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politicsanalysisThe Conversation (US)
America’s 2-party system seems weird, but adding a 3rd party could make voter representation worse
The United States has two dominant parties mainly because of how it counts votes. Each district elects one representative, and whoever gets the most votes wins, so voting for a party with no chance of winning wastes a vote and discourages third parties. Proportional systems, used in most other democracies, award seats roughly in line with vote share, which supports many parties. A political scientist argues the two US parties are 'umbrella' coalitions: Pew identifies nine ideological voter types that in another country might form separate parties. On that view, two big tents can represent voters about as well as the multiparty systems of Canada or the UK, which use the same winner-take-all rule and whose extra parties can distort representation.
With one seat per district, a candidate needs only a plurality. Voters fear 'splitting' their side's vote, so they back whichever of the two leading candidates is closer to them, and smaller parties rarely win seats.
Counting rules shape how many choices voters have. Critics see the US system as limiting; this view says the major parties already contain many factions, so a third party might not improve representation.
Political scientists call the tendency of single-winner plurality elections to produce two parties 'Duverger's law', after the French scholar Maurice Duverger. Countries with the same system, like Canada and the UK, have still developed additional regional parties, so the pattern is a tendency rather than a rule.
background
A two-party system is a political party system in which two major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term is used to refer to one of two kinds of party systems. Both result from Duverger's law, which demonstrates that "winner-take-all" or "first-past-the-post" elections produce two dominant parties over time.
From Wikipedia: Two-party system (CC BY-SA 4.0) ↗ · text CC BY-SA 4.0The Conversation
