It is, indeed, a tangled web…
These days most of us likely think of a “rule of thumb” as a general rule, a quick and common-sense method for accomplishing a task or solving a problem. Though such rules aren’t strictly accurate or applicable to every situation, they are often a useful way of thinking about or approaching a problem. One well-known rule of thumb that comes to mind is the photographic rule of thirds, a compositional tool that suggests the key elements of an image should be lined up on the lines or intersections of an imaginary 3×3 grid of the photographic frame.
Like many phrases and idioms we use today, the definition for “rule of thumb” has evolved significantly from its original usage. The phrase has two other meanings in addition to the modern one discussed above. The first is its historical origin while the other is a well-publicized, but generally debunked, alternative theory of its origin.
Rule of thumb is historically associated with a simple and conveniently available method for measuring, especially since the width of the thumb of an average adult male is approximately one inch. Its earliest usage is often attributed to woodworkers who used their thumbs to make small measurements as they worked. Before more accurate measuring devices were widely available, people devised a number of body-based measurements including the foot (approx. 12 inches) and the distance from nose to fingertip (approx. one yard) to estimate distance or dimensions. Finally, the traditional method for measuring the height of a horse by hands (now standardized at 4 inches) is, in fact, based on the width of the palm and closed thumb.
Another example, described in an excerpt from Gulliver’s Travels, illustrates a long-time tailors’ rule of thumb:
Then they measured my right Thumb, and desired no more; for by a mathematical Computation, that twice around the Thumb is once around the Wrist, and so on to the Neck and Waist, and by the help of my old Shirt, which I displayed on the Ground before them for a Pattern, they fitted me exactly.”
The debunked theory of the term’s origin has to do with historical references to statements made by a British judge in 1782 supposedly permitting a man to beat his wife with a stick as long as the stick wasn’t thicker than his thumb. There is no direct written record that the judge ever made such a statement, though a number of standard references and biographies of the time refer to it. Whether or not the statement was actually ever made, the judge was criticized for his statement in a cartoon published shortly after the incident.
Much later, in 1976, a feminist activist reviewed the findings of several 19th century American judges who, in turn, had discussed (and rejected) the earlier British opinion (using that term very loosely). The activist wrote that common law had been modified to allow a husband to whip his wife, provided the switch he used wasn’t bigger than his thumb, and referred to the entire matter as “a rule of thumb, so to speak.”
Her reasoning and phraseology was subsequently incorporated into a 1982 report prepared for the United States Commission on Civil Rights. That and other sources are occasionally cited as references for “rule of thumb,” but it appears there is no other connection to the historical or current meaning of the term than the series of misinterpretations described above.
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Posted for Jenny Matlock’s Alphabe-Thursday study of the letter “R.” For Round 5 of this long-running meme, I am focusing on colloquialisms and idioms—words and phrases that are unique to a region or have meanings that aren’t necessarily discernible from the combined meanings of the individual words. I hope you’ve learned as much from this week’s exploration as I have.
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Sources for this post include:
Commentary: Domestic Violence, Folk Etymologies, & “Rule of Thumb”
debunker.com ~ The “Rule of Thumb for Wife-Beating” Hoax
Wikipedia ~ Rule of Thumb
World Wide Words ~ Rule of Thumb