First-past-the-post voting

First-past-the-post (FPTP)—also called choose-one, first-preference plurality (FPP), or simply plurality—is a single-winner voting rule. Voters mark one candidate as their favorite, or first-preference, and the candidate with more first-preference votes than any other candidate (a plurality) is elected, even if they do not have more than half of votes (a majority).

FPP has been used to elect part of the British House of Commons since the Middle Ages before spreading throughout the British Empire. Throughout the 20th century, many countries that previously used FPP have abandoned it in favor of other electoral systems, including the former British colonies of Australia and New Zealand. FPP is still officially used in the majority of US states for most elections. However, the combination of partisan primaries and a two-party system in these jurisdictions means that most American elections behave effectively like two-round systems, in which the first round chooses two main contenders (of which one of them goes on to receive a majority of votes).

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:

The preferences of each region's voters are:

In FPTP, only the first preferences matter. As such, the votes would be counted as 42% for Memphis, 26% for Nashville, 17% for Knoxville, and 15% for Chattanooga. Since Memphis has the most votes, it would win a FPTP election, even though it is far from the center of the state and a larger majority of voters would more strongly prefer Nashville than any other option. Conversely, instant-runoff voting would elect Knoxville, the easternmost city. This makes the election a center squeeze.

By contrast, both Condorcet methods and score voting would return Nashville (the capital of Tennessee).

Perhaps the most striking effect of FPP is the fact that the number of a party's seats in a legislature has little to do with its vote count in an election, only in how those votes were geographically distributed. Parties with few votes sometimes take more than few seats; often the most-popular party takes 20 percent more seats than its portion of the popular vote. Some criticize FPP for this, arguing that a fundamental requirement of an election system is to accurately represent the views of voters. FPP often creates "false majorities" by over-representing larger parties (giving a majority of the parliamentary/legislative seats to a party that did not receive a majority of the votes) while under-representing smaller ones.

In Canada, majority governments have been formed often but usually they are made up of a party that received less than a majority of votes in the election. A party forming a majority government and also winning a majority of the votes cast has happened only six times since 1900: 1900; 1904; 1917; 1940, 1958 and 1984.