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Le Paradoxe d'Allais: Comment lui rendre sa signification perdue? (Allais's Paradox: How to Give It Back Its Lost Meaning?)

  • Mongin, Philippe

    ()

De tous les problèmes conçus par la théorie de la décision, le paradoxe d'Allais est peut-être celui qui aura suscité l'intérêt le plus persistant. La théorie y a consacré assez de travaux techniques remarquables pour qu'il soit désormais possible à l'histoire et à la philosophie des sciences de l'examiner réflexivement. Dans sa partie historique, l'article restitue le contexte d'apparition du paradoxe - le colloque de Paris, en 1952, auquel assistaient les principaux théoriciens de la décision du moment. L'axiomatique de von Neumann et Morgenstern en 1947 leur avait donné des raisons nouvelles d'approuver l'hypothèse de l'utilité attendue, et le contre-exemple d'Allais visait précisément à ébranler leur conviction. Les questions de la controverse étaient de type normatif, mais elles se perdirent quand le "paradoxe d'Allais" gagna tardivement la célébrité dans des travaux des années 1980 qui le traitaient comme une simple réfutation empirique. Ils en firent l'enjeu de "théories de l'utilité non-espérée" qu'ils développaient de même sous le seul angle empirique. Dans sa partie philosophique, l'article cherche à évaluer ce déplacement d'interprétation. D'un certain côté, les théoriciens de la décision firent bien de libérer leur travail expérimental des complications du normatif, car ils parvinrent ainsi à des résultats éclairants : l'hypothèse de l'utilité espérée était empiriquement réfutée, la responsabilité principale en revenait à l'axiome d'indépendance de von Neumann-Morgenstern, et l'étape suivante était de transformer adéquatement cet axiome. D'un autre côté, ils eurent tort de négliger un trait fondamental de leur domaine : les comportements observés ne sont informatifs que si les agents sont prêts à les assumer de manière réfléchie, c'est-à-dire à leur prêter une certaine valeur normative. D'après la reconstruction proposée ici, Allais ne voulait faire porter les expériences de choix que sur des sujets rationnels, ou bien sélectionnés au départ, ou bien révélés comme tels par l'expérience. L'article développe ces intuitions en revenant aux travaux des années 1970, aujourd'hui très peu connus, qui, sous l'influence d'Allais, proposèrent des traductions expérimentales de la rationalité, et il invite finalement la théorie de la décision à diversifier ses méthodes en s'inspirant de ces tentatives originales. Few problems in decision theory have raised more persisting interest than the Allais paradox. It appears that sufficiently many brilliant works have addressed it from within decision theory proper for history and philosophy of science now to enter stage. In its historical side, the paper recounts the paradox as it arose, i.e., in 1952, at a Paris conference attended by the main decision theorists of the time. They had drawn renewed confidence in expected utility theory (EUT) from the way von Neumann and Morgenstern had axiomatized it in 1947, and Allais devised his puzzle precisely to shaken their confidence. The issues between the two camps were normative, but they became lost in the developments of the 1980s that belatedly brought fame to the "Allais paradox". These works restricted the paradox to be a straightforward empirical refutation, turning it into a stake of also exclusively empirically oriented non-EU theories. In its philosophical vein, the paper tries to evaluate this shift of interpretation. To an extent, decision theorists were right because their experimental work was thus freed from a major complication and amenable to illuminating results: EUT was empirically refuted, the independence axiom of von Neumann and Morgentern was the main culprit, and the next theoretical stage was to modify this axiom appropriately. However, they were also wrong in not addressing an essential feature of their field, i.e., that observed behaviour is informative only if agents are prepared to endorse it reflectingly, i.e., to endow it with some normative value. As reconstructed here, Allais meant to reserve choice experiments to rational subjects, who were either selected at the outset, or identified as such by the experimental results. The paper tries to flesh out Allais's intuitions by turning to by now little known works of the 1970s, which under his influence provided experimental renderings of rationality, and it eventually suggests that decision theory might diversify its methods by taking inspiration from these original attempts.

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Paper provided by HEC Paris in its series Les Cahiers de Recherche with number 1021.

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Length: 42 pages
Date of creation: 30 Jun 2013
Date of revision:
Handle: RePEc:ebg:heccah:1021
Contact details of provider: Postal: HEC Paris, 78351 Jouy-en-Josas cedex, France
Web page: http://www.hec.fr/

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