This is mainly of interest to economists, but given the importance of these issues, I have tried to write it in an accessible manner.
“Part of what defines a Keynesian (new or old), is that a Keynesian thinks that his or her views are "mainstream," and that the rest of macroeconomic thought is defined relative to what Keynesians think - Keynesians reside at the center of the universe, and everything else revolves around them.”
In that post I was careful to distinguish between academic research and policy. Of course macroeconomists research many things, and only a minority are using New Keynesian models, and probably even some of those do not really need the New Keynesian bit. That is the great thing about abstraction. Working with what can be called ‘flex price’ models does not imply that you think price rigidity is unimportant, but instead that it can often be ignored if you want to focus on other processes. So in terms of research I talked about the significant divide being between mainstream and heterodox. In terms of research, mainstream macroeconomists talk the same language.
I used the term anti-Keynesian in the context of macroeconomic policy, and in this context I was not talking about academics, but the set of economists involved with macro policy. They could be academics, but they could be working for central banks, a finance ministry, or an international organisation like the IMF or OECD. For this group, I think we have good reason to believe that the large majority are not anti-Keynesian.
Just look, for example, at any central bank publication discussing recent movements in output. This will typically focus on movements in components of aggregate demand: consumption, investment etc. The reason is a belief that output in the short run is demand determined. That, for me, is the defining feature of Keynesian analysis. If you look at the core models used in central banks (which, unlike models used by academics, need to be ‘horses for all courses’) the same will be true.
Now Nick Rowe and David Glasner suggest that this view is not uniquely Keynesian - I could equally call it monetarist, for example. But what then are the criteria you will use to restrict the Keynesian set today? Different views about unconventional monetary policy? Different views about the efficacy of fiscal policy at the zero lower bound? This seems way too narrow. People have views about the relative merits of fiscal policy for all kinds of reasons, which may be very context specific, so this does not look like a good method of defining a label for economists today.
Yet not everyone is a Keynesian using my deliberately broad definition. The only logical way to make sense of statements like those discussed here, for example, is to imagine we are in a world where output is determined from the supply side, so if one particular component of demand, like government spending on goods and services, goes down its impact on output will be offset by some means. That is an anti-Keynesian view. My first anti-Keynesian myth is that among economists involved with policy this is not a minority view.
The second myth is that all you need to justify this anti-Keynesian view is to observe that wages and prices move in response to booms and recessions. For example Roger Farmer points to negative inflation following the Great Depression. Language can be confusing here. As an analogy, suppose someone has been ill, and you ask them whether they are now better. Do you mean better than they were (but still ill), or completely recovered? For us to take an anti-Keynesian view, we do not just require prices to move, we require them to move by just the amount needed so that we can ignore demand. So, for example, in an open economy under fixed exchange rates, for a devaluation to have no demand impact requires prices to immediately rise by the same amount. Prices will begin to rise for sure, but ‘flexible prices’ means more than that.
If we take a simple closed economy, then ‘flexible prices’ is short for the real interest rate (nominal rates less expected inflation) always being at its ‘natural level’, which is the level that ensures demand matches supply. This immediately tells you that we are not just talking about price flexibility, but also monetary policy. Imagine in this economy there is a negative demand shock, caused by a fall in government spending. In this economy, the immediate impact is that firms will reduce output as well as prices. To offset this, the natural interest rate will fall to increase private consumption. Will the actual real interest rate do the same? This could happen without prices changing if the central bank cut nominal rates by exactly the required amount. It could happen without the central bank doing anything to nominal rates if expected inflation rose by exactly the required amount. Or it could be some combination of the two.
One justification for assuming that the real interest rate is always at its natural level is that monetary policy is super efficient, moving nominal rates to always offset the impact of demand shocks. For some reason this is not an argument anti-Keynesians usually make. The alternative justification is that, conditional on whatever monetary policy does, prices move by just the amount required to give you the expected inflation rate necessary to generate the natural real interest rate, and therefore offset the demand shock.
This becomes clear when nominal interest rates are stuck at the zero lower bound. In that case, the natural real interest rate is large and negative, but monetary policy cannot get there because nominal interest rates cannot be negative. For flexible prices to get you to that real rate you would need expected inflation to be significantly positive. (We now believe there is no independent Pigou effect (or real balance effect) that will save the day.) As Roger shows, actual inflation from 1929 to 1933 was persistently negative. One must presume that inflation expectations were also negative. So clearly although prices were moving, they were not moving in the way required for the anti-Keynesian view to hold. Far from casting doubt on the Keynesian story, falling prices during the Great Depression show how unrealistic the anti-Keynesian view is.