The Open Future in Historical and Conceptual Perspective

Peter Øhrstrøm (Aalborg University)

The open future is a common and important idea in modern temporal logic. Ontological, epistemological and logical aspects of this idea appear to have been essential in temporal logic right from A.N. Prior’s first formulations of his tempo-modal logic in the early 1950s. Over the years, Prior obviously regarded this idea as more and more important for a satisfactory understanding of time and existence.  Significant contributions to a deeper understanding of the open future can be found in his published books and papers as well as in his Nachlass. The aim of the present paper is to discuss Prior’s reflections on the ideas of the open future as well as his reasons for emphasising these ideas. Furthermore, the paper focuses on the formal representation of the open future in terms of symbolic logic. A selection of Prior’s examples illustrating his views on the open future will be analysed. Finally, the paper includes a discussion of the further elaborations and developments of Prior’s suggestions in the decades after his death in 1969. In particular, the use of new types branching time models will be considered.