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Comment by cardiffspaceman | Hacker News Reader

Arrow's impossibility theorem https://en.wikipedia.org/wiki/Arrow%27s_impossibility_theore... is often trotted out in the discussion of RCV and similar systems. It seems to me that the problem with mentioning that theorem is that if you admit that every system for judging among more than 3 choices has some flaw, and that flaw makes the system anti-democratic because it allows tactical voting, then why not admit that the status quo is worse, under the same framework, and therefore admit that something else other than plurality voting should be used?

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I can't completely follow the argument, but I think Arrow's is mostly used to counter the "utopians" (roughly; people who argue that one system is Inherently Unfair(tm) and the alternative is Inherently Fair(tm)).

You're replacing one flawed system with another flawed system, so you should not argue in terms of the presence or absence of flaws, but rather argue why one is better than the other.

RCV can still have outcomes that a majority will disagree with, but it should be less common than FPTP, and also make third parties competitive in practise. That may be better than the old system (and it also may not be), but it's not going to resolve the fundamental tensions of representative democracy.

Instant runoff matches four of the postulates, including all three that FPTP matches. It is a superset of the fairness of the other, they are not "equally unfair in different ways" or anything like that.

Edit time threshold passed so I'll have to reply to myself.

I've just read up on Arrow, and this theory only has four postulates not five: I'm pretty sure I've either misremembered or am talking about a different theory. Apologies, anyway.

Can someone shed some light on why we should care about the non-dictatorship requirement in Arrow's theorem? Reading the non-dictatorship section on the Stanford encyclopedia of philosophy makes it sound like it's a meaningless assumption. http://plato.stanford.edu/entries/arrows-theorem/#NonDic If someone's preferences always aligning with society's preferences results in them being a "dictator", so what?

Exactly. This is why Arrow's theorem has no applicability to practical use of voting systems in the real world. The dictatorship property is often misinterpreted.

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