Where did we get the phrase, “Rule of thumb?” One common explanation is that it refers to a legal precept that states a man was entitled to punish his wife with a stick no thicker than the thickness of his thumb. This explanation is widespread. The notion is bizarre, which encourages people to share it. Spousal abuse has been widespread and accepted throughout much of history. It is easy to imagine that there might have been legal limitations on the accepted severity of the abuse.
I’m not sure where this explanation originated, but it’s bullshit. Turns out, it was never part of British or American law.
It would seem to me that there is a simpler explanation. Might it not be that the distance from the knuckle of the thumb to its tip is roughly one inch? The word, “rule” can refer to a measuring device, a ruler. So you’d have the thumb acting as a rough measure of one inch.
I performed two searches on Google with the phrase, “rule of thumb.” In one search I included the word “wife,” and in the other search I included the word, “inch.” The hits including “wife” were about three times the hits for “inch” – 23.4 million versus 7.79 million. I’m not sure what this means, except perhaps that it reflects the emotional impact of the two possibilities.