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Why do people continue smoking or eating unhealthy food when the arguments against doing so are as strong as they are?

And how come some people believe more in what religious scriptures tell them about the origin of life than what the hard evidence of science says?

Although scientists probably pull their hair out over creationists and pro-life activists, who have more faith in what the bible says than in scientific fact, perhaps the religious scriptures are not as irrational as a hard-core scientist may think.

According to the researcher behind a new study, Jens Koed Madsen, a Danish postdoctoral fellow at Birkbeck College, London, people have different approaches to arguments depending on their existing beliefs. We therefore need to break with the idea that some arguments are always more rational than others.

Rationality Is Not Mathematics

”Many people think of a rational argument as if it were an equation which must follow a specific structure and requires specific proof in order to be valid and sound,” says Madsen.

“One consequence of this is that many believe that as long as an argument is good enough, it will persuade people.”

He points out that even though people may not be persuaded by an, objectively speaking, valid argument, we are actually quite consistent in our attitudes, as long as it is taken into account how we generally evaluate arguments, information and sources.

”If you speak to people who say they have faith in what the bible says, then it also makes pretty good sense for them to say that abortion should be banned, even though there may be fallacies elsewhere in their argumentation.”

This does not, however, mean that creationism is as strong a theory as the theory of evolution, but this is a different discussion, which, according to Madsen, we will need to put to the side if we are to have any hope of convincing people who have a different approach to sources and the credibility of arguments.

“One of the things that drives, say, political discussions, is that people can look at the same information and arrive at entirely different conclusions. We therefore need to understand how the people we wish to persuade evaluate various types of information and sources.”

Model Predicts if the Arguments Work

For this purpose, Madsen has started developing a cognitive psychological model, designed to enable us to predict the degree to which a given argument will work on different people.

”By examining how people relate to various types of arguments and sources, we can predict with a pretty high degree of certainty how much they will be persuaded by a given argument,” says Madsen.

”We have, for example, exposed some study participants to arguments from sources with varying degrees of credibility and expertise – such as statements from doctors and rock stars about an imaginary drug. Based on the participants’ evaluation of the information and the sources, we could predict fairly reliably how they would respond to various arguments.”

Madsen is currently preparing a scientific article in which he, based on the participants’ evaluation of the reliability of sources and the reported strength of their arguments, has managed to explain a high percentage of the differences in people’s responses to arguments.