Philosophical roots of model validation: two paradigms

System dynamics models, as causal models, are much like scientific theories. Hence, in evaluating such models, we assume certain norms of scientific inquiry. Most critics hold that the system dynamics approach does not employ formal, objective, quantitative model validation tests. This article argues that this type of criticism presupposes the traditional logical empiricist philosophy of science, which assumes that knowledge is an objective representation of reality and that theory justification can be an objective, formal process. According to the more recent relativist philosophy of science, knowledge is relative to a given society, epoch, and scientific world view. Theory justification is therefore a semiformal, relative social process. We show that relativist philosophy is consistent with the system dynamics paradigm and discuss the practical implications of the two philosophies of science for system dynamics modelers and their critics.