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Two-party system
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Two-party system

A two-party system is a type of party system where only two political parties have a realistic chance of winning an election. Usually this means that all, or nearly all, elected offices are held only by the candidates of the two highest vote-getting parties. Coalition governments are rare in two party systems, though each party may internally look like a coalition.

Table of contents
1 Why it occurs
2 Examples
3 Arguments for and against
4 External links

Why it occurs

Two-party systems naturally get installed when the voting system used for elections discriminates against third or smaller parties, because the number of votes received for a party in a whole country is not directly proportional to the number of seats it receives in the country's assembly/assemblies. The most widely used system which has this effect is a simple plurality system (First past the post). Some representation systems such as a single elected president or mayor dominating the government, may encourage two-party systems since ultimately the contest will be between the two most popular candidates.

When candidates are elected from constituencies (districts), all votes that are not for the winner are discounted. This is another factor that encourages a two party system because smaller parties often cannot win all the votes in a constituency because they have smaller support and sometimes more scattered support than larger parties. Often a first-past-the-post electoral system and candidates being elected from constituencies (districts) are combined; this means that some smaller parties can have a significant proportional of votes nationally, but receive few seats and cannot realistically expect to compete with larger parties.

In countries that use proportional representation (PR), especially where the whole country is one constituency, like Israel, the electoral rules discourage a two party system; the number of votes received for a party is directly proportional to the number of votes received and new parties can develop an electoral niche. Duverger identified that the use of proportional representation would make a two party system less likely.

Often, two-party systems are consequences of various factors, mostly the use of first-past-the-post, rather than deliberately engineered. They tend to favor two major political parties, as recognized in Duverger's law.


Such systems have evolved in the United States and United Kingdom, as well as in many small or newly independent countries such as Jamaica. While Americans and citizens of the UK often see the two-party system as natural, based on their long experiences with it, it is in fact a product of the particular rules in place. The two parties that dominate thus have an incentive to keep the rules as they are, so as to prevent electoral losses to smaller parties.

Arguments for and against

The two-party system's defenders argue that Against the argument that the two-party system leads to more stable governance, critics of the two-party system argue variously that: The two-party system is also criticised for the following flaws: The electoral systems which tend to favour two-party systems (notably the "biggest pile of votes wins" system) are also criticised because: See also: Duopoly

External links