Abstract: In various professional and private contexts, it is often necessary to aggregate different opinions about whether a given claim is true or false. A doctrinal paradox occurs when this claim is akin to a logical formula combining several propositions, and it turns out that the claim itself is true (resp., false) for a majority of judges, whereas a majority of judges has opinions on the propositions that would make the claim false (resp., true). The doctrinal paradox is a serious formal concern for judgment aggregation, which has generated intense normative research in various scientific fields. Behavioral psychologists, though, still have to undertake systematic research on this important problem. This article provides a brief introduction to the doctrinal paradox and its formal study, summarizes available behavioral data, and points to perspective for future behavioral research.

Key words: opinion, aggregation, paradox, vote