Proceedings of the Annual Meeting of the Cognitive Science Society

The discussion of conjunction fallacies or, more generally, inclusion fallacies (IFs) is usually limited to dyadic rela-tionships. Bayesian logic formalizes a rational intensional probability, predicting IFs and supplementing standard extensionalprobabilities (von Sydow, 2011, 2016). They treat logical patterns as explanatory patterns (explanans) given some data (theexplanandum). We here address the even more basic issue of nested hypotheses in a single polytomous dimension (von Sydow,2015) and present a corresponding variant of Bayesian logic (BL). The experiments use materials from the Linda tasks (oneconcerned with jobs, the other with political attitude) and they explore the polysemous character of ‘AND’ (Hertwig, Benz &Krauss, 2008; von Sydow, 2014). BL stresses that pattern probabilities should depend on the representation of subclasses. Aspredicted, the results show substantial deviations from standard probability and here corroborate a pattern approach. They arealso at odds with a confirmation account.