September 18, 2001

knock on wood

I've looked in many books on slang terms to find the origin of knock on wood and even touch wood, as my friend from the U.K. says, and cannot seem to find anything.

This saying is commonly invoked when knocking on something wooden to assure continued good luck, or to ward off bad luck: "The car's still in good shape, knock on wood." It's a standard English idiomatic expression, so you won't find it in a book on slang.

The origin of the expression is almost certainly connected with a religious belief or superstition, but the exact nature of the belief or superstition is unknown. It may derive from an ancient pagan belief that knocking on a tree was a way to ward off evil spirits, or to call upon protective spirits who supposedly lived in certain trees, especially the oak. Another possible connection is the Christian ritual of touching a wooden crucifix when taking an oath or praying for good fortune. The early Christians may have thought they were touching part of the genuine cross used in the Crucifixion. Later it was thought that touching any wooden crucifix, or part of a crucifix, would confer the same benefits, as would touching any piece of wood that once was part of a sacred tree.

The British equivalent, as you point out, is touch wood, an expression first recorded in 1908 in the Westminster Gazette. In the 1800s there was a game called "wood tag" or "touch-wood" in which the player who succeeded in touching wood was safe from capture. But the fact that the game was also called "touch-iron," a piece of iron being substituted for wood, makes the connection between this game and the expression touch wood fairly unlikely.

A few cross-cultural notes: Germans knock on wood (auf Holz klopfen), but Norwegians knock on the table.

It's hard to find a piece of solid wood indoors. I can understand knocking on a table with a pathetically thin wood veneer, but not on Formica painted to look like wood. And why do some people knock on their heads when saying knock on wood?

Carol