Arthur Norman Prior was born on \(4{\mathrm{th}}\) December 1914. Thus 2014 marked his centenary, which was celebrated through a major conference at Balliol College, Oxford, in August 2014. The present volume is a result of presentations and work initiated at this event. The centenary conference also marked the launch of Prior’s Nachlass, which is now available online at www.priorstudies.org along with various other material related to Prior’s logic and philosophy. Several of the papers in this volume are based on studies of texts in Prior’s Nachlass. Nevertheless, the contributions to this volume cannot be said to be mainly of a historical nature. A systematical interest in the issues raised in Prior’s work and an endeavour to bring forward its insights are quite manifest.

It is a clearly shared assumption throughout the present volume that Prior’s works are generally still of direct relevance and that his books and papers should be read not only for historical reasons. As suggested by Per Hasle and Peter Øhrstrøm in their paper, Prior’s paradigm for the study of time and its methodological motivation, Prior’s main achievement may be understood as an introduction of a new paradigm for the study of time according to which tense logic should be seen as the key to a deeper understanding of the temporal aspects of reality. Moreover, they show how the varied issues in Prior’s work, also those going beyond time and tense, all fit into an overall fabric defined by some fundamental methodological assumptions.

The continuing systematical importance of course does not detract from the fact that the historical aspects are still important. It is striking that many of Prior’s philosophical ideas can in fact be traced back to religious and political problems that Prior dealt with during the 1930s and 1940s. In the papers, An illusion close to life and An angry young man: A close reading of Arthur Prior’s contribution to social ontology, David Jakobsen and Niko Strobach offer valuable insights into the problems that Prior was struggling with during this early period. Both papers involve careful studies of Prior’s Nachlass.

In addition to his interest in religious and political issues, Prior had in his early years a strong interest in ethics and classical logic. The paper by Federico L. G. Faroldi Ethical copula, negation and responsibility judgments: Prior’s contribution to the philosophy of normative language as well as the paper The logic of ‘Logic and the Basis of Ethics’ by Adriane Rini are both investigating aspects of Prior’s works on ethics. The papers Possible worlds in ‘The Craft of Formal Logic’ by Aneta Markoska-Cubrinovska, Prior on Aristotle‘s Logical Squares by Zuzana Rybaříková, and Yoshihiro Maruyama’s Prior’s tonk, notions of logic, and levels of inconsistency: vindicating the pluralistic unity of science in the light of categorical logical positivism all discuss aspects of Prior’s early contributions to the study of basic questions in formal logic.

Prior had a clear interest in the logical analysis of concepts and reasoning in natural language. Besides of course temporal issues he in particular focused on the logic of objects, individuals and existence. Hartley Slater’sFootnote 1 Prior’s individuals, Jack Copeland’s Prior, translational semantics, and the Barcan formula, Giulia Felappi’s Why fuss about these quirks of the vernacular? Propositional attitude sentences in Prior’s nachlass, James Van Cleve’s Objectivity without objects: a Priorian program, and James Levine’s Prior, Berkeley, and the Barcan formula are all papers dealing with topics within that field.

It is commonly agreed that Prior’s greatest contribution was his founding of the logic of time through the means of, and as part of, formal logic. A dominant feature of this achievement was his emphasis of the first person perspective, the primacy of tense and time as seen from within. Questions relating to this perspective have been studied in Solving Prior’s problem with a Priorean tool by Martin Pleitz, ‘Spurious egocentricity’ and the first person by James Doyle, and Prior’s Thank-Goodness Argument Reconsidered by Matt LaVine. Such studies are of course part of wider investigations into Prior’s development of modal and tense logic as well as the further development of this logic after Prior’s death. The papers Prior on the semantics of modal and tense logic by Max Cresswell, Prior and temporal sequences for natural language by Tim Fernando, Partial and paraconsistent approaches to future contingents in tense logic by Seiki Akama, Tetsuya Murai and Yasuo Kudo, and Prior and possibly not existing by Michael Nelson all deal with important aspects of the development of modal and tense logic initiated by Prior.

Prior was not only the founder of modern tense logic, but he also conceived and anticipated a related branch of logic which later came to be known as hybrid logic. This framework made it possible for Prior to explain the notion of a temporal instant and to handle various formal problems in temporal logic. In the papers Arthur Prior and ‘Now’ and Reichenbach, Prior and hybrid tense logic Patrick Blackburn and Klaus Frovin Jørgensen discuss some important problems regarding the use of hybrid logic in temporal logic.

The papers Tense, propositions, and facts by Ulrich Meyer, Where have all the Californian tense-logicians gone? by Woosuk Park, and Worlds, times and selves revisited by Tero Tulenheimo offer discussions of problems related to further developments of Priorean tempo-modal logic.