A Computational Model of the Semantics of Tense and Aspect

The PUNDIT natural-language system processes references to situations and the intervals over which they hold using an algorithm that integrates the analysis of tense and aspect. For each tensed clause, PUNDIT processes the main verb and its grammatical categories of tense, perfect, and progressive in order to extract three complementary pieces of temporal information. The first is whether a situation has actual time associated with it. Secondly, for each situation that is presumed to take place in actual time, PUNDIT represents its temporal structure as one of three situation types: a state, process, or transition event. The temporal structures of each of these situation types consist of one or more intervals. The intervals are characterized by two features: kinesis, which pertains to their internal structure, and boundedness, which constrains the manner in which they get located in time. Thirdly, the computation of temporal location exploits the three temporal indices proposed in Reichenbach 1947: e v e n t time, speech time, and reference time. Here, however, event time is formulated as a single component of the full temporal structure of a situation in order to provide an integrated treatment of tense and aspect.