The recent intense interest in conspiratorial thinking is fuelled by the perception that belief in conspiracies is highly irrational. However, there have been few studies that have examined the associations of conspiracy belief with a comprehensive battery of rational thinking tasks that tap both epistemic and instrumental rationality. The Comprehensive Assessment of Rational Thinking (CART) provides an opportunity to do just that because one of the subtests on the CART assesses the tendency to believe false conspiracies. That subtest is in (...) the part of the CART that measures the presence of contaminated mindware—stored declarative knowledge that embodies poorly justified beliefs. Converging analyses (N = 747) using the 18 subtests and four thinking dispositions measured on the CART indicated that three variables were key predictors of conspiratorial thinking: superstitious thinking, actively open-minded thinking, and probabilistic reasoning. Theoretical consideration of these best predictors, and of the variables that predict the endorsement of true conspiracies, led us to rethink the classification of conspiracy belief as contaminated mindware and move instead towards a conception of conspiratorial thinking as a cognitive style. (shrink)