Abstract
It is commonly argued that factual knowledge about a political issue increases attitude polarization due to politically motivated reasoning. By this account, individuals ignore counter-attitudinal facts and direct their attention to pro-attitudinal facts; reject counter-attitudinal facts when directly confronted with them; and use pro-attitudinal facts to counterargue, all making them more polarized. The observation that more knowledgeable partisans are often more polarized is widely taken as support for this account. Yet these data are only correlational. Here, we directly test the causal effect of increasing issue-relevant knowledge on attitude polarization. Specifically, we randomize whether N = 1,011 participants receive a large, credible set of both pro- and counter-attitudinal facts on a contentious political issue - gun control - and provide a modest incentive for them to learn this information. We find evidence that people are willing to engage with and learn policy-relevant facts both for and against their initial attitudes; and that this increased factual knowledge shifts individuals towards more moderate policy attitudes, a durable effect that is still visible after one month. Our results suggest that the impact of directionally motivated reasoning on the processing of political information might be more limited than previously thought.