Probability, Confirmation, and the Conjunction Fallacy

The “conjunction fallacy” has been a key topic in discussions and debates on the rationality of human reasoning and its limitations. Yet the attempt of providing a satisfactory account of the phenomenon has proven challenging. Here we propose a new analysis. We suggest that in standard conjunction problems the fallacious probability judgments experimentally observed are typically guided by sound assessments of confirmation relations, meant in terms of contemporary Bayesian confirmation theory. The proposed analysis is shown robust (i.e., not depending on various alternative ways of measuring degrees of confirmation), consistent with available data, and prompting further empirical investigations. The present approach emphasizes the relevance of the notion of confirmation in the assessments of the relationships between the normative and descriptive study of inductive reasoning