On the (robust) ex post stability of constitutions

This paper explores the concept of ex post stability in voting systems, shifting the focus from the traditional ex ante perspective, where preferences are uncertain, to a setting where agents' preferences are fully known. We offer a comprehensive characterization of ex post stable constitutions within deterministic voting rule environments. We bridge the theoretical gap between ex post and ex ante stability, shedding light on their intricate relationship and implications for the design and evolution of voting systems. Additionally, our research further evaluates the resilience of these constitutions to changes in the voting environment, particularly their flexibility in response to varying alternative rule sets. This study not only contributes to a deeper understanding of constitutional stability but also provides insights into the dynamics of collective decision-making processes.