In quantified modal logic, the Barcan formula and the converse Barcan formula (more accurately, schemata rather than formulae) (i) syntactically state principles or interchange between quantifiers and modalities; (ii) semantically state a relation between domains of possible worlds. The formulae were introduced as axioms by Ruth Barcan Marcus, in the first extensions of modal propositional logic to include quantification.
Related formulas include the Buridan formula, and the converse Buridan formula.
Read more about Barcan Formula: The Barcan Formula, Converse Barcan Formula
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