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Condorcet

From iA wiki

See also Enlightenment | Democracy

Pronounce: co-dor-sa (the first "o" is nasal; the "a" is long and pronounced)

Marie-Jean-Antoine-Nicolas de Condorcet aka Marquis de Condorcet (1745-1794) was a French philosopher in the age of Enlightenment (18th century). He developed various theories, particulary on voting issues and social choice.

Contents

Voting issues

Condorcet suggested a criterion which is considered more democratic than our current election model of which plurality is the most common election model currently implemented by democratic (considered) countries in which voting is based on criteria like "the best of 2 evils", "first and only choice", "strategic voting" which are fallacies or dishonest voting behaviour.

In short, every voter is able to vote on every option he/she wishes to in an order of preference. Note that in most implementations one is able to state non-preference on one or several options. The counting can be described as a "virtual round robin", that is information gets extracted about which option would win if only 2 options were running. The outcomes of all possible duels are checked. If one option wins every duel, that option is the "Condorcet Winner".

Always selecting the Condorcet Winner if one exists is called the "Condorcet Criterion". An option that wins every duel exists in most cases. Given that in those cases removing losing options from the ballot does not change which option wins every duel, satisfying the Condorcet Criterion goes a long way in reducing the problem of spoilers.

Condorcet schemes

If one candidate is preferred over each of the other candidates, that candidate is the "Condorcet winner". Sometimes there is no Condorcet winner. Various schemes exist to solve this problem.

  • MinMax
  • Schulze method
  • Ranked Pairs (RP)

Voting criteria

The Schulze method is the only election method currently known which matches the following criteria:

  • Condorcet Criterion (CC)
  • Generalized Condorcet Criterion (GCC)
  • Strategy-Free Criterion (SFC)
  • Generalized Strategy-Free Criterion (GSFC)
  • Strong Defensive Strategy Criterion (SDSC)

Additionaly, it also matches criteria also matched by other election methods:

  • Monotonicity Criterion (MC)
  • Weak Defensive Strategy Criterion (WDSC)
  • Summability Criterion (SC)

It does however not match

  • Favorite Betrayal Criterion (FBC)
  • Participation Criterion (PC)

Plurality only matches the Monotonicity Criterion (MC), the Participation Criterion (PC), and the Summability Criterion (SC). IRV, an election method currently popular at reformers and used by the Australian government, doesn't match any of the above criteria.

Condorcet implementations

The Debian project uses the Schulze method. Theoretically, collectives and anarchists would prefer consensus because 1 opinion is formed after arguing and discussion. Consensus is however not scalable. Implementation of the condorcet election method by anarchists, collectives are unknown to my best knowledge.

Related

Software