Duverger's law

Duverger's law is a principle in political science, named after the French sociologist Maurice Duverger, which states that elections in which the candidate with the most votes in each district wins, as in the United Kingdom and the United States, tend to produce a two-party system. Duverger identified two mechanisms: a mechanical effect, by which small parties win fewer seats than their share of the vote, and a psychological effect, by which voters avoid wasting their votes on candidates unlikely to win and vote for one of the major parties instead. By contrast, proportional representation tends to allow several parties to survive. Some countries, such as Canada and India, show exceptions, because regional parties can win seats in particular areas.

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