# [EM] Which method isn't "vulnerable to compromise"?

Markus Schulze markus.schulze at alumni.tu-berlin.de
Sun Apr 11 03:14:06 PDT 2004

```Dear Mike,

please remember that already in my 8 Sep 2003 mail I told you
that at least every single-winner election method that satisfies
the majority criterion is vulnerable to compromising. I wrote
(8 Sep 2003):

> Actually, it can be shown that at least every
> election method that satisfies the majority
> criterion encourages voters to compromise.
>
> Example:
>
>    40 A > B > C.
>    35 B > C > A.
>    25 C > A > B.
>
>    Suppose that the used election method meets the majority
>    criterion.
>
>    Suppose that A wins the elections. Then the 35 BCA
>    voters can change the winner from A to C by voting CBA
>    (i.e. by "compromising").
>
>    Suppose that B wins the elections. Then the 25 CAB
>    voters can change the winner from B to A by voting ACB
>    (i.e. by "compromising").
>
>    Suppose that C wins the elections. Then the 40 ABC
>    voters can change the winner from C to B by voting BAC
>    (i.e. by "compromising").

Markus Schulze

```