A.N. Prior’s work with Peirce’s philosophy and investigations into the formalisation of temporal ontology give rise to some important questions regarding time and existence. Some answers to these questions are considered in this paper, which deals mainly with A.N. Prior’s ideas on time and existence. The focus is on Prior’s analysis of problems concerning the ontology of objects which exist for a limited time only. This work led him to some interesting ideas concerning tensed ontology. In particular, the paper discusses Prior’s own contribution to tensed ontology, which may be seen as a further development of Leśniewski’s ontology. Finally, the paper presents some challenges regarding the significance of tensed ontology in philosophy and information architecture.