We investigate what it means for one act to be more ambiguous than another. The question is evidently analogous to asking what makes one prospect riskier than another, but beliefs are neither objective nor representable by a unique probability. Our starting point is an abstract class of...

We examine a variety of preference-based definitions of ambiguous events in the context of the smooth ambiguity model.  We first consider the definition proposed in Klibanoff, Marinacci, and Mukerji (2005) based on the classic Ellsberg two-urn paradox (Ellsberg (1961)), and show that it...

Are foundations of models of ambiguity-sensitive preferences too flawed to be usefully applied to economic models?  Al-Najjar and Weinstein (2009) say such is indeed the case.  In this paper, first, we point out that many of the key arguments by Al-Najjar and Weinstein do not apply to quite a...

Epstein (2009) describes three Ellsberg-style thought experiments and argues that they pose difficulties for the smooth ambiguity model of decision making under uncertainty developed by Klibanoff, Marinacci and Mukerji (2005).  We revisit these thought exeperiments and find, to the contrary,...