Epistemology i/ɨˌpɪstɨˈmɒlədʒi/ (from Greek ἐπιστήμη (epistēmē), meaning “knowledge, understanding”, and λόγος (logos), meaning “study of”) is the branch of philosophy concerned with the nature and scope of knowledge. It questions what knowledge is, how it is acquired, and to what extent it is possible for a given subject or entity to be known.
Edmund Gettier is remembered for his 1963 argument, which called into question the theory of knowledge that had been dominant among philosophers for thousands of years. In a few pages, Gettier argued that there are situations in which one’s belief may be justified and true, yet fail to count as knowledge. That is, Gettier contended that while justified belief in a true proposition is necessary for that proposition to be known, it is not sufficient. As in the diagram above, a true proposition can be believed by an individual (purple region) but still not fall within the “knowledge” category (yellow region).
According to Gettier, there are certain circumstances in which one does not have knowledge, even when all of the above conditions are met. Gettier proposed two thought experiments, which have come to be known as “Gettier cases,” as counterexamples to the classical account of knowledge. One of the cases involves two men, Smith and Jones, who are awaiting the results of their applications for the same job. Each man has ten coins in his pocket. Smith has excellent reasons to believe that Jones will get the job and, furthermore, knows that Jones has ten coins in his pocket (he recently counted them). From this Smith infers, “the man who will get the job has ten coins in his pocket.” However, Smith is unaware that he also has ten coins in his own pocket. Furthermore, Smith, not Jones, is going to get the job. While Smith has strong evidence to believe that Jones will get the job, he is wrong. Smith has a justified true belief that a man with ten coins in his pocket will get the job; however, according to Gettier, Smith does not know that a man with ten coins in his pocket will get the job, because Smith’s belief is “…true by virtue of the number of coins in Jones’s pocket, while Smith does not know how many coins are in Smith’s pocket, and bases his belief…on a count of the coins in Jones’s pocket, whom he falsely believes to be the man who will get the job.” (see p. 122.) These cases fail to be knowledge because the subject’s belief is justified, but only happens to be true by virtue of luck. In other words, he made the correct choice (in this case predicting an outcome) for the wrong reasons. This example is similar to those often given when discussing belief and truth, wherein a person’s belief of what will happen can coincidentally be correct without them having the actual knowledge to base it on.