Aggregating sets of von Neumann–Morgenstern utilities

We analyze the preference aggregation problem without the assumption that individuals and society have fully determined and observable preferences. More precisely, we endow individuals and society with sets of possible von Neumann–Morgenstern utility functions over lotteries. We generalize the classical Pareto and Independence of Irrelevant Alternatives axioms and show they imply a generalization of the classical neutrality assumption. We then characterize the class of neutral social welfare functions. This class is considerably broader for indeterminate than for determinate utilities, where it basically reduces to utilitarianism. We finally characterize several classes of neutral social welfare functions for indeterminate utilities, including the utilitarian and “multi-utilitarian” classes.