 (named for Ruth Barcan, later Ruth Barcan Marcus, who discussed it as early as the late 1940s). To see its implausibility, consider this instance: ‘If everything is necessarily a product of the big bang, then necessarily everything is a product of the big bang’. It may well be true that everything (in the actual world) is necessarily a product of the big bang—i.e., that nothing in this world would have existed without it. But it does not seem necessary that everything is a product of the big bang, for other universes are possible in which things that do not exist in the actual world have other ultimate origins. Because of the restrictiveness and implausibility of fixed-domain semantics, many modal logicians loosen Kripke’s strictures and adopt free logics.