On Krugman’s reading list

28 September, 2012 at 11:07 | Posted in Economics | 3 Comments

As we all know Paul Krugman is very fond of referring to and defending the old and dear IS-LM model.

John Hicks, the man who invented it in his 1937 Econometrica review of Keynes’ General TheoryMr. Keynes and the ‘Classics’. A Suggested Interpretation – returned to it in an article in 1980 – IS-LM: an explanation – in Journal of Post Keynesian Economics. Self-critically he wrote:

I accordingly conclude that the only way in which IS-LM analysis usefully survives — as anything more than a classroom gadget, to be superseded, later on, by something better – is in application to a particular kind of causal analysis, where the use of equilibrium methods, even a drastic use of equilibrium methods, is not inappropriate. I have deliberately interpreted the equilibrium concept, to be used in such analysis, in a very stringent manner (some would say a pedantic manner) not because I want to tell the applied economist, who uses such methods, that he is in fact committing himself to anything which must appear to him to be so ridiculous, but because I want to ask him to try to assure himself that the divergences between reality and the theoretical model, which he is using to explain it, are no more than divergences which he is entitled to overlook. I am quite prepared to believe that there are cases where he is entitled to overlook them. But the issue is one which needs to be faced in each case.

When one turns to questions of policy, looking toward the future instead of the past, the use of equilibrium methods is still more suspect. For one cannot prescribe policy without considering at least the possibility that policy may be changed. There can be no change of policy if everything is to go on as expected-if the economy is to remain in what (however approximately) may be regarded as its existing equilibrium. It may be hoped that, after the change in policy, the economy will somehow, at some time in the future, settle into what may be regarded, in the same sense, as a new equilibrium; but there must necessarily be a stage before that equilibrium is reached …

I have paid no attention, in this article, to another weakness of IS-LM analysis, of which I am fully aware; for it is a weakness which it shares with General Theory itself. It is well known that in later developments of Keynesian theory, the long-term rate of interest (which does figure, excessively, in Keynes’ own presentation and is presumably represented by the r of the diagram) has been taken down a peg from the position it appeared to occupy in Keynes. We now know that it is not enough to think of the rate of interest as the single link between the financial and industrial sectors of the economy; for that really implies that a borrower can borrow as much as he likes at the rate of interest charged, no attention being paid to the security offered. As soon as one attends to questions of security, and to the financial intermediation that arises out of them, it becomes apparent that the dichotomy between the two curves of the IS-LM diagram must not be pressed too hard.

Back in 1937 John Hicks said that he was building a model of John Maynard Keynes’ General Theory. He wasn’t.

What Hicks acknowledges in 1980 is basically that his original review totally ignored the very core of Keynes’ theory – uncertainty. In doing this he actually turned the train of macroeconomics on the wrong tracks for decades. It’s about time that neoclassical economists – as Krugman, Mankiw, or what have you – set the record straight and stop promoting something that the creator himself admits was a total failure. Why not study the real thing itself – General Theory – in full and without looking the other way when it comes to non-ergodicity and uncertainty?



  1. Intressant att läsa att IS-LM var på utgång redan för över 30 år sedan, med tanke på att jag gick kurser i början av detta årtusende (på Södertörn) där läraren slet med alla dessa diagram som skulle passa ihop!

  2. Prof. Syll,
    Could it be said that IS-LM model and its variations are vulnerable to the Sraffa’s critique that there is no equilibrium in the model because cetereris paribus principle of independence between the curves is not applicable (Sraffa 1925, 1926)? I was never really good at ‘getting’ this model, I admit.

    • Maybe, but as far as I remember Sraffa’s articles, and especially “Sulle relazioni fra costo e quantità prodotta” he mainly showed that certain supply side parts of the Marshallian theory (external returns to scale) was at odds with the partial analysis and static assumptions, while other supply side parts (internal returns to scale) were inconsistent with the assumption of free competition. Later I think he drew the correct conclusion that as soon as any kind of imperfection is introduced into the analysis, the equilibrium become far from the one in free competition and rather more like in the monopoly case.

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