Abstract

Beliefs shape how people interpret information and may impair how people engage in logical reasoning. In three studies, we show how ideological beliefs impair people’s ability to (1) recognize logical validity in arguments that oppose their political beliefs and (2) recognize the lack of logical validity in arguments that support their political beliefs. We observed belief bias effects among liberals and conservatives who evaluated the logical soundness of classically structured logical syllogisms supporting liberal or conservative beliefs. Both liberals and conservatives frequently evaluated the logical structure of entire arguments based on the believability of arguments’ conclusions, leading to predictable patterns of logical errors. As a result, liberals were better at identifying flawed arguments supporting conservative beliefs and conservatives were better at identifying flawed arguments supporting liberal beliefs. These findings illuminate one key mechanism for how political beliefs distort people’s abilities to reason about political topics soundly.