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Why must a claim be true for someone to know it?

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Four colored straws in a glass of water appear bent at the water's surface, visually demonstrating the refraction of light. — Epistemology The refraction (bending) of light as it passes from air into water causes an optical illusion: straws in the glass of water appear broken or bent at the water's surface.

In the field of epistemology, the requirement that a claim must be true for someone to know it is a fundamental principle. As Plato argued in the Theaetetus, knowledge is, at a minimum, true belief.

The necessity of truth arises because knowledge is fundamentally distinct from mere belief or opinion. If a claim is false, it cannot be considered knowledge, regardless of how strongly an individual believes it or how convinced they are that they know it. While a person may mistakenly believe they possess knowledge about something that is actually false, they are simply mistaken; they do not "know" the claim in the epistemological sense because knowledge requires a connection to reality.1

Consequently, truth serves as a necessary condition for knowledge. Without truth, a belief—even one that is justified—lacks the essential accuracy required to be classified as knowledge.1