Extension Rules or What Would the Sage Do?

Quite often, decision makers face choices that involve new aspects and alternatives never considered before. Scenarios of this sort may arise, for instance, as a result of technological progress or from individual circumstances such as growing awareness. In such situations, simple inference rules, past experience, and knowledge about historic choice problems may prove helpful in determining what would be a reasonable action to take vis-a-vis a new problem. In the context of decision making under uncertainty, we introduce and study an extension rule that enables the decision maker to extend a preference order defined on a restricted domain.