Perfectivity is often assumed to entail the completion of the event described by eventdenoting stems and their arguments. Although some scholars have noted that perfective markers do not always entail completion, their formal definitions contradict their informal descriptions. We show that these traditional models of perfective aspect cannot account for the aspectual system of Thai. In Thai, perfective markers do not entail that the event was completed: the resulting state of sentences that are in appareance telic in their 'inner aspect' need not have been reached. We call these non-completive perfective markers semiperfectives. We propose a formal model of semi-perfectivity within Discourse Representation Theory that relies on the inclusion of an imperfective operator in the lexical meaning of Thai accomplishment verbs as well as the notion of maximal event relative to an event description. We show that this latter notion is strictly weaker than the traditional notion of telicity, thus demonstrating that (a)telicity is not the sole property of event descriptions relevant to the semantics of grammatical aspect. Perfectivity is often assumed to entail the completion of the event described by event-denoting stems and their arguments (see Herweg 1991, 1991b for an explicit expression of this assumption). In particular, if the stem belongs to the accomplishment Aktionsart class, perfectivity-which we informally define for now as the requirement that the event that the sentence describes is bounded-entails that the accomplishment's resulting state holds at the reference time interval. 1 Some scholars, such as Binnick (1991) and Smith (1997), have noted that perfective markers do not always entail completion of the event denoted by ' Following Smith (1997), we call the combination of a verb and its arguments, to the exclusion of tense or aspect marking, a verb constellation. We assume that Aktionsart classes are defined, as in Dowty (1979), via statements of the following kind: i. If P is an accomplishment and a is a specified quantity (in the sense of Verkuyl 1993), then, if P(a) is true at interval /, it is not true at all subintervals of/ (adapted from. Dowty 1979 p. 166). Since this paper is only concerned with sentences in which accomplishment predicates combine with arguments that are specified quantities, we use the term accomplishment verb/stem to mean a verb/stem whose meaning includes an accomplishment predicate P combining with arguments that are specified quantities. We also sometimes refer to verb constellations, clauses, or sentences whose main verb stems belong to the accomplishment class as accomplishment verb constellations, clauses, or sentences.
