Political scientists and historians usually focus on a few key elements of Texas's legal-institutional framework, political culture, and political history to explain the development of the two-party system in American and Texas politics.
The core institutional element used to explain the endurance of the two-party system is single-member district representation. Most political offices in the U.S. and Texas (e.g., President, congressman, Governor, state legislator) represent single-member districts - meaning that only one individual running for that office will win, even if there are several attractive candidates and parties. Over time, parties whose candidates consistently lose will either merge with stronger parties or die away.
A single-member district system of representation is most commonly compared to a proportional representation system where parties fill a slate of offices based on the proportion of the total vote each party receives in a district, state, province, or country. In such a system, even parties that win only a few percent of the total vote can gain seats in representative bodies. In these systems, the chief executive - the prime minister - is chosen from the majority party or from a coalition of parties that constitutes a majority.
In a system of proportional representation, even a minor party can win at least some seats. Since votes for a minor party are not perceived as "wasted," some parties are willing to take positions outside the ideological middle - offering meaningful choices to voters who may prefer something other than the middle of the road. Some jurisdictions in Texas and the U.S. have experimented with proportional voting or other alternatives to the single-member district system with plurality voting, as discussed in this chapter's Rules Matter feature on Cumulative Voting in Texas. Most historians and political scientists agree, nevertheless, that widespread change in the single-member district system in Texas and the U.S. is unlikely.
The institutional and legal foundation of elections is not the only factor that explains the enduring nature of the two-party system in the U.S. and Texas. Some scholars have emphasized what seem to be qualities unique to political culture in the United States - which, together, are often called American exceptionalism. Observers of American political culture argue that the United States is characterized by an unusually strong and unusually deeply rooted popular commitment to liberty, egalitarianism, individualism, and free markets. While other countries may be building long term records of democratic politics, these scholars claim, their political cultures are less individualistic and less deeply committed to both political and economic liberty.
American exceptionalism is often linked to the two-party system because the consensus on core political convictions in the United States limits demand for alternative political ideologies and political parties to represent them. Without a strong tradition of more collectivist political ideologies, the U.S. has never had significant constituencies for a broader range of political parties. Instead, such interpretations suggest, the political spectrum in the United States is limited to two parties that differ more in matters of degree and emphasis or personalities, than in fundamental values.
Texas fits the overall pattern of American exceptionalism, perhaps even more so than the U.S., political culture in Texas is marked by a particularly strong strain of individualism and a strong tradition of pro-business sentiment. Within a country exceptionally committed to a public ethic of classical liberalism, Texas is perhaps still more exceptional.
Although answers to the question "why two parties?" typically emphasize either institutional or ideological factors, both factors work together to produce the two-party system. The rules governing elections and representation keep the two-party system in place. The relatively narrow ideological spectrum tends to limit the demand for changes in those rules, even as the duopoly of the Democratic and Republican parties enables their adherents to defeat or co-opt proponents of significant changes.