What is knowledge? Or what does it mean to truly "know" something to be true? According to Plato, knowledge can be defined as a justified true belief. This definition has been generally accepted in epistemology.
More clearly stated, in order to have knowledge you must:
1) Believe it to be true
2) Justify/provide evidence that it is true
3) The fact must actually be true
Edmund Gettier came up with examples where someone meets all the criteria, however, the person still seems to fall short of knowledge. In these cases the protagonist believes something to be true, it is true, but the justification does not directly prove that it is true. For example:
Smith and Jones have just applied to a job. Smith states that
a) Jones will be the man for the job and Jones has 10 coins in his pocket and therefore
b) The man for the job will have 10 coins in his pocket.
Given that Smith had counted the coins in Jones' pocket 10 minutes ago, he is justified in believing that the man for the job will have 10 coins in his pocket. However, it is also possible that Smith will get the job. Imagine that Smith coincidentally has 10 coins in his pocket as well. Smith is correct that the man for the job will have 10 coins in his pocket, however, his justification is because he thinks Jones will get the job whom he knows has 10 coins. Can we really justify this as knowledge even though Smith
a) Believes that the man for the job will have 10 coins in his pocket
b) Has reasoning/evidence for his belief
c) The belief is, in fact, true
Part II of the example:
Smith has a justified belief that Jones owns a Ford. Smith therefore states, "Jones owns a Ford, or Brown is in Barcelona" even though Smith has no information on the whereabouts of Brown. However, Smith is still correct in his justified belief. Jones actually does not own a Ford, but it just so happens that Brown is in Barcelona.
How should we respond to this?
Affirmations of Justified True Belief
Some will still hold that knowledge is a justified true belief regardless of the examples. The examples do not exemplify knowledge because there is insufficient evidence to account for the "justification" portion of knowledge.
Fourth Condition Response
In this response, we accept that the protagonist in the examples does not exemplify knowledge. While knowledge still needs to be justified, true, and believed, there is an additional condition that needs to be met for someone to truly have knowledge of a fact.
Justification Replacement Response
Lastly, another response to the case is that the protagonist does not exemplify knowledge because the criteria for knowledge is wrong. Instead of it being a justified true belief, we need to replace "justification" with some other criteria.