Justified true belief

Justified true belief is one definition of knowledge that states in order to know that a given proposition is true, one must not only believe the relevant true proposition, but one must also have justification for doing so. In more formal terms, a subject S knows that a proposition P is true if, and only if:

1. P is true
2. S believes that P is true, and
3. S is justified in believing that P is true

The 'justified true belief' theory of knowledge suffered a significant setback with the discovery of Gettier problems, situations in which the above conditions were met but that many philosophers disagree that anything is known. Robert Nozick suggested a clarification of "justification" which he believed eliminates the problem: the justification has to be such that were the justification false, the knowledge would be false.

See also

• Theory of justification
• Validity
• Gettier problem
• Ryan Glynn's gay sexplorations