A two-party system is a form of party system where two major political parties dominate voting in nearly all elections, at every level. As a result, all, or nearly all, elected offices end up being held by candidates endorsed by one of the two major parties. Coalition governments occur only rarely in two-party systems.
Under a two-party system, one of the two parties typically holds a majority in the legislature (or a legislative house in a bicameral system), and is referred to as the majority party. The other party is referred to as the minority party.
Notable examples of countries with "two party systems" include the United States and Jamaica. Some other countries that feature weak third or fourth parties, such as the United Kingdom, Canada, Spain, Malaysia, Portugal and Australia are often thought of as being two party states as well, as actual governance of the country may be dominated by only two parties even though other parties may have reasonable bases of support.
Generally, a two party system becomes a dichotomous division of the political spectrum with an ostensibly right and left party, Tories vs. Labour in some commonwealth countries, Republicans vs. Democrats in the US, etc.
Advantages and disadvantages
- In the presence of more than two political parties, a majority of voters may be split between two candidates with similar platforms (see vote splitting above). This would result in the selection of what is, from a majority point of view, the third best choice as the winner. For example, in a three party system, if 60% of a population favors "viewpoint A" and there are two candidates who support "viewpoint A" it is likely that each will receive about 30% of the vote, with the remaining party receiving 40%. This simplified example can be extrapolated to the results of any electoral process with more than two choices and any number of issues, with the result that the winner will actually be opposed to the majority and this multiparty electoral process will therefore be invalid.
- A two party system is the natural tendency of any electoral system for the reasons described above. Even in elections where more than one winner is allowed, i.e. proportional representation, politicians will naturally begin to include positions that will bring them a larger portion of votes. A party system thereby developed which will tend toward a two party system. The framework of a government may provide safeguards against this, however the efficacy of these safeguards is questionable for reasons including their own susceptibility to the political forces previously mentioned.
- The platforms of both parties include mostly middle-of-the-road type policies and opinions, due to the desire to identify with a majority of voters, and this may contribute to a stability in government policies.
- Narrowly based ideological factions can force the major parties to help them in exchange for their support. This can create a chaotic and fluctuating system of alliances that intensifies confusion among voters. Additionally, this "tie-breaker" influence minor parties achieve can serve to undermine the true positions of the major parties.
- The ruling party's majority may still be based on a smaller segment of the population than coalition governments due to lower turnout, and votes cast that do not lead to the desired representative The majority of this body (20% plus one) rules the nation.
- Elections based on geographical district representation can become subject to gerrymandering.
- If one of the two parties becomes weak, a dominant-party system may develop. In fact, a dominant party system has developed in almost every single country that has used first past the post (FPTP), at least at a regional level. Mexico had a dominant party system until constitutional reforms added fairer proportional representation to the scheme.
- Campaign contributions can more easily corrupt a two-party system - since it has fewer players to receive donations.
- In The Federalist No. 10, James Madison decried the liability of representative legislatures to be controlled by single factions holding a majority of the seats. Madison argues that because getting rid of factions is nearly impossible and leads to highly undesirable side-effects, ensuring that all factions are represented reduces the likelihood that any one faction will control all of the seats and institute any and all changes they desire, thus preventing majority tyranny. A two-party system often leads to one faction winning a majority of the seats and governing without compromise. A multi-party system or proportional non-partisan system could be more consensus-based, allowing for laws to be passed less hastily and with more sincere debate on the issues.
- Some voters tend to have one issue that highly motivates - or even completely motivates - which party they will vote for. Because two dominant, opposing parties tend to take opposite sides on many issues, these "one issue voters" will automatically vote for the party that represents their view on the one issue, even though they may disagree with most of their other positions. Candidates often concentrate on popular issues (especially issues considered "moral" or ethical in character) to influence voters who are undecided or "swing voters." The issue at hand tends to be one that sparks a lot of emotion - in the United States, for example, the issue of abortion rights carries strong emotions on both sides of the fence, and a candidate's position on those rights is, for some voters, the deciding factor, even if most of their political ideals are espoused by the other candidate.
- Smaller parties suffer from under-representation: they will not receive a number of seats in the country's assembly that reflects the number of votes they receive (and therefore the amount of support they could or do receive). Some see this as undemocratic, arguing that citizens who vote for small parties should receive fair representation. Others see it as fair to discourage unpopular opinions.
- Special interests can establish a lock on political discourse, media, etc. and establish a narrow dominant ideology which both parties serve so that in effect it is a one-party system tending to corporatism, although this is a feature of all governments and is not specific to the two party system.