Proceedings of the Annual Meeting of the Cognitive Science Society

A key phenomenon in the psychology of reasoning is belief bias, a tendency to accept the conclusion of an argument basedon whether it is believable, regardless of logical status. The traditional notion of belief bias assumes a contrast betweenlogic and beliefs: we are either logical, or we are biased away from logic by our beliefs. But this contrast is unnecessaryin probabilistic theories of reasoning that generalise logic to cover uncertain degrees of belief. An experiment examinedwhether reasoners inferences about conditional syllogisms conform to principles of probabilistic coherence and whetherthis was affected by the believability of argument premises. Inferences for a majority of syllogisms showed above-chancecoherence regardless of the believability of argument premises. When deviations from coherence did occur these mostoften reflected underconfidence in arguments with unbelievable premises. These results show that positing two distinctreasoning processes is not necessary to explain belief bias.