McCarthy, D., Mikkola, K., Thomas, T., Utilitarianism with and without expected utility.
Journal of Mathematical Economics 87 (2020): 77113.
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AbstractWe give two social aggregation theorems under conditions of risk, one for constant population cases, the other an extension to variable populations. Intra and interpersonal welfare comparisons are encoded in a single ‘individual preorder’. The theorems give axioms that uniquely determine a social preorder in terms of this individual preorder. The social preorders described by these theorems have features that may be considered characteristic of Harsanyistyle utilitarianism, such as indifference to ex ante and ex post equality. However, the theorems are also consistent with the rejection of all of the expected utility axioms, completeness, continuity, and independence, at both the individual and social levels. In that sense, expected utility is inessential to Harsanyistyle utilitarianism. In fact, the variable population theorem imposes only a mild constraint on the individual preorder, while the constant population theorem imposes no constraint at all. We then derive further results under the assumption of our basic axioms. First, the individual preorder satisfies the main expected utility axiom of strong independence if and only if the social preorder has a vectorvalued expected total utility representation, covering Harsanyi’s utilitarian theorem as a special case. Second, stronger utilitarianfriendly assumptions, like Pareto or strong separability, are essentially equivalent to strong independence. Third, if the individual preorder satisfies a ‘local expected utility’ condition popular in nonexpected utility theory, then the social preorder has a ‘local expected total utility’ representation. Fourth, a wide range of nonexpected utility theories nevertheless lead to social preorders of outcomes that have been seen as canonically egalitarian, such as rankdependent social preorders. Although our aggregation theorems are stated under conditions of risk, they are valid in more general frameworks for representing uncertainty or ambiguity.

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