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

Causal systems often include mutually exclusive events: events which cannot occur simultaneously. However, when events in a causal system are exclusive, the normative properties of the whole system change substantially. Are adults sensitive to the consequences of exclusivity for causal reasoning? Here, we systematically manipulated common-effect causal systems to have either exclusive or non-exclusive causes while holding all other factors constant. Adults showed a rich understanding of exclusive systems in making both predictive (Experiment 1) and diagnostic (Experiments 2 and 3) causal inferences. Adults’ success in these tasks suggests that exclusivity is an important dimension in human causal reasoning.

Real people sometimes appear in fiction, for example,Napoleon in War and Peace. Readers may also believe that aperson who never actually appears in a novel couldpotentially appear there. In two experiments, we find evidencethat readers think that a real person could appear in specificnovels and physically interact with a character. This effect ismagnified when the person and character share spatial andtemporal elements of their setting.