Britannica Sources used in this answer

Why does epistemic logic require that knowledge claims be true?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Marble bust of Aristotle with a beard and draped robe, showing detailed facial features and wavy hair, set against a dark background. — Truth Detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust of Aristotle (c. 325 bce); in the collection of the Museo Nazionale Romano, Rome.

In epistemic logic, the requirement that knowledge claims be true is a fundamental principle often expressed as the validity of the inference from "P knows that A" to "A is true." This requirement is rooted in the broader philosophical consensus that one cannot have "propositional knowledge" of something that is not true; put simply, a necessary condition for "A knows that p" is that p must be the case.123

From a logical perspective, this constraint functions as a dichotomy in the space of "possible worlds." If a person knows that A, they are entitled to disregard all scenarios in which A is false. Consequently, the truth conditions for an epistemic proposition are defined such that a person knows A if and only if A is true in all of that person's "epistemic alternatives."1

While this principle is widely accepted, some philosophers suggest that imposing such a strong requirement on knowledge may be impractical for certain systems. For this reason, some argue that epistemic logic is more accurately viewed as a logic of information rather than a logic of knowledge in the strictly traditional, philosophically demanding sense.1