From Scientific American:
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.