In a thoughtful post about the former Fed chairman, Brad DeLong writes:

There is, however, active debate over whether there was a fourth mistake: whether Alan Greenspan's decision in 2001-2004 to push and keep nominal interest rates on Treasury securities very very low in order to try to keep the economy near full employment was a fourth mistake. Should Alan Greenspan have kept interest rates higher and triggered a much bigger recession with much higher unemployment back then in order to head off the growth of a housing bubble? If we push interest rates up, Alan Greenspan thought, millions of extra Americans will be unemployed and without incomes to no benefit--they will not enjoy the prolonged "staycations" they will be taking, and the rest of us won't have the stuff they could make. If we allow interest rates to fall, Alan Greenspan thought, these extra workers will be employed building houses and making things to sell to all the people whose incomes come from the construction sector and making things to sell to the people whose incomes come from making things to sell to people whose incomes come to the construction sector. Full employment is better than high unemployment if both can be accomplished without inflation, Alan Greenspan thought. If a bubble does develop, and if the bubble does not deflate but crashes, and if the crash threatens to cause a depression--well, Greenspan thought, then will be the time to deal with that, and the Federal Reserve is a very powerful institution with policy tools that can short-circuit that chain leading to catastrophe at any point. [emphasis added.]

With hindsight Alan Greenspan was wrong. Catastrophe does stare us in the face. His policies have crapped out. But not every good policy is certain to have a good outcome. The question is: was the bet that Alan Greenspan made a favorable one? Whenever in the future we find ourselves in a situation like 2003 should we try to keep the economy near full employment even at some risk of a developing bubble?

I am genuinely not sure which side I come down on in this debate. Central bankers have long recognized that it is imprudent to lower interest rates in pursuit of full employment if the consequence is an inflationary spiral in wages, resource prices, or consumer prices. On Tuesdays and Thursdays I think that going forward central bankers must now also recognize that it is imprudent to lower interest rates in pursuit of full employment when doing so risks an asset price bubble. On Mondays, Wednesdays, and Fridays I think that even with the extra information about the structure of the economy we have learned in the past two years that Greenspan's decisions in 2001-2004 were prudent and committed us to a favorable and acceptable bet. And I am writing this on a Friday.

I guess my problem with this analysis is that I don't think it's right to lump the years 2001-2004 together. From early 2001 to early 2003, the economy was indeed very weak, and it's hard to quibble with Greenspan's decision to ease interest rates aggressively and stay easy. But by mid-2003, the economy was growing at a decent clip. It may not have been quite at full employment, but certainly stable. And yet Greenspan lowered the fed funds rate another quarter point to an eye-popping 1 percent in June of 2003, and kept it there through June of 2004. (And though the tightening began at that point, the fed funds rate was still at a mere 2.25 percent through January of 2005.) During the four quarters between June '03 and June '04, the economy grew at a real rate of 7.5 percent, 2.7 percent, 3 percent, and 3.5 percent. So when people talk about a monetary policy mistake, I think they're generally refering to that final year of easing, not the 2001 through mid-2003 period.

The stated reason for this continued easing was that Greenspan wanted to take out an insurance policy against deflation, of which there were some mild hints at the time, though even Greenspan referred to them as remote. In retrospect, this concern was probably unwarranted, as inflation chugged along either at or well-above the Fed's implicit target through all of 2004. Worse, all the easing appears to have resulted in a massive real estate bubble.

But, as DeLong says, the question isn't whether a policymaker is wrong in retrospect. The question is whether he or she made a reasonable bet at the time. DeLong thinks maybe. I lean the other way. Here's why: DeLong's defense of Greenspan hinges on the idea that, if it turned out the Fed was wrong about the necessity of easing--so wrong it created a bubble that later popped and threatened a deflationary spiral--the Fed had enough powerful tools at its disposal to prevent a depression at that point.

Problem is, once you break the 2001-2004 easing into its 2001-3 and 2003-4 subcomponents, and you acknowledge that the point of the 2003-4 period was to prevent a deflationary spiral, Greenspan's reasoning starts to look extremely circular. That is, Greenspan was lowering interest rates in order to prevent a costly deflation at the risk of creating a bubble which could lead to an even costlier deflation. But if you have the tools to prevent the costlier deflation from destroying the economy, then you have the tools to prevent the less costly deflation from destroying the economy, and there's no need to pre-empt it.

--Noam Scheiber