Tactical Voting

Tactical voting (also called strategic voting or, in the UK, tactical voting) occurs when an elector does not vote sincerely for their first-choice candidate but instead supports a more viable alternative to influence the result. It is most pronounced under single-member plurality ("first-past-the-post") systems, where votes for trailing candidates are effectively wasted, but it also appears in two-round runoff, single transferable vote, and even proportional systems with electoral thresholds.

The theoretical foundation comes from Duverger's law (Maurice Duverger, 1951/1954), which argues that plurality rule tends to produce two-party competition partly because voters abandon third parties to avoid "splitting" the vote. Formal treatments by William Riker and others, and the Gibbard–Satterthwaite theorem (1973, 1975), show that essentially every non-dictatorial voting rule with three or more options is susceptible to strategic manipulation.

Common patterns include:

• Compromising: ranking or voting for a more electable second choice (e.g., a UK Liberal Democrat voter backing Labour to defeat a Conservative).
• Burying or push-over strategies in ranked or runoff systems.
• Coalition-directed voting in proportional systems, where supporters of a large party lend votes to a smaller coalition partner to keep it above the threshold — a recurring feature of German Bundestag elections, where FDP voters have sometimes been courted by CDU/CSU sympathisers.

Evidence of tactical voting is typically inferred from constituency-level swings, tactical voting websites (such as those active in the UK 2017, 2019, and 2024 general elections), and post-election surveys like the British Election Study. Estimates vary, but BES analyses have suggested that roughly a fifth to a third of UK voters consider tactical considerations in a given general election, though the share who actually switch is smaller. Critics argue tactical voting distorts mandates; defenders see it as a rational response to disproportional electoral rules.