It has been suggested that this article should be split into articles titled First past the post and Plurality (voting). (discuss) (May 2024)

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Plurality voting refers to electoral systems in which the candidate in an electoral district who poll more than any other (that is, receive a plurality) are elected.^[1]

Under single-winner plurality voting, and in systems based on single-member districts, plurality voting is called single member plurality (SMP),^[2][3] which is widely known as "first-past-the-post". In SMP/FPTP the leading candidate, whether or not they have a majority of votes, is elected.^[4]

There are several versions of plurality voting for multi-member district.^[5] The system that elects multiple winners at once with the plurality rule and where each voter casts multiple X votes in a multi-seat district is referred to as plurality block voting. A semi-proportional system that elects multiple winners elected at once with the plurality rule and where each voter casts just one vote in a multi-seat district is known as single non-transferable voting.

Plurality voting is widely used throughout the English-speaking world as a result of its spread by the British Empire, including in most of the United States. Outside of the English-speaking world, it is slightly less popular than its close relatives, the runoff family of methods.^{[citation needed]}

Social choice theorists and electoral reform advocates generally oppose plurality voting and its variants, citing major issues such as a high vulnerability to spoilers, a tendency towards duopoly and lesser of two evils voting, and their bias toward extremist candidates (as a result of failing the median voter theorem).

Plurality voting procedures

Single-winner and single-member systems

In single-winner plurality voting (first-past-the-post), each voter is allowed to vote for only one candidate, and the winner of the election is the candidate who represents a plurality of voters or, in other words, received more votes than any other candidate. In an election for a single seat, such as for president in a presidential system, voters may vote for one candidate from a list of the candidates who are competing, and the winner is whichever candidate receives the highest number of votes. Compare first-past-the-post to a majority system, the two-round system, where usually the top two candidates in the first ballot progress to the second round, also called the runoff. A runoff is by default not held, if a candidate already received an absolute majority in the first ballot (more than half of votes), and in the second ballot, where there are only two candidates, one of the candidates will (except for a tie) receive a majority. Under plurality rules, the candidates are not at any point in the election required to have majority support.

In an election for a legislative body with single-member seats, each voter in a geographically defined electoral district may vote for one candidate from a list of the candidates who are competing to represent that district. Under the plurality system, the winner of the election then becomes the representative of the whole electoral district and serves with representatives of other electoral districts. That makes plurality voting among the simplest of all electoral systems for voters and vote counting officials;^[4] however, the drawing of district boundary lines can be contentious in the plurality system (see gerrymandering). The system is also independent of parties; the party with the most votes may not win the most seats (electoral inversion). Note that issues arising from single-member districts are still in place with majority voting systems, like the two-round system and instant-runoff voting too.

The same principle used in single-winner plurality voting (electing the candidate with the most votes) is also used in approval voting, however with very different effects, as voters can choose to support as many or few candidates as they choose, not just one. For this reason, approval voting is usually distinguished from plurality voting, while technically being a sub-type of it.

Multi-winner systems

Multi-member plurality elections are only slightly more complicated. The n candidates who get more votes than the others are elected.^[6] In a multiple-member plurality election with n seats available, the winners are the n candidates with the highest numbers of votes. The rules may allow the voter to vote for one candidate, up to n candidate, or some other number.

When voters may vote for only one candidate, it is called the single non-transferable vote. While seemingly most similar to first-past-the-post, in effect it is a semi-proportional system allowing for representation of electoral minorities within a district. When voters can vote for one or more candidates, but in total less than the number of winners, it is called limited voting.

The multi-winner version considered to be the extension of first-past-the-post to multi-winner cases is plurality block voting. Here voters may vote for as many candidates as there are winners, which means usually candidates from the same party will fill all the seats in the district. The party-list version of plurality voting in multi-member districts is called party block voting. Here the party receiving a plurality of votes gets all of the seats available by default.

Ballot types

Generally, plurality ballots can be categorized into two forms. The simplest form is a blank ballot in which the name of a candidate(s) is written in by hand. A more structured ballot will list all the candidates and allow a mark to be made next to the name of a single candidate (or more than one, in some cases); however, a structured ballot can also include space for a write-in candidate.

Examples

Single-winner

This is a general example for single-winner plurality voting ("first-past-the-post"), using population percentages taken from one state for illustrative purposes.

Suppose that Tennessee is holding an election on the location of its capital. The population is concentrated around four major cities. All voters want the capital to be as close to them as possible. The options are:

• Memphis, the largest city, but far from the others (42% of voters)
• Nashville, near the center of the state (26% of voters)
• Chattanooga, somewhat east (15% of voters)
• Knoxville, far to the northeast (17% of voters)

The preferences of each region's voters are:

If each voter in each city naively selects one city on the ballot (Memphis voters select Memphis, Nashville voters select Nashville, and so on), Memphis will be selected, as it has the most votes 42%. The system does not require that the winner have a majority, only a plurality. Memphis wins because it has the most votes even though 58% of the voters in the example preferred Memphis least. That problem does not arise with the two-round system in which Nashville would have won. (In practice, with FPTP, many voters in Chattanooga and Knoxville are likely to vote tactically for Nashville: see below.)

Multi-winner

Candidates are running in a 3-member district of 10 000 voters. Under non-transferable (and non-cumulative) plurality voting, voters may not cast a more than one vote for a single candidate.

• Under block voting, the standard multiple non-transferable vote, voters may cast 3 votes (but do not have to)
• Under limited voting, voters may cast 2 votes maximum
• Under the single non-transferable vote, voters may cast 1 vote

Party A has about 35% support among the electorate (with one particularly well-liked candidate), Party B around 25% (with two well-liked candidates) and the remaining voters primarily support independent candidates, but mostly lean towards party B if they have to choose between the two parties. All voters vote sincerely; there is no tactical voting. (Percentage of votes under MNTV and Limited Voting is the percentage of voters who voted for the candidate, not the percentage of votes cast.)