After many centuries of designing engineering structures and systems within a deterministic framework, it has become fashionable to deal explicitly with uncertainty as an important component of planning and design strategies. Advances in applied statistical decision theory, coupled with the wide availability of computing machinery, are at the root of this transformation, and the recent literature is replete with studies of systems, large and small, under various conditions of uncertainty. This paper deals with a few rules for decision-making under a special category of uncertainty -- namely that associated with the occurrence of events which could not be foretold, let alone assigned a prior probability of realization within a given design horizon
