  Prior catalysed the field with his detailed proposals for a modal logic of time-distinctions. His tense logic was nothing less than a new paradigm for the study of time (Hasle and Øhrstrøm 2016). Prior went on to use his tense logic to articulate theories about the structure and metaphysics of time and to mount a robust defence of freewill and indeterminism. Tense logic is now also employed for the manipulation of time-dependent data and has numerous applications in computing, including database management, program verification, and commonsense reasoning in artificial intelligence.