With the US economy mostly recovered from the Great Recession, arguments about monetary policy have died down a bit. But the lessons of the slow recovery are still percolating through the economics profession.
The years 2008 through 2014 saw some monetary experiments that were unprecedented in the US - a long period of zero interest rates, several versions of quantitative easing, new types of forward guidance and the payment of interest on excess reserves. Although these experiments give us a lot of new information, the lessons are not clear, and continue to provoke spirited debate.
One of the most interesting debaters is Mr Narayana Kocherlakota, former president of the Federal Reserve Bank of Minneapolis. He became famous for switching his outlook on macroeconomic policy; once among the most hawkish of the inflation hawks, he now wants to use easy monetary policy to boost employment. Mr Kocherlakota has recently begun to make his thoughts known on Twitter, and has started blogging as well.
His main argument is that the US central bank's policy, with rates at 0.50 per cent, is too tight right now. Not only does he fear that this is keeping people out of work, but he also worries that the Fed is sacrificing its credibility.
It is raising interest rates even though inflation expectations are well below its official 2 per cent target. That could convince the public that the Fed is being disingenuous about its inflation target - that it regards 2 per cent as a ceiling on the acceptable rate of inflation, rather than the target to aim for.
Credibility is very important for the Fed; if the public stops believing that the Fed means what it says, then future efforts to combat deflation, or even inflation, might be much harder.
Credibility is very important for the Fed; if the public stops believing that it means what it says, then future efforts to combat deflation, or even inflation, might be much harder.
That should be fairly uncontroversial. Even if you believe - as a few macroeconomists still do - that the Fed can't really affect unemployment, you probably still want it to be transparent and maintain its credibility as a stabiliser of prices. However, Mr Kocherlakota's case rests on a big hidden assumption - monetary policy has to work the way mainstream macroeconomists think it does.
Most macroeconomists think that lowering interest rates - or promising to keep them lower for longer - raises the rate of inflation. Everyone - from Milton Friedman to the New Keynesians - believes in this basic idea. But recently, the notion has come under fire from a group of economists called Neo-Fisherians (a term I coined, which they have adopted), who say that low interest rates actually cause low inflation, at least in the long run.
Mr Steve Williamson, one of the original Neo-Fisherians, uses this idea to criticise Mr Kocherlakota. If we really want to hit a 2 per cent inflation target, Mr Williamson and his fellow-travellers say, we shouldn't cut the nominal interest rate - we should raise it to 2 per cent and keep it there. Although Mr Kocherlakota himself was one of the first to suggest the Neo-Fisherian idea, back in 2010, he now disavows it, and he and Mr Williamson have engaged in vigorous debate.
This debate is interesting, because the two sides should really be agreeing on policy. Neo-Fisherians like Mr Williamson are generally inflation hawks, and would probably not mind if inflation stayed around 1 per cent forever, or even lower - and they believe that keeping interest rates low will accomplish this.
Monetarists like Mr Kocherlakota would rather try to boost employment, and keep inflation around 2 per cent; they believe that keeping interest rates low will accomplish this! So although they disagree over theory, they should agree on keeping rates low.
The more important point, though, is that no one really knows what is going on with monetary policy right now. No one knows what the Fed is really trying to accomplish, or what it can accomplish, or how to go about accomplishing it. Is it still set on raising interest rates in order to avoid the semblance of abnormality from keeping them close to zero? Is it worried about demand-side shocks from China's slowdown? Does it want the US public to think that it will never let inflation go above 2 per cent, or does it want us to think that 2 per cent is in the middle of the acceptable range?
Is it trying to raise inflation and failing? And if it did want to raise inflation to 2 per cent, would it do so by keeping interest rates low, or by raising them?
It's becoming clearer that the Fed's experiments during the Great Recession, dramatic as they were, taught us little about how monetary policy works.