I remember reading once that it is still not understood how the giraffe manages to pump an adequate blood supply all the way up to its head; but it is hard to imagine that anyone would therefore conclude that giraffes do not have long necks. At least not anyone who had ever been to a zoo.
Solow wrote those words at the height of the macro wars. I was very much on his side at the time, and this post will explain the sense in which I am still on his side.
Think of the task of macroeconomics as completing a mineshaft between the “outside” (what we observe in the world) and the “inside” (a mathematical model that is “pure” in its microfoundations). The Old Keynesians, including Solow, took an outside-in approach: let’s work from what we observe, build a crude model to handle that, and maybe eventually we can dig deeper and find the microfoundations. Start from the fact that there is a giraffe, and try to figure out how it maintains its blood supply. Do not start from a model of blood supply that precludes the existence of giraffes.
For the Old Keynesians, macroeconometric models were a tool with which to observe the world. They provided the starting point for the outside-in approach. Then Robert Lucas came along with his “critique,” which said that if you took an inside-out approach that included rational expectations, macroeconometric models would break down. The Lucas Critique launched the macro wars.
Lo and behold, macroeconometric models did break down. However, I do not think that the Lucas Critique had much to do with it. You can get more on my perspective by reading this paper and by reading my macro book.
The New Keynesians took up Lucas’ challenge by adopting an inside-out approach. Stan Fischer’s course at MIT was 100 percent inside-out theory, and I viscerally hated it. At the start of one class, I stood up, proclaiming loudly and sarcastically to Fischer and my fellow students how much I enjoyed the topic of “monetary growth models,” which was the particularly pointless mathematical, er, self-abuse that he was teaching us that week.
I chose Solow as my dissertation adviser, and I wrote an outside-in thesis, working backwards from what we observe to a theory of price rigidity. Not having a thesis that focused on rational expectations and not having Fischer plugging for me were career-altering. I was doomed to failure if I tried academia, and so I wound up on a different track. I don’t think I was the one who lost out on that deal.
So if you are trying to follow the methodological discussions among Mark Thoma, Paul Krugman, Noah Smith, and others, you will find me still on the side of the Old Keynesians. I still despise inside-out macro, and I still prefer the outside-in approach.
What has happened to me since I left MIT is that I no longer think that macroeconometric models provide a valid lens into observing the real world, and I no longer think that Keynesianism is the One True Way. The real world is still out there, and I still think it should be our starting point for digging the mineshaft. I still respect the Old Keynesian approach of starting with observations about the world rather than starting at the bottom of the mine with a “pure” model. However, I am willing to entertain theories that differ considerably from the Old Keynesian one. Hence, PSST, which you can also read more about in my essays/papers.