In this paper I show how the denotations of certain temporal adverbials depend in part on an aspect of world knowledge: stereotypical intervals. The focus of this study will be the temporal adverbials not yet and never in English. Traditional denotations for not yet do not fully specify its truth conditions because the span of time for which an event is felicitously asserted to not have occurred varies depending on the type of event, i.e., the interval(s) of time within which a given event typically occurs: the stereotypical interval. In particular, the standard type of denotation for not yet fails to differentiate it from never. I show how Semantic Frames (Fillmore, 1982) can be used, in conjunction with Discourse Representation Structures (Kamp et al., forthcoming) to capture the type of world knowledge needed to accurately specify the truth conditions of not yet.