The Possibility of Bayesian Social Choice

• Applicant: Professor Dr. Stephan Hartmann, since 9/2021
• Subject Area: Theoretical Philosophy ; Practical Philosophy
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426170771

This project is concerned with understanding rational collective decision-making. Its working hypothesis is that collective rationality is fruitfully modelled after individual rationality. Its starting point is that while Bayesianim is widely taken to be the golden standard for individual rationality, recent results in social choice theory—i.e., the theory of collective decision-making—reveal that Bayesianism does not extend well from the individual to the collective level. In some contexts, it is impossible to reconcile Bayesianism with appealing forms of social aversion to risk or inequality. In others, it is even impossible to consistently impose Bayesianism at both the individual and the collective level. Thus, the possibility of a specifically Bayesian form of social choice is problematic.The applicant’s goal is to elucidate the possibility conditions for a specifically Bayesian form of social choice. To do so, he will pursue the following objectives. First, there is an implicit constraint in the above results, namely, collectively endorsing any decision that is agreed upon by all the individuals engaged in the collective decision. For Bayesian social choice to get off the ground, this constraint must be relaxed. The applicant will provide a unified theory of why and how this should be done, which is lacking from the current literature. Second, there is a hidden assumption in the above results, to the effect that the same method can be appropriate for aggregating both the preferences and the beliefs of the individuals involved. The applicant will give grounds to reject this unquestioned assumption, and he will explore forms of joint, but heterogeneous, aggregation of preferences and beliefs. Third, there is a recurring restriction in the above results. The invoked attitudes towards risk or inequality are typically restricted to cases where what is at stake is a continuous good, such as money. The applicant will waive this restriction, which has not been done hitherto in the literature. He will introduce notions of attitude towards risk or inequality that apply over general domains, and he will explore how they shape individual and social choice. Thus, the proposed research will contribute primarily to decision theory, social epistemology, and social choice theory. It will also bear on the philosophy of economics and political philosophy.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Jean Baccelli, Ph.D., until 8/2021