This discussion of voting systems raises an interesting point. Arrow's impossibility theorem lays out a bunch of reasonable expectations about voting and then goes on to prove that no voting system can satisfy the entire set. The conclusion is that no voting system is ideal and we should attempt to develop a voting system that comes as close as possible to meeting the reasonable expectations while recognizing that any system will have some undesireable outcomes.
Maybe a better way to approach voting is to throw out Arrow's expectations and develop a new set. The place to start is probably monotonicity and independence of irrelevant alternatives. (Just because I find it helpful, I'm going to restate both of them. Monotonicity states that voting for a candidate will never make that candidate less likely to win. Independence of irrelevant alternatives states that removing any particular candidate from the set of candidates doesn't change the ordering of the remaining candidates. Plurality voting fails on irrelevant alternatives. IRV fails on monotonicity. (Condorcet fails on generating a unique ranking, one of the other expectations.))
What I want in a voting system is for third parties to be viable. As I see it, a good voting system would both provide that elections with more than two major parties get resolved reasonably while ensuring that minor parties can't act as spoilers. (I suspect that these two statements are basically equivalent to monotonicity and irrelevant alternatives, but the focus is different.) Plurality voting fails on spoilers. IRV and Condorcet fail on multiple major parties.
I wonder about the merits of a hybrid system. Have each voter rank the candidates. Look at the percentage of first place votes and eliminate everyone below a certain threshold. Have all voters who voted for an eliminated candidate fall back to their first remaining candidate, and then have a plurality vote.
Small third parties would not function as spoilers, but the plurality vote among the major parties prevents the strategic voting weirdness of IRV. The only question is what happens to candidates whose popularity is right around the threshold. I fear that might be ugly enough to make the whole system break down, but I can't really tell.
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Maybe a better way to approach voting is to throw out Arrow's expectations and develop a new set. The place to start is probably monotonicity and independence of irrelevant alternatives. (Just because I find it helpful, I'm going to restate both of them. Monotonicity states that voting for a candidate will never make that candidate less likely to win. Independence of irrelevant alternatives states that removing any particular candidate from the set of candidates doesn't change the ordering of the remaining candidates. Plurality voting fails on irrelevant alternatives. IRV fails on monotonicity. (Condorcet fails on generating a unique ranking, one of the other expectations.))
What I want in a voting system is for third parties to be viable. As I see it, a good voting system would both provide that elections with more than two major parties get resolved reasonably while ensuring that minor parties can't act as spoilers. (I suspect that these two statements are basically equivalent to monotonicity and irrelevant alternatives, but the focus is different.) Plurality voting fails on spoilers. IRV and Condorcet fail on multiple major parties.
I wonder about the merits of a hybrid system. Have each voter rank the candidates. Look at the percentage of first place votes and eliminate everyone below a certain threshold. Have all voters who voted for an eliminated candidate fall back to their first remaining candidate, and then have a plurality vote.
Small third parties would not function as spoilers, but the plurality vote among the major parties prevents the strategic voting weirdness of IRV. The only question is what happens to candidates whose popularity is right around the threshold. I fear that might be ugly enough to make the whole system break down, but I can't really tell.