On the relationship between keynes´s conception of evidential weight and the ellsberg paradox

A number of scholars have noted that Ellsberg’s seminal 1961QJE critique of the subjective expected utility model bears certain resemblances to ideas expressed in J. M. Keynes’s earlier 1921 A Treatise on Probability. Ellsberg did not mention Keynes’s work in his article, but did do so in his doctoral dissertation submitted in 1962 and recently published in 2001. This gives rise to a number of interesting questions concerning the relationship between the contributions of the two authors. The present paper, drawing in part on a conversation with Ellsberg, attempts to answer these questions. The main conclusions that emerge are that Ellsberg formulated the ideas advanced in the QJE article before having read, and thus independently of, Keynes’s work, and that, even though he later recognised the importance and originality of Keynes’s work in his PhD dissertation, he did not fully appreciate the constructive part of Keynes’s analysis. 1. Introduction The last twenty years have seen a revival of