It is routinely observed in NLP that sentences seem to “evoke” situations (where I use this term comprehensively to cover events, episodes, eventualities, processes, etc.). Much like discourse entities evoked by explicit noun phrases, these evoked situations can be referred to anaphorically, as for instance in (1) and (3) below, and can be modified in various ways, for instance by supplying their duration and location, as in (2) and (4).

Reichenbach's event, reference and speech times are interpreted semantically by stringing and superposing sets of temporal formulae, structured within regular languages. Notions of continuation branches and of inertia, bound (in a precise sense) by reference time, are developed and applied to the progressive and the perfect.