Mas também não é o caso de que conceitos sejam absolutamente falsos. O conceito encapsulado na Hipótese de Mercados Eficientes (EMH) é um exemplo importante em questão. Em seu blog, Scott Sumner tem uma discussão (aqui):
I need to constantly repeat a very important point; I’m not arguing the EMH is true. I’m arguing the EMH is useful and that anti-EMH models are not useful. The reason I don’t think the EMH is true is because I believe market participants do have cognitive illusions. And the reason I don’t think the anti-EMH theory is useful is because I think academics and policymakers are equally susceptible to cognitive illusions.
Paul Einzig made the same basic argument back in 1937:
“On June 9, 1937, this veteran monetary expert [Cassel] published a blood-curdling article in the Daily Mail painting in the darkest colours the situation caused by the superabundance of gold and suggesting a cut in the price of gold to half-way between its present price and its old price as the only possible remedy. He took President Roosevelt sharply to task for having failed to foresee in January 1934 that the devaluation of the dollar by 41 per cent would lead to such a superabundance of gold. If, however, we look at Professor Cassel’s earlier writings, we find that he himself failed to foresee such developments, even at much later dates. We read in the July 1936 issue of the Quarterly Review of the Skandinaviska Kreditaktiebolaget the following remarks by Professor Cassel: ‘There seems to be a general idea that the recent rise in the output of gold has been on such a scale that we are now on the way towards a period of immense abundance of gold. This view can scarcely be correct.’ . . . Thus the learned Professor expected a mere politician to foresee something in January 1934 which he himself was incapable of foreseeing two and a half years later. In fact, it is doubtful whether he would have been capable of foreseeing it at all but for the advent of the gold scare, which, rightly or wrongly, made him see things he had not seen before. It was not the discovery of any new facts, nor even the weight of new scientific argument that converted him and his fellow-economists. It was the subconscious influence of the panic among gold hoarders, speculators, and other sub-men that suddenly opened the eyes of these supermen. This fact must have contributed in no slight degree towards lowering the prestige of economists and of economic science in the eyes of the lay public.” (1937, pp. 26-27.).
Luigi Zingales tem uma exelente discussão (aqui). Um ponto importante está ressaltado nessa passagem: (Vale a pena ler o ensaio todo)
Besides the intellectual appeal of Friedman’s argument and the supporting empirical evidence, the EMT was also very attractive for its practical implications. By providing an objective metric for performance, the shared belief in efficient markets made everyone’s life easier. It was not one expert’s opinion against another’s: the market was the absolute and impartial judge. Once we lose this objective criterion, we are back in the world of self-interested opinions. All corporate executives will argue that the market undervalues their stock and that any drop in their stock price is due to market irrationality (while any increase is entirely justified by their actions). All politicians will claim that the rise in the yield of their government’s bonds is not the result of their profligacy, but of evil speculation or market irrationality (while ready to take credit for any reduction in the yield). Finally, all charlatans will feel entitled to claim that they have an investment strategy that can beat the market systematically. This is the uncharted territory where the crisis leaves us: a world where confidence in the rationality of the market is shaken but where there is no clear, viable alternative.