Harsanyi invested his Aggregation Theorem and Impartial Observer Theorem with utilitarian sense, but Sen redescribed them as "representation theorems" with little ethical import. This negative view has gained wide acquiescence among economists. Against it, we support the utilitarian interpretation by a novel argument relative to the Aggregation Theorem. We suppose that an exogeneously defined utilitarian observer evaluates social states by the sum of individual utilities and we apply the assumptions of the Aggregation Theorem to this observer. Adding technical conditions from microeconomics, we conclude that any social observer who is subjected to the assumptions of the Aggregation Theorem evaluates social states in terms of a weighted variant of the utilitarian sum. Hence, pace Sen, utilitarianism and the Aggregation Theorem are mutually relevant. The argument is conveyed by means of a main theorem, an algebraic refinement of this theorem, and a variant in which the utilitarian sum is unconventionally defined on lotteries. Each result encapsulates Harsanyi's original one as a particular step.
The full paper can be found here
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