Interpreting Temporal Adverbials

INTERPRETING TEMPORAL ADVERBIALS* Chung Hee Hwang & Lenhart K. Schubert Department of Computer Science, University of Rochester Rochester, New York 14627-0226 Abstract We take for granted that sentences describe situations [2, 12]. One of the most important properties of situations are then their tempo- ral locations, which are indicated by tense and aspect and temporal adverbials in the surface form. In [10, 22], we offered a formal the- ory for English tense and aspect and an algorithm that computes the temporal relationships between the situations implicitly introduced by a text. In the present paper, we propose a systematic approach to temporal adverbials, fully integrated with our tense-aspect theory and the inte~retive algorithms, using the Episodic Logic (EL) formalism [9, 11, 12, 211. 1. INTRODUCTION Previous theoretical work on temporal adverbials has mostly concentrated on adverbials specifying temporal locations (e.g., "yesterday"), durations (e.g., "for a month") and time spans (e.g., "in three hours"). It appears that interest in the first kind of adverbial originated from the desire to correct the erroneous analyses provided by Priorean tense logics, in particular, their treatment of the interaction between time adverbials and tense. The second and third kinds of adverbials were often consid- ered in connection with the aspectual classes of the vPs or sen- tences those adverbials modify (e.g., durative adverbials may modify only stative sentences, whereas adverbials of time span may modify only accomplishment sentences). However, other kinds of temporal adverbials have received little attention, in- cluding ones specifying repetition: The engineer shut down the motor twice yesterday. The engine frequently broke down. The operator checked the level of oil every half hour. The inspector visits the lab every Monday. On our analysis, these sentences describe complex events, consisting of a sequence of subevents of specified types, and the given adverbials modify the structure of these complex events: the cardinality of component events ("twice"), the frequency or distribution pattern of component events ("fre- quently," "regularly," "every half hour," etc.), and the temporal location of cyclic events that occur synchronously with other recurrent time frames or events ("every Monday" or "every time the alarm went off''). Other issues that deserve further investigation are the interac- tions between multiple temporal adverbials, and various kinds of aspectual class shift due to aspectual class constraints on the use of adverbials (occurring singly or jointly with others). The following sentences illustrate these issues. *This research was supported in part by NSF Research Grant IRI- 9013160 and ONR/DARPA Research Contracts No. N00014-82-K-0193 and No. N00014-92-J-1512. The authors benefited from example sentences by Greg Carlson and Phil Harrison. John ran for half an hour every morning for a month. John stepped out of his office for fifteen minutes. Mary is going to Boston for three days. Mary won the competition for four years. John saw Mary twice in two years. Our aim is to provide a uniform analysis for all kinds of tem- poral adverbials. Our approach is compositional in that the lexicon supplies meanings at the word level (or …

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