[The theory is founded on the concept of markedness and rests on two fundamental assumptions:] (1) that narrative constitutes a marked category of linguistic performance whose grammar differs in certain respects from that of ordinary interactive discourse; (2) that adult linguistic competence includes, as one of its components, a 'narrative norm', an internalized set of shared conventions and assumptions about what constitutes a well-formed story. The narrative norm is defined in terms of markedness values for a set of properties, operative at different levels of the linguistic system, which collectively define its unmarked tense: the Perfective Past, or Preterit. A major claim this paper makes is that when in a narrative the Present tense  —  or any tense other than the Preterit  —  is chosen, the narrator's objective (conscious or unconscious) is to neutralize one or more of the properties that collectively define the Preterit as the unmarked tense of narration, and in turn establish the norms for narrative discourse. To depart from the Preterit is to depart from narration, understood as an activity through which the unordered raw data of experience, real or imagined, are retrospectively converted into language and in the process configured into a meaningful construct: a story. 

(c) Suzanne Fleischman. Toward a theory of tense-aspect in narrative discourse