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A two-party system is a system where two major political parties dominate voting in nearly all elections at every level of government and, as a result, all or nearly all elected offices are members of one of the two major parties. Under a two-party system, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority party while the other is the minority party. While the term two-party system is somewhat imprecise and has been used in different countries to mean different things, there is considerable agreement that a system is considered to be of a two-party nature when election results show consistently that all or nearly all elected officials only belong to one of the two major parties, such as in the United States. This can lead to nondemocratic measures that reduce ballot access for other parties. In these cases, the chances for third party candidates winning election to any office are remote, although it's possible for groups within the larger parties, or in opposition to one or both of them, to exert influence on the two major parties.
There is strong agreement that the United States has a two-party system; historically, there have been few instances in which third party candidates won an election. In countries such as Britain and Spain, two major parties emerge which have strong influence and tend to elect most of the candidates, but a multitude of lesser parties exist with varying degrees of influence, and sometimes these lesser parties are able to elect officials who participate in the legislature. A report in the Christian Science Monitor, for example, suggested that Spain was moving towards a "greater two-party system" while acknowledging that Spain has "many small parties." In political systems based on the Westminster system, which is a particular style of parliamentary democracy based on the British model and found in many commonwealth countries, a majority party will form the government and the minority party will form the opposition, and coalitions of lesser parties are possible; in the rare circumstance in which neither party is the majority, a hung parliament arises. Sometimes these systems are described as two-party systems but they are usually referred to as multi-party systems. There is not always a sharp boundary between a two-party system and a multi-party system.
Generally, a two-party system becomes a dichotomous division of the political spectrum with an ostensibly right-wing and left-wing party: Nationalist Party vs. Labour Party in Malta, Liberal vs. Labor in Australia, Republicans vs. Democrats in the United States and the Conservative Party vs. the Labour Party in the United Kingdom.
Examples of countries with two-party systems include the United States, Jamaica and Malta. Other parties in these countries may have seen candidates elected to local or subnational office, however. Historian John Hicks claims that the United States has never possessed for any considerable period of time the two party system in its pure and undefiled form.
In some governments, certain chambers may resemble a two-party system and others a multi-party system. For example, the politics of Australia are largely two-party (if the Liberal Party and National Party are considered the same party at a national level due to their long-standing alliance) for the Australian House of Representatives, which is elected by Instant Runoff Voting, (known within Australia as preferential voting). However, third parties are more common in the Australian Senate, which uses a proportional voting system more amenable to minor parties.
India too is showing characteristics of two party system with United Progressive Alliance (UPA) and National Democratic Alliance (NDA) as the two main players. It is to be noted that both UPA and NDA are not two political parties but alliances of several smaller parties. Other smaller parties not aligned with either NDA or UPA exist.
The Politics of Malta are somewhat unusual in that while the electoral system is single transferable vote (STV), traditionally associated with proportional representation, minor parties have not earned much success. No third parties won any seats in the Parliament in Malta's most recent election, for example. The Labour Party and the Nationalist Party are the dominant parties. This is not the most common party system.
Comparisons with other party systems 
Two-party systems can be compared with:
- Multi-party systems. In these, the effective number of parties is greater than two but usually fewer than five; in a two-party system, the effective number of parties is two (according to one analysis, the actual average number of parties varies between 1.7 and 2.1.) The parties in a multi-party system can control government separately or as a coalition; in a two-party system, however, coalition governments rarely form. Examples of nations with multi-party systems include Brazil, Canada, Denmark, Finland, France, Germany, India, Indonesia, Ireland, Israel, Italy, Mexico, the Netherlands, New Zealand, Norway, Portugal, Sweden, and Taiwan.
- Single-party systems or dominant-party systems happen in nations where opposing parties are outlawed or restricted by the dominant party which wields power. Examples include rule by the Communist party of China, United Russia, and the People's Action Party of Singapore.
There are several reasons why, in some systems, two major parties dominate the political landscape. There has been speculation that a two-party system arose in the United States from early political battling between the federalists and anti-federalists in the first few decades after the ratification of the Constitution, according to several views. In addition, there has been more speculation that the winner-takes-all electoral system as well as particular state and federal laws regarding voting procedures helped to cause a two-party system.
