The Walras-Marshall Divide in Neoclassical Theory, Part I

This year, 2021, puts us squarely in the midst of the sesquicentennial period of the great marginal revolution in economics that began with the almost simultaneous appearance in 1871 of Menger’s Grundsatze der Volkwirtschaft and Jevons’s Theory of Political Economy followed in 1874 by Walras’s Elements d’Economie Politique Pure. Jevons left few students behind to continue his work, so his influence pales in comparison with that of his younger contemporary Alfred Marshall who, working along similar lines, published his Principles of Economics in 1890. It was Marshall’s version of marginal utility theory that defined for more than a generation what became known as neoclassical theory in the Anglophone world. Menger’s work, via his disciples, Bohm-Bawerk and Wieser, was actually the most influential work on marginal-utility theory for at least 50 years, the work of Walras and his successor, Vilfredo Pareto, being too mathematical, even for professional economists, to become influential before the 1930s.

But after it was restated in a form not only more accessible, but more coherent and more sophisticated by J. R. Hicks in his immensely influential treatise Value and Capital, Walras’s work became the standard for rigorous formal economic analysis. Although the Walrasian paradigm became the standard for formal theoretical work, the Marshallian paradigm remained influential for applied microeconomic theory and empirical research, especially in fields like industrial organization, labor economics and international trade. Neoclassical economics, the corpus of economic mainstream economic theory that grew out of the marginal revolution was therefore built almost entirely on the works of Marshall and Walras, the influence of Menger, like that of Jevons, having been largely, but not entirely, assimilated into the main body of neoclassical theory.

The subsequent development of monetary theory and macroeconomics, especially after the Keynesian Revolution swept the economics profession, was also influenced by both Marshall and Walras. And the question whether Keynes belonged to the Marshallian tradition in which he was trained, or became, either consciously or unconsciously, a Walrasian has been an ongoing dispute among historians of macroeconomics since the late 1940s.

The first attempt to merge Keynes into the Walrasian paradigm led to the first neoclassical synthesis, which gained a brief ascendancy in the 1960s and early 1970s before being eclipsed by the New Classical rational expectations macroeconomics of Lucas and Sargent that led to a transformation of macroeconomics.

With that in mind, I’ve been reading Michel De Vroey’s excellent History of Macroeconomics from Keynes to Lucas and Beyond. An important feature of De Vroey’s book is its classification of macrotheories as either Marshallian or Walrasian in structure and orientation. I believe that the Walras vs. Marshall distinction is important, but I would frame that distinction differently from how De Vroey does. To be sure, De Vroey identifies some key differences between the Marshallian and Walrasian schemas, but I question whether he focuses on the differences between Marshall and Walras that really matter. And I also believe that he fails to address adequately the important problem that both Marhsall and Walras failed to address, namely their inability adequately describe a market mechanism that actually does, or even might, lead an economy toward an equilibrium position.

One reason for De Vroey’s misplaced emphasis is that he focuses on the different stories told by Walras and Marshall to explain how equilibrium — either for the entire system (Walras) or for a single market (Marshall) – is achieved. The story that Walras famously told was the tatonnement stratagem conceived by Walras to provide an account of how market forces, left undisturbed, would automatically bring an economy to a state of rest (general equilibrium). But Walras eventually realized that tatonnement could never be realistic for an economy with both exchange and production. The point of tatonnement is to prevent trading at disequilibium prices, but assuming that production is suspended during tatonnement is untenable, because production cannot be interrupted until the search for the equilibrium price vector is successfully completed.

Nevertheless, De Vroey treats tatonnement, despite its hopeless unrealism, as sine qua non for any model to be classified as Walrasian. In chapter 19 (“The History of Macroeconomics through the lens of the Marshall-Walras Divide”), DeVroey provides a comprehensive list of differences between the Marshallian and Walrasian modeling approaches which makes tatonnement a key distinction between the two approaches. I will discuss the three that seem most important.

1 Price formation: Walras assumes all exchange occurs at equilibrium prices found through tatonnement conducted by a deus-ex-machina auctioneer. All agents are therefore price takers even in “markets” in which, absent the auctioneer, market power could be exercised. Marshall assumes that prices are determined in the course of interaction of suppliers and demanders in distinct markets, so that the mix of price-taking and price-setting agents depends on the characteristics of those distinct markets.

