Barcan formula

== English == === Etymology === Introduced by the logician Ruth Barcan Marcus. === Proper noun === the Barcan formula (logic) In quantified modal logic, the formula ∀ x ◻ F x → ◻ ∀ x F x {\displaystyle \forall x\Box Fx\rightarrow \Box \forall xFx} , meaning "if every x is necessarily F, then it is necessary that every x is F".