Political scientists such as Maurice Duverger and William H. Riker claim that there are strong correlations between voting rules and type of party system. Jeffrey D. Sachs agreed that there was a link between voting arrangements and the effective number of parties. Sachs explained how the First Past The Post voting arrangement tended to promote a two-party system:
The main reason for America's majoritarian character is the electoral system for Congress. Members of Congress are elected in single-member districts according to the "first-past-the-post" (FPTP) principle, meaning that the candidate with the plurality of votes is the winner of the congressional seat. The losing party or parties win no representation at all. The first-past-the-post election tends to produce a small number of major parties, perhaps just two, a principle known in political science as Duverger's Law. Smaller parties are trampled in first-past-the-post elections.—Sachs, The Price of Civilization, 2011
Consider a system in which voters can vote for any candidate from any one of many parties. Suppose further that if a party gets 15% of votes, then that party will win 15% of the seats in the legislature. This is termed proportional representation or more accurately as party-proportional representation. Political scientists speculate that proportional representation leads logically to multi-party systems, since it allows new parties to build a niche in the legislature:
Because even a minor party may still obtain at least a few seats in the legislature, smaller parties have a greater incentive to organize under such electoral systems than they do in the United States.—Schmidt, Shelley, Bardes (2008), 
In contrast, a voting system that allows only a single winner for each possible legislative seat is sometimes termed a plurality voting system or single-winner voting system and is usually described under the heading of a winner–takes–all arrangement. Each voter can cast a single vote for any candidate within any given legislative district, but the candidate with the most votes wins the seat, although variants, such as requiring a majority, are sometimes used. What happens is that in a general election, a party that consistently comes in third in every district is unlikely to win any legislative seats even if there is a significant proportion of the electorate favoring its positions. This arrangement strongly favors large and well–organized political parties that are able to appeal to voters in many districts and hence win many seats, and discourages smaller or regional parties. Politically oriented people consider their only realistic way to capture political power is to be either a Republican or Democrat.
In the U.S., forty-eight states have a standard winner-takes-all electoral system for amassing presidential votes in the Electoral College system. The winner–takes–all principle applies in presidential elections, since if a presidential candidate gets the most votes in any particular state, all of the electoral votes from that state are awarded. In all but two states, Maine and Nebraska, the presidential candidate winning a plurality of votes wins all of the electoral votes, a practice called the unit rule.
Duverger concluded that "plurality election single-ballot procedures are likely to produce two-party systems, whereas proportional representation and runoff designs encourage multipartyism." He suggested there were two reasons why winner–takes–all systems leads to a two-party system. First, the weaker parties are pressured to form an alliance, sometimes called a fusion, to try to become big enough to challenge a large dominant party and, in so doing, gain political clout in the legislature. Second, voters learn, over time, not to vote for candidates outside of one of the two large parties since their votes for third party candidates are usually ineffectual. As a result, weaker parties are eliminated by voters over time. Duverger pointed to statistics and tactics to suggest that voters tended to gravitate towards one of the two main parties, a phenomenon which he called polarization, and tend to shun third parties. For example, some analysts suggest that the Electoral College system in the United States, by favoring a system of winner–takes–all in presidential elections, is a structural choice favoring only two major parties.
Gary Cox suggested that America's two-party system was highly related with economic prosperity in the country:
The bounty of the American economy, the fluidity of American society, the remarkable unity of the American people, and, most important, the success of the American experiment have all mitigated against the emergence of large dissenting groups that would seek satisfaction of their special needs through the formation of political parties.—Cox, according to George Edwards
Third parties 
Third parties, meaning a party other than one of the two dominant parties, are possible in two-party systems, but they are unlikely to exert much influence by gaining control of legislatures or by winning elections. While there are occasional opinions in the media expressed about the possibility of third parties emerging in the United States, for example, political insiders such as the 1980 presidential candidate John Anderson think the chances of one appearing in the early twenty-first century is remote. A report in The Guardian suggested that American politics has been "stuck in a two-way fight between Republicans and Democrats" since the Civil War, and that third-party runs had little meaningful success.
Third parties in a two-party system can be:
- built around a particular ideology or interest group
- split off from one of the major parties or
- focused on a charismatic individual.
