Complete ignorance and independence axiom: Optimism, pessimism, indecisiveness

Abstract This paper studies the compatibility between a group of axioms characterizing rational behavior under complete ignorance and Savage's independence axiom. The axioms of complete ignorance include symmetry with respect to events, dominance and transitivity of strict preferences — possibly a very partial ordering of the choices, incomparabilities being admitted. Savage's independence axiom is a basic requirement in many theories of choice under uncertainty or risk. It is shown here that these requirements are indeed compatible, but conjointly imply that the decision-maker only exhibits zones of either pure optimism or pure pessimism or indecisive patterns of behavior.