This work examines the linguistic constructions which speakers use to talk about events that occurred in the past and states which held in the past. Laura Michaelis argues that the fundamental conceptual division between events and states forms the basis of systems of verbal aspect in all languages, and that one cannot talk about the meaning of a past-tense assertion without making reference to the event-state distinction. Focusing on English data, the author examines the semantic and functional overlap between assertions about the past and assertions involving events: when one asserts that an event of a given kind exists, one is making an assertion about the past. This semantic overlap can be evoked as a way of characterizing the close relationship between the past-tense construction and the past-perfect construction: while a past tense assertion like She left is used to describe the past, a present-perfect assertion like She has left is used to assert the existence of an event by invoking its aftermath (her absence). Dr. Michaelis argues that the two constructions are semantically equivalent, but distinguished by their function in narrative. This study presents a semantic framework for analyzing all aspectual constructions in terms of the event-state distinction, and describes the grammatical expression of aspectual meaning in terms of a theory of grammatical constructions. In this theory, grammatical constructions, like words, are conventionalized form-meaning pairs, which are best described not only with respect to their intrinsic semantic values, but also with respect to the functional opposition in which they participate. Michaelis argues that many of the otherwise puzzling grammatical constraints which characterize the English present-perfect construction can be motivated in terms of the functional opposition between present perfect and past tense.