We say “rule of thumb” for an approximate measurement or rough guideline when we are uncertain, yet there’s a big misconception about this metaphor’s origin. The OED Online advises readers that “A suggestion that the phrase refers to an alleged rule allowing a husband to beat his wife with a stick the thickness of his thumb cannot be substantiated.” Wikipedia’s entry likewise calls this a “modern folk etymology.”
A quick Google search revealed a 1998 article from The Baltimore Sun, where writer Stephanie Shapiro, noting an earlier debunking by William Safire, states that “In the Encyclopedia of Word and Phrase Origins, ‘rule of thumb’ is additionally defined as a method by which brewers once tested the temperature of a batch of beer: They dipped a thumb in the brew.”
I know one fellow who works in the brewing industry. That rule of thumb no longer applies, if it ever did. Whether that origin from the field of zymology is true or not, I enjoy redeeming a useful metaphor like ours.
Perhaps we need a better rule of thumb for judging words and phrases in fraught times, before we condemn them?
Please nominate a word or metaphor useful in academic writing by e-mailing me (jessid -at- richmond -dot- edu) or leaving a comment below.
Image courtesy of Timothy Valentine at Flickr.