Liberals and conservatives often take opposing positions on moral issues. But what makes a moral position liberal or conservative? Why does public opinion tend to become more liberal over time? And why does public opinion change especially fast on certain issues, such as gay rights? We offer an explanation based on how different positions connect with different kinds of moral arguments. Based on a formal model of opinion dynamics, we predicted that positions better connected to harm and fairness arguments will be more popular among liberals and will become more popular over time among liberals and conservatives. Finally, the speed of this trend will be faster the better the position connects to harm and fairness arguments. These predictions all held with high accuracy in 44 years of polling on moral opinions. The model explains the connection between ideology and moral opinions, and generates precise predictions for future opinion change.
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All codes used to reproduce the results of this paper are available at https://github.com/irinavrt/moralopinion.
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This research was supported by the Knut and Alice Wallenberg Foundation grants 2015.0005 and 2017.0167. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.
The authors declare no competing interests.
Peer review information: Primary Handling Editor: Mary Elizabeth Sutherland.
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