The JTB Account and The Gettier Problem

Knowledge is traditionally defined in philosophy as Justified True Belief. The truth condition is necessary because it seems impossible to know something false; for instance, I may believe that I am an extraterrestrial, but philosophers don’t want to say that I know it. The belief condition is, of course, necessary because philosophers want to avoid situations where you know something that you’ve never even considered. In fact, the belief condition can be viewed as the means of attaching knowledge to the knower. The justification condition is, probably, the less obvious of the three conditions. However, it is necessary in order to rule out cases of accidental knowledge; in particular, philosophers don’t want to count a guess as knowledge. This account of knowledge dominated western philosophy until a 3 page paper, called “Is Justified True Belief Knowledge?”, was published by Edmund Gettier in 1963.

Gettier’s Method

In his revolutionary paper, Edmund Gettier supplies two devastating examples that both employ a similar methodology. That is, the alleged knower is justified in believing something that, as it turns out, is in fact true, but it is not true because of the reasons they thought. Since this person didn’t arrive at their belief through the right avenue, philosophers are inclined to say that it is comparable to guessing (which is precisely the type of belief that justification is supposed to preclude) so it doesn’t count as knowledge. By creating examples this way Gettier is able to demonstrate instances where a person can have a justified true belief that isn’t knowledge. This overturned the traditional definition of knowledge in philosophy, or at least weakened it. Many philosophers have since scrambled to plug the holes of the JTB theory, modifying justification, suggesting a fourth condition be added, and sometimes even declaring that the theory should be scrapped altogether.

Gettier Examples

Smith and Jones have both applied for the same job. Smith has strong evidence for his belief that Jones will get the job. Smith also has strong evidence that Jones has 10 coins in his pocket. Reasoning 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 himself also happens to have 10 coins in his pocket.  Yet, according to the JTB theory, Smith has knowledge that the man who will get the job will have 10 coins in his pocket.

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 his justified belief that Jones owns a Ford, Smith constructs three propositions at random. 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.


The Gettier problem has become a central issue in epistemology and many ideas have been suggested as to how to address it.  These include causal theory, reliabilism, evidentialism, and tracking theory. Hopefully I’ll be able to compose a post describing some of these theories in detail soon. Until then, thanks for reading.

Posted in Legacy.


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