One Theory or Two? Walras’s Critique of Ricardo Heinz D. Kurz and Neri Salvadori There are essentially two views about the development of economic the- ory. According to the one that nowadays appears to be almost universally accepted, the history of economic theory is a one-way avenue leading from primitive conceptualizations of the demand and supply approach to all sorts of economic phenomena to ever more sophisticated ones, merely leaving behind errors of reasoning and unnecessarily restrictive assumptions.According to the alternative view, the history of our subject is not characterized by a linear development. A theory that once domi- nated the discussion rather tends to get abandoned for a variety of rea- sons, some of which are internal to that theory and concern its scope and coherence, while others are external to it and concern its ability to explain the facts. A theory may be replaced by fundamentally different ones: a theory may be “submerged and forgotten” at some stage, as one commentator remarked perceptively; it need not, but may, come back at a later stage, especially when new formulations of the theory succeed in overcoming the difficulties encountered by its earlier versions. In this essay we will attempt to support the discontinuity thesis by considering an important episode in the history of our subject: the Correspondence may be addressed to Neri Salvadori, Dipartimento di Scienze Economiche, Università di Pisa, Via Ridolfi 10, I-56124, Pisa, Italy. We would like to thank Christian Bidard, David Collard, Jan van Daal, John Eatwell, Duncan Foley, Pierangelo Garegnani, Christian Gehrke, Rodolfo Signorino, Ian Steedman, Donald Walker, and two anonymous referees for valuable comments on an earlier draft of this essay. We are responsible for any remaining errors and omissions. History of Political Economy 34:2 © 2002 by Duke University Press.