Plato's theory of knowledge

Knowledge is justified, true belief. That is the modern version of Plato's definition. On this view, our beliefs will only count as knowledge when they are true (accord with the objective facts) and when the person who holds the belief has evidence or justification for it.

In Plato's theory of knowledge, reality operates as a standard against which belief and perception can be measured. Belief is created by perceptions of reality.

True belief alone is not the same as knowledge. In order to have genuine knowledge of reality, we must have both a true belief about it and sufficient justification (evidence) for that belief.

Read more about this on Stanford Encyclopedia of Philosophy