[EM] Criteria that don't mention preferences?

[Markus Schulze]

Dear Mike,

in so far as election methods are defined only on the cast
preferences and not on the sincere preferences, whether a
given election method satisfies a given criterion must be
reflected in the way this method uses the cast preferences.
Therefore, there is no need to include the sincere
preferences in the definition of a criterion.

You wrote (2 Feb 2004):

> It isn't entirely clear what you mean. For example, some of
> us would like to require a method to not give voters defensive
> strategic need to bury their favorite, at least under conditions
> under which there are methods that won't do that.  Are you saying
> that that requirement can be made by a motivational statement
> instead of by the criteriion.

For example, Steve Eppley uses the following formulation
in his website:

> minimal defense: If more than half of the voters prefer
>   alternative y over alternative x, then that majority must have
>   some way of voting that ensures x will not be elected and
>   does not require any of them to rank y equal to or over any
>   alternatives preferred over y. (Another wording is nearly
>   equivalent: Any ordering of the alternatives must be an
>   admissible vote, and if more than half of the voters rank y
>   over x and x no higher than tied for bottom, then x must not
>   be elected. This criterion, in particular the first wording,
>   is promoted by Mike Ossipoff under the name Strong Defensive
>   Strategy Criterion. Satisfaction means a majority can defeat
>   "greater evil" alternatives without having to pretend to prefer
>   some compromise alternative as much as or more than favored
>   alternatives.  Since voters in public elections cannot be
>   relied upon to misrepresent their preferences in this way,
>   non-satisfaction means that elites will sharply limit the
>   set of nominees that voters are asked to vote on, by offering a
>   system in which there are only two viable parties, each of which
>   nominates only one alternative.)

I would call

   "If more than half of the voters prefer alternative y over
   alternative x, then that majority must have some way of voting
   that ensures x will not be elected and does not require any of
   them to rank y equal to or over any alternatives preferred over y."

the "motivation" of this criterion and

    "Any ordering of the alternatives must be an admissible vote,
    and if more than half of the voters rank y over x and x no higher
    than tied for bottom, then x must not be elected."

the "definition" of this criterion.

The _motivation_ refers to the sincere preferences and explains why this
criterion is desirable. The _definition_ is formulated in such a manner
that it is possible to prove whether a given election method satisfies
this criterion without having to know its motivation.

Markus Schulze