As Wikipedia says, Arrow's impossibility theorem states that no rank-order electoral system can be designed that always satisfies these three "fairness" criteria:
- If every voter prefers alternative X over alternative Y, then the
group prefers X over Y. - If every voter's preference between X and Y remains unchanged, then the group's preference between X and Y will also remain
unchanged (even if voters' preferences between other pairs like X and Z, Y and Z, or Z and W change). - There is no "dictator": no single voter possesses the power to always determine the group's preference.
Is there a known example of a voting system which fulfills the first two criteria, (and therefore fails to fulfill the third,) for which an example set of votes can be shown to contain one or more dictators?
Edit:
Voting systems that literally, directly, choose a dictator are not satisfying to me regarding this question. However if it can be demonstrated that directly choosing a dictator is the only way a voting system can fail the third criteria, then I would find that satisfying.
After asking this question and reading further, I have come to the conclusion that it is the case that if a voting system meets the first two criteria, then the voting system will be doing some form of directly choosing the dictator.
In particular, I found working through this proof of Arrow's Impossibility theorem (Wayback link) finally convinced me.