The impartial observer theorem of social ethics

Abstract

The Impartial Observer Theorem attempts to derive utilitarianism from the rational choices of an individual situated behind a veil of ignorance. A rigorous axiomatic reconstruction reveals that the transition from the concept of impartiality to the utilitarian mean rule depends upon several problematic assumptions, most notably the uniformity of extended preferences and the principle of equal chance. If extended preferences—the capacity to rank being a specific person in a specific social state—are not uniform across observers, the theorem yields only observer-dependent additive formulas rather than a unique social welfare function. Replacing the traditional equiprobability assumption with a Bayesian framework of subjective probability assessments offers a more robust decision-theoretic foundation, yet this approach similarly falls short of the utilitarian objective by resulting in individualized weights for social members. While the causal account of interpersonal comparisons attempts to ground these judgements in objective psychological laws, it fails to provide a formal proof for uniform preferences. Ultimately, the theorem demonstrates that while impartiality and von Neumann-Morgenstern rationality imply an additive social evaluation, they are insufficient to mandate the specific weights and utility scales required by classical utilitarianism. – AI-generated abstract.