Many people with religious convictions feel that their faith is rock solid. But a new study finds that prompting people to engage in analytical thinking can cause their religious beliefs to waver, if only a little. Researchers say the findings have potentially significant implications for understanding the cognitive underpinnings of religion.

Psychologists often carve thinking into two broad categories: intuitive thinking, which is fast and effortless (instantly knowing whether someone is angry or sad from the look on her face, for example); and analytic thinking, which is slower and more deliberate (and used for solving math problems and other tricky tasks). Both kinds of thinking have their strengths and weaknesses, and they often seem to interfere with one another. "Recently there's been an emerging consensus among [researchers] … that a lot of religious beliefs are grounded in intuitive processes," says Will Gervais, a graduate student at the University of British Columbia, Vancouver, in Canada and a co-author of the new study, published today in Science.

One example comes from a study by neuroscientist and philosopher Joshua Greene and colleagues at Harvard University, published last September in the Journal of Experimental Psychology. They asked hundreds of volunteers recruited online to answer three questions with appealingly intuitive answers that turn out to be wrong. For example, "A bat and ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?" Although $0.10 comes easily to mind (it's the intuitive answer), it takes some analytical thought to come up with the correct answer of $0.05. People who chose more intuitive answers on these questions were more likely to report stronger religious beliefs, even when the researchers controlled for IQ, education, political leanings, and other factors.

In the same study, another group of volunteers wrote a paragraph about a time in their lives when either following their intuition or careful reasoning led to a good outcome. Those who wrote about intuition reported stronger religious beliefs on a questionnaire taken immediately afterward. If intuitive thinking encourages religious belief, as Greene's study suggested, analytical thinking might encourage disbelief—or so Gervais and his adviser, social psychologist Ara Norenzayan, hypothesized.

To test this idea, the duo devised several ways to subconsciously put people in what they considered a more analytical mindset. In one experiment with 57 undergraduate students, some volunteers viewed artwork depicting a reflective thinking pose (such as Rodin's The Thinker) while others viewed art depicting less intellectual pursuits (such as throwing a discus) before answering questionnaires about their faith. In another experiment with 93 undergraduates and a larger sample of 148 American adults recruited online, some subjects solved word puzzles that incorporated words such as "analyze," "reason," and "ponder," while others completed similar puzzles with only words unrelated to thinking, such as "high" and "plane." In all of these experiments, people who got the thinking-related cues reported weaker religious beliefs on the questionnaires taken afterward than did the control group.

In a final experiment, Gervais and Norenzayan asked 182 volunteers to answer a religious questionnaire as usual, while others answered the same questionnaire printed in a hard-to-read font, which previous studies have found promotes analytic thinking. And indeed, those who had to work harder to comprehend the questionnaire rated their religious beliefs lower.

Because people were randomly assigned to the analytical-thinking and control groups, and because the results were consistent across all their experiments, Gervais says it's very unlikely the findings could result from one group being more religious to begin with. Moreover, in two of these experiments, the researchers administered religious belief questionnaires to the participants a few weeks beforehand and found no difference between the groups.

The effects of the analytical-thinking manipulations were modest. "We're not turning people into atheists," says Gervais. Rather, when the questionnaire responses of all subjects in an experiment are taken together, they indicate a small shift away from religious belief.

"It's very difficult to distinguish between what a person believes and what they say they believe," says Daniel Kahneman, a psychologist and Nobel laureate at Princeton University who has done pioneering work on the contributions of intuitive and analytical thinking to human decision making. "All they have shown, and all that can be shown, is that when you're thinking more critically you reject statements that otherwise you would endorse," Kahneman says. "It tells you that there are some religious beliefs people hold that if they were thinking more critically, they themselves would not endorse."

To Gervais and Norenzayan, the findings suggest that intuitive thinking, likely along with other cognitive and cultural factors, is a key ingredient in religious belief. Greene agrees: "Through some combination of culture and biology, our minds are intuitively receptive to religion." He says, "If you're going to be unreligious, it's likely going to be due to reflecting on it and finding some things that are hard to believe."

"In some ways this confirms what many people, both religious and nonreligious, have said about religious belief for a long time, that it's more of a feeling than a thought," says Nicholas Epley, a psychologist at the University of Chicago. But he predicts the findings won't change anyone's mind about whether God exists or whether religious belief is rational. "If you think that reasoning analytically is the way to go about understanding the world accurately, you might see this as evidence that being religious doesn't make much sense," he says. "If you're a religious person, I think you take this evidence as showing that God has given you a system for belief that just reveals itself to you as common sense."

ScienceNOW, the daily online news service of the journal Science