 Instant-based models of time are often not suitable for reasoning about events with duration, which are better modeled if the underlying temporal ontology uses time intervals, i.e. periods rather than instants, as the primitive entities. The roots of interval-based temporal reasoning can be traced back to Zeno and Aristotle (Øhrstrøm and Hasle 1995). In an interval-based setting, Zeno’s famous flying arrow paradox (“If at each instant the flying arrow stands still, how is movement possible?”) does not arise. Other examples that naturally require interval-based reasoning are: “Last night Alice cried a lot while writing the letter, and then she calmed down” and “Bill was drinking his tea when the postman came”.