Introduction

Some years ago, George Katona argued that, while mainstream economic analysis generally “continues to disregard psychological studies, it is not devoid of psychological assumptions. Most commonly it proceeds on the premise that human beings behave mechanically,” so that they are effectively depicted as “automatons.” Hence, orthodox economics should be “described as ‘economics with mechanistic psychology,’ rather than as ‘economics without psychology’ ” (1975, 5, 6). This chapter attempts to provide a historical perspective on that mechanistic approach by explaining how it first appeared in postclassical (or marginalist) supply and demand theory. Specifically, the chapter is concerned with the depiction of economic behavior in W. S. Jevons's Theory of Political Economy (1871; hereafter TPE). This was the first postclassical English text that depicted the theoretical object of “scientific” political economy as a type of constrained optimization, discussed all prices in terms of “the laws of supply and demand” and explained all economic actions in terms of marginal utility, using the calculus and geometry. One reason for focusing on TPE is that its detailed treatment of the behavioral theory distinguished it from the work of the other postclassical pioneer, L. Walras (Jaffe 1983, ch. 17).