First past the post

The mechanism is about as simple as electoral rules get. A constituency returns one member. Each voter marks one candidate. The candidate with more votes than any other wins — not a majority, just a plurality. There is no threshold, no runoff, no quota. If five candidates split a vote 31–25–22–14–8, the first candidate takes the seat with fewer than a third of the ballots cast. The others are gone.

The name is a horse-racing metaphor: the winner passes a post nobody else has yet reached. It is also slightly misleading, because there is no post — no fixed number to reach. The winner's vote share is determined only after the fact, by whoever turned up. Political scientists more precisely call this single-member plurality, or SMP, and that label captures both the structural feature (one seat per district) and the decision rule (a plurality suffices).

The system is used, in broadly comparable form, in the United Kingdom, Canada, India, and the United States for its House of Representatives. Each jurisdiction inherited the mechanism from British parliamentary practice and, with varying degrees of debate, has kept it.

The most documented consequence is the manufacture of majorities. A party that wins many constituencies by modest margins and loses others heavily can convert a nationwide vote share in the thirties or forties into a parliamentary majority well above half. The phenomenon arises because plurality victories in individual districts are binary — you win the seat or you don't — and surplus votes beyond a simple plurality transfer nothing to anyone. A party that piles up large wins in safe seats is, in a sense, wasting votes it did not need, while a party that wins narrowly across a broad range of seats extracts maximum seat-yield from minimum vote-margins.

The systematic relationship between vote shares and seat shares was captured by the so-called cube rule, an empirical observation made by British scholars in the mid-twentieth century: if two parties split the national vote in ratio A:B, their seats tend to split roughly A³:B³. In practice the exponent varies by election, but the directional claim holds — the leading party is consistently rewarded with a seat bonus disproportionate to its vote lead. Later work refined this into what is sometimes called the seats-votes curve, but the core finding is stable: plurality systems amplify the gap between first and second place.

The second well-documented consequence is the squeeze on smaller parties. A voter who prefers a minor party faces a calculation: if that party cannot win locally, a vote for it might — depending on one's framing — be a vote that helps the least-preferred major-party candidate by denying support to the preferred major-party one. This is the logic of tactical voting, and it operates as constant pressure toward a two-party system. Duverger's law — the political scientist Maurice Duverger's mid-century observation — holds that plurality systems in single-member districts tend over time toward exactly two parties, because voters and donors alike desert parties that cannot win seats. The mechanism is not inexorable: regional parties can thrive by concentrating support geographically, winning pluralities in a defined area even with a low national vote share. But parties spread thinly across the country, with support that is wide and shallow, are efficiently punished.

The third consequence is the volume of votes that elect nobody. Every ballot cast for a losing candidate in any district contributes nothing to any outcome. Every ballot cast for a winning candidate beyond the number needed to beat the nearest rival is similarly inert — those votes were not needed to secure the seat. Both categories are sometimes lumped under the term "wasted votes", though the phrase is contested: the losing votes demonstrate preference even if they produce no seat, and the excess winning votes at least contributed to a margin that deterred a recount challenge. Still, the arithmetic of how many ballots are cast in aggregate for candidates who don't win, or beyond what winners needed, is genuinely large in most plurality elections — commonly more than half of all votes cast.

Because a single-member plurality system turns geography into representation, where the district boundaries fall matters enormously. The same votes, redistricted differently, can produce a different parliamentary majority. This structural sensitivity to boundary-drawing means that the process of packing and cracking — concentrating opposing voters into a few unwinnable seats, or diluting them across many — is capable of manufacturing a durable seat advantage with no change in underlying voter preferences at all. It also means that malapportionment, districts of unequal population, compounds plurality's existing tendency toward disproportionality.

Defenders of the system point to a different register of consequences: government stability and accountability. Because manufactured majorities are common, single-party majority governments are common too, and single-party governments are easier to hold responsible at the next election than coalition governments negotiated after the count. The voter who is dissatisfied knows precisely which party to remove. The system also tends to produce strong local links: each member represents a defined territory and a defined set of constituents, and constituency work — surgery, casework, local advocacy — is a standard part of the job in systems where it operates.

These are real arguments about real effects, though they sit in tension with each other. A system that routinely produces governments commanding a parliamentary majority without a popular majority is not straightforwardly easy to evaluate on democratic grounds alone. It produces stable governments, and it produces governments that may govern contrary to the preferences of more than half the electorate. Whether the first outweighs the second is a question electoral designers have answered differently across different constitutional moments.

What is not genuinely disputed is the mechanism itself. A plurality in each district. One seat per district. The votes that don't make up a plurality, gone. The rest — manufactured majorities, the two-party squeeze, the wasted-vote total — follows from the arithmetic with considerable regularity.