First-Past-the-Post in Single-Member Districts

Under first-past-the-post, a country is carved into single-member districts, each electing exactly one legislator. Voters pick one candidate, and whoever gets the most votes wins the seat, no runoff, no majority required. If four candidates split a district 34, 31, 22, and 13 percent, the candidate with 34 percent takes the seat outright. Every vote cast for the other three candidates elects nobody. That is the whole mechanism: winner takes all, loser's votes vanish, and there is no mechanism to carry support over to the next district or into the national chamber.

Run this across hundreds of districts and the distortions compound. A party can win a bare plurality in district after district and rack up a huge share of seats while its national vote share sits far lower. In the 2024 British general election, Labour took just 33.7 percent of the national vote but won 411 of 650 House of Commons seats, about 63 percent of the chamber, because it finished first in district after district even where its local margins were thin. A seat majority is a count of districts won, not a tally of total voter support, so it can wildly outpace the party's actual backing.

This sets up the rest of the unit's comparison. Proportional representation systems award seats to match national vote share, which is exactly what first-past-the-post refuses to do. A small party whose support is spread evenly, say 10 percent everywhere, can win zero seats under first-past-the-post because it never finishes first anywhere, even though under proportional rules that same 10 percent would buy it real representation.