Events occupy a central place in natural language. Accordingly, an understanding of them is crucial if one is to have any kind of a theoretically well-motivated account of natural language understanding and generation. It is proposed here that speakers create a cognitive structure for each discourse and process it as they introduce sentences into the discourse. The structure for each sentence depends systematically on its tense, aspect and the situation type; its effect on the discourse also depends on the structures of the sentences that precede it. It is also argued that the perfective aspect introduces the structure of the given event in its entirety. The progressive, by contrast, introduces only the core of the structure of the given event excluding, in particular, its preparatory processes and resultant state. Similarly, the perfect and the perfective can be distinguished on the basis of the temporal schemata they introduce. While the perfective presents the event as complete, the perfect presents it as complete and closed; i.e., the perfect prevents succeeding discourse from being interpreted as falling during the given event. This is surprising since the perfect is otherwise simply the combination of the perfective and a tense. This paper also provides a key motivation for distinguishing between the preparatory processes and the preliminary stages of an event. This observation, which is crucial in distinguishing between the perfective and the progressive has not been made in the literature.