What’s a 2-party system?

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A two-party system is a form of government where two dominant parties hold office at all levels of politics. It is associated with plurality voting systems and third-party candidates can run for office. Third parties can play a spoiler role in elections. Maurice Duverger theorized that two-party systems are the natural result of nations electing officials with a majority vote on a single ballot.

A two-party system is a form of government in which two dominant parties hold office at all levels of politics, from regional to national. It should not be confused with the idea that voters only have the option of voting for one of two parties. As in the United States and many other countries, governments run by a two-party system often allow third-party candidates to run for any office if they can win enough votes from the two dominant parties. Two-party systems are a political phenomenon associated with plurality voting systems, where the candidate with the most votes wins political office. Duverger’s law theorizes that plurality voting systems have a high probability of resulting in two-party systems.

Many nations around the world have had two-party systems: Democrats are pitted against Republicans in the US, Conservatives against the Labor Party in the United Kingdom (UK), and the Democratic Party against the Liberal Democratic Party in Japan. Governments acting on the cooperation of more than two parties are called coalition governments. Coalition governments are often parliamentary in style. Some governments operating in a two-party system have the potential to move to a coalition government in the event of separate elections, such as with England following the 2010 election, which saw the Liberal Democrats and Conservative parties form a coalition.

It is difficult for third parties to destabilize a two-party system for multiple reasons. In some countries, voter loyalty, or perhaps equally powerful familiarity, with two dominant parties makes it difficult for lesser known and less established third parties to win effective numbers of votes. That doesn’t mean, however, that third parties don’t play an important role. Indeed, they play one of the most important roles in two-party politics: that of the spoiler. Even if a third party doesn’t win any elections, it has the potential to snatch some votes from one of the dominant parties, perhaps enough to influence the outcome of an election. In 1912, Teddy Roosevelt, a Progressive candidate in the United States, won nearly 28 percent of the popular vote, beating Republican candidate Taft’s 23 percent. With Taft’s votes severely weakened by Roosevelt, Democrat Woodrow Wilson won the presidency.

Maurice Duverger, French politician and sociologist, theorized that two-party systems are the natural result of nations electing their officials with a majority vote on a single ballot. He argued that parties with similar views would merge to avoid being overwhelmed by opposing parties, which would cause other parties with similar views to merge as well. Any third party, he thought, would rarely, if ever, stand a significant chance for majority rule given this phenomenon; the two-party system would only continue to strengthen. His views are commonly taught in political science.




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