Ancient Economists: Two Views

John Cochrane, reporting from the NBER Summer Institute:

The use of ancient quotations came up several times. I  complained a bit about Eggertsson and Mehrotra's long efforts to tie their work to quotes from verbal speculations of Keynes, Alvin Hansen, Paul Krugman and Larry Summers. Their rhetorical device is, "aha, these equations finally explain what some sage of 80 years ago or Important Person today really meant."  Ivan Werning really complained about this in Paul Beaudry's presentation. What does this complex piece of well worked out "21st century economics" have to do with long ago muddy debates between Keynes and Hayek? It stands on its own, or it doesn't. (In his view, it did, so why belittle it?) 

Physics does not write papers about "the Newton-Aristotle debate." Our papers should stand on their own too. They are right or wrong if they are logically coherent and describe the data, not if they fulfill the vague speculations of some sage, dead or alive. It's especially unhelpful to try to make this connection, I think, because the models differ quite sharply from the speculations of the sage. Alvin Hansen certainly did not think that a Taylor interest rate rule with a phi parameter greater than one was a central culprit in "secular stagnation." I haven't checked against the speech, but I doubt he thought that inflation would completely cure the problem in the first place. 

Sure, history of thought is important; tying ideas to their historical predecessors is important; recognizing the centuries of thinking on money and business cycles is important. But let's stand up for our own generation; we do not exist simply to finally put equations in the mouths of ancient economists. 

But, tying it all up, perhaps I'm just being an old fogey. Adam Smith wrote mostly words. Marx like Keynes wrote big complicated books that people spent a century writing about "this is what they really meant." Maybe models are at best quantitative parables. Maybe economics is destined to return to this kind of literary philosophy, not quantified science.

(via Suresh, who was also there.)

For the case in favor of ancient economists, here is Axel Leijonhufvud:

According to Sir Peter Medawar

A scientist's present thoughts and actions are of necessity shaped by what others have done and thought before him: they are the wave-front of a continuous secular process in which The Past does not have a dignified independent existence of its own. Scientific understanding is the integral of a curve of learning; science therefore in some sense comprehends its history within itself.

... Not every field of learning can claim to "comprehend its history within itself." For the current state of the art to be the "integral of past learning" in Medawar's sense, the collective learning process must be one that remembers everything of value and forgets only the errors and the false leads. But this requires the recognized capability to decide what is correct or true and what is in error or false. These decisions, moreover, must compel general assent. Once an answer is arrived at, it must be generally agreed to be the answer. The field must be one in which answers kill questions so definitively that the sense of alternative possibilities disappears. ... 

A science, or a subfield within it, may come to approximate these conditions because of its positive successes. But two other mechanisms that are not so nice will also be at work. First, the people in the field agree that certain questions, which they would have a hard time deciding, are somebody else's responsibility. So economics among the social sciences, like physics among the natural sciences, had first pick of problems and left the really hard ones, on which their methods did not give them a firm grip, for the younger sister disciplines to deal with as best they might. Second, the insiders to the field will agree to exclude some people who refuse to assent to the manner in which certain important questions have been settled. Both the exclusion of undecidable questions from the field of inquiry and the exclusion of undecided people from the professional group help to achieve collective concentration and intensive interaction within the group. … 

These reflections … offer some suggestions about when scientists might find the history of their field relevant and useful to current inquiry. One suggestion is to look for situations when a research program has bogged down, when anomalies have cropped up that cannot be reduced to or converted into ordinary puzzles within the paradigm. Another is to look for cases in which three conditions seem to be met:
a) certain central questions cannot be decided in a way that commands assent,
b) the (for the time being) undecidable questions cannot very well be left for somebody else to worry about, and
c) the people who withhold their assent from some popular suggested answer cannot be ignored or excommunicated.

... Economists are wont to reduce everything to choices. Economics itself develops through the choices that economists make. To use the past for present purposes, we should see the history of the field as sequences of decisions, of choices, leading up to the present. Imagine a huge decision tree, with its roots back in the time of Aristotle, and with the present generation of economists -- not all of them birds of a feather! -- twittering away at each other from the topmost twigs and branches. 

The branching occurs at points where economists have parted company, where problematic decisions had to be made but could not be made so as to command universal assent. The two branches need not be of equal strength at all; in many cases, universal agreement is eventually reached ex post so that one branch eventually dies and falls away. The oldest part of the tree is, perhaps, just the naked trunk; but the sap still runs in some surprising places. 

If you want to translate Medawar's image of science into my decision tree metaphor, you will have to imagine his sciences as fir trees -- with physics, surely, as the redwood – majestic things with tall, straight trunks and with live branches only at the very top. Economics, in contrast, would come out as a rather tangled, ill-pruned shrub … 

As long as "normal" progress continues to be made in these established directions, there is no need to reexamine the past … Things begin to look different if and when the workable vein runs out or, to change the metaphor, when the road that took you to the "frontier of the field" ends in a swamp or in a blind alley. A lot of them do. Our fads run out and we do get stuck occasionally. Reactions to finding yourself in a cul-de-sac differ. Tenured professors might often be content to accommodate themselves to it, spend their time tidying up the place, putting in a few modern conveniences, and generally improving the neighborhood. Braver souls will want out and see a tremendous leap of the creative imagination as the only way out -- a prescription, however, that will leave ordinary mortals just climbing the walls. Another way to go is to backtrack. Back there, in the past, there were forks in the road and it is possible, even plausible, that some roads were more passable than the one that looked most promising at the time. At this point, a mental map of the road network behind the frontier becomes essential.