Proceedings of the Annual Meeting of the Cognitive Science Society

planation and evidence play important and non?interchangeable roles in argument. However, previous research has shown that subjects often confuse explanation and evidence (Kuhn, 1991). This study investigates the circumstances under which this confusion occurs. In Experiment 1, subjects generated arguments about issues of popular interest such as problems in schools and drug abuse. In Experiments 2 and 3, subjects rated the strength of evidence presented to them. The results of the protocol analyses and ratings tasks suggest that subjects tend to overestimate the strength of explanations when they lack sufficient knowledge of the domain or when they are unable to generate alternatives to the hypotheses presented to them. W e consider reasons why relying on explanations in these circumstances might be a valuable heuristic