The problem if 3 Ls win in the above example is that if the L party passes a law with their majority, and the C and R voters dislike that law, they would constitute a majority of voters but wouldn’t have a majority of representatives, so they couldn’t overturn the law. Here’s a possible fix: for the final STV seat, if there’s a Condorcet winner based on the non-exhausted ballots, elect them, otherwise just run STV as normal.
If run on the above example, after exhausting 4 Hare Quotas of votes and electing L1, L2, R1, and R2, you have:
7 L3 > C
6 C > L3
7 R3 > C
C pairwise beats L3 13 to 7 and beats R3 13 to 7, so they’re elected. (Under standard STV rules, C would have the fewest votes and be eliminated, then L3 would beat R3 13 to 7.) Now you have 2 Ls, 1 C, and 2 Rs, and the majority of voters are fairly represented.
Some points on this modification:
- FairVote, if they were to accept a Condorcet method, would like it because in the single-winner case, it devolves into “elect the Condorcet winner, otherwise run IRV”, so they have a way to unify their voting method offerings in the single and multi-winner cases.
- Cardinal advocates would prefer to guarantee electing Condorcet winners in single-winner races rather than IRV winners
- FV won’t like it because it technically fails later-no-harm and all the other things Condorcet fails, but not in a very harmful way at least, since it should only really apply to the strategic voting for the final seat (plus they’re getting PR enacted, so it’s doubtful this would be the deal-breaker, but who knows)
P.S. It is possible to do “if there is no Condorcet winner on the final seat, eliminate the candidate with the fewest votes, transfer their voters’ votes to their next choice, and then check if there’s a Condorcet winner, if not, repeat” but that’s much more complicated for little gain.
Edit: C can fail to get elected if the votes are modified such that there are say, 5 L candidates and they each get 9 or 10 votes from the L faction. Then nobody on that side will have an outright quota and C will get eliminated before the final seat comes into play. It seems the only way to really ensure C wins is to either have voters Favorite Betray, equally rank, or have the voting method automatically elect a Condorcet winner before running STV on the remaining seats.
If a Condorcet winner is automatically elected before starting the STV count, maybe the ballot exhaustion could be done by prioritizing the ballots that ranked the Condorcet Winner highest (i.e. ballots ranking C 1st get exhausted first, then ballots ranking C 2nd, etc.) until a quota is exhausted.