Still Very Much Dead and Alive: Incoherence in Conspiracism as a Departure from Bayesian Rationality

Incoherence has long been considered a hallmark of belief in conspiracy theories, though recent research has cast doubt on this claim. We identify theoretical and methodological shortcomings in previous assessments of incoherence and propose a more rigorous definition of logical incompatibility, coupled with a Bayesian framework for measuring incoherence. Reanalyzing data from 8 studies involving 8,590 participants, we examined the relationship between conspiracy mentality (an individual’s generalized propensity to endorse conspiracy theories) and belief in mutually incompatible conspiracy theories (e.g., “Princess Diana was murdered” and “Princess Diana faked her own death”). We demonstrate that when incoherence is defined as a departure from Bayesian principles of rational belief, a robust association with conspiracy mentality emerges. Approximately 40% of participants high in conspiracism endorsed at least one logically incompatible CT, with the strongest believers showing a 91% probability of being incoherent.