Arthur Prior and Hybrid Logic

Patrick Blackburn (Roskilde University)

Abstract. It is well known that Arthur Prior was the creator of tense logic; it is less well known that he also founded what has become known as hybrid logic, and that this second creation raised difficult questions for his own views on time. Prior held an A-series of view of time, and his tense logic was meant to reflect - indeed, to constitute - this view. But as he himself showed, his hybrid logic was capable of something very much like B-series talk, and (as he also realised) this raised a difficult question anew: What was so special about tensed talk after all? In my presentation, I will outline some of the ideas that led Prior to this realisation. I will not presuppose any previous knowledge of tense or hybrid logic: Prior's ideas have a simplicity and elegance that make them straightforward to present. But these ideas also led him to a problematic place; I will take the audience there, and then indicate a way out.