Anaphora resolution in human-machine dialogue systems is often based on models and algorithms that were designed for text. But dialogue brings out a situation, i.e., an immediate physical environment and events that are perceived simultaneously by the participants. This situation can be at the origin of referential expressions called “exophora”, “antecedentless anaphora” or “anaphora with a non-linguistic antecedent”. Attributing some referents to such expressions is difficult for two reasons. First, because situational factors are numerous and implicit. Second, because ambiguities can appear between a potential situational antecedent and a potential linguistic one. In this paper we focus on the nature of situational factors and we investigate how they can be taken into account when doing anaphora resolution in dialogue and then in text. Our points of departure are the notion of salience and the nature of the events that intervene in dialogue and that can be described in text. We propose a characterization of such events and we draw some theoretical conclusions on the principles that can be added to existing anaphora resolution algorithms.