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Logical Reasoning: An Antidote or a Poison for Political Disagreement?

The concept of logical thinking. Geometric shapes on a wooden background.

Washington, DC - Star Trek’s Spock would not be surprised: People are “illogical.” New research exploring American liberals and conservatives shows that regardless of political affiliation, tribal instincts kick in and people’s ability to think logically suffers when it comes to arguments related to their political belief systems. When confronted with the unsound reasoning of opposing groups, people become better able to identify flawed logic.  

The research was recently published in Social Psychological and Personality Science.

In their first study, the researchers studied ideological belief bias - the tendency to judge logical arguments based on the believability of their conclusions rather than whether or not the arguments' premises support the conclusions - effects among 924 liberals and conservatives from Visitors to the site evaluated the logical soundness of classically structured logical syllogisms supporting liberal or conservative beliefs. Of 16 syllogisms, half were structured as sound arguments, and half unsound.*

On average, participants correctly judged 73% of the syllogisms. But their ability to judge correctly depended on their political views.

“Liberals were better at identifying flawed arguments supporting conservative beliefs and conservatives were better at identifying flawed arguments supporting liberal beliefs,” says Anup Gampa (University of Virginia), a lead coauthor of the paper.

In a second study, they observed ideological belief bias effects among 1,489 participants from The participants in this study were trained in logical reasoning before evaluating political syllogisms using language similar to what they might encounter in popular media.

Even with the training, the ability to analyze arguments fell into the same patterns.  The authors found similar patterns of bias in a nationally representative sample containing 1,109 liberals and conservatives.

In the era of fake news, these logical fallacies can be even more potent.

“When two sides don’t share a common view of even seemingly objective facts, these differences become embedded in our collective reasoning ability,” says Sean Wojcik (University of California, Irvine), a lead coauthor of the paper. “Our biases drive us apart not only in our disagreements about political and ideological worldviews, but also in our understanding of logic itself.”

Both Gampa and Wojcik agree that in our political world, “we might not be as vigilant as we think” about the logical grounding of our own beliefs and “we might be unreasonably harsh about the logical grounding of the belief of those we disagree with.”

Despite this, being able to hear the other side can open us to our own flawed arguments, suggest the researchers.

Study Gampa, Anup, Sean P. Wojcik, Matt Motyl, Brian A. Nosek, and Peter H. Ditto. (Ideo)Logical Reasoning: Ideology Impairs Sound ReasoningSocial Psychological and Personality Science, (March 5, 2019). doi:10.1177/1948550619829059.

Funding: The nationally representative study was made possible by funding from TimeSharing Experiments for Social Sciences (TESS; NSF Grant 0818839, Jeremy Freese and James Druckman, Principal Investigators).

Social Psychological and Personality Science (SPPS) is an official journal of the Society for Personality and Social Psychology (SPSP), the Association for Research in Personality (ARP), the European Association of Social Psychology (EASP), and the Society for Experimental Social Psychology (SESP). Social Psychological and Personality Science publishes innovative and rigorous short reports of empirical research on the latest advances in personality and social psychology.

Data sources:

  • Study 1: 1,374 visitors (30.1% female, Mage ¼ 40.09, SDage ¼ 16.50) to, a psychological research website where volunteers complete psychological surveys in exchange for personalized feedback about their results.
  • Study 2: 1743 participants (65.4% female; Mage ¼ 34.25, SDage ¼ 13.39) entered the study at Project Implicit.
  • Study 3: 1,109 participants (48.3% female; Mage ¼ 49.81, SDage ¼ 17.16). Time-Sharing Experiments for Social Sciences funded the sampling for the study and GfK Group implemented the survey. The final sample was 552 liberals and 557 conservatives.

*A syllogism is a form of reasoning based on two premises and a conclusion, and depending on how it is written could be “sound” (i.e., the conclusion follows logically from the premises) or “unsound” (the conclusion does not follow logically from the premises). See below for examples:

Sound syllogism:

All things made of plants are healthy.

Salads are made of plants.

Therefore, salads are healthy.



All things made of plants are healthy.

Vaccines are healthy.

Therefore, vaccines are made from plants.

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