Abstract

A r anderson and n d belnap, Jr., Maintained in their 1962 article, "the pure calculus of entailment," that necessary propositions can be entailed only by necessary propositions, And not by contingent ones. Against this r w ashby offered an apparently conclusive counterexample in "entailment and modality" (1963). In support of anderson and belnap, The author of the present paper develops a definition of entailment and argues that contingent propositions never entail necessary ones. However, Psychological factors may intervene in our logical perceptions to produce an appearance or illusion of entailment between a contingent and a necessary proposition. (staff)