The Gettier problem shows that justified true belief may not be sufficient for knowledge. A person can hold a belief that is justified and true but still appear not to possess knowledge because the belief is true only by luck.
The traditional account states that a subject, S, knows a proposition, P, if:
- P is true.
- S believes P.
- S is justified in believing P.
Edmund Gettier challenged this account in 1963 through counterexamples. Consider this simplified Gettier case:
Smith has strong evidence that Jones owns a Ford, so Smith believes, “Jones owns a Ford.” Smith then infers, “Either Jones owns a Ford or Brown is in Barcelona.” Smith has no information about Brown.
Unknown to Smith, Jones does not own a Ford. However, by coincidence, Brown is in Barcelona. Smith’s second belief is therefore true, and it is justified through a logically valid inference from his evidence. Nevertheless, its truth depends on epistemic luck, so it seems incorrect to say that Smith knows it.
| Requirement | Status in the Gettier case |
|---|---|
| Belief | Smith believes the disjunctive proposition. |
| Truth | Brown really is in Barcelona. |
| Justification | Smith has evidence for Jones owning a Ford and uses valid inference. |
| Knowledge | Apparently absent because the belief is accidentally true. |
The problem demonstrates that the three traditional conditions can be individually necessary yet not jointly sufficient. Philosophers have proposed additional conditions, including no false lemmas, reliabilism, and a requirement that knowledge exclude relevant forms of epistemic luck. Each response faces further counterexamples.
A common misconception is that Gettier proved knowledge is impossible. It did not; it challenged one particular analysis of knowledge.
In an IB Philosophy response, clearly define justified true belief, reconstruct a Gettier case, and explain exactly where luck enters. For an evaluate question, assess whether a proposed fourth condition successfully excludes Gettier cases without excluding ordinary knowledge.
