[EM] ironclad pro-Condorcet argument?

Adam Tarr atarr at purdue.edu
Mon Aug 23 15:04:57 PDT 2004

At 05:37 PM 8/23/2004 -0400, Warren Schudy wrote:

>On Mon, 23 Aug 2004, James Green-Armytage wrote:
> >       If there is a Condorcet winner with regard to the sincere preference
> > rankings of voters, and the voting method is plurality, then the Vote is
> > only at equilibrium when the Condorcet winner is selected.
> > changing their vote.
>Your argument implicitly relies on the assumption that half the population
>can coordinate a change their votes, which is very difficult, especially
>with secret balloting.

Not necessarily.  Don't consider whether or not the votes actually 
change.  Just imagine that post-election, everyone's true preferences are 
known.  If a CW exists, then only that candidate winning will not cause 
anyone to regret their vote.  By regret their vote, I mean that they will 
think "If only I, and like-minded individuals, had voted differently, we 
would have gotten a better outcome".

So, it's not the actual act of group action that we're depending on, just 
group regret.

James, this argument has been advanced before.  Look up Nash Equilibria in 
the archives.


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