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Across different cultures, variations of this tradition exist. In Turkey, individuals pull their left earlobe and knock on wood twice. Italians and those in Catalonia say “tocca ferro,” translating to “touch iron.” Sweden’s twist involves throwing pepper over one’s shoulder while saying “peppar, peppar, ta i trä,” which means “pepper, pepper, knock on wood.” Interestingly, in Brazil and Portugal, the practice involves knocking three times on furniture without legs, making many standard pieces ineligible.

What connects these diverse customs, and what insights do they offer into human nature?

The Ancient Tree Spirit Theory and Its Critiques

The most enchanting explanation links “knock on wood” to pagan traditions from ancient times. This theory posits that Celtic and Indo-European cultures believed spirits resided in trees—particularly oak, ash, and hazel. Knocking on a tree trunk may have been a way to awaken these spirits to seek protection, express gratitude for luck, or banish malevolent entities from the woods.

It’s a romantic narrative. Throughout ancient Europe, sacred groves served as meeting points between the divine and humanity. The Druids revered the oak tree, while the Scandinavians considered the ash tree as central to their cosmology, exemplified by Yggdrasill. The Germanic Norns—a trio of fate-wielding goddesses—symbolized destiny through the World Tree.

However, folklorists Jacqueline Simpson and Steve Roud argue in A Dictionary of English Folklore that there is no concrete link between these ancient beliefs and our current practice of knocking on wood. Over a millennium separates the Christianization of Europe from the first documented mention of touching wood, suggesting discontinuity in the tradition.

The Game of Tag That May Have Started It All

What about the phrase’s true origin? The most supported theory traces it back to a Victorian-era children’s game.

The earliest documented reference to “touch wood” as a superstitious practice appears in Ballads in the Cumberland Dialect, published in 1805 by R. Anderson. Folklorists link it to a game called “Tiggy Touchwood,” a version of tag where players remain safe from being caught as long as they touch something wooden, like a door or a tree. The act of touching wood was perceived as a protective measure.

Roud, a prominent scholar in folklore, supports this connection in The Lore of the Playground:

“Given that the game revolved around ‘protection’ and was well-known to both children and adults, it almost certainly birthed our superstitious practice of saying, ‘touch wood.’ The notion of it originating from tree spirits is unfounded.”

Religious and Historical Theories

While the game theory stands out due to its solid backing, it’s also intriguing to consider the other narratives associated with the superstition.

The Christian Cross Theory posits that the act of knocking on wood invokes the protective powers associated with Christ’s crucifixion. While various religious relics, such as the True Cross, were venerated for their supposed safeguarding capabilities, this theory seems more a reinterpretation through a Christian lens than a reflection of the practice’s original roots. Scholars note the absence of medieval references linking this practice to superstition, suggesting it likely evolved later among those seeking divine protection.

The Jewish Persecution Theory links this custom to covert signals allegedly employed by Jewish communities for safe passage during the Spanish Inquisition. While this theory offers another potential motivation for the act, verifying it is challenging, and it appears infrequently in academic discussions. Its inclusion highlights the vast array of explanations people have devised for this custom.

The Miners and Sailors Theory suggests a more pragmatic basis: knocking on wooden beams to test their stability, which may have led to caution in superstitions about safety. Similarly, sailors would knock on wooden decks for good luck while at sea. Together, these theories illustrate how everyday safety behaviors can transform into superstition over time—even without direct evidence.

Why Our Brains Continue the Habit

This is where it gets intriguing. Many individuals who recognize the irrationality of their actions still continue to do them. The reason lies in certain cognitive processes, distinct from notions of tree spirits or sacred relics.

Jane Risen, a behavioral science professor at the University of Chicago, has explored this contradiction in depth. In a 2016 article in Psychological Review, she discovered that people can recognize certain beliefs as irrational yet still choose not to challenge them—a phenomenon she identifies as “acquiescence.” She explained:

“We find individuals holding onto beliefs that they consciously acknowledge as irrational. They might say, ‘I know this is silly, but I’ll do it anyway.’ These beliefs arise from fundamental cognitive processes.”

Human thought operates on two systems. The fast, intuitive one reaches conclusions before the slow, deliberative one can catch up. As Risen illustrated, “Detecting an intuitive error doesn’t necessarily prompt correction. Some instincts are notably hard to shake.”

Moreover, researchers from the University of Chicago Booth School of Business published a 2013 study in the Journal of Experimental Psychology, indicating that the physical act of knocking on wood is as significant as the verbal expression of the phrase.

The study revealed that participants who knocked downward—pushing their hands away from their bodies—perceived bad outcomes as less likely than those who knocked upward or simply held an object. This suggests that the physical motion correlates with a feeling of dispelling bad luck—a concept similar to other rituals like spitting or tossing salt.

Additionally, there’s an emotional benefit involved. As Risen mentioned, “These beliefs and actions can help regulate our emotions.” When you knock on wood, it often alleviates some worries.

Researcher Jacqueline Woolley at the University of Texas at Austin found that belief in superstitions tends to peak around ages five and six, before skepticism sets in. Meanwhile, Nadia Brashier, a Harvard researcher, noted that adults around age 70 usually display fewer superstitious tendencies compared to those around 19, primarily due to experience recalibrating their perception of cause and effect.

The Meaning Behind the Knock

What both folklore and research agree on is that the expression “knock on wood” is likely not rooted in ancient practices as some may suggest. Its historical basis is traceable to the 19th century, probably linked to children’s games of tag. While the theories surrounding paganism, Christianity, or persecution are compelling, they lack substantial evidence.

The enduring quality of this tradition can be attributed to psychology. Regardless of whether it originated from a game like Tiggy Touchwood, a relic of the True Cross, or a covert knock on a synagogue’s door, the behavior persists because it resonates with human cognition. We inherently seek to exert control over the unpredictable, and this small, tangible action—touching something solid and pushing away bad energy—provides a fleeting sense of security.

Next time your hand instinctively reaches for the nearest wooden surface after a hopeful declaration, remember: you’re participating in a practice that spans cultures for at least two centuries, possibly longer. Whether it’s seen as habit, superstition, or a brief manifestation of hope, the underlying drive remains unchanged: to cling to the positivity in our lives.