When third parties are built around an ideology which is at odds with the majority mindset, many members belong to such a party not for the purpose of expecting electoral success but rather for personal or psychological reasons. In the U.S., third parties include older ones such as the Libertarian Party and the Green Party and newer ones such as the Pirate Party. Many believe that third parties don't affect American politics by winning elections, but they can act as "spoilers" by taking votes from one of the two major parties. They act like barometers of change in the political mood since they push the major parties to consider their demands. An analysis in New York Magazine by Ryan Lizza in 2006 suggested that third parties arose from time to time in the nineteenth century around single-issue movements such as abolition, women's suffrage, and the direct election of senators, but were less prominent in the twentieth century.
A so-called third party in the United Kingdom are the Liberal Democrats. In the 2010 election, the Liberal Democrats received 23% of the votes but only 9% of the seats in the House of Commons. While electoral results do not necessarily translate into legislative seats, the Liberal Democrats can exert influence if there is a situation such as a hung parliament. In this instance, neither of the two main parties (at present, the Conservative Party and the Labour Party) have sufficient authority to run the government. Accordingly, the Liberal Democrats can in theory exert tremendous influence in such a situation since they can ally with one of the two main parties to form a coalition. This happened in the Coalition government of 2010. Yet in that more than 13% of the seats in the British House of Commons are held in 2011 by representatives of political parties other than the two leading political parties of that nation, contemporary Britain is considered by some to be a multi-party system, and not a two-party system.
Some historians[who?] have suggested that two-party systems promote centrism and encourages political parties to find common positions which appeal to wide swaths of the electorate. It can lead to political stability which leads, in turn, to economic growth. Historian Patrick Allitt of the Teaching Company suggested that it is difficult to overestimate the long term economic benefits of political stability. Sometimes two-party systems have been seen as preferable to multi-party systems because they are simpler to govern, with less fractiousness and harmony, while multi-party systems can sometimes lead to hung parliaments. Italy, with a multi-party system, has had years of divisive politics since 2000, although analyst Silvia Aloisi suggested in 2008 that the nation may be moving closer to a two-party arrangement.
Two-party systems have been criticized for downplaying alternative views, and putting a damper on debate within a nation. In The Tyranny of the Two–party system, Lisa Jane Disch criticizes two-party systems for failing to provide enough options since only two choices are permitted on the ballot. She wrote:
Herein lies the central tension of the two–party doctrine. It identifies popular sovereignty with choice, and then limits choice to one party or the other. If there is any truth to Schattschneider's analogy between elections and markets, America's faith in the two–party system begs the following question: Why do voters accept as the ultimate in political freedom a binary option they would surely protest as consumers? ... This is the tyranny of the two–party system, the construct that persuades United States citizens to accept two–party contests as a condition of electoral democracy.—Lisa Jane Disch, 2002
There have been arguments that the winner-take-all mechanism discourages independent or third-party candidates from running for office or promulgating their views. Ross Perot's former campaign manager wrote that the problem with having only two parties is that the nation loses "the ability for things to bubble up from the body politic and give voice to things that aren’t being voiced by the major parties." One analyst suggested that parliamentary systems, which typically are multi-party in nature, lead to a better "centralization of policy expertise" in government. Multi-party governments permit wider and more diverse viewpoints in government, and encourage dominant parties to make deals with weaker parties to form winning coalitions. While there is considerable debate about the relative merits of a constitutional arrangement such as that of the United States versus a parliamentary arrangement such as Britain, analysts have noted that most democracies around the world have chosen the British multi-party model. Analyst Chris Weigant of the Huffington Post wrote that "the parliamentary system is inherently much more open to minority parties getting much better representation than third parties do in the American system."
See also 
- "Sideshow in the streets: Spain’s prime minister has more to worry about than a general strike". Economist. 2010-09-30. Retrieved 2010-11-07. "Spain is a "de facto" two-party system. Other parties may influence policies if the government is in minority but, except for the Socialist and the Popular Parties, no other has, at the moment, any possibility of winning the elections. ..."
- Robert Marquand (March 11, 2008). "In Spain's elections, Socialists win with liberal appeal". Christian Science Monitor. Retrieved 2010-11-07. "The outcome also suggests that Spain, which has many small parties, is moving toward a greater two-party system – even as basic splits between right and left are deepening and becoming more contentious."
