Strategy and Manipulation in Medieval Elections
Sara L. Uckelman, and Joel Uckelman
Paper given at the COMSOC seminar, Amsterdam, The Netherlands, 28 October 2010
When developing electoral protocols, desiderata include a system which is transparent, non-manipulable, honest, and not open to strategizing. However, these desiderata are in tension with each other: Often, transparent electoral procedures are the least strategy resistant, and many honest procedures encourage manipulation. Thus, a balance between these different goals must be sought. In modern times, since the seminal result on vote manipulation, the Gibbard-Satterthwaite Theorem, much attention has been devoted to developing voting rules where manipulation is never in the best interest of the voters, or which are computationally too complex for the average bounded agent to be able to manipulate. In medieval times, such computational routes were generally not available, meaning that other constraints had to be put in place to discourage strategizing and manipulation. We discuss various voting rules and electoral procedures used in the Middle Ages in both ecclesiastical and secular context, highlighting some protocols with unique properties.
Elections in the Middle Ages were used for the same reasons that they are today: To select suitable candidate(s) for a particular office, duty, or obligation. Great importance was put on the suitability of the winner, thus the purity or canonicity of the electoral procedure was paramount. The electoral procedure should be reliable and not easily manipulable, and the electors should not be coerced in their votes. Ensuring that an election had these qualities could be done by both internal and external means. Externally, measures could be introduced which discouraged interference by means of social pressure, for example, the oath that electors in 12th century Pistoia were required to take, that they “would form no combinations, would not yield to any power outside the city, would neither take nor give any bribes or promises, and would make no oaths or agreements, in short, would do nothing to hamper in any way their action as free agents”, or the procedural requirement in the statutes of Bologna and Sienna that “insisted that the election should follow immediately upon the choosing of the electors”. Other external pressures include the use of voting in seclusion, and the restriction of diet the longer it takes for consensus to be achieved. External measures against manipulation are still in practice today; e.g., vote buying is today illegal in political elections, both federally and in all 50 U.S. states, but enforcement is often difficult.