Bipartisanship is the tradition or structure of a political regime that consists of two large parties or coalitions that dominate the political scene of the region or country.

Bipartisanship or bipartisan system stipulates constitutionally or through suffrages the two parties that dominate power in a particular government. It differs from multiparty because the latter does not limit political diversity and balances the extreme polarization of positions.

Bipartisanship is a trend that arises after the French Revolution (1789-1799), whose original idea was to create a government with a party in defense of the aristocracy and another in defense of the bourgeoisie.

Then, with the birth of Marxist ideas in the world in the mid-nineteenth century, bipartisanship becomes a party in defense of the bourgeoisie and another in defense of the proletariat.

Currently, the two parties or coalitions that represent the bipartisan system are often opponents with respect to the ideologies and traditions of each country.

Duverger’s Law

The French jurist Maurice Duverger (1917-2014) describes in his work The political parties, published in 1951, two factors that would determine bipartisanship in majority votes:

• The mechanical effect: parties that do not belong to the two dominant parties do not have enough representation to win.
• The psychological effect: the votes usually go to the two majority parties so they are not “wasted”.

Taking into account that the two basic methods of electoral representation are:

• By majority: it is about reducing the complexity of a massive will in some representatives.
• By electoral representation: the parliament tries to ensure that every important minority is represented.

Duverger’s laws determined the functioning of electoral systems and the influence he exerts on the number of political parties. In 1959 he proposed three formulas that he would later call laws:

• A system where the majority is relative and simple leads to bipartisanship that alternates the exercise of the power of parties in government.
• Proportional representation leads to multi-party with stable and independent parties, little given to form coalitions.
• A system that includes a second-round election leads to multipartyism with relatively stable parties, but likely to form coalitions or alliances.