Agreeing on Decisions

Robert J. Aumann and Sergiu Hart

Long Abstract
The Decision Agreement Principle, originally promulgated by Cave and Bacharach (independently), asserts that if like-minded decision makers commonly know each other's decisions, then the decisions are the same. Subsequently, Moses and Nachum discovered a flaw in the reasoning underlying the principle. Here we provide a careful, coherent, and correct formulation of the principle, which avoids the Moses-Nachum flaw, and enables us to understand just when the principle applies, and when it doesn't.

• The Hebrew University of Jerusalem, Center for Rationality (2005, in preparation)