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Is Justified True Belief Knowledge? According to Plato’s theory that knowledge is justified true belief, in order to know that a given proposition is true, one must not only believe the relevant true proposition, but one must also have a good reason for doing so. In his paper, Edmund Gettier argued that there are situations in which one’s belief may be justified and true, yet fail to count as knowledge.

He presented two examples to show that it is possible for a person to be justified in believing something that is thought to be true, but is not true because of the reasons they thought. Gettier claimed that it was possible to have “justified true belief” about something and yet it would not be considered knowledge. In other words, justified true belief might be necessary for knowledge, but it is not sufficient for claiming that one really has knowledge on a certain subject.

By providing counterexamples Gettier is able to illustrate where a person can have a justified true belief that is not knowledge. In Gettier’s first example Smith and Jones have both applied for the same job. Smith has strong evidence to believe that Jones will get the job. Smith also has strong evidence that Jones has 10 coins in his pocket. From these justified beliefs, Smith concludes that the man who will get the job will have 10 coins in his pocket.

However, Smith does not realize that he himself will actually be selected for the job and that he also happens to have 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 provide suitable knowledge. Yet, according to the JTB theory, Smith has knowledge that the man who will get the job will have 10 coins in his pocket. In Gettier’s second example: we see that Smith has strong evidence for his belief that his friend Jones owns a Ford.

Smith also has a friend named Brown whose whereabouts are unknown to him. Based upon Smith’s justified belief that Jones owns a Ford, he constructs three propositions that: 1) Either Jones owns a Ford or Brown is in Boston. 2) Either Jones owns a Ford or Brown is in Barcelona 3). Either Jones owns a Ford or Brown is in Brest-Litovsk. However, as it turns out, Jones does not own a Ford and Brown happens to be in Barcelona. Again, Smith had a belief that was true and justified, but not knowledge. One can’t derive knowledge from false proposition.

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