WHEN THE CHRYSLER car company released a new model of its Dodge Coronet in 1967, the theme of its advertising campaign was the “White Hat Special.” Some of the ads featured cartoon cowboys riding around “keepin’ the prices low,” whereas others had the ubiquitous “Dodge Girl” in her signature white Stetson, chirping: “Only the good guys could put together a deal like this.”

These ads did not need any elaboration. Madison Avenue knew that potential buyers had all been raised on film and TV Westerns and were familiar with the symbolism of white hats. Roy Rogers, Gene Autry, the Lone Ranger—these cinematic heroes wore white hats, and bad guys wore black. It was all very simple.

Simple, but maybe not all that original. The colors white and black have carried layers of moral meaning since long before Americans’ infatuation with cowboys and automobiles. Indeed, some scientists believe that our conception of blackness and sin may be entangled with a fundamental and ancient fear of dirt and contagion that remains deeply wired in our neurons today.

Mental Mismatch

Two University of Virginia psychologists recently decided to explore this provocative idea in the laboratory. Gary D. Sherman and Gerald L. Clore wanted to know if common metaphors may be more than mere rhetorical devices, if in fact they might be deep embodiments of moral thinking. They decided to test the link between white and virtue (and black and sin) as part of this larger question.

The psychologists adapted a reaction-time test from the 1930s called the Stroop test. You may know it from the Internet, where it circulates as a kind of parlor game. In the test the names of colors are printed in a mismatched color—say, the word “blue” may be yellow in hue—and you must very quickly indicate the color rather than the word’s meaning. The task is hard because our mind wants to read the word, and slow reaction time is taken as a sign of cognitive disconnect or conflict.

In Sherman and Clore’s version of the Stroop, volunteers read not the names of colors but words with strong moral overtones: greed and honesty, for example. Some of the words were printed in black and some in white, and they flashed rapidly on a screen. As with the original Stroop, a fast reaction time was taken as evidence that a connection was mentally automatic and natural; hesitation was taken as a sign that a connection did not ring true. The researchers wanted to see if the volunteers automatically linked immorality with blackness, as in black ink, and virtue with whiteness.

And they did, so quickly that the connections could not possibly be deliberate. When moral words were printed in white and immoral words in black, reaction time was significantly faster than when words of virtue were black and sin were white. Just as we unthinkingly—almost unconsciously—“know” a lemon is yellow, we instantly know that sin and crime are black and that grace and virtue are white.

Dirt and Sin

Why would this intrinsic association exist? One possibility is that the metaphor is more complex, embodying not just right and wrong but purity and contagion, too. Think of the metaphor “new-fallen snow.” It is not only white, it is also virginal and unadulterated, like a wedding dress. And blackness not only discolors it, it stains it, taints its purity. With this in mind, the psychologists ran another experiment, adding this dimension of contagion, of feeling morally “dirty.” They deliberately primed some volunteers’ immoral thoughts by having them read a story about a self-serving, immoral lawyer and then compared them with volunteers primed for ethical thinking.

The idea was that people who were feeling morally dirty would be quicker to make the connection between immorality and blackness on the moral Stroop test, which is exactly what the researchers found. And what’s more, they found the link using much looser definitions of morality and immorality—including words such as dieting, gossip, duty, partying, helping, and so forth. In other words, those primed for misbehavior linked blackness not only with crime and cheating but with being irresponsible, unreliable, self-centered slackers.

This result offers pretty convincing evidence in itself that the connection between black and bad is not just a metaphor we all have learned over the years, but rather it is deeply associated with our ancient fear of filth and contagion. But Sherman and Clore wanted to look at the question yet another way. If the association between sin and blackness really does reflect a concern about dirt and impurity, then this association should be stronger for people who are preoccupied with purity and pollution. Such fastidiousness often manifests as personal cleanliness, and a proxy for personal cleansing might be the desire for cleaning products. The researchers tested this string of psychological connections in a final study, again ending with the Stroop test.

The results were unambiguous. As reported in the August issue of Psychological Science, those who expressed the strongest desire for an array of cleaning products were also those most likely to link morality with white and immorality with black. But here is the really interesting part: The only products to show such an association were Dove soap and Crest toothpaste, products for personal cleanliness. Items such as Lysol and Windex did not activate the sin-blackness connection. In short, concerns about filth and personal hygiene appear central to seeing the moral universe in black and white.

These findings have obvious implications for our understanding of racial prejudice. Although scientists have not yet investigated whether people of different races perform the same way on the moral Stroop test, research on other types of unconscious associations has shown racial differences [see “Buried Prejudice,” by Siri Carpenter; Scientific American Mind, April/May 2008]. As Sherman and Clore note, this country once had a “one drop of blood” rule, which meant that even a trace of African lineage “tainted” an otherwise white lineage. These official practices may be gone, but this new study may help explain why black is linked to immorality and impurity on a fundamental level in many people’s minds.