The Revolution — The Margin, Plate xi

The marginal revolution has an arresting date and an untidy beginning. Jevons published The Theory of Political Economy in 1871; Menger published his Grundsätze in the same year; the first instalment of Walras's Éléments followed in 1874, with the second in 1877. Three writers, working in England, Austria and Switzerland, had made the relation between wants and scarce quantities central to their accounts of value. The proximity invites the thought that an idea had reached its moment. Yet the books were the visible arrivals of inquiries that had begun earlier, and the inquiries were less alike than the convenient name suggests. The question is how several independent routes converged, and why the convergence later came to look like one event. To answer it requires keeping two things together: the insight that made the last unit newly consequential, and the different structures into which each author put it.

For Jevons, the last unit belonged to a calculus of pleasure and pain. The total usefulness of a stock and the additional usefulness of a little more were different magnitudes; exchange depended on the latter, after the quantities available to the participants had been taken into account. Bentham supplied a language of pleasures to be weighed, and mathematics supplied a way of following their variation. Jevons had already published an outline of his theory in 1862, nearly a decade before the book that now marks the revolution's familiar date. His own retrospective account also points to a less celebrated source of encouragement: Lardner's treatment of railway economics, whose mathematical and graphical analysis of supply and demand he had known since 1857. The road to the book passed through particular readings and an extended attempt to make economic reasoning exact. Its appearance in 1871 records a stage in that work, rather than the instant at which the margin first entered his mind.¹

1. W. Stanley Jevons, The Theory of Political Economy, Preface to the Second Edition (1879), especially the discussion beginning “Turning now to the theory itself” and the later account of Gossen. Jevons identifies Lardner's influence, Bentham's role and his 1862 outline. His retrospective account is evidence of his own intellectual route and priority claims; it does not by itself explain the timing of the other authors' work.

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Menger approached the problem through the dependence of human purposes on particular goods. A person with a limited supply must decide which wants can still be met, and the importance of the satisfaction that would be lost gives a unit its value. The analysis also follows that dependence backward, from final goods to the resources needed to make them. Its emphasis is on a causal sequence of needs, knowledge and available means. William Jaffé's study of the three authors brings out how far this differs from treating Menger as a writer who happened to omit the symbols from the same calculus. Menger's economic actors acquire information, face uncertainty and bargain within limits that need not determine one exact price. His objection to mathematics as a method of discovery concerned what he thought it could explain about those underlying causes. The common concern with the importance of an additional unit therefore supported a distinct research program. The Austrian contribution was already more than a different notation for the English one.²

2. William Jaffé, “Menger, Jevons and Walras De-Homogenized”, Economic Inquiry 14 (1976), pp. 519–522, examines Menger's text and correspondence, including the distinction between mathematical exposition and his preferred causal method. The characterization here follows that documented interpretation, without treating every later Austrian position as a proposition already contained in 1871.

Walras's route ran through the connected market system before marginal utility completed his explanation of demand. Jaffé's examination of manuscripts and correspondence reverses the simple picture in which Walras first found the margin and then built an economy around it. Walras had worked on interdependent exchange for years; the problem was how to connect the demands in that system to the wants of the participants. His father's analysis of scarcity supplied an inherited question, and the mathematician Paul Piccard helped him formulate the relation between utility, its derivative and the exchange decision toward the end of 1872. Walras publicly presented the mathematical exchange theory in 1873. His rareté then did a particular job: it helped generate demand within a system intended to determine prices together. Jevons and Menger had important insights into connected choices, but neither supplied Walras's comprehensive construction. The three books meet around the margin while differing in what they ask that margin to explain.³

3. Jaffé, pp. 513–518, especially the manuscript sequence and notes 12 and 21, reconstructs Walras's route and Piccard's contribution. The 1873 presentation precedes the two instalments of the first Éléments, 1874 and 1877; the publication history is recorded on p. 524. This is Jaffé's documentary reconstruction, rather than an assertion that the three writers followed an identical order of discovery.

Earlier discoveries make the question of timing sharper, because an idea can be written down without becoming available to the people who later need it. In 1879 Jevons described learning of Gossen's 1854 book only after his friend Robert Adamson obtained a copy in August 1878. He acknowledged the extent of the anticipation while carefully identifying both differences and his own dependence on Adamson's help in reading the German. The same preface widened his account of predecessors to include Dupuit and Cournot, whose contributions he distinguished rather than treating them as interchangeable versions of his own. It also described the practical work of recovering that literature: lists sent to economists, additions returned by correspondents, books found and examined. Jevons and Walras were by then helping circulate a bibliography. Independence at an early stage thus coexisted with later exchange. A theory's history includes the channels through which a neglected book becomes readable, a result becomes visible and an apparent novelty acquires predecessors.⁴

4. Jevons, 1879 Preface, the complete bibliographical discussion from “Turning now to the theory itself” through the paragraph on Mansfield Merriman. The Gossen discussion records the August 1878 discovery, Adamson's assistance and Jevons's qualified acknowledgment. The account of the 1878 bibliography expressly names Walras's additions and circulation of the list. The already-published Increment treats Gossen's substantive principles.

The evidence supports a shared intellectual opportunity more securely than a single cause that made discovery inevitable. Questions about utility, scarcity and exchange had accumulated; mathematical methods and earlier analyses offered resources for some of the writers; dissatisfaction with inherited explanations gave revision a purpose. But the resources were unevenly known and differently used. A common utilitarian psychology cannot explain Menger's method, and a universal spread of calculus cannot explain a contribution whose author disputed its role. Nor does publication within a few years show that all three discovered their central ideas within those same years. Jaffé's objection to grouping them too easily is useful precisely here: once their projects are separated, the history has room for both common problems and particular encounters. The claim that the time was ripe becomes an invitation to investigate those connections. It ceases to serve as a complete explanation merely by repeating that several books appeared close together.⁵

5. Jaffé, pp. 511–513 and 522–523, states the historiographical problem and its implications. His note 6 on p. 512 also identifies Walras's own 1889 grouping of the three as codiscoverers, so the shared label is not simply an invention by later outsiders. The conclusion about timing is an interpretation of the differentiated evidence, not a demonstrated single causal account of the 1870s.

The revolution's lasting force lay in what the new vantage made it possible to ask. Value could be examined through the use that an available unit still served; choice through the alternative that one more commitment displaced; production through the additional output that another input made possible. These questions could travel between traditions even where their accounts of mind, method and market remained at odds. To call their convergence a revolution is to recognize that change of reach while leaving the chronology and the differences intact. Jevons, Menger and Walras gave later economics related starting points, not a finished common doctrine. The volume has followed some of the developments that made those beginnings powerful. Its last plate, The Return, brings the argument back to production. The last unit there is another hand, another machine, another acre, and the question is what it can add when the things beside it have not increased.