Definitions and measurements
According to DiMaggio et al. (1996), "Polarization is both a state and a process. Polarization as a state refers to the extent to which opinions on an issue are opposed in relation to some theoretical maximum. Polarization as a process refers to the increase in such opposition over time." Polarization can be benign, natural, and democratizing, or it can be pernicious, having longterm malignant effects on society and congesting essential democratic functions. Some political scientists argue that polarization requires divergence on a broad range of issues, while others argue that only a few issues are required.
Political scientists typically distinguish between two levels of political polarization: elite and mass. "Elite polarization" focuses on the polarization of the political elites, like party organizers and elected officials. "Mass polarization" (or popular polarization) focuses on the polarization of the masses, most often the electorate or general public.
Conventionally, political polarization is viewed in terms of issue positions or policy attitudes, including ideological distance between elites (political parties, party manifestos, or legislative voting) or the masses (voters self-sorting into increasingly homogenous political parties or self-placement on ideological scales). Some political scientists assert that contemporary polarization depends less on policy differences on a left and right scale, but increasingly on other divisions such as: religious against secular; nationalist against globalist; traditional against modern; rural against urban.
Political polarization in the United States House of Representatives (DW-Nominate scores)
Elite polarization refers to polarization between the party-in-government and the party-in-opposition. Polarized political parties are internally cohesive, unified, programmatic, and ideologically distinct; they are typically found in a parliamentary system of democratic governance.
In a two-party system, a polarized legislature has two important characteristics: first, there is little-to-no ideological overlap between members of the two parties; and second, almost all conflict over legislation and policies is split across a broad ideological divide. This leads to a conflation of political parties and ideologies (i.e., Democrat and Republican become nearly perfect synonyms for liberal and conservative) and the collapse of an ideological center.
The vast majority of studies on elite polarization focus on legislative and deliberative bodies. For many years, political scientists measured polarization in the US by examining the ratings of party members published by interest groups, but now, most analyze roll-call voting patterns to investigate trends in party-line voting and party unity. Gentzkow, Shapiro, and Taddy used the text of the Congressional Record to document differences in speech patterns between Republicans and Democrats as a measure of polarization, finding a dramatic increase in polarized speech patterns starting in 1994.
Mass polarization, or popular polarization, occurs when an electorate's attitudes towards political issues, policies, and celebrated figures are neatly divided along party lines. At the extreme, each camp questions the moral legitimacy of the other, viewing the opposing camp and its policies as an existential threat to their way of life or the nation as a whole.
Many political scientists consider political polarization a top-down process, in which elite polarization leads to – or at least precedes – popular polarization. However, polarization among elites does not necessarily produce polarization within the electorate, and polarized electoral choices can often reflect elite polarization rather than voters' preferences.
Political scientists who study mass polarization typically rely on data from opinion polls and election surveys. They look for trends in respondents' opinions on a given issue, their voting history, and their political ideology (conservative, liberal, moderate, etc.), and they try to relate those trends to respondents' party identification and other potentially polarizing factors (like geographic location or income bracket). Political scientists typically limit their inquiry to issues and questions that have been constant over time, in order to compare the present day to what the political climate has historically been.
In political science, pernicious polarization occurs when a single political cleavage overrides other divides and commonalities to the point it has boiled into a single divide which becomes entrenched and self-reinforcing. Unlike most types of polarization, pernicious polarization does not need to be ideological. Rather, pernicious polarization operates on a single political cleavage, which can be partisan identity, religious vs secular, globalist vs nationalist, urban vs rural, etc. This political divide creates an explosion of mutual group distrust which hardens between the two political parties (or coalitions) and spreads beyond the political sphere into societal relations. People begin to perceive politics as "us" vs "them."
According to Carothers & O'Donohue (2019), pernicious polarization is a process most often driven by a single political cleavage dominating an otherwise pluralistic political life, overriding other cleavages. On the other hand, Slater & Arugay (2019) have argued that it's not the depth of a single social cleavage, but the political elite's process for removing a leader which best explains whether or not polarization truly becomes pernicious. Lebas & Munemo (2019) have argued pernicious polarization is marked by both deeper societal penetration and segregation than other forms of political polarization, making it less amenable to resolution. It is agreed, however, that pernicious polarization reinforces and entrenches itself, dragging the country into a downward spiral of anger and division for which there are no easy remedies.
Effect on governance
Pernicious polarization makes compromise, consensus, interaction, and tolerance increasingly costly and tenuous for individuals and political actors on both sides of the divide. Pernicious polarization routinely weakens respect for democratic norms, corrodes basic legislative processes, undermines the nonpartisan nature of the judiciary and fuels public disaffection with political parties. It exacerbates intolerance and discrimination, diminishes societal trust, and increases violence throughout the society. In country-by-country instances of pernicious polarization, it is common to see the winner exclude the loser from positions of power or using means to prevent the loser from becoming a threat in the future. In these situations, the loser typically questions the legitimacy of the institutions allowing the winner to create a hegemony, which causes citizens to grow cynical towards politics. In these countries, politics is often seen as a self-referential power game that has nothing to do with people.
Effect on public trust
Perniciously polarized societies often witness public controversies over factually provable questions. During this process, facts and moral truths increasingly lose their weight, as more people conform to the messages of their own bloc. Social and political actors such as journalists, academics, and politicians either become engaged in partisan storytelling or else incur growing social, political, and economic costs. Electorates lose confidence in public institutions. Support for norms and democracy decline. It becomes increasingly difficult for people to act in a morally principled fashion by appealing to the truth or acting in line with one's values when it conflicts with one's party interests. Once pernicious polarization takes hold, it takes on a life of its own, regardless of earlier intentions.
Several political scientists have argued that most types of political polarization are beneficial to democracy, as well as a natural feature. The simplifying features of polarization can help democratization. Strategies which depend on opposition and exclusion are present in all forms of observed politics. Political polarization can help transform or disrupt the status quo, sometimes addressing injustices or imbalances in a popular vs. oligarchic struggle.
Political polarization can serve to unify, invigorate, or mobilize potential allies at the elite and mass levels. It can also help to divide, weaken, or pacify competitors. Even the most celebrated social movements can be described as a "group of people involved in a conflict with clearly defined opponents having a conflictual orientation toward an opponent and a common identity."
Political polarization can also provide voting heuristics to help voters choose among candidates, enabling political parties to mobilize supporters and provide programmatic choices. Polarizing politics can also help to overcome internal differences and frame a common identity, based in part on a common opposition to those resisting reforms. Still, polarization can be a risky political tool even when intended as an instrument of democratization, as it risks turning pernicious and self-propagating.