Editing Condorcet method (section)

==Circular ambiguities==
{{Unreferenced section|date=March 2021}}
As noted above, sometimes an election has no Condorcet winner because there is no candidate who is preferred by voters to all other candidates. When this occurs the situation is known as a 'Condorcet cycle', 'majority rule cycle', 'circular ambiguity', 'circular tie', 'Condorcet paradox', or simply a 'cycle'. This situation emerges when, once all votes have been tallied, the preferences of voters with respect to some candidates form a circle in which every candidate is beaten by at least one other candidate ([[Intransitivity#Cycles|Intransitivity]]).

For example, if there are three candidates, [[Rock-paper-scissors|Candidate Rock, Candidate Scissors, and Candidate Paper]], there will be no Condorcet winner if voters prefer Candidate Rock over Candidate Scissors and Scissors over Paper, but also Candidate Paper over Rock. Depending on the context in which elections are held, circular ambiguities may or may not be common, but there is no known case of a governmental election with ranked-choice voting in which a circular ambiguity is evident from the record of ranked ballots. Nonetheless a cycle is always possible, and so every Condorcet method should be capable of determining a winner when this contingency occurs. A mechanism for resolving an ambiguity is known as ambiguity resolution, cycle resolution method, or ''Condorcet completion method''.

Circular ambiguities arise as a result of the [[voting paradox]]—the result of an election can be intransitive (forming a cycle) even though all individual voters expressed a transitive preference. In a Condorcet election it is impossible for the preferences of a single voter to be cyclical, because a voter must rank all candidates in order, from top-choice to bottom-choice, and can only rank each candidate once, but the paradox of voting means that it is still possible for a circular ambiguity in voter tallies to emerge.

The idealized notion of a [[political spectrum]] is often used to describe political candidates and policies. Where this kind of spectrum exists, and voters prefer candidates who are closest to their own position on the spectrum, there is a Condorcet winner ([[Single peaked preferences|Black's Single-Peakedness Theorem]]).

In Condorcet methods, as in most electoral systems, there is also the possibility of an ordinary tie. This occurs when two or more candidates tie with each other but defeat every other candidate. As in other systems this can be resolved by a random method such as the drawing of lots. Ties can also be settled through other methods like seeing which of the tied winners had the most first choice votes, but this and some other non-random methods may re-introduce a degree of tactical voting, especially if voters know the race will be close.

The method used to resolve circular ambiguities is the main difference between the various Condorcet methods. There are countless ways in which this can be done, but every Condorcet method involves ignoring the majorities expressed by voters in at least some pairwise matchings. Some cycle resolution methods are Smith-efficient, meaning that they pass the [[Smith criterion]]. This guarantees that when there is a cycle (and no pairwise ties), only the candidates in the cycle can win, and that if there is a [[mutual majority criterion|mutual majority]], one of their preferred candidates will win.

Condorcet methods fit within two categories:

* Two-method systems, which use a separate method to handle cases in which there is no Condorcet winner
* One-method systems, which use a single method that, without any special handling, always identifies the winner to be the Condorcet winner

Many one-method systems and some two-method systems will give the same result as each other if there are fewer than 4 candidates in the circular tie, and all voters separately rank at least two of those candidates. These include Smith-Minimax (Minimax but done only after all candidates not in the Smith set are eliminated), Ranked Pairs, and Schulze. For example, with three candidates in the Smith set in a Condorcet cycle, because Schulze and Ranked Pairs pass [[Independence of Smith-dominated alternatives|ISDA]], all candidates not in the Smith set can be eliminated first, and then for Schulze, dropping the weakest defeat of the three allows the candidate who had that weakest defeat to be the only candidate who can beat or tie all other candidates, while with Ranked Pairs, once the first two strongest defeats are locked in, the weakest cannot, since it'd create a cycle, and so the candidate with the weakest defeat will have no defeats locked in against them).