political spectrum, a model for classifying political actors, parties, or ideologies along one or more axes that compare them. Tradition dating back to the French Revolution places ideologies that prioritize social, political, and economic equality on the left side of the spectrum and ideologies that prioritize various forms of hierarchy on the right side of the spectrum. Though many other ways of classifying political positions have been proposed, both for scientific rigour and to apply more broadly across cultures, this left/right axis remains the dominant way of describing political ideologies, particularly in Western countries.

The origin of the left/right political axis is generally dated to 1789, when the French National Assembly met in Versailles. During the several days of this meeting, the legislators who upheld revolutionary values tended to group themselves on the left of the assembly, while those who supported the monarchy were grouped on the right. This helped establish a persistent association between the left and revolutionary values, which tended toward egalitarianism, and between the right and traditionalist or hierarchical values. Some thinkers have suggested that this left/right dichotomy was a natural outgrowth of a broader tendency among human cultures, based in widespread right-handedness, to characterize the concept of “right” with attributes related to strength and stability and the concept of “left” with attributes related to danger or disorder. This could then have led to an easy association between the right and politics that uphold the status quo, while the left became associated with politics that challenge it.

Many people have attempted to establish more complex descriptions of the political spectrum. American psychologist L.L. Thurstone, a pioneer in psychometrics, was one of the first to attempt to describe the political spectrum scientifically. Thurstone used survey results and a statistical tool called factor analysis to find two major axes of American political ideology, which he described as Radicalism-Conservatism and Nationalism-Internationalism. The Radicalism-Conservatism axis is analogous to the common left/right axis and has subsequently been duplicated in many other analyses. L.W. Ferguson performed a similar analysis and arrived at somewhat different axes, related to Religionism, Humanitarianism, and Nationalism.

German-born British psychologist Hans Eysenck built upon this work. Eysenck proposed a two-axis model with one axis following a Radicalism-Conservatism spectrum (sometimes called the R-axis) and the other axis following a proposed dichotomy of “tender-minded” and “tough-minded” (or the T-axis). Eysenck’s T-axis was intended to capture differing levels of authoritarianism, where “tough-minded” political actors would be more willing to employ harsh or dictatorial methods and “tender-minded” political actors would be more libertarian. For example, though Stalinist communists would fall to the extreme left on the traditional left/right axis and Nazis would fall to the extreme right, Eysenck’s model would classify both as extreme examples of “tough-mindedness.”

Eysenck’s two-dimensional model has been very influential, and many subsequent models, both academic and popular, have attempted to map politics onto two dimensions. Organizations such as Gallup often place people on a political spectrum based on both “social” and “economic” ideas, while a popular Internet quiz called the Political Compass places users on a two-dimensional graph with axes for Left-Right and Libertarian-Authoritarian. However, the scientific basis for these models has frequently been questioned, with the Political Compass in particular being criticized as a tool for propagating libertarian ideas. Parodies of the Political Compass model have become a popular Internet meme, often satirizing common stereotypes of the ideologies represented by each quadrant.

One tool often used by political scientists to analyze political ideologies in the context of legislatures is called DW-NOMINATE, short for Dynamic Weighted Nominal Three-step Estimation. DW-NOMINATE is a mathematical procedure that compares legislators based on their voting behaviour and generates a two-dimensional political spectrum to place them on. Using this method, legislators with similar voting methods appear closer together in the political space, while those who vote differently appear further away. DW-NOMINATE found that legislators throughout most of U.S. history have correlated well with a traditional left-right axis. The secondary dimension has been less consistent, often reflecting views on different issues relevant to the day, including slavery, immigration, and civil rights.

The single-axis description of politics along a left-right dimension remains relevant to politics in the United States. Increased political polarization among the two major parties tends to collapse political differences into a one-dimensional spectrum. Rather than adding dimensions to this spectrum, some political scientists have attempted to better describe the political behaviour of voters by creating categories within the spectrum. Pew Research, for example, created a political typology that groups the population into buckets based on not only the two major American parties but also the disagreements within those parties and the characteristics of those who don’t habitually align with either. The spectrum that results roughly places the most extreme adherents of either party at the ends, with less vehement supporters toward the middle.

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