Knocking on wood, and the spoken expression "knock on wood" or "touch wood" are used to express a desire to avoid "tempting fate" after making some boast or speaking of one's own death.
The expression is usually used in the hope that a good thing will continue to occur after it has been acknowledged. So, for example, one might say: "The rain looks like it's holding off, touch wood", or "Knock on wood, I'm much better now.". Another Example would be "I have never had to use my gun before, touch wood".
Brief HistoryIt is commonly thought that knocking on wood has been a superstitious action to ward off evil throughout history involving Pagan belief systems. The same reference claims that knocking on wood is also used in some form of Christianity, but in a different context, where the wood represents the cross. offers another explanation, where here the wood represents the rosary.
Another explanation for this practice is the pagan belief that spirits (dryads) lived in trees.By knocking on the wood of a tree while making some sort of a bold statement, the speaker could prevent the spirit from hearing him and stop the spirit from interfering[citation needed] or out of respect for the wood spirit, touching a tree indicated seeking protection from the particular spirit.
However historian Steve Roud finds no evidence in the British Isles for the earlier theories, suggesting that the superstitions have not been traced beyond children's games of tag of the early nineteenth century. According to Roud, the earliest documented references to "touching wood" are from 1805 and 1828 and concern chasing games like "Tiggy-touch-wood", where you are safe from being "tagged" if you "touch wood", says Roud, "'Tiggy-touch-wood" was an extremely well-known game, and it is more than likely that the phrase was passed into everyday language.
(改编)