The traditional answer is that knowledge requires justified true belief: a person knows a proposition when it is true, they believe it, and they are justified in believing it. However, Gettier cases suggest that these three conditions are not jointly sufficient because a belief may be justified and true only through luck.
The Traditional Account
A necessary condition must be present for something to qualify as knowledge. A sufficient condition, or set of conditions, guarantees that it qualifies as knowledge.
For a subject, S, to know a proposition, P, the traditional tripartite account requires:
| Condition | Why it is required |
|---|---|
| Truth | P must be true. A false proposition cannot be known, even if S sincerely accepts it. |
| Belief | S must believe P. It would be contradictory to claim that S knows P while not believing P. |
| Justification | S must have adequate reasons or evidence for believing P rather than merely guessing correctly. |
These conditions are traditionally treated as individually necessary and jointly sufficient. In other words, knowledge is defined as justified, true belief.
The Gettier Problem
Suppose S looks at a clock showing 2:00 and forms the belief that it is 2:00. The clock stopped exactly twelve hours earlier, but it happens to be 2:00 now. The belief is true, and checking a clock normally provides justification, yet its truth is accidental.
This challenges sufficiency: S has a justified true belief but does not appear to possess knowledge. Philosophers have therefore proposed additional conditions, including no false lemmas, reliability, or an anti-luck condition, but no analysis is universally accepted.
A common misconception is that Gettier showed truth, belief, and justification are unnecessary. He showed only that they may not be sufficient together.
IB Exam Technique
For a command term such as evaluate, define necessary and sufficient conditions, explain the tripartite account, present a Gettier counterexample, and reach a reasoned conclusion about whether an added condition successfully removes epistemic luck.
