Objective: Political polarisation is a common problem that has gained increasing attention, and opinions are often divided along party lines. Moral foundations theorysuggests that there are some foundations, appealing to individual autonomy, that are part of everyone’s morality, while other foundations, concerning bounds to yourgroup, appeal only to conservatives. We here test the hypothesis that arguments that build on individualising foundations can persuade everyone, while binding argumentscan persuade only conservatives. This gives a prediction of what we can eventually agree on, and can explain why moral values tend to become more liberal/progressiveover time, despite polarisation.
Methods: We used a classic experimental design (N=379) where respondents from the US were given moral arguments for nine moral stances. The respondents were firstasked for their opinion, and a week later, they were given individualising, binding or no arguments for the stances, and were asked for their opinion again. We measuredaverage opinion change across the issues depending on treatment and the political ideology of the respondent.
Results: The results were in line with the hypothesis. There was a general significant effect across the political spectrum from being given individualising arguments, whilebinding arguments for the same moral stances had an effect only when given to conservative respondents. Those in the control condition who received no arguments didnot change their opinion significantly.
Conclusion: In line with cognitive dissonance theory, the moral foundation support of respondents predicts the type of arguments to which they are susceptible. Thesefindings suggests that there are tools for finding common ground in polarising issues. Further, along with previous studies on which type of moral argument supports whichmoral position in the public debate, these findings provide a mechanistic explanation for public opinion change, and in particular for the empirical observation that moralvalues are becoming more liberal and progressive.