When people are asked to list their favorite metaphor, they typically cite great works of poetry, literature or oratory. Indeed, many metaphors are born from creative insight—Romeo likening Juliet to the rising sun or poet Robert Burns comparing his love to a red rose.

But there is more to metaphor than this.

Some metaphors are not literary creations at all—instead they seem to be built from the ground up, given to us by experience. For example, knowledge—an intangible, abstract concept—is often recast in terms of the concrete experience of sight. To know something is to see it, and so we often say that we see someone’s point or that an idea is clear. Metaphors of this sort—linking the abstract to the concrete, perceptual, and visceral—were studied systematically by the UC-Berkley cognitive linguist George Lakoff and philosopher Mark Johnson, at Brown University.

What they and others realized is that our concepts are fundamentally shaped by the fact that our minds reside in fleshy, physical bodies. As a result, even our most abstract concepts often have an “embodied” structure. In a classic example, people seem to understand moral virtue as if it were akin to physical cleanliness. To be virtuous is to be physically clean and free from the impurity that is sin. As the University of Pennsylvania psychologist and disgust expert Paul Rozin has shown, experiencing morality in terms of the embodied dimension of contagion can lead to some striking behaviors, such as the refusal to wear a sweater belonging to an evil person because it seems somehow contaminated by the evil essence of that person.

It’s clear that people talk about morality in purity terms—whether explicitly expressing concerns about contamination by evil or asserting that one’s “conscience is clean”—but do they also experience morality that way? Could it be that the embodied structure of morality operates covertly to guide moral judgment and behavior?

The Morality of Hand-Washing

Simone Schnall, Jennifer Benton and Sophie Harvey, psychologists at the University of Plymouth, have demonstrated just how this can happen. Having shown in previous studies that inducing disgust or a sense of dirtiness can make people’s moral judgments more severe, they set out to explore the opposite. Might physical cleanliness encourage less severe moral judgments? To test this idea, they had participants read brief vignettes describing morally questionable behaviors, such as falsifying information on a resume. Prior to reading and responding to these vignettes, “cleanliness” was induced either through the activation of purity-related concepts or through the direct experience of hand-washing.

In one study, participants were asked to form sentences from sets of several words. Some sets contained purity-related words, such as clean and pristine, whereas others (in the control condition) contained neutral (non-purity) words. In a second study, participants watched a disgust-inducing segment of the movie “Trainspotting,” after which they went to another room where they read the moral vignettes. Half of these participants were first asked to wash their hands in order to keep the staff room that was being used clean.

In both studies, the experience of “cleanliness”—either through the subtle priming of concepts about cleanliness or by actual cleansing—reduced people’s tendencies to see the behaviors described in the vignettes as morally wrong. Apparently, participants’ sense of physical purity influenced their evaluations of the actions of others (just as the induction of disgust had done in Schnall’s earlier studies). When they themselves were clean and pure, so were others.

Embodied Virtue

This finding, published in the December issue of the journal Psychological Science, contributes to our emerging understanding of the embodied structure of morality. In particular, it demonstrates its bidirectional nature. Previous research has shown that thinking about one’s sins evokes thoughts of, and desires for, physical cleansing. Now we know the opposite is also true—thinking about, or experiencing, cleansing can influence judgments of morality. What’s more, the effect appears to act completely outside of awareness. The metaphorical structure of concepts can guide moral intuition and moral judgment without ever entering conscious thought.

As this finding illustrates, cleanliness—with all its physical manifestations—is part of the concept of virtue. However useful the metaphor of moral purity may be for talking about morality, it does much more—it also infuses the concept of morality itself and may even be fundamental to moral meaning. It’s hard even to imagine a disembodied, purity-free conception of virtue. More than a rhetorical tool, embodied metaphor shapes the very way we experience the world.

Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters editor Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust Was a Neuroscientist. His latest book is How We Decide.