“If we cannot puncture some of the mythology around austerity … then we are doomed to keep on making more and more mistakes”
Barack Obama, New York Times, April 2016
I have just completed a working paper based on my talk to the Royal Irish Academy at the end of last year. (Yes, I know, that was six months ago - it’s all the media training I have to do :-)) It has the title of this post: in part an allusion to Keynes who had been here before, but also because its scope is ambitious. The first part of the paper tries to explain why austerity is nearly always unnecessary, and the second part tries to understand why the austerity mistake happened.
I start by making a distinction which helps a great deal. It is between fiscal consolidation, which is a policy decision, and austerity, which is an outcome where that fiscal consolidation leads to an increase in aggregate unemployment. If you understand why monetary policy can normally stop fiscal consolidation leading to austerity, but cannot when interest rates are stuck near zero, then you are a long way to understanding why austerity was a mistake. Fiscal consolidation in 2010 was around 3 years too early. A section of the paper is devoted to showing that the idea that markets prevented such a delay in consolidation is a complete myth.
I say that austerity is nearly always unnecessary because (given the title) I also cover the case of an individual monetary union member that has an unusually (relative to the rest of the union) large government debt problem. Here some austerity is required, but not for the reason you might think. It has nothing to do with markets: the Eurozone crisis from 2010 to 2012 was a result of mistakes by the ECB. If a union member’s government debt is not sustainable, there needs to be some form of default (Greece). If it is sustainable, then the central bank should back that government, as the ECB ended up doing with OMT in 2012. The reason some austerity is necessary is that to support financing this unusually high debt, the union member needs a real depreciation, and in a monetary union that has to occur via lower wages and prices relative to other union members.
None of this theory is at all new: hence the allusion to Keynes in the title. That makes the question of why policy makers made the mistake all the more pertinent. One set of arguments point to an unfortunate conjunction of events: austerity as an accident if you like. Basically Greece happened at a time when German orthodoxy was dominant. I argue that this explanation cannot play more than a minor role: mainly because it does not explain what happened in the US and UK, but also because it requires us to believe that macroeconomics in Germany is very special and that it had the power to completely dominate policy makers not only in Germany but the rest of the Eurozone.
The set of arguments that I think have more force, and which make up the general theory of the title, reflect political opportunism on the political right which is dominated by a ‘small state’ ideology. It is opportunism because it chose to ignore the (long understood) macroeconomics, and instead appeal to arguments based on equating governments to households, at a time when many households were in the process of reducing debt or saving more. But this explanation raises another question in turn: how was the economics known since Keynes lost to simplistic household analogies.
This question can be put another way. Why was this opportunism so evident in this recession, but not in earlier economic downturns? There are a number of reasons for this, which I also discuss here, but one that I think is important in Europe is the spread of central bank independence, coupled with a phobia that European central bank governors have about fiscal dominance. In the UK, for example, the Bank of England played a key role in 2010 in convincing policymakers and the media that we needed immediate and aggressive fiscal consolidation. Keynesian demand management has been entrusted to institutions whose leaders (but not those who work for them) threw away the manual. But as Ben Bernanke showed, it does not have to be this way. 
If my analysis is right, it means that we cannot be complacent that when the next liquidity trap recession hits the austerity mistake will not be made again. Indeed it may be even more likely to happen, as austerity has in many cases been successful in reducing the size of the state. My paper does not explore how to avoid future austerity, but it hopefully lays the groundwork for that discussion.
 Here is Bernanke is October 2010 saying “indeed, premature fiscal tightening could put the recovery at risk”, although no doubt he could have said it louder.