I recall this idea being originally raised to my consciousness in a question by some student at a town hall meeting, but I can't find a reference to this incident. In any event, I find Greg Mankiw's concept of an explicitly negative interest rate to be fascinating. I've got no idea if it would be good policy for the Fed to do such a thing, but the idea is interesting to think about.
Let’s start with the basics: What is the best way for an economy to escape a recession?
Until recently, most economists relied on monetary policy. Recessions result from an insufficient demand for goods and services — and so, the thinking goes, our central bank can remedy this deficiency by cutting interest rates. Lower interest rates encourage households and businesses to borrow and spend. More spending means more demand for goods and services, which leads to greater employment for workers to meet that demand.
The problem today, it seems, is that the Federal Reserve has done just about as much interest rate cutting as it can. Its target for the federal funds rate is about zero, so it has turned to other tools, such as buying longer-term debt securities, to get the economy going again. But the efficacy of those tools is uncertain, and there are risks associated with them.
In many ways today, the Fed is in uncharted waters.
So why shouldn’t the Fed just keep cutting interest rates? Why not lower the target interest rate to, say, negative 3 percent?
How to encourage people to pay money for the privilege of lending: The Fed could promise future inflation.
As he explains in a follow-up blog post, we've already got negative interest rates, but since we can't set them explicitly we get to the same destination via circuitous routes.
If we want to prop up aggregate demand to promote full employment, what is the alternative to monetary policy aimed at producing negative real interest rates? Fiscal policy. Essentially, the private sector is saying it wants to save. Fiscal policy can say, "No you don't. If you try to save, we will dissave on your behalf via budget deficits." That fiscal dissaving would push equilibrium interest rates upward. But is that policy really welfare-improving compared to allowing interest rates to fall into the negative region? If people are feeling poorer and want to save for the future, why should we stop them? Unless we think their additional saving is irrational, it seems best to try to funnel that saving into investment with the appropriate interest rate. And given the available investment opportunities, that interest rate might well be negative.