Łukasiewicz, Bocheński, and Feys: Their Impact on the Early Prior

We investigate how Arthur Prior became a tense-modal logician, and which moderns influenced him in his early thinking about modality. His unpublished manuscript The Craft of Formal Logic, written in the period 1949–51, is in effect a record of his rather isolated apprenticeship as he trained himself in formal logic, during the two years before the commencement of his torrent of publications on modality. We analyse sections of this rich record of his logical development, especially those dealing with modal logic, and we extract a detailed account of the pattern of influences exhibited in The Craft. The Craft reveals that Prior’s first encounters with modern symbolic modal logic were the pioneering explorations by Bocheński, Feys, and Lewis. Von Wright was also an early influence. It was through Bocheński’s writings that Prior learned of Łukasiewicz’s approach to modality, and Łukasiewicz’s work quickly became a beacon for Prior. The roles of Lewis and von Wright appear to have been smaller than those of Łukasiewicz, Bocheński, and Feys—hence our focus on these three figures. As well as biographical material on these three outstanding logicians, we include numerous previously unpublished passages from The Craft in order to establish the nature and extent of their impact on Prior.