Agreeing to Disagree Politically

13 Pages Posted: 5 Sep 2019

See all articles by Brad R. Taylor

Brad R. Taylor

University of Southern Queensland

William Bosworth

London School of Economics & Political Science (LSE) - Department of Government

Date Written: August 29, 2019


Robert Aumann's agreement theorem and subsequent work shows that people who are rational in a certain Bayesian sense cannot agree to disagree on matters of fact, as long as there is common knowledge of this common rationality. This result hinges on a type of epistemic impartiality: a rational person will not give extra weight to a piece of evidence simply because they themselves discovered it rather than someone else. Of course, "Good Bayesians" who agree on matters of fact can nevertheless disagree due to differences of preference and value. We question the possibility of reasonable political disagreement for liberals. On our reading, a “Good Liberal” must not give extra weight in public deliberations to their own preferences or values simply because they are their own. This political impartiality mirrors the epistemic impartiality of Aumann's theorem and we argue that disagreement on policy is impossible in a world of "Good Liberal Bayesians," assuming common knowledge of both Bayesian rationality and Liberal reasonableness. The persistence of disagreement in the real world provides support for expressive accounts of political behaviour and points to the important role of epistemic trust in politics.

Keywords: Agreeing to Disagree, Political Liberalism, Political Disagreement, Rationality, Bayesian Rationality

JEL Classification: D63, D7, D83

Suggested Citation

Taylor, Brad and Bosworth, William, Agreeing to Disagree Politically (August 29, 2019). Available at SSRN: or

Brad Taylor (Contact Author)

University of Southern Queensland ( email )

Springfield, Queensland

William Bosworth

London School of Economics & Political Science (LSE) - Department of Government ( email )

Houghton St
London, WC2A 2AE
United Kingdom

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