Here is a Krugman post on the question, here are earlier posts from Sumner and Yglesias. I will put my remarks under the fold…This topic is easiest to understand if you sub out the United States and sub in Greece. There is no AD boost that can (anytime soon, without a lot of extra growth kicking in), restore Greece to its previous output peak and its previously expected performance-to-come. Circa 2006, Greece was in an unsustainable position, if for no other reason the market didn’t understand the correct risk premium for Greece. Once the correct risk premium is applied, Greek output falls and furthermore numerous (related) bad events kick in and also a whole set of previous plans are shown to be unsustainable (and no this doesn’t have to be an Austrian argument!). The gap between Greece’s current path, and the path previously envisioned for Greece is thus:
a. part AD gap which can be fixed by AD policy
b. part a difference in risk premia, and for Greece the old risk premium, when the country borrowed at very low rates, was wrong and is gone more or less forever. The concomitant financial and fiscal stability is gone too.
c. part a difference in enthusiasm in supply, based on the differences between earlier expectations that “get rich quick” really does apply to Greece, and the current more pessimistic expectation that “get rich quick” is now unlikely, and thus “smaller-scale, scrabble-around projects just to make ends meet” are the order of the day. DeLong gets at some of this here.
Greece does have to rebuild a) — don’t get sucked into aggregate demand denialism! — but it also has to rebuild b) and c) and perhaps other factors too. This follows rather directly from — dare I breathe the words? — the synthetic real business cycle/neo Keynesian models which form the backbone of contemporary macroeconomics and which Krugman apparently still doesn’t wish to recognize. (To various commentators and other bloggers: when I write macro on this blog I usually take knowledge of these models for granted; if you don’t know those models that is fine, call me arcane, but it doesn’t mean I am the one who is wrong.) Krugman runs through a bunch of weak arguments and responses, and counters them well enough, but he doesn’t see or consider the baseline response that would follow from standard contemporary macro, with the possible exception of his brief parenthetical phrase about credit conditions.
Turning for a moment to broader points, the astute reader will note that in this framework the current sluggishness of recovery need not be evidence for Old Keynesianism. An ineffective response to fiscal policy does not per se have to mean we just didn’t do enough fiscal policy. And so on. Maybe yes, maybe no, but all of a sudden there is a lot more room for agnosticism about macroeconomics and more broadly there is more room for epistemic modesty.
Contra Tim Duy, you can hold this mixed view without wanting to see the Fed raise interest rates. Just avoid the AD denialism.
Krugman defines “potential GDP is a measure of how much the economy can produce” but keep in mind that this quite possibly won’t be a unique number. With what risk premium? With what enthusiasm of supply? See my Risk and Business Cycles for an extended discussion and also numerous citations.
It’s also worth noting that while gdp is a useful “we can all agree upon what to measure” kind of concept, its real meaning is conceptually fairly slippery and “potential gdp” is not likely to be better pinned down at its foundations. Let’s not reify that concept above and beyond what it is worth.
In any case, we can be agnostic about the size of the potential gdp gap with regard to the United States today and indeed my original post very carefully used a question mark in its title. But there is no incoherence to assert that part of the apparent gap is due to the real side. The new learning about America is not about the correct risk premium for our debt (not yet at least), but about our financial fragility, how well our politics responds to crises, some worrying long-term trends in the labor market, possible misreadings of the productivity numbers, and a few other real factors. It really is possible that previous investment plans were based on expectations of the real economy that were wrong and unsustainable and now have been (partially?) corrected, with negative growth penalties looking forward.
Stephen Williamson offers very detailed comment, noting also that the recession started well over four years ago, which gives plenty of time for nominal resets, and we’ve seen no downward cascading spiral, so maybe there is a non-AD problem with getting back on track at the preferred rate. He also eschews AD denialism. Today Krugman has a brief note along the lines that the views of his opponents on these questions are “even worse than your first impression” but that is best thought of as a) his occasional churlishness, and that b) his writings on this topic do not, at least not to date, reflect a very thorough knowledge of the relevant literature(s).