Single-member plurality electoral systems tend to produce two-party competition.
Duverger's 1951 statement. Both mechanisms are mechanical and psychological: plurality rules waste third-party votes, and voters anticipating the waste stop casting them.
In practice
- Two smaller parties with overlapping platforms split a seat and hand it to the party a majority opposed, then merge before the next election.
- A committee election with three candidates for one post produces a winner nobody would have chosen in a run-off.
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- Law & Politics
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- What can be proved and measured about power