 The contemporary field of judgment-aggregation theory was inspired by a series of ‘paradoxes’, with which we begin. Kornhauser and Sager (1986) described the following problem, now known as the ‘doctrinal paradox’. (A structurally similar problem was discovered by Vacca 1921 and, as Elster 2013 points out, by Poisson 1837.) A three-judge court has to make judgments on the following propositions: