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 parties that get the most votes. Coalition governments are rare in two-party systems, though each party may internally look like a coalition.
Why it occurs
Two-party systems are naturally 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. However, new parties are not guaranteed under any system: Malta provides an example of a stable two-party system using the single transferable vote.
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 Britons 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
- it produces more stable governance than multiparty systems, because coalition is highly unlikely to occur with two parties dominating.
- it keeps 'undesirable' extremist parties out of power, like the British National Party (which most Brits perceive to be racist) in the United Kingdom.
- uncommon, unconventional ideas and ideologies are non-influential, so policies and governments do not change rapidly; though there is some controversy as to whether this is an advantage. While smaller parties find this exceptionally frustrating, proponents suggest that it enhances stability while allowing for ideas that gain favor to become politically influential.
- it gives a more transparent choice to voters: coalitions are created internally before the election rather than externally after it; it is easier to judge whether an elected government has delivered its promises since it cannot blame component parties' diversity for failure.
- the dynamics of a two party system drives both parties' policies towards the position of a mythical median voter while remaining distinctive enough to motivate their core support.
- and even that two party systems, especially those where power often changes hands, are less prone to revolutions, coups, or civil wars.
Against the argument that the two-party system leads to more stable governance, critics of the two-party system argue variously that:
- stability is not desirable in itself.
- the two-party system produces stable governments, rather than stable democracy, and the latter is what should be desired.
- two-party systems are not intrinsically any more stable, citing such examples of stable democracies as Germany, which has a multi-party system through proportional representation.
The two-party system is also criticised for the following flaws:
- Candidates are motivated to run negative campaigns, pointing out the flaws in the "other person" (usually the leader of the other party) and staking out only those positions that are necessary to differentiate themselves from their primary opponent and not constructive or beneficial to citizens.
- If the opposition party is weak, a dominant-party system may develop.
- Debate in the assembly of the country can often be adversarial and not constructive, sometimes revolving around narrowly perceived policy ideas, rather than larger political issues. Sometimes adversarial politics can lead to the opposition disagreeing with everything the government proposes (and vice versa) for the sake of disagreeing. This can lead to important legislation, especially reforms, being blocked that may be beneficial for the country.
- The system is more easily corrupted by campaign contributions since there are fewer players to donate to.
- In an effort to attract voters, each party will adopt planks of the other party's platform, leading to the appearance in some skeptics' minds of a one-party system. Examples include the American notion of a "Republicrat."
The electoral systems which tend to favour two-party systems (notably the "biggest pile of votes wins" system) are also criticised because:
- Most electors are forced to engage in tactical voting, voting for candidates that may not be their first choice.
- Smaller parties will be unrepresented: they will not receive a number of seats in the country's assembly that reflect the number of votes received for them (and therefore the amount of support for them). Some argue that this is undemocratic, as citizens who vote for small parties should be represented fairly.
- Smaller parties often represent unconventional or 'alternative' (compared to the main parties) ideologies and formulate policy on the basis of this ideology. It can be argued that in a democracy, all ideologies should be fairly represented.
- Larger parties will benefit from being overrepresented; some argue this is undemocratic.
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