Krugman is actually right on ISLM and Minsky

I tend to disagree a lot with Krugman, at least on theoretical issues. His brand of Keynesianism supposes that the system doesn't work because of imperfections. For him, the current slow recovery is due to the fact that the natural rate of interest is basically negative and you cannot use monetary policy to stimulate the economy (see critique of this here). However, on his recent debate with Lars Syll (and here; Brad De Long also posted here), a post-Keynesian, with whom I probably share a more radical interpretation of Keynes and its relevance for economic theory, Krugman seems to get things right.

The main points in Lars initial post, based on Minsky's book John Maynard Keynes is that traditional representations of Keynes do not emphasize the cyclical component of Keynes' theory and that true or fundamental (non-probabilistic) uncertainty is often ignored. Lars adds a little bit more on his response to Krugman and De Long, but essentially is the same argument. Keynes didn't like the ISLM (which is from a historical point of view difficult to defend, after all the only stuff he wrote on this, to Hicks, was quite positive, even if it is of little relevance), that it is static (not paying attention to cyclical or dynamic phenomena), and perhaps more interestingly that the interaction of real and monetary variables in the model is simplistic.

Krugman points out that the General Theory (GT) is NOT about cyclical fluctuations per se. It is about the determination of the long run level of output and employment, around which the economy fluctuates, and he correctly notes that cycles only appear as an afterthought in chapter 22 of the GT. And that is precisely correct. The GT is revolutionary because it suggests that with price flexibility (not price rigidity as in the old Neoclassical Synthesis or the New Keynesian stories) the system gets stuck in a situation of unemployment equilibrium. Emphasis on equilibrium. Yes, unemployment at less than full employment and output below its potential level are both together in an equilibrium situation.

Patinkin suggested that Keynes meant unemployment disequilibrium, since within the neoclassical framework, unless there is a rigidity of some sort, and the system should go to its long run equilibrium position with full employment. Minsky (1975, p. 268), in the book cited above, says that Keynesian economics should be seen as the: "economics of permanent disequilibrium." That has no basis on the GT. Actually, the GT would be a less radical book if it only said that with instability the system might be always in a disequilibrium position. Keynes was very radical since he argued that the very notion of a natural rate should be abandoned (on this Paul and Brad have a lot to learn). Some Post Keynesians tend to dislike the idea of equilibrium (echoes of Joan Robinson's late critique of the idea), which ends up making them closer in many respects to the modern mainstream authors with their dislike for long term equilibrium positions.

So the GT is not about cycles (Keynes' Treatise on Money, a very conventional and Wicksellian book was about cyclical disequilibrium caused by differences between the natural and banking rates of interest, which, interestingly enough is closer to Krugman's way of thinking than the GT, or than to Lars, who is aware of the limitations of the natural rate concept). But that's not all that Krugman got right this time.

He quotes the famous passage in which Keynes says that the system is not violently unstable (GT, p. 249). And while Post Keynesians are correct to note the relevance of fundamental uncertainty, it is important also to consider the stabilizing role of conventions and institutions, to which Keynes alludes. Expectations play a role, but investment is not completely volatile, and it was a problem for Keynes only when "the capital development of a country becomes the by product of the activities of a casino" (GT, p. 159). In fact, given the relevance of the accelerator in determining investment, the central role of expectations is about the level of demand. For example, in the US investment has been subdued since demand is not growing fast and there are not reasonable expectations that it will any time soon.

Where New Keynesians go wrong, and in this case is actually Brad, not Paul (but he would certainly agree) is on the relevance of the marginal efficiency of capital, criticized by Minsky (even though it's far from clear that Minsky abandoned it). Brad thinks that Minsky critique of it is myopic and basically a PR problem. He says that it is: 

"Short-sighted, in that it is not Hicks who would be Minsky’s long-run intellectual adversary but rather Freidman [sic], Lucas, and Hayek, and so building bridges to the Hicksians ought to be a very high priority."

Probably true, but from a policy point of view. From a theoretical point of view, Hicks use of the marginalist notion of an investment function inversely related to the rate of interest (something Keynes also used) implies that there would be a rate of interest low enough that would produce full employment, that is a natural rate, which would preclude Keynes' claim about unemployment equilibrium (and the absence of a natural rate). In other words, with the marginal productivity of capital you have that unemployment must be a disequilibrium situation caused by some imperfection that inhibits the system from reaching the natural rate.

And yes the capital debates are relevant since they show that the inverse relation is only possible in a one commodity world. No natural rate, and no need to think about imperfections. And that's why the comment by Lars on the connection between real and monetary variables being simplistic within the ISLM is right on the mark. The idea that the central bank controls a monetary rate, that may get out of whack with the natural, and that by manipulating it can affect real variables is limited at best.

PS: For my previous defense of a modified ISLM go here and here.