[toastermoster]

When you say "trapped at the zero bound" are you saying the control output is saturated basically? I'm thinking in terms of feedback control loops. I would agree that the FOMC doesn't have a lot of room to work with if we were to enter another downturn but they do have some range left in their controller. During the last downturn they reduced the federal funds rates to 0% and that stayed there for years but they are now back up to 2.4% I think. When dropping rates to 0% wasn't enough in 2008 they also reduced longer term rates by buying Treasury securities (operation twist etc). The ended up adding $4.5T of Treasury securities to their balance sheet by the end of it. They have been unwinding those positions for over a year now but the balance is only slightly less than $4T. So I guess one could say there isn't much left in the accelerator pedal if we need it again. Especially given the recent tax reductions while the economy was already improving. That's just one less tool that can be used for the next time. Hopefully we won't have a next time until the Fed is able to get rates over 5% and the Fed balance sheet under $1T. https://www.federalreserve.gov/monetarypolicy/bst_recenttren...

[zozbot123]

From a feedback control perspective, it amounts to trying to balance an inherently unstable system. Think of a cart-and-pole apparatus where the top end of the "pole" (that is, the natural rate) is constantly being pushed around by unpredictable, outside shocks, and you have to move the "cart" (the policy rate) in the same direction to make up for those and keep the whole thing from falling over (into hyperinflation or extreme deflation - an illusory "boom" or a very real and persistent "bust"). The zero bound is only a leftwards boundary for the "cart", not the "pole" - but when it's hit, you do need something like QE to push the top end of the "pole" rightwards again independently of the "cart".

(The way out of the mess is to stop trying to use monetary policy to manipulate market interest rates, and to instead shift to a short-term policy target that fosters stability rather than instability. Such as, e.g. the money-price of gold. Or some measure of the money supply. Or the market forecast of nominal incomes x months in the future. There are lots of plausible choices!)