The reasonableness of necessity

AbstractProspects for normative consensus between probabilists and advocates of the necessity calculus are nuanced. Necessity syntactically restates some probability distributions’ orderings and satisfies Cox’s “probabilistic” reasonableness standards, as possibility is now known to do. Used as a possibilistic tie breaker, necessity both restates probabilistic orderings and brings possibility closer to de Finetti’s quasi-additive standard. Nevertheless, variations in necessity’s credal orderings when beliefs change strain consensus. Moreover, in domains like the evaluation of scientific hypotheses, mathematical conjectures, and judicial findings, the negation of a hypothesis, needed to define necessity, may be ill-specified. Necessity may be less helpful to possibility in those domains, where professions of “belief” sometimes reflect not only credibility but also utilitarian or aesthetic preferences. Unbroken ties allow possibility to express both credibility and preference simultaneously