Must-Read: Superb from the extremely sharp Martin Sandbu! Only three quibbles:

  1. There are indeed “three great economists” in the mix here, but their names are Summers, Krugman, and Blanchard…
  2. This isn’t really a conversation that would have taken place even in an academic setting. If I have ever been in the same room at the same time with Larry, Paul, and Olivier–let alone all of Olivier’s coauthors, Michael Woodford, Danny Vinit, and Lukasz Rachel and Thomas Smith–I cannot remember it. And discussions and exchanges in scholarly journal articles are formal and rigid in an unhelpful way.
  3. Do note that Keynes was on Summers’s side with respect to the importance of maintaining business confidence: cf.: General Theory, ch. 12, “The State of Long-Term Expectation”

Martin Sandbu: Free Lunch: On Models and Making Policy: “The internet has… open[ed] up to the public…

…discussions… that previously took place mostly in face-to-face gatherings or scholarly journal articles. Neither medium was particularly accessible….

Summers posted a characteristically succinct statement on why he disagreed with the Federal Reserve’s decision to begin tightening… His analysis is well worth reading in full, but the trigger of the ensuing debate was his explanation for why the Fed thinks differently: ‘I suspect it is because of an excessive commitment to existing models and modes of thought. Usually it takes disaster to shatter orthodoxy.’… DeLong expressed doubts that the Fed’s analysis was indeed compatible with existing models; Krugman asserted that conventional models straightforwardly showed the Fed to be in the wrong, and that… policy was driven… by… ‘a conviction that you and your colleagues know more than is in the textbooks’….

Summers then responded… showed a fascinating divergence…. DeLong and Krugman think the Fed erred by ignoring… models…. Summers thinks the Fed erred by ignoring things that such models do not capture…. Summers is also much more comfortable with the notion that policymakers should aim to underpin market confidence. That notion has often been derided by Krugman…. Two quotes rather nicely capture the methodological disagreement here. Summers writes: ‘I think maintaining confidence is an important part of the art of policy…. Paul is certainly correct in his model but I doubt that he is in fact.’ DeLong responds: ‘Larry, however, says: We know things that are not in the model. Those things make Paul’s claim wrong. My problem with Larry is that I am not sure what those things are.’…

What is a policymaker to do if she thinks this is the case in reality, even if no extant model captures it? Surely not wait for 30 years in the hope that new mathematical techniques enable economists to model that reality. In his willingness to listen to those who may have an untheoretical ‘feel’ for the market, and in his intellectual respect for the limits of his own knowledge, Summers comes across as the most Keynesian of these three…