Lifted from Robert Waldmann's Stochastic Thoughts:

I am overwhelmed by admiration for Brad DeLong (happens a lot) who reposted his review of Krugman's “The Return of Depression Economics” from 1999 “Just in case I get a swelled-head and think I am right more often than I am …”

Way back in the last century, Brad thought he had a valid criticism of Paul Krugman's argument that Japan (and more generally countries in a liquidity trap) need higher expected inflation. I think the re-post is not just admirable as a self criticism session, but also shows us something about the power of Macroeconomic orthodoxy. Brad is just about as unorthodox as an economist can be without being banished from the profession, but even he was more influenced by Milton Friedman and Robert Lucas than he should have been. I reproduce the offending passage below.

The context is that Japan had slack aggregate demand at a safe nominal interest rate of 0 — that is it was in the liquidity trap. Krugman argued that higher expected inflation would cause negative expected real interest rates and higher aggregate demand and solve the problem. Brad was unconvinced (way back then).

But at this point Krugman doesn't have all the answers. For while the fact of regular, moderate inflation would certainly boost aggregate demand for products made in Japan, the expectation of inflation would cause an adverse shift in aggregate supply: firms and workers would demand higher prices and wages in anticipation of the inflation they expected would occur, and this increase in costs would diminish how much real production and employment would be generated by any particular level of aggregate demand.Would the benefits on the demand side from the fact of regular moderate inflation outweigh the costs on the supply side of a general expectation that Japan is about to resort to deliberate inflationary finance? Probably. I'm with Krugman on this one. But it is just a guess–it is not my field of expertise–I would want to spend a year examining the macroeconomic structure of the Japanese economy in detail before I would be willing to claim even that my guess was an informed guess.

And there is another problem. Suppose that investors do not see the fact of inflation–suppose that Japan does not adopt inflationary finance–but that a drumbeat of advocates claiming that inflation is necessary causes firms and workers to mark up prices and wages. Then we have the supply-side costs but not the demand-side benefits, and so we are worse off than before.