Two experiments investigate the question of why dialogues tend to be easier for anyone to understand than monologues. One possibility is that overhearers of dialogue have access to the different perspectives provided by the interlocutors, whereas overhearers of monologue have access to the speaker's perspective alone (Fox Tree, 1999). Directors first described a set of geometric shapes to matchers in monologue or dialogue eight times. Experiment 1 found that descriptions taken from dialogue were easier to understand than descriptions taken from monologue or descriptions taken from dialogue in which the matcher's contributions were excised. This advantage occurred on early trials (when the matcher made a considerable contribution) but also on late trials (when the matcher simply accepted a description). Experiment 2 replicated this finding and ruled out an explanation in which the advantage of dialogue is due to its use of discourse markers. We argue that the ease of dialogue occurs because interlocutors negotiate a perspective that they can agree on (Clark, 1996). This grounded perspective is likely to be objectively easier to understand than a perspective that has not been grounded. (Contains 6 tables and 2 figures.)