Character  &  Context

The Science of Who We Are and How We Relate
Editors: Mark Leary, Shira Gabriel, Brett Pelham
Oct 17, 2016

When Political Ideology Undermines Logical Reasoning

by Anup Gampa
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By Anup Gampa

I can’t get into an agreement to become a McDonald’s sandwich. Because I’m not! I can smell like McDonald’s sandwich, but I can never be a McDonald’s sandwich. And so, two men can never be a marriage.

E. W. Jackson – Conservative Activist


Ebola is not an epidemic in America and a trusted Surgeon General would ease the fear and anxiety among the growing number of [worried] Americans.  Because, the qualified Surgeon General candidate believes in easing the proliferation of guns, the National Rifle Association, Republicans, and a few gun-shy Democrats will not allow his confirmation. Thanks To the NRA, The US Has No Surgeon General Overseeing the Ebola Threat. – Liberal Site

When one encounters such ideological arguments, liberals might argue that conservatives are deficient in their ability to reason logically. Similarly, conservatives might argue that liberals are deficient in their ability to reason logically. This could be understood as the reason for ideological disagreement - if only the other side were able to reason, then we would all agree.

Political partisans not only dislike claims made by the “other side”, they also seem to find each other’s arguments to be illogical. It is even more difficult to debate the content of different positions if opposing positions use logical fallacies in their own arguments while perceiving logical fallacies in the others’ that are not there. If partisans cannot appreciate each other’s claims and logical reasoning, then the promise of bipartisanship, or even just productive discussion between political parties, may be a distant ideal. The result is a seemingly intractable partisan disagreement on issues of great importance such as abortion, climate change, taxation, foreign policy, and social welfare programs.

Why are partisans quick to jump to the conclusion that their opponents are illogical? Prior research has shown that people judge arguments as more logically sound when they personally support the argument’s conclusion—a robust reasoning bias known as belief bias. Even more troubling is that we are prone to believe that our judgments remain free from bias. However, we are at least able to recognize the impact of bias on the judgments of others. And, unsurprisingly we are also readily biased by our group affiliations such as political partisanship or religion. For example, Israelis are likely to endorse a peace proposal if it is believed to be authored by Israelis, and to reject the very same proposal if it is believed to be authored by Palestinians (vice-versa with Palestinians). These biases appear to occur automatically, which makes them even more difficult to avoid. Surprisingly, these reasoning biases are not necessarily due to partisans exerting less effort when evaluating an argument or interpreting data; instead even those of us with greater quantitative skills might use our reasoning capacities selectively to mold the interpretation of the data to fit our political attitudes.

Building on prior work, we investigated if belief bias exacerbates the problem of ideological disagreements by biasing the partisans’ evaluation of logical arguments, of both theirs’ and their opponents’. We asked a nationally representative sample of 1100 participants (half liberals, half conservatives) to complete reasoning tasks in which they were required to judge the logical soundness of arguments. All the arguments had two premises followed by a conclusion.  An argument is considered sound as long as the conclusion follows from the two premises. Importantly, the veracity of the premises or conclusion does not affect the logical soundness of the argument - something that belief bias causes people to disregard.

Given that each side believes the other side is illogical (liberal example, conservative example), we first tested whether liberals and conservatives had differences in logical reasoning when they evaluated arguments without ideological content. On this task, there were no differences in logical reasoning between liberals and conservatives.  In fact, both liberals and conservatives tended to label even unsound arguments as sound, illustrating difficulties with logical reasoning across partisan lines.

Then, we had participants judge the logic of four arguments about either affirmative action, capital punishment, government intervention, or abortion. (All the arguments are presented here.) Participants’ ratings of their agreement with these arguments confirmed that arguments with liberal conclusions appealed more to liberal participants, and the arguments with conservative conclusions appealed more to conservative participants. But the soundness of the argument did not impact the participant’s agreement with the conclusion of the argument.

What happens when people confront logical arguments where the content is ideological in nature? After accounting for other factors that might influence ratings of arguments, such as education and age, we found that liberals find liberal arguments sounder, and conservatives find conservative arguments sounder, regardless of the actual soundness of the argument. Moreover, liberals' and conservatives' belief bias was explained entirely by their agreement with the syllogisms' conclusions.

Is biased logical reasoning then a problem or solution for resolving partisan disputes?  Our results suggest that the answer might be both. On the one hand, belief bias exacerbates political disagreement by pushing liberals and conservatives apart in the evaluation of the logical soundness. Conclusions and arguments that appear agreeable and therefore logically sound to liberals appear disagreeable and therefore unsound to political conservatives, and vice versa, regardless of actual soundness.

On the other hand, understanding these predictable biases in human reasoning can also help improve reasoning about political issues. The tendency in people to better recognize failures in others’ logic can be useful if we collaborate across ideological lines by evaluating each others’ arguments. Belief bias may impair both liberals’ and conservatives’ ability to reason soundly, but it also enables them to identify logical flaws in the reasoning of political opponents.

Anup is a graduate student at the University of Virginia. He practices critical social psychology and studies different forms of oppression in order to help drive radicall social change. Research presented here is a collaboration with Sean Wojcik, Matt Motyl, Brian Nosek, and Pete Ditto.


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Everything that people think, feel, and do is affected by some combination of their personal characteristics and features of the social context they are in at the time. Character & Context explores the latest insights about human behavior from research in personality and social psychology, the scientific field that studies the causes of everyday behaviors.  

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