MODELS AND MODELLING IN ECONOMICS Mary S. Morgan and Tarja Knuuttila 1 INTRODUCTION Interest in modelling as a specific philosophical theme is both old and new. In the nineteenth century the word model usually referred to concrete objects, often- times to the so-called mechanical models, that were built in an effort to grasp the functioning of unobserved theoretical entities (e.g. [Bolzmann, 1911]). Since then, the kinds of things called models in science have multiplied: they can be physical three-dimensional things, diagrams, mathematical equations, computer programs, organisms and even laboratory populations. This heterogeneity of models in sci- ence is matched in the widely different philosophical accounts of them. Indeed, discussion of models in the philosophy of science testifies to a variety of theoretical, formal, and practical aspirations that appear to have different and even conflict- ing aims (e.g. [Bailer-Jones, 1999]). In addition to approaches concerned with the pragmatic and cognitive role of models in the scientific enterprise, attempts have been made to establish, within a formal framework, what scientific models are. The syntactic view of models, once the “received view”, and the semantic approach to models, the prevailing model-theoretic approach until recently, were both attempts of this kind. Yet the discussion of models was originally motivated by practice-oriented considerations, guided by an interest in scientific reasoning. This is perhaps one reason why the general philosophy of science has tended to downplay models relative to theories, conceiving them merely as — for example — heuristic tools, interpretations of theories, or means of prediction. Recently, however, this situation has changed as models have come to occupy an ever more central epistemological role in the present practice of many different sciences. Models and modelling became the predominant epistemic genre in economic science only in the latter part of the twentieth century. The term “model” ap- peared in economics during the 1930s, introduced by the early econometricians, even though objects we would now call models were developed and used before then, for example, Marshall’s [1890] supply-demand scissor diagrams (see [Morgan, 2011]). Yet, it was only after the 1950s that modelling became a widely recognised way of doing economic science, both for statistical and empirical work in econo- metrics, for theory building using mathematics, and in policy advice. Indeed, it became conventional then to think of models in modern economics as either math- ematical objects or statistical objects thus dividing the economics community for Handbook of the Philosophy of Science. Volume 13: Philosophy of Economics. Volume editor: Uskali M¨aki. General Editors: Dov M. Gabbay, Paul Thagard and John Woods. c  2012 Elsevier BV. All rights reserved.