This dichotomy between the Walrasian and Marshallian accounts of how prices are determined sheds light on the motivation that led Marshall and Walras to adopt their differing modeling approaches, but there is an important distinction between a model and the intuition that motivates or rationalizes the model. The model stands on its own whatever the intuition motivating the model. The motivation behind the model can inform how the model is assessed, but the substance of the model and its implications remain in tact even if the intuition behind the model is rejected.

2 Market equilibrium: Walras assumes that no market is in equilibrium unless general equilibrium obtains. Marshall assumes partial equililbrium is reached separately in each market. General equilibrium is achieved when all markets are in partial equilibrium. The Walrasian approach is top-down, the Marshallian bottom-up.

3 Realism: Marshall is more realistic than Walras in depicting individual markets in which transactors themselves engage in the price-setting process, assessing market conditions, and gaining information about supply-and-demand conditions; Walras assumes that all agents are passive price takers merely calculating their optimal, but provisional, plans to buy and sell at any price vector announced by the auctioneer who then processes those plans to determine whether the plans are mutually consistent or whether a new price vector must be tried. But whatever the gain in realism, it comes at a cost, because, except in obvious cases of complementarity or close substitutability between products or services, the Marshallian paradigm ignores the less obvious, but not necessarily negligible, interactions between markets. Those interactions render the Marshallian ceteris-paribus proviso for partial-equilibrium analysis logically dubious, except under the most stringent assumptions.

The absence of an auctioneer from Marshall’s schema leads De Vroey to infer that market participants in that schema must be endowed with knowledge of market demand-and-supply conditions. I claim no expertise as a Marshallian scholar, but I find it hard to accept that, given his emphasis on realism, Marshall would have attributed perfect knowledge to market participants. The implausibility of the Walrasian assumptions is thus matched, in De Vroey’s view, by different, but scarcely less implausible, Marshallian assumptions.

De Vroey proceeds to argue that Keynes himself was squarely on the Marshallian, not the Walrasian, side of the divide. Here’s how, focusing on the IS-LM model, he puts it:

As far as the representation of the economy is concerned, the economy that the IS-LM model analyzes is composed of markets that function separately, each of them being an autonomous locus of equilibrium. Turning to trade technology, no auctioneer is supposedly present. As for the information assumption, it is true that economists using the IS-LM model scarcely evoke the possibility that it might rest on the assumption that agents are omniscient. But then nobody seems to have raised the issue of how equilibrium is reached in this model. Once raised, I see no other explanation than assuming agents’ ability to reconstruct the equilibrium values of the economy, that is, their being omniscient. On all these scores, the IS-LM model is Marshallian.

A History of Macroeconomics from Keynes to Lucas and Beyond, p. 350

De Vroey’s dichotomy between the Walrasian and Marshallian modeling approaches leads him to make needlessly sharp distinctions between them. The basic IS-LM model determines the quantity of money, consumption, saving and investment, income and the rate of interest rate. Presumably, by autonomous locus of equilibrium,” De Vroey means that the adjustment of some variable determined in one of the IS-LM markets adjusts in response to disequilibrium in that market alone, but even so, the markets are not isolated from each other as they are in Marshallian partial-equilibrium analysis. The equilibrium values of the variables in the IS-LM model are simultaneously determined in all markets, so the autonomy of each market does not preclude simultaneous determination. Nor does the equilibrium of the model depend, as De Vroey seems to suggest, on the existence of an auctioneer; the role of the auctioneer is merely to provide a story (however implausible) about how the equilibrium is, or might be, reached.

Elsewhere De Vroey faults Keynes for characterizing cyclical unemployment as involuntary, because that characterization is incompatible with a Marshallian analysis of the labor market. Without endorsing Keynes’s reasoning, I cannot accept De Vroey’s argument against Keynes, because the argument is based explicitly on the assumption of perfect foresight. Describing the difference between a strict Marshallian approach and that taken by Keynes, De Vroey writes as follows:

When the strict Marshallian viewpoint is adopted, everything is simple: it is assumed that the aggregate supply price function incorporates wages at their market-clearing magnitude. Instead, when taking Keynes’s line, it must be assumed that the wage rate that firms consider when constructing their supply price function is a “false” (i.e., non-market-clearing) wage. Now, if we want to keep firms’ perfect foresight assumption (and, let me repeat, we need to lest we fall into a theoretical wilderness), it must be concluded that firms’ incorporation of a false wage into their supply function follows from their correct expectation that this is indeed what will happen in the labor market. That is, firms’ managers are aware that in this market something impairs market clearing. No other explanation than the wage floor assumption is available as long as one remains in the canonical Marshallian framework. Therefore, all Keynes’s claims to the contrary notwithstanding, it is difficult to escape the conclusion that his effective demand reasoning is based on the fixed-wage hypothesis. The reason for unemployment lies in the labor market, and no fuss should be made about effective demand being [the reason rather] than the other way around.

