Chiastic order is an ancient expression for cross-classification. As such, it is the primordial form of non-quantified modelling and combinatory heuristics. This book presents an epistemological history of non-quantified modelling: its prehistory in the form of rhetorical and epistemic chiasmus; its early (pre-symbolic) use by Plato as a cross-order (paradigmatic) modelling method; its prototype development by Ramon Llull as a heuristic ars combinatoria; its “modern” use by Gottfried Leibniz based on a calculus of concepts; and Fritz Zwicky’s 20th-century promotion of the “morphological approach”. Examples of contemporary computer-aided combinatorial modelling are presented in the areas of operational research, policy analysis, scenario development and design theory.