Dr. Krugman is referring to his waning belief in the ideas that are the basis for much of the neoclassical synthesis. The neoclassical synthesis, without getting too wonky, is the synthesis of Keynesian ideas with some of the neoclassical micro. From this we got wonderful things like loanable funds based IS/LM models (which don’t apply entirely to an endogenous monetary system), general equilibrium theory, the ergodic axiom (the idea that the future is already predetermined), etc. In essence, you got a whole bunch of stuff that might sound fancy and look cool in an economic model, but doesn’t exactly translate over into an actual view of the economy.
Love him or hate him, I think you have to respect the way Paul Krugman has remained open-minded to alternative ideas. Especially in recent years. For instance, Dr. Krugman had expressed some confusion about the divergence in Italian bond yields and Japanese bond yields back in 2011 and I wrote a piece describing that the confusion was really rather simple. Japan was a contingent currency issuer who could never “run out of money”. Therefore, the solvency issue was not a matter of lacking money as it was in Italy thereby creating a real solvency constraint. Dr. Krugman later realized the error and totally changed his position. That’s a pretty substantial change in thinking from a Nobel Prize winner, and in my opinion, a pretty fantastic display of open-mindedness.
You could say I’ve had my own sort of “synthesis lost” in recent years. After all, I used to adhere to Modern Monetary Theory (MMT) before recognizing what I believe are some flaws in it. It’s why Monetary Realism exists. Is it problematic when one realizes that a past position is potentially erroneous or flawed and searches out for the truth? I would surely hope not. After all, evolution and learning is largely about finding what’s wrong. None of us has all the answers and the most dangerous people around us are the ones who pretend they do. Learning is really a sequence of mistakes and errors that get resolved and improved. I hope Dr. Krugman embraces the synthesis lost and finds a more accurate understanding of the world. After all, that’s what evolution of thought is all about.