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Krugman’s misapplication of neoclassical growth models

Summary:
From Lars Syll The fallacies loanable funds theory commits might be explainable by the misapplication​ of some ideas and concepts of neoclassical growth models … to the sphere of money and finance … The Ramsey and Solow models are models of real investment only. Financial markets, financial assets and financial saving do not play any role in those models. There is only one good which, for simplicity, will be called “corn”. Corn has three functions: it can be consumed, invested and used as a means of payment since wages and interest payments are made with it. Full employment is assumed … Without money and other financial assets, the only way units can save is to increase their tangible assets, i.e. to invest … Since the problems of different financial saving plans are not dealt with in

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from Lars Syll

The fallacies loanable funds theory commits might be explainable by the misapplication​ of some ideas and concepts of neoclassical growth models … to the sphere of money and finance …

Krugman’s misapplication of neoclassical growth modelsThe Ramsey and Solow models are models of real investment only. Financial markets, financial assets and financial saving do not play any role in those models. There is only one good which, for simplicity, will be called “corn”. Corn has three functions: it can be consumed, invested and used as a means of payment since wages and interest payments are made with it. Full employment is assumed … Without money and other financial assets, the only way units can save is to increase their tangible assets, i.e. to invest …

Since the problems of different financial saving plans are not dealt with in Solow’s model, the model cannot be used to make any predictions about economic units’ financial saving behavior, its inconsistencies and thus about the paradox of thrift – neither in the short, medium or long run. There is no miraculous way of short-run financial saving somehow being transformed into long run investment in tangible assets. The two are simply quite different phenomena …

How pervasive this approach is, is shown by Eggertsson and Krugman (2012) who add some features … to a basic neoclassical model. Again, no money but goods are borrowed and lent. Naturally, potential lenders have to save some of their goods before they can lend them to borrowers. But since in the real world money is normally not eaten or planted and keeps circulating in the economy when it is spent or lent, those models cannot be any guide for the analysis of a monetary economy. Specifically, what is true in a one good economy – units have to consume less to lend and invest more – is fundamentally wrong in a monetary economy.

Fabian Lindner

This should come as no surprise. Paul Krugman has repeatedly over the years argued that we should continue to use neoclassical hobby horses like Ramsey style growth, IS-LM, and AS-AD models.

Money and finance don’t​ matter in mainstream neoclassical macroeconomic models. That’s true. According to the ‘classical dichotomy,’ real variables — output and employment — are independent of monetary variables, and so enables mainstream economics to depict the economy as basically a barter system.

But in the real world in which we happen to live, money certainly does matter. Money is not neutral and money matters in both the short run and the long run:

The theory which I desiderate would deal … with an economy in which money plays a part of its own and affects motives and decisions, and is, in short, one of the operative factors in the situation, so that the course of events cannot be predicted in either the long period or in the short, without a knowledge of the behaviour of money between the first state and the last. And it is this which we ought to mean when we speak of a monetary economy.

J. M. Keynes A monetary theory of production (1933)

Lars Pålsson Syll
Professor at Malmö University. Primary research interest - the philosophy, history and methodology of economics.

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