Physical and moral purity are interchangeable, allowing people to truly wash away their sins

Credit: The University of Vermont

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SYDNEY, 8 September 2006: Physical and moral purity are psychologically intertwined – even interchangeable in some cases, new research shows.

"Lady Macbeth's hope that a little bit of water would clear her of the treacherous murder of King Duncan might not have been a product of literary creativity, but of Shakespeare's acute understanding of the psyche," write Chen-Bo Zhong of the University of Toronto in Ontario, and Katie Liljenquist of Northwestern University in Chicago.

They refer to the famous scene in Shakespeare's Macbeth, where Lady Macbeth - wracked with guilt at her crimes - tries to wash away her sins along with imaginary bloodstains on her hands.

In a paper published today in the U.S. journal Science, Zhong and Liljenquist argue that throughout history and across cultures, people have always felt the need to clean themselves when their moral purity is at stake – a phenomenon they dub "the Macbeth effect".

To test their theory, Zhong and Liljenquist asked volunteers to focus on ethical or unethical deeds, and then to make choices relating to physical cleanliness. According the researchers, volunteers who had been thinking about unethical deeds were more likely to make choices indicating a desire to be washed.

For example, they were more likely to interpret the word fragment "w _ _ h" as "wash" rather than "wish", and to rate cleaning products as more desirable than other products. They were also more likely to choose an antiseptic wipe over a pencil as a gift.

Zhong and Liljenquist then set out to test their theory that physical and moral purity are interchangeable – that physical cleansing acts as a surrogate for moral purification.

Volunteers were asked to describe an unethical deed from their past, and were then given the option of cleaning their hands with an antiseptic wipe.

Afterwards, participants who had chosen to clean were less likely to volunteer their time to help a desperate graduate student with another research study. They were also less likely to express feelings of guilt, regret, shame or embarrassment in a survey.

According to the researchers, these findings suggest that physical cleansing restores our moral self-image. They conclude that the desire to wash is a human coping mechanism, which has evolved to alleviate feelings of guilt when we behave unethically.

"Physical cleansing has been a focal element in religious ceremonies for thousands of years," they write, pointing to rituals involving washing that are central to Christian, Islamic and Hindu faiths.

"Daily hygiene routines such as washing hands, as simple and benign as they might seem, can deliver a powerful antidote to threatened morality, enabling people to truly wash away their sins.

"Lady Macbeth's desperate obsession with trying to wash away her bloodied conscience while crying, ‘Out, damned spot!' … may not have been entirely in vain."