The problems faced by consumers when there is uncertainty have frequently arisen in our discussion to date. Indeed, uncertainty is pervasive in almost all decision making and is inevitable whenever an action or decision and its consequence are separated by a space of time, however short. Even for consumption decisions involving the most highly perishable commodities, some uncertainty is always present. An ice cream may melt before it can be eaten; its quality or flavor may be very different from that anticipated, or it may or may not cause indigestion at some unpredictable time after consumption. All these are trivial enough, but become of the greatest importance in considering any sort of intertemporal decision making, whether buying a car, planning savings, or choosing the assets in which to hold wealth. Because of such considerations, a fully satisfactory treatment of consumers' behavior would allow for uncertainty right from the start. However, as we shall see, although a consistent and well-articulated theory for choice under uncertainty does exist, its applications to date are partial in coverage and are very considerably more complex than the corresponding results under certainty. Moreover, the omnipresence of uncertainty does not imply that it is always important.

Only in the last twenty years, dating essentially from the work of Savage (1954), has a full, axiomatic treatment of choice under uncertainty been available, although, as in the case of the axioms of choice under certainty, there has been considerable refinement by later writers.