Justified True Belief

The Justified True Belief [JTB] account of knowledge is the claim that knowledge can be conceptually analyzed as justified true belief, which is to say that the meaning of sentences such as "Smith knows that it rained today" can be given with the following set of conditions, which are necessary and sufficient for knowledge to obtain:

1) A subject S knows that a proposition P is true if and only if: P is true, and
2) S believes that P is true, and
3) S is justified in believing that P is true

Necessity and sufficiency - A necessary condition is a condition that must be present for an event to occur. A sufficient condition is a condition or set of conditions that will produce the event.

A belief is any claim that you accept. A true belief is any claim you accept that corresponds to how things are in the world, and a justified true belief is a true belief that has proper evidence.