Finite order implications of common priors in infinite models

Abstract

Lipman [Lipman, B., 2003. Finite order implications of common priors, Econometrica, 71 (July), 1255–1267] shows that in a finite model, the common prior assumption has weak implications for finite orders of beliefs about beliefs. In particular, the only such implications are those stemming from the weaker assumption of a common support. To explore the role of the finite model assumption in generating this conclusion, this paper considers the finite order implications of common priors in the simplest possible infinite model, namely, a countable model. I show that in countable models, the common prior assumption also implies a tail consistency condition regarding beliefs. More specifically, I show that in a countable model, the finite order implications of the common prior assumption are the same as those stemming from the assumption that priors have a common support and have tail probabilities converging to zero at the same rate.