The partisan penalty: The effect of partisanship on evaluating reasons for political belief

Polarization may operate not only through disagreement over political positions, but through disagreement about what counts as a good reason. We test two hypotheses: that partisans rate outparty reasons as lower quality than ingroup reasons even when they share ideological stances (what we call the content partisan penalty), and that the same reason is judged weaker when attributed to a contrapartisan rather than a copartisan (what we call the source partisan penalty). Across four studies (N = 4,406), participants rated the quality of political reasons supporting or opposing issue statements they had endorsed or rejected. Studies 1, 2, and 3 support H1: evaluators consistently discounted outparty reasons, including when contrapartisans shared the same stance, and the effect generalized to partisan leaners as well as self-identified Democrats or Republicans. Study 4 directly supports H2 by manipulating partisan source cues for the same reason. Evaluations tracked the presented label, reversing when partisan labels were swapped. Exploratory Bayesian analyses suggest outparty warmth attenuates the penalty and anger under disagreement amplifies it.