Temporal Centering

We present a semantic and pragmatic account of the anaphoric properties of past and perfect that improves on previous work by integrating discourse structure, aspectual type, surface structure and commonsense knowledge. A novel aspect of our account is that we distinguish between two kinds of temporal intervals in the interpretation of temporal operators-discourse reference intervals and event intervals. This distinction makes it possible to develop an analogy between centering and temporal centering, which operates on discourse reference intervals. Our temporal property-sharing principle is a defeasible inference rule on the logical form. Along with lexical and causal reasoning, it plays a role in incrementally resolving underspecified aspects of the event structure representation of an utterance against the current context. The Problem The past tense has been compared with anaphoric definite pronouns ([20] [22]) and definite noun phrases ([27]). The supporting observation is that in two consecutive past tense descriptions of events, as in (1) below (from [18]), the second sentence refers to a time (t') whose identity depends on the time (t) of the event described in the first sentence. (1)a. The Lone Ranger got on his horse. (t) b. He rode off into the sunset. (t') Tense interpretation also involves common-sense inferences in that the specific relation between the two event times may vary. In (1), the relation inferred to hold is temporal progression (t-~ t'), but other ordering relations are also possible (see [6] [27]). Any temporal relations are in fact possible for two consecutively described events in discourse. A number of factors affect the interpretation as to whether successive past tenses are anaphor-ically related, and if they are, what the relative order of the associated events is. The determinant factors have been argued to be discourse structure ([27] [14]), aspectual type ([61 [12] [17]), surface structure ([7] [14]), and commonsense knowledge ([19] [271 [13]). However, no account has adequately addressed all four factors. The problem in tense interpretation that we address is illustrated with Example (2) (from [27]). (2)a. John went over (el) to Mary's house. b. On the way, he had (t2) stopped (t3) by the flower shop for some roses. (t3-~ t2 (=tl)) c. Unfortunately, they failed (t4) to cheer her up. (t3-~ tl-~ t4) c'. He picked out (t4') 5 red ones, 3 white ones and 1 pale pink. (t3-< t4'-< tl) (2c) and (2c') are alternative third sentences. Although both are in the simple …