preserved by entailment. For example, if a belief that P is justified, and the truth of P entails Q, then a belief that Q is also justified.

Gettier's first example:

Smith has applied for a job, but has a justified belief that "Jones will get the job". He also has a justified belief that "Jones has 10 coins in his pocket". Smith therefore (justifiably) concludes (by the rule of the transitivity of identity) that "the man who will get the job has 10 coins in his pocket".

In fact, Jones does not get the job. Instead, Smith does. However, as it happens, Smith also has 10 coins in his pocket. So his belief that "the man who will get the job has 10 coins in his pocket" was justified and true. But it does not appear to be knowledge.

Gettier's second example:

Smith has a justified belief that "Jones owns a Ford". Smith therefore (justifiably) concludes (by the rule of disjunction introduction) that "Jones owns a ford, or Brown is in Barcelona", even though Smith has no knowledge whatsoever about the location of Brown.

In fact, Jones does not own a Ford, but by sheer coincidence, Brown really is in Barcelona. Again, Jones had a belief that was true and justified, but not knowledge.

False premises

In both of Gettier's actual examples, the justified true belief came about as the result of entailment from justified false beliefs. This led some early responses to Gettier to conclude that the definition of knowledge could be easily adjusted, so that knowledge was justified true belief that depends on no false premises.

More general Gettier-style problems

The "no false premises" (or "no false lemmas") solution was not the end of the matter, however, as more general Gettier-style problems have also been proposed, in which the justified true belief does not seem to be the result of a chain of reasoning from a justified false belief.

For example:

Smith enters a room and seems to see Jones. He immediately forms the justified belief that "Jones is in the room".

In fact, Smith did not see Jones, but rather, a lifelike replica. However, as it happens, Jones is in the room, though Smith has not seem him yet. Once again, Smith has a justified true belief that does not seem to be knowledge, yet this time it is more debatable whather he used any false premises in his reasoning.

Other responses to Gettier

Other responses to Gettier include externalist responses, such as the theory that knowledge is justified true belief that is caused (in the right sort of way) by the relevant facts, or Robert Nozick's view that knowledge is a belief which is true, and which the believer would not have had if it was false. There are also many other theories of knowledge.

Finally, one can say that knowledge really is justified true belief, but "justification" must be understood in such a way that justified beliefs are never false. Since very few beliefs are justified to the extent of absolute certainty, this implies philosophical skepticism - the view that knowledge is usually impossible.

External links:


  • Edmund Gettier: Is Justified True Belief Knowledge? in Analysis, volume 23.

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