[EM] Condorcet Criterion for plurality.

[Markus Schulze]

Dear Mike,

you wrote (14 Dec 2000):
> Markus wrote (14 Dec 2000):
> > Mike wrote (13 Dec 2000):
> > > Markus wrote (13 Dec 2000):
> > > > The intention of IIAC is to guarantee that the result of
> > > > the elections cannot be manipulated by running additional
> > > > candidates who change the result of the elections without
> > > > being elected. But you define IIAC is such a manner that
> > > > even plurality --which is highly vulnerable to this strategy--
> > > > meets this criterion. Therefore your definition of IIAC has
> > > > nothing to do with the original intention of this criterion.
> > > > Therefore --and this is what Blake is saying-- you have to
> > > > present an additional justification for your definition of
> > > > IIAC. And in so far as you are unwilling or unable to
> > > > justify your definition of IIAC, the usefulness of your
> > > > "universally accepted" concept is questionable.
> > >
> > > Justify IIAC? I've repeatedly said that IIAC doesn't mean
> > > anything to me. Its importance derives entirely from the fact
> > > that lots of people, including IRVies, keep bringing it up.
> > > That's great when they do that, since the only complete IIAC
> > > definition that I've heard of says that Approval is better than
> > > IRV and that even Plurality is better than IRV. Obviously there
> > > are many reasons why those methods are better than IRV, but when
> > > the IRVies' own citation of Arrow counts against IRV, that makes
> > > IIAC useful. _That's_ my justification of IIAC. Maybe Arrow's
> > > own definition of IIAC is different from mine. Maybe it's
> > > justified in some way that mine isn't. Fine. I don't care.
> >
> > Of course, when you define IIAC in such a manner that IIAC has
> > nothing to do with the original intention of this criterion,
> > then --unless you can give an additional explanation why your
> > IIAC should be desirable-- the observation that plurality
> > meets your IIAC is quite meaningless. The usefulness of your
> > "universally accepted" concept is questionable, when you cannot
> > explain why the resulting criteria describe desirable properties. 
>
> Markus, you're being a fruitcake. I didn't say that IIAC is desirable.
> I said that it doesn't mean anything to me. That means too that I
> don't claim that it should mean anything to you. So why do you want
> me to give an explanation for why it should be desirable? This is
> plailn repetition of an argument that I've already answered in my
> previous message. Are you taking lessons from Don Davison? I admit
> & assert that I cannot explain why IIAC is desirable. My definition
> isn't.

Could you please explain why you believe that there could possibly be
someone who might consider the fact that plurality meets your IIAC and
IRV violates your IIAC to be meaningful? Or is your argumentation
completely arbitrary?

You wrote (14 Dec 2000):
> So, as I said, then, what's questionable is why you think that the
> fact that I can't explain the desirability of a criterion that I say
> is not really desirable has anything to do with the validity of "my"
> "concept" that Plurality doesn't collect or use rankings.

Plurality met your IIAC only when it couldn't be defined on
preferential ballots. When plurality is defined on preferential
ballots, then plurality violates your IIAC. Therefore your
"universally accepted" concept that plurality couldn't be defined
on preferential ballots is a necessary presumption of your
argumentation that as plurality met your IIAC and IRV violated
your IIAC plurality was better than IRV.

Markus Schulze