Kelton and Krugman — MMT vs IS-LM

by
Lars Pålsson Syll
My articles My siteAbout meMy booksMy videos
Follow on:Twitter

Kelton and Krugman — MMT vs IS-LM

Is there some reason the straightforward framework Krugman laid out is wrong? Yes, as even its creator went on to acknowledge. MMT rejects the IS-LM framework that Krugman uses to demonstrate the conclusion that widening budget deficits put upward pressure on interest rates and crowd out private investment.

The model remains the workhorse for many mainstream Keynesians. MMT considers it fundamentally flawed …

Keep this in mind: Higher deficits give rise to higher interest rates, which give rise to lower investment. The last bit is referred to as “crowding out.” This is the inherent tradeoff that MMT denies and Krugman defends.

And it’s easy for him to defend it because his model assumes a fixed money supply, which paves the way for the crowding-out effect!

Krugman’s framework treats investment as a simple function of the interest rate. Higher rates mean lower investment, and vice versa. Central banks can juice (or slow) the economy simply by lowering (or raising) interest rates. It’s Pavlovian in its simplicity: stimulus-response.

Keynes’s analysis was more nuanced. Investment decisions were forward-looking, heavily influenced by “animal spirits,” and overwhelmingly dependent on the state of profit expectations. When the profit outlook is sufficiently grim, no amount of rate cutting will entice businesses to borrow and invest in new plant and equipment (think Great Recession).

Stephanie Kelton

Again — as so often — it turns out that when we economists disagree it ultimately boils down to methodology .  And here — again — we are back to the question if Krugman’s and other ‘New Keynesians’ hobbyhorse IS-LM interpretation of Keynes is fruitful and relevant for understanding monetary economies.

My own view is that IS-LM is not fruitful and relevant and that it does not adequately reflect the width and depth of Keynes’s insights on the workings of monetary economies:

1  Almost nothing in the post-General Theory writings of Keynes suggests him considering Hicks’s IS-LM anywhere near a faithful rendering of his thought. In Keynes’s canonical statement of the essence of his theory — in the famous 1937 Quarterly Journal of Economics article — there is nothing to even suggest that Keynes would have thought the existence of a Keynes-Hicks-IS-LM-theory anything but pure nonsense. John Hicks, the man who invented IS-LM in his 1937 Econometrica review of Keynes’ General Theory — “Mr. 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 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.” What Hicks acknowledges in 1980 is basically that his original IS-LM model ignored significant parts of Keynes’ theory. IS-LM is inherently a temporary general equilibrium model. However — much of the discussions we have in macroeconomics is about timing and the speed of relative adjustments of quantities, commodity prices and wages — on which IS-LM doesn’t have much to say.

2  IS-LM forces to a large extent the analysis into a static comparative equilibrium setting that doesn’t in any substantial way reflect the processual nature of what takes place in historical time. To me, Keynes’s analysis is in fact inherently dynamic — at least in the sense that it was based on real historical time and not the logical-ergodic-non-entropic time concept used in most neoclassical model building. And as Niels Bohr used to say — thinking is not the same as just being logical …

3  IS-LM reduces interaction between real and nominal entities to a rather constrained interest mechanism which is far too simplistic for analyzing complex financialised modern market economies.

4  IS-LM gives no place for real money, but rather trivializes the role that money and finance play in modern market economies. As Hicks, commenting on his IS-LM construct, had it in 1980 — “one did not have to bother about the market for loanable funds.” From the perspective of modern monetary theory, it’s obvious that IS-LM to a large extent ignores the fact that money in modern market economies is created in the process of financing — and not as IS-LM depicts it, something that central banks determine.

5  IS-LM is typically set in a current values numéraire framework that definitely downgrades the importance of expectations and uncertainty — and a fortiori gives too large a role for interests as ruling the roost when it comes to investments and liquidity preferences. In this regard, it is actually as bad as all the modern microfounded Neo-Walrasian-New-Keynesian models where Keynesian genuine uncertainty and expectations aren’t really modelled. Especially the two-dimensionality of Keynesian uncertainty — both a question of probability and “confidence” — has been impossible to incorporate into this framework, which basically presupposes people following the dictates of expected utility theory (high probability may mean nothing if the agent has low “confidence” in it). Reducing uncertainty to risk — implicit in most analyses building on IS-LM models — is nothing but hand waving. According to Keynes we live in a world permeated by unmeasurable uncertainty — not quantifiable stochastic risk — which often forces us to make decisions based on anything but “rational expectations.” Keynes rather thinks that we base our expectations on the “confidence” or “weight” we put on different events and alternatives. To Keynes, expectations are a question of weighing probabilities by “degrees of belief,” beliefs that often have preciously little to do with the kind of stochastic probabilistic calculations made by the rational agents as modeled by “modern” social sciences. And often we “simply do not know.”

6  IS-LM not only ignores genuine uncertainty, but also the essentially complex and cyclical character of economies and investment activities, speculation, endogenous money, labour market conditions, and the importance of income distribution. And as Axel Leijonhufvud so eloquently notes on IS-LM economics — “one doesn’t find many inklings of the adaptive dynamics behind the explicit statics.” Most of the insights on dynamic coordination problems that made Keynes write General Theory are lost in the translation into the IS-LM framework.

Given this, it’s difficult not to side with Stephanie Kelton. The IS/LM approach is not fruitful or relevant for understanding modern monetary economies. And it does not capture Keynes’ approach to the economy other than in name.