Mark Johnson and George Lakoff have written several compelling books based on the premise that humans must use conceptual metaphors to understand abstract concepts.  For example, we say “Things are looking up” to express optimism (i.e., good is up).

Lakoff and Johnson actually go further. They argue that without metaphors, we would have no meaningful understanding of most abstract concepts.  One of those otherwise elusive abstract concepts is morality.

In Philosophy in the Flesh (1999), Lakoff and Johnson write about many of the metaphors we use to understand moral goodness (we often use more than one metaphor to express an abstract concept).  One of the metaphors we often use for talking and thinking about moral purity is cleanliness.

Purity is . . . contrasted with being soiled, tainted, blemished and stained.  For the most part, in the metaphor of moral purity, it is the body that is the source of impurity.  In more extreme versions of the metaphor the body is seen as disgusting and even evil . . . Being pure . . . means being rational, following only the commands of reason, and not letting [ourselves] be tainted by anything of the body, such as desires, emotions or passions.

(Page 306).  Lakoff and Johnson point out that moral purity is the opposite of immorality, thus giving rise to expressions like the following:

• She’s pure as the driven snow.
• He’s a dirty old man. 
• She has a pure heart.
• Let me be without a spot of sin.
• That was a disgusting thing to do!
• They need to clean up their act.

As Lakoff and Johnson point out, the doctrine of original sin holds that humans are inherently tainted and impure, and that they therefore “act immorally when left to their own devices.”

But can this sensory-motor basis for morality be tested? In the September 8, 2006 edition of Science, Chen-Bo Zhong and Katie Liljenquist describe several experiments in an article titled “Washing Away Your Sins: Threatened Morality and Physical Cleansing.”  [The article is only available online to subscribers].  The authors focused on exploring the well-known psychological association between bodily purity and moral purity.

As a preliminary matter, the authors noted that physical cleansing such as bathing and washing hands is at the core of the religious rituals of Christians, Mandaeanists, Sikhs, Muslims and Hindus.  The authors recognized the work of Lakoff and Johnson in suggesting that humans are “predisposed to use categories that are based on bodily experience (such as clean versus dirty) to construct complex social categories (such as moral versus immoral).”

Sure enough, the three psychological studies conducted by the authors provided evidence for the “MacBeth Effect”: Exposure to one’s own and even to others’ moral indiscretions “poses a moral threat and stimulates a need for a physical cleansing.”  Further, physical cleansing resulted in a reduction of “moral emotions” (but did not influence nonmoral emotions).  The details are in the article, but the authors sumarize it as follows:

This effect revealed itself through an increased mental acessibility of cleansing-related concepts, a greater desire for cleansing products, and  a greater likelihood of taking antiseptic wipes.

There you have it. These experiments constitute additional examples of the connection between sensory motor experiences and systematic high-level abstract thought. 

For more on the theory of Lakoff and Johnson, I heartily recommend Metaphors We Live By, Philosophy in the Flesh and Moral Imagination.