Id. pp. 22-23

De Vroey seems to be saying that if firms anticipate an equilibrium outcome, the equilibrium outcome will be realized. This is not an argument; it is question-begging, question-begging which De Vroey justifies by warning that the alternative to question-begging is to “fall into a theoretical wilderness.” Thus, Keynes’s argument for involuntary unemployment is rejected based on the argument that the in the only foreseeable outcome under the assumption of perfect information, unemployment cannot be involuntary.

Because neither the Walrasian nor the Marshallian modeling approach gives a plausible account of how an equilibrium is reached, De Vroey’s insistence that either implausible story is somehow essential to the corresponding modeling approach is misplaced, each approach committing the fallacy of misplaced concreteness in focusing on an equilibrium solution that cannot plausibly be realized. For De Vroey instead to argue that, because the Marshallian approach cannot otherwise explain how equilibrium is realized, the agents must be omniscient is akin to the advice of one Senator during the Vietnam war for President Nixon to declare victory and then withdraw all American troops.

I will have more to say about the Walras-Marshall divide and how to surmount the difficulties with both in a future post (or posts).

6 Responses to “The Walras-Marshall Divide in Neoclassical Theory, Part I”


  1. 1 Henry Rech August 29, 2021 at 12:11 pm

    De Vroeyis always an interesting read on history of economic thought matters.

    But you can be sure that he will always fall in behind the laissez faire approach.

  2. 2 David Glasner August 31, 2021 at 10:30 am

    I agree that De Vroey is worth reading, and I was surprised that he would make an argument like the one he made about involuntary unemployment, especially since he has in other publications noted that there are two levels of optimization: (1) individual optimization and (2) social (market) optimization. The second level of optimization is not possible unless the optimizing decisions of individuals are mutually consistent. Lucasian macro assumes that such consistency is automatically assured so that it is unproblematic to use a representative agent can as a simplifying assumption. De Vroey has recognized that that is a significant logical gap in modern macro, but he seems to have no qualms about making virtually the same logical leap in his criticism of involuntary unemployment.

  3. 3 paul wolfson September 3, 2021 at 6:17 pm

    Some minor corrections (in the spirit of Poobah’s “Merely corroborative detail, intended to give artistic verisimilitude to an otherwise bald and unconvincing narrative.”)

    The senator in question was George Aiken of VT.
    Although I have heard pretty much the same tale recounted here about declaring victory and withdrawing, that is apparently not quite what he said (although it does make for a better story).
    Finally, the statement in question dates to 1966, when LBJ was not yet even half way through his full term as president.

    Search for “Vietnam” in this WIkipedia article for details.

  4. 4 Henry Rech September 4, 2021 at 2:50 pm

    De Vroey writes:

    ” Therefore, all Keynes’s claims to the contrary notwithstanding, it is difficult to escape the conclusion that his effective demand reasoning is based on the fixed-wage hypothesis. ”

    Perhaps. But neoclassical economics sympathizers believe that macroeconomic issues can be dealt with by changes in relative prices. They almost cannot countenance the fact that Keynes eschewed relative price effects. Keynes focused on changes in the level of income and spending.

    Keynes attempted to go down the theory of value route in his Treatise on Money but found it wanting.

  5. 5 David Glasner September 12, 2021 at 2:34 am

    Henry, I agree with you in part and disagree with you in part. I think Keynes did use a fixed wage as a convenient assumption, but he also argued that wage cuts would not fix the problem and that it is the point that De Vroey was challenging. And my point was that De Vroey’s argument was based on extreme information and expectation assumptions about agents in the model.


  1. 1 The Walras-Marshall Divide in Neoclassical Economics, Part II | Uneasy Money Trackback on September 1, 2021 at 7:24 pm

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About Me

David Glasner
Washington, DC

I am an economist in the Washington DC area. My research and writing has been mostly on monetary economics and policy and the history of economics. In my book Free Banking and Monetary Reform, I argued for a non-Monetarist non-Keynesian approach to monetary policy, based on a theory of a competitive supply of money. Over the years, I have become increasingly impressed by the similarities between my approach and that of R. G. Hawtrey and hope to bring Hawtrey's unduly neglected contributions to the attention of a wider audience.

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