Indifference Curves and the Ordinalist Revolution

The development of ordinalism was fostered by the idea of dispensing with external psychological arguments in utility theory and building the whole theory of the consumer upon indifference curves (and maps). Yet the pioneers of ordinalism, Fisher and Pareto, did not make clear whether indifference curves should be considered as an observational, experimental, or purely theoretical construction (possibly based upon introspection). Indeed, the exact status of indifference curves for the theory of choice was not seriously debated before the 1930s and 1940s, in the United States. An experiment by the psychologist Louis Leon Thurstone was then the starting point for some clarifications about the role of experimental economics for the new theory of the consumer. The aim of this article is to throw light on the ins and outs of this issue of the ordinalist revolution. Thurstone’s experiment was the occasion for a debate on the status of indifference curves and more broadly on the role of experiments within the theory of choice. It would lead economists (such as Georgescu-Roegen, Wallis, Friedman, and Samuelson) to clarify the methodological foundations of the theory of choice and to express strong divergences about the usefulness of the theory.