[EM] Markus: MMC. Why WV vs Margins matters.

[MIKE OSSIPOFF]

Markus--

You wrote:

MMC says:

If there is a set of candidates such that a majority of the voters
strictly prefers each candidate of this set to each candidate
outside this set, then the winner must be a candidate of this set.

I reply:

If that were MMC, then no method would meet MMC. Saying that a majority
prefer the candidates in set S to all the other candidates, but
not saying anything about how they vote, no one can guarantee who
will win then.

Either you should speak of a majority _voting_ the candidates in S
over all the other candidates, or else, when saying only that they
prefer the candidates in S to all the others, you should add the stipulation 
that they vote sincerely.

The latter wording is better, since then we don't have the embarrassment
of having to say "Don't apply this criterion to Plurality, because
if you do, Plurality will pass." I suspect, however, that when the
academic authors say "prefer", in criteria like that, they really
are talking about voted preferences rather than sincere preferences.
It would be better if people would say what they mean.

We've talked about this before here, in connection to Condorcet's
Criterion, which, as usually worded, no method passes. And if we
translate "prefer...to..." to "vote...over...", then Plurality passes
unless we specify that the criterion not be applied to Plurality,
as a way of keeping Plurality from passing.

You continued:

[...]

By the way: I believe that the strong opinion of some participants
on the "boring margins/winning-votes debate" (Rob LeGrand) is mainly
a relic from those times when only very few Condorcet methods
(e.g. MinMax method, Copeland method) were known to this mailing
list and when all of these Condorcet methods had serious problems.
In those times, it was necessary to put much weight in the
majoritarian argumentation to be able to justify the proposed
Condorcet method against the attacks e.g. of the IRV supporters.
However, the currently discussed Condorcet methods are so
sophisticated that it is not necessary anymore that the reader
agrees to a certain opinion of the "lesser-of-2-evils problem"
to see the beautifulness and the elegance e.g. of the Ranked Pairs
method or the beat path method.

I reply:

Speaking for myself, I prefer wv to Margins because of important
criteria that wv meets and which Margins fails. I, at least, consider
those criteria important because they're about plausible conditions
under which it's possible to guarantee that certain drastically
insincere strategies won't be needed.

Some might agree with me on that. Others prefer wv to Margins because
it fudamentally makes more sense to not avoidably violate voted
majority wishes. That's a good reason too.

But maybe to Blake & Rob L.G., other things are more important, and
no one can tell someone else what should be most important to them.

Beauty & elegance give voting systems appeal, but, by themselves, they
aren't enough, if we want the method to do, or not do, certain things.

Mike Ossipoff



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