The origin of this phrase has some controversy and it is not generally known for certainty were it originates. There are a number of different potential origins for this phrase but I will focus on one common explanation. One common explanation has to do with the custom that men were allowed to beat their wife as long as the item that they used was no larger than the man’s thumb.
It appears that this custom was in practice in the 17th century and perhaps even earlier. However, it does not appear that the rule of thumb was ever a set law in
As the feminist movement evolved and women were granted more rights this phrase began to change and no longer referred to the beating of a wife. I am glad that this phrase has evolved over time and that its original meaning is no longer the common practice in most Western societies.