Reasoning beyond predictive validity: the role of plausibility in decision-supporting social simulation

Practical and philosophical arguments speak against predictability in social systems, and consequently against the predictive validity of social simulations. This deficit is tolerable for description, exploration, and theory construction but serious for all kinds of decision support. The value of plausibility, however, as the most obvious substitute for predictive validity, is disputed for good reasons: it lacks the solid grounds of objectivity. Hence, on the one hand, plausibility seems to be in contradiction to scientific inquiry in general. On the other hand, plausibility is paramount and ubiquitous in practical decision making. The article redefines plausibility in order to render it more precise than colloquial usage. Based on the experiences with military applications different lines of reasoning with plausible trajectories based on computer simulation are analyzed. It is argued that the rationale behind such reasoning is often substantially stronger than a mere subjective expert opinion can be.