Some years ago, George J. Stigler reminded the community of historians of economic thought that a great thinker of the last century, Adolphe Quetelet, had made a real methodological breakthrough in the social sciences by opening the door to quantification. Stigler himself tried to implement this method in the history of economic thought.

Our concern is John Stuart Mill's methodological pronouncements, his actual practice, and the relationship between them. We argue that verification played a key role in Mill's method, both in principle and in practice. Our starting point is the celebrated declaration regarding verification in the essay On the Definition of Political Economy; and on the Method of Investigation Proper to It (1836/ 1967; hereafter Essay): “By the method à priori we mean … reasoning from an assumed hypothesis; which … is the essence of all science which admits of general reasoning at all. To verify the hypothesis itself à posteriori, that is, to examine whether the facts of any actual case are in accordance with it, is no part of the business of science at all, but of the application of science” (Mill 1836/1967, p. 325). The apparent position that the basic economic theory is impervious to predictive failure emerges also in a sharp criticism of the à posteriori method:

William Petty (1623–87)—medical doctor, Oxford professor of anatomy, Gresham College professor, surveyor of Ireland for the Cromwellian Protectorate, Fellow of the College of Physicians, founding member of The Royal Society, and inventor of political arithmetic—is now most particularly remembered for his contributions to the formation of political economy. When Petty left Ireland for the last time in 1685 and returned to London, he took with him a very large collection of unpublished papers and correspondence. These largely remained in the property of his descendants—together with some important later additions—until 1993, when they were sold to The British Library. Petty's collected, published economic writings were edited and republished a century ago, together with some other materials (Hull 1899). In the 1920s Petty's descendant, the sixth Marquis of Lansdowne (H.E.W. Petty-Fitzmaurice), published two collections of manuscripts from what by then had become known as “The Petty Papers” archive (Lansdowne 1927, 1928). All these volumes have subsequently been republished in facsimile a number of times.

The history of economics can be compared to a calm sea that once in a while happens to be shaken by heavy storms. This arises when works come out aimed at turning upside down the received interpretation of a great bygone economist's views. Professor Donald A. Walker's recent book, Walras's Market Models (1996), is likely to be among them. Its main thrust is that the view present-day economists have of Léon Walras is incorrect. The basic reason, he claims, is that to date all interpretations of Walras have been based on the last (posthumous) edition of the Eléments d' économie pure (henceforth the Elements), itself a slightly amended version of its fourth edition. To him this is a pity because Walras's most interesting theoretical ideas are to be found in its second and third editions—the embodiment of what he calls Walras's mature phase of theoretical activity—yet were abandoned by him when he revised his work for the fourth edition. The aim of Walker's book, then, is to bring to the fore the picture of what he considers to be the real Walras: an economist interested in the functioning of real-world markets and abiding by a realistic methodology who is attentive to the institutional set-up underlying his system of equations, and who is keen to provide his readers with disequilibrium models. In other words, Walker is trying to make the same claim apropos Walras as Axel Leijonhufvud (1968) did thirty years ago about Keynes when defending the view of a breach between the economics of Keynes and Keynesian economics. To Walker, modern Walrasian economics, or neo-Walrasian theory as it is more often called, is a betrayal of Walras's economics.

When Walras's Market Models was published, a friend wrote to me that he hoped that it would stimulate research on Walras's work. I am very pleased that his wish is coming true. A number of writers have reexamined it from new perspectives. It is, perhaps, inevitable that the quality and tone of the texts is uneven, and it is to be hoped that in the future all Walrasian research can be done carefully, in good taste, in a dispassionate fashion, and without rhetorical devices and patronizing remarks. In any event, I have presented in my book the results of 30 years of study of Walras's work, and I invite the reader to contrast what I have written with differing expositions. I have nothing to add to those results at this time, except the data which follow.