Time and Tense in English

Time and Tense in English Mary P. Harper and Eugene Charniak Brown University Department of Computer Science Box 1910 Providence, RI 02912 Abstract Tense, temporal adverbs, and temporal connectives provide information about when events described in English sentences occur. To extract this temporal information from a sentence, it must be parsed into a semantic representation which captures the meaning of tense, temporal adverbs, and temporal connectives. Representations were developed for the basic tenses, some temporal adverbs, as well as some of the temporal connectives. Five criteria were suggested for judging these representations, and based on these criteria the representations were judged. Introduction English sentences contain many types of temporal information. Tense is used to inform the reader (listener) of when the event associated with the main verb occurs with repect to the time of utterance. That is, tense informs the reader that an event occurs before, after, or during the time of utterance. Temporal adverbs (such as tomorrow or now) add additional information about the events in a sentence. Temporal connectives tell the reader about the temporal relationship between the events in the main clause and the events in the subordinate clause. While there is other temporal information that can be found in sentences, the following will concentrate on these three. To extract temporal information from a sentence, it must be parsed into a semantic representation which captures the meaning of tense, temporal adverbs, and temporal connectives. A temporal representation of tense, adverbs, and temporal connectives must : 1. provide a way to reject temporally incorrect sentences, such as * "I will run yesterday." 2. allow one to reason about the temporal relationship between events. For instance, the sentence "I had run when he arrived" implies that the run event occurs before the arrival, whereas in the sentence "I was running when he arrived," the arrival and run events overlap. 3. allow the exact time of event to be unfixed until it is pinpointed based on contextual information or adverbial modification. 4. allow reference to points and intervals of time (eg. precisely at 3 PM VS. for 5 hours). This work has been supported in part by the National Science Foundation under grants IST 8416034 and IST 8515005, and Office of Naval Research under grant N00014-79-C-0529. 5. allow parsing of temporal information in sentences to be simple and compositional. These criteria were used to judge previous temporal representation research (Bruce (1972), Hornstein (1977, 1981), Yip (1985)). None fulfilled all five criteria. The criteria will also be used to judge the representations developed here. Tense The representations for tense, adverbs, and temporal connectives developed here is based on McDermott's (1982) temporal logic. McDermott's "point-based" temporal logic was chosen because it is not unusual to talk about the beginning and end points of a period of time or an event. In fact, the semantics of tense developed here relate the endpoints of events in sentences. This representation of tense provides a flexibility not found in many other representations of tense (eg. (Hornstein, …

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