Merci de votre réponse à ma chronique sur la « dérive formaliste » de la science économique contemporaine (voir LA MATHÉMATISATION DE L'ÉCONOMIE: POUR, p. 10). Vous me permettrez toutefois de saisir l'occasion pour vous relancer la balle, en espérant que vous trouverez le temps d'éclairer davantage ma lanterne.

          For the first two or three days of the meeting, since few of the physicists had had much exposure to the subject beyond undergraduate Economics 101, [economists were asked] to give survey talks on the standard neoclassical theory. As the axioms and theorems and proofs marched across the overhead projection screen, the physicists could only be awestruck at their counterparts' mathematical prowess – awestruck and appalled. They had the same objection that [...] many other economists had been voicing within the field for years. « They were almost too good, » says one young physicist, who remembers shaking his head in disbelief. « It seemed as though they were dazzling themselves with fancy mathematics, until they really couldn't see the forest from the trees. So much time was being spent on trying to absorb the mathematics that I thought they often weren't looking at what the models were for, and what they did, and whether the underlying assumptions were any good. In a lot of cases, what was required was just some common sense. Maybe if they all had lower IQs, they'd have been making some better models. »  
  
          The physicist had no objections to the mathematics itself, of course. But what most of the economists didn't know – and were startled to find out – was that physicists are comparatively casual about their math. « They use a little rigorous thinking, a little intuition, a little back-of-the-envelope calculation – so their style is really quite different, » says [Nobel Prize winner Kenneth] Arrow. And the reason is that physical scientists are obsessive about founding their assumptions and their theories on empirical fact. [The physicists were disconcerted] at how seldom the economists seemed to pay attention to the empirical data that did exist. Again and again, for example, someone would ask a question like « What about noneconomic influences such as political motives in OPEC oil pricing, and mass psychology in the stock market? Have you consulted sociologists, or psychologists, or anthropologists, or social scientists in general? » And the economists – when they weren't curling their lips at the thought of these lesser social sciences, which they considered horribly mushy – would come back with answers like « Such noneconomic forces really aren't important »; « They are important, but they are too hard to treat »; « They aren't always too hard to treat, and in fact, we're doing so in specific cases »; and « We don't need to treat them because they're automatically satisfied through economic effects. »   
  
          And then there was this business of « rational expectations. » [As economist Brian Arthur pointed out] « Our particles in economics [banks, firms, consumers, governments, etc.] are smart, whereas yours in physics are dumb. » In physics, an elementary particle has no past, no experience, no goals, no hopes or fears about the future. Immediately, [Arthur] says, he could see all the physicists in the room sitting up: « Here was a subject that wasn't trivial. It was like their subject, but it has these two interesting quirks – strategy and expectations. » Unfortunately, the economists' standard solutions to the problem of expectations – perfect rationality – drove the physicists nuts. The only problem, of course, is that real human beings are neither perfectly rational nor perfectly predictable – as the physicists pointed out at great length. Furthermore, as several of them also pointed out, there are real theoretical pitfalls in assuming perfect predictions, even if you do assume that people are perfectly rational. In nonlinear systems, chaos theory tells you that the slightest uncertainty in your knowledge of the initial conditions will often grow inexorably. After a while, your predictions are nonsense.  
  
          The physicists were shocked at the assumptions the economists were making – that the test was not a match against reality, but whether the assumptions were the common currency of the field. [Physicist] Phil Anderson, laid back with a smile on his face [said] « You guys really believe that? » The economists, backed into a corner, would reply, « Yeah, but this allows us to solve these problems. If you don't make these assumptions, then you can't do anything. » And the physicist would come right back, « Yeah, but where does that get you – you're solving the wrong problem if that's not reality. » 

« Pour utiliser une analogie un peu boiteuse, j'ai souvent l'impression que certains économistes utilisent un marteau-pilon pour planter des fleurs et qu'au bout du compte leurs modèles créent plus de confusion qu'autre chose par rapport aux écrits des "vieux auteurs". »

          Let me begin with an embarrassing admission: until I began working on this paper, I had never actually read Ohlin's Interregional and International Trade. I suppose that my case was not that unusual: modern economists, trained to think in terms of crisp formal models, typically have little patience with the sprawling verbal expositions of a more leisurely epoch. To the extent that we care about intellectual history at all, we tend to rely on translators – on transitional figures like Paul Samuelson, who extracted models from the literary efforts of their predecessors. And let me also admit that reading Ohlin in the original is still not much fun: the MIT-trained economist in me keeps fidgeting impatiently, wondering when he will get to the point – that is, to the kernel of insight that ended up being grist for the mills of later modelers.   
  
          Moreover, one can argue that Ohlin actually gains something in the translation: Samuelson famously found implications in Ohlin's own view of trade that the great thinker himself, due to his « diplomatic style » (in Tjalling Koopman's phrase), had missed. And yet what Ohlin disparagingly called « model mania » can lead to a narrowing of vision. Samuelson himself entitled his 1971 article expounding what has since come to be known as the specific-factors model « Ohlin was right », conceding that in a multi-factor model some of Ohlin's skepticism about the full factor-price equalization and strong Stolper-Samuelson effects that arise in a two-by-two model turns out to be justified after all. What else might Ohlin have been right about? In particular, did Ohlin's informal exposition of a theory of interregional and international trade contain the essence of what later came to be known as the « new trade theory » and the « new economic geography »? The answer, it turns out, is yes and no. But let me start with my startling discovery: the extent to which Ohlin in the original anticipates a view of trade that the « new trade » theorists had to rediscover some 50 years later.  

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