Erik Moberg ã:
A Theory of Democratic Politics
5.1 - MAJORITARIAN ELECTIONS
The plurality method, also called the first-past-the-post method, is used when the problem is to elect one member from each constituency, and it is the simplest method serving that purpose. The candidate which gets most votes, that is a plurality, wins. If for example candidate A gets 20 000 votes, candidate B 15 000 votes, candidate C 15 000 votes and candidate D 25 000 votes, then candidate D wins.
The method has been criticized on the ground that a candidate who in reality enjoys only quite a weak support may be elected. Suppose, for instance, that all people who support A, or B, or C in the example above prefer anyone of these candidates to D. If so A, or B, or C would get 50 000 votes if put alone in a contest against D, who still would get just 25 0000 votes. D:s winning in the original example is thus, in a sense, due to the opposition's division.
Several methods have been designed in order to mitigate this problem and the double ballot method is one of them. As the name indicates the method stipulates the use of two ballots separated by some time, for example a week. If some candidate gets an absolute majority in the first ballot, then that candidate is elected. Otherwise there will be a second ballot, and in that second ballot plurality is enough for winning.
Illustrating with the same example as above, and assuming that the figures represent the result of the first ballot, we see that none of the four candidates A, B, C and D has an absolute majority. Therefore there will be a second ballot. What happens there is, however, impossible to predict without further assumptions. We may for example assume that the candidates B and C are politically rather close to each other, that both are somewhat distant from A, and that both are very hostile towards D. If so B and C may make the agreement that C shall withdraw from the second ballot and urge its supporters in the first ballot to vote for B in the second ballot. If they succeed with that A will get 20 000 votes in the second ballot, B 30 000 votes and D 25 000 votes. B thus gets a plurality and wins. There is a variant of the method, it should be mentioned, in which the second ballot is restricted to the two candidates with the highest number of votes in the first ballot, and thus it is ensured that the final winner gets an absolute majority of the votes.
It is important to note that neither the plurality method, nor the double ballot method, presupposes any political parties. The candidates may be supported by, or even appointed by, parties, but they may, also, be free, independent individuals who, on their own, decide to compete. The methods work perfectly well in both cases.