Knock on wood

The other day, walking past two young men who were having a bit of a chat about football, matches and other such seasonal topics, I overheard one of them say "knock on wood". I realized that I use and hear the expression very often, but never thought about where it comes from.

I use the expression out of superstition, to ward off bad luck or unpleasant consequences of actions. I sometimes warn the interlocutor, almost as a verbal reflex, to knock on wood when they say something they don't want to happen. I discreetly knock on wood when I hear of a tragedy or some dire prediction. I'm sure many of you do the same. That's why I thought I'd find out more about the expression.

The origin of the expression is unknown, but some authors point to pagan rituals, when spirits or deities were believed to live in trees. By knocking on wood, they were summoned for protection and to ward off evil. It was also used as a gesture of thanksgiving when the spirits brought well-being and good luck.

The significance of wood carving in other peoples

In Irish folklore the wood is touched to thank the goblins living inside for good luck. The Greeks worshipped the oak because it was the sacred tree of Zeus and the Celts believed that spirits lived in trees. Touching these trees brought good luck.

Like many pagan beliefs, superstition has become part of the Christian faith. Some people associate it with the cross. The Jewish version of the origin of the expression takes us back to the 15th century, during the Inquisition. Jews took refuge from the inquisitors in hidden synagogues built of wood. When newcomers wanted to be let in, they would beat a certain code into the wood, known to the insiders. Many lives were saved in this way and the act of knocking on wood has remained as a gesture of good luck.

The expression itself is relatively modern. In the UK the saying has the form "touch the wood", and records can be traced back to 1899. The American equivalent - knoch on wood - is even more recent, first appearing in a document in 1905.

We now see the expression everywhere: in everyday language, on decorative objects, in literature, even in music.