In a polarizing political climate, citizens frequently experience a clash of values when debating pressing societal issues. A central question in political psychology has been how the general ideologies that represent these values drive human cognition, emotion, and behavior. Notably, the rigidity-of-the-right model stipulates that the political left and right differ in their cognitive styles, as reflected in increased closed-mindedness among individuals on the right (Jost, 2017). In recent years, however, researchers have increasingly recognized that not only political orientation but also political extremism meaningfully predict people’s responses to societal and political events. We define political extremism as the extent to which regular citizens are polarized into, and strongly identify with, generic left- or right-wing ideological outlooks on society. In this article, we examine psychological features of extreme political ideologies. In what ways are political left- and right-wing extremists actually quite similar to one another and different from moderates?

The basic idea that left- and right-wing extremists share a range of psychological similarities is consistent with theories of extremism and radicalization (e.g., Kruglanski et al., 2014; see also Greenberg & Jonas, 2003; Hoffer, 1951). The goal of this article is to examine the psychology of extreme political ideologies by integrating these prior theoretical insights with recent findings. We specifically propose four interrelated psychological features that characterize political extremism. Moreover, although we do not dispute that political orientation predicts important psychological variables (e.g., acceptance of inequality), we illuminate how some psychological features that were historically attributed to the political right might more accurately be attributed to both political extremes.

Political Extremism: Four Psychological Features

Although we do not claim that the propositions reviewed here represent the only psychological features of political extremism, they are well supported by empirical evidence, have been frequently studied by psychologists, and jointly contribute to a parsimonious understanding of this phenomenon. We specifically examine the relationships between political extremism and (a) psychological distress, (b) cognitive simplicity, (c) overconfidence, and (d) intolerance.

Overconfidence The third psychological feature is that political extremists are overconfident in their judgments. This proposition is closely tied with the insight that political extremism predicts cognitive simplicity. While simplistic causal models of reality enable extremism by addressing the epistemic need to make the world more predictable (Kruglanski et al., 2006), they also enhance beliefs that one accurately understands reality. Put differently, people are more confident about judgment domains that seem simple. Such overconfidence is reflected in findings that both left- and right-wing extremists consider their political beliefs to be superior on a range of topics, including health care, immigration, and affirmative action, compared with moderates (Toner, Leary, Asher, & Jongman-Sereno, 2013). Belief superiority is a poor predictor of actual knowledge, however, and predicts a tendency to select agreeable but ignore disagreeable information (Hall & Raimi, 2018). Furthermore, political extremists display increased confidence in numeric estimation tasks (Brandt, Evans, & Crawford, 2015), suggesting overconfidence also in nonpolitical judgment domains. Finally, one study assessed Dutch participants’ domain-specific knowledge and judgmental certainty about the EU refugee crisis. Results revealed that left- and right-wing extremists did not differ from moderates in their domain-specific knowledge of this geopolitical event, yet they did experience increased judgmental certainty. Consistent with our theorizing, findings showed that the relationship between political extremism and judgmental certainty was statistically accounted for by the belief that the solution for the refugee crisis is simple (van Prooijen et al., 2018). The findings reviewed here suggest that political extremists—on both ends of the spectrum—are overconfident in their beliefs.