epistemology ref name stanfordepistemic ref ref name britannicaepistemic ref ref name macmillanmodal ref name britannica aims capture logic knowledge belief modal operators expressing knowledge belief usually expressed symbols stands propositions socrates wise expresses proposition agent knows socrates wise expresses proposition agent believes socrates wise axioms governing operators formulated express various epistemic principles ref name macmillanmodal ref name stanfordepistemic ref name britannicaepistemic example axiom schema expresses whenever something known true reflects
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