The Gettier Problem: Challenging the Definition of Knowledge
For centuries, philosophers have accepted the definition of knowledge as “justified
true belief” (JTB). This classical view, dating back to Plato, holds that for
someone to know a proposition, three conditions must be met: the person must
believe it, it must be true, and they must have justification for believing it.
However, in 1963, Edmund Gettier published a short but revolutionary paper titled
“Is Justified True Belief Knowledge?” that challenged this long-standing
definition. Through a series of thought experiments, Gettier showed that it is
possible for someone to have a justified true belief without actually having
knowledge.
This essay will explore the structure of the traditional JTB account, explain
Gettier’s challenge, analyze his famous counterexamples, and consider the
implications and responses that followed in epistemology.
The Classical Account: Justified True Belief (JTB)
According to the JTB model, a person S knows a proposition P if:
P is true (Truth)
S believes that P (Belief)
S is justified in believing P (Justification)
For example, if I believe it is raining outside, I see water falling from the sky
through the window, and it is indeed raining, then I would have justified true
belief—and therefore knowledge—according to this model.
For centuries, philosophers accepted this as an adequate analysis of knowledge.
However, Gettier’s paper revealed that even when all three conditions are met,
something essential can still be missing.
Gettier’s Counterexamples
In his paper, Gettier presented two short thought experiments that showed
individuals having justified true beliefs that intuitively do not count as
knowledge.
Example 1: Smith and Jones
Smith and Jones are job applicants. Smith has strong evidence (say, the company
president told him) that Jones will get the job. He also sees Jones put ten coins
in his pocket. Smith then concludes:
“The man who will get the job has ten coins in his pocket.”
As it turns out, Smith—not Jones—gets the job, and by coincidence, Smith also has
ten coins in his pocket. So his belief is true, and he was justified in believing
it, but it seems wrong to say he knew that “the man who will get the job has ten
coins in his pocket.” It was luck, not knowledge.
Example 2: The Broken Clock
Imagine someone looks at a clock that shows the time as 2:00 PM. The person
believes it is 2:00 PM, and it happens to be correct. However, the clock is broken
and has been stuck at 2:00 PM for days. The person’s belief is both true and
justified (they looked at a normally reliable clock), but it seems clear they don’t
really know the time—they got it right by accident.
These examples show that justified true belief can occur by coincidence, meaning
that something more is needed for real knowledge.
The Problem Defined
The Gettier problem can be summarized as follows:
It is possible to have a belief that is true and justified, yet still fail to count
as knowledge.
Therefore, the JTB account of knowledge is incomplete.
Gettier cases typically involve luck or accident, where the justification is
disconnected from the truth in a way that undermines genuine knowledge.
Responses and Proposed Solutions
Gettier’s challenge sparked a wave of responses in epistemology. Philosophers have
proposed various modifications to the JTB model:
Adding a Fourth Condition
Some propose a “No False Lemmas” condition—knowledge cannot be based on any false
assumptions. Others suggest a “defeasibility” condition, meaning that if any
additional information would undermine the justification, then it’s not knowledge.
Reliabilism
This view, associated with Alvin Goldman, argues that justification should be
replaced by a reliable process. If a belief is formed through a reliable method
(e.g., perception, memory), and it is true, then it counts as knowledge—even if the
person isn’t aware of the justification.
Virtue Epistemology
This approach, advanced by thinkers like Ernest Sosa and Linda Zagzebski, ties
knowledge to intellectual virtues. Knowledge arises when a person forms a true
belief through cognitive skill, not through luck.
Contextualism and Pragmatism
Some contemporary epistemologists argue that knowledge depends on context or
practical stakes. In low-stakes situations, a justified true belief may be enough,
but in high-stakes cases, more stringent standards apply.
Conclusion: Why Gettier Still Matters
The Gettier problem remains one of the most important challenges in modern
epistemology. It revealed that the classical definition of knowledge is too
simplistic and that knowledge is more than just a combination of belief, truth, and
justification. While no single solution has been universally accepted, Gettier's
work has deepened our understanding of how beliefs connect to truth and
reliability.
In a broader sense, the Gettier problem highlights the fragility of human
knowledge, and the ever-present role of luck in our understanding of the world. It
reminds us that philosophical analysis must be flexible, careful, and open to
surprising counterexamples—even those found in a two-page paper.