- "The Tyranny of the Two-Party System - Lisa Jane Disch - Google Books". Books.google.com. Retrieved 2012-10-29.
- "United Progressive Alliance (UPA)". electionaffairs.com.
- "National Democratic Alliance (NDA)". electionaffairs.com.
- "Political Parties in India". electionaffairs.com. Retrieved 7 August 2012.
- "Electoral Systems and Party Systems: A Study of Twenty-Seven Democracies ... - Arend Lijphart - Google Books". Books.google.com. Retrieved 2012-10-29.
- Schmidt, Steffen W., Shelley, Mack C., Bardes, Barbara A (2008). "American Government and Politics Today 2008-2009". Wadsworth Publishing Company. Retrieved 2010-11-22.
- MICHIKO KAKUTANI (book reviewer) American Creation (book by Joseph J. Ellis) (November 27, 2007). "The Timing, Luck and Lust Behind the Forming of That More Perfect Union". The New York Times. Retrieved 2010-11-07. "... the standoff between the Federalists and their opponents, which led to the modern two-party system;"
- Edwards III, George C. (2011). Why the Electoral College is Bad for America (Second edition ed.). New Haven and London: Yale University Press. pp. 176–7. ISBN 978-0-300-16649-1.
- Sachs, Jeffrey (2011). The Price of Civilization. New York: Random House. p. 107. ISBN 978-1-4000-6841-8.
- Kristina dell (Nov. 01, 2004). "The Electoral College Explained". Time Magazine. Retrieved 2010-11-07. "Forty-eight states have the standard “winner-takes-all” electoral system: whichever presidential ticket amasses the most popular votes in a state wins all the electors of that state."
- Kristina dell (Nov. 01, 2004). "The Electoral College Explained". Time Magazine. Retrieved 2010-11-07.
- Ryan Lizza (Apr 16, 2006). "But Is a Third Party Possible?". New York Magazine. Retrieved 2010-12-07.
- Paul Harris (19 November 2011). "'America is better than this': paralysis at the top leaves voters desperate for change". The Guardian. Retrieved 2012-01-17.
- Jack Schofield (8 June 2009). "Sweden's Pirate Party wins EU seat (updated)". The Guardian. Retrieved 2011-03-28. "The Pirate Party ... wants to legalise internet file-sharing and protect people's privacy on the net ... There *IS* a UK Pirate Party ... and there's a US ... one, and one in a few dozen others.""
- Ryan Lizza (Apr 16, 2006). "But Is a Third Party Possible?". New York Magazine. Retrieved 2010-12-07. "In the nineteenth century, third parties were single-issue creatures that grew up around great causes that the major parties were ignoring. Abolition, women’s suffrage, and the direct election of senators all started as third-party movements."
- United Kingdom general election, 2010#Results, The detailed "Results" section of the Wikipedia article "United Kingdom General Election, 2010".
- "What mean will we regress to?". The Economist. Oct 5th 2010. Retrieved 2010-11-07. "Certainly, there have been a whole lot of hung parliaments and slow-forming coalitions around the world lately. (Canada, Australia, Britain, the Netherlands, Iraq...)"
- Silvia Aloisi (Apr 15, 2008). "Election pushes Italy towards two-party system". Reuters. Retrieved 2010-11-07. "Italy's next parliament will have far fewer parties than the previous assembly, pushing the country closer to the two-party system that many commentators say is the only way to end years of political instability. ..."
- Lisa Jane Disch (2002). "The tyranny of the two-party system". Columbia University Press. Retrieved 2010-10-22.
- Kristina dell (Nov. 01, 2004). "The Electoral College Explained". Time Magazine. Retrieved 2010-11-07. "Some argue that the winner-take-all mechanism in 48 states discourages independent or third party candidates from running because it would be difficult for them to get many electoral votes."
- "The advantages of parliamentarianism". The Economist. Jan 21, 2010,. Retrieved 2010-11-07.
- Chris Weigant (April 7, 2010). "Exceptional Democracy". Huffington Post. Retrieved 2010-11-07. "And, as a result, more parties are represented in their parliament after the elections. The Italian Parliament, for instance, recently had more than 70 parties represented. ... These deals are cut with the smaller parties by offering them the chance to fill high government offices..."