The choice of scenarios

Abstract Scenarios are general descriptions of future conditions and events. Which conditions and events-which variables-are to be described within the scenario? Which alternative sets of values are to be chosen? This article sets out a strategy for dealing with these problems that involves the structured application of a modelling technique. The conventional techniques available often require data which are not available; the implementation of such models involves guesses at the precise values of parameters which critically determine the behaviour of the model. This article outlines a novel “four-value logical” modelling procedure which has requirements better adjusted to data limitations, and to the plurality of alternative futures.