rule of thumb

The phrase is almost certainly an allusion to the fact that the first joint an adult thumb measures roughly one inch, literally a rule (or ruler) of thumb. Since human dimensions vary, any measurement so taken would be only a rough approximation and not to be trusted where precision was required. Rule of thumb dates to 1692, when it appears in William Hope’s The Compleat Fencing-Master:

What he doth, he doth by rule of Thumb, and not by Art.

There is a false legend that has attached itself to the phrase. It says that the original rule of thumb appeared in English Common Law. The alleged law said that it was illegal for a man to beat his wife with a stick that was thicker than his thumb. Beating her with smaller sticks was permitted, and in some regions encouraged, to keep the woman in her place.

While the belief that such a legal doctrine existed is quite old, the specific claim that the phrase rule of thumb comes from such a legal doctrine is quite recent, appearing in feminist texts starting in the 1970s. From Del Martin’s 1976 Battered Wives:

For instance, the common-law doctrine had been modified to allow the husband “the right to whip his wife, provided that he used a switch no bigger than his thumb"—a rule of thumb, so to speak.

While it was certainly true that in many places in the past (and unfortunately to this present day), men were permitted to beat their wives, but this so-called rule was never codified. In fact, this explanation does not appear until relatively recently and its appearances are in American courts that claim such an old English law exists without citing it specifically.

Blackstone in his Commentaries on the Laws of England (1765) contends that in times past a man might be permitted to give his wife “modest punishment,” but states that hitting one’s wife was quite illegal by the late 17th century, about the time the phrase appears, and Blackstone makes no mention of thumbs at all:

the husband also (by the old law) might give his wife moderate correction. [...] But this power of correction was confined within reasonable bounds; and the husband was prohibited to use any violence to his wife, aliter quam ad virum, ex causa regiminis et castigationis uxoris suae, licited et rationabiliter pertinet [other than what is reasonably necessary to the discipline and correction of the wife]. The civil law gave the husband the same, or a larger, authority over his wife; allowing him, for some misdemeanors, flagellis et fustibus acriter verbare uxorem [to wound his wife severely with whips and fists]; for others, only modicam castigationem adhibere [to apply modest corrective punishment]. But, with us, in the politer reign of Charles the second, this power of correction began to be doubted, and a wife may now have security of the peace against her husband; or, in return, a husband against his wife. Yet the lower rank of people, who were always fond of the old common law, still claim and exert their ancient privilege, and the courts of law will still permit a husband to restrain a wife of her liberty, in the case of any gross misbehavior.

And as far as American law goes, the Massachusetts Bay Colony specifically outlawed spousal beatings in 1655. And by 1870, almost all the US states had laws on the books to punish wife beaters, some with very severe punishments attached.

There is considerable legal commentary on the permissibility of wife beating, but only three cases, all American, specifically refer to the alleged doctrine permitting hitting with sticks narrower than a thumb. While these cases reference the alleged doctrine, they do not uphold it. The first is Bradley v. Mississippi (1824), where the judge writes:

I believe it was in a case before Mr. Justice Raymond, where the same doctrine was recognized, with proper limitations and restrictions well suited to the condition and feelings of those who might think it proper to use a whip or rattan, no bigger than my thumb, in order to enforce the salutary restraints of domestic discipline.

Raymond is probably Lord Robert Raymond, a British judge who served from 1724-33. But despite this reference in the Mississippi case, no one has been able to find a ruling by Raymond on wife beating.

In North Carolina v. A.B. Rhodes (1868), the trial judge declared Rhodes not guilty because the switch he used was smaller than a thumb. This was overturned on appeal and the appellate court wrote:

Nor is it true that a husband has a right to whip his wife. And if he had, it is not easily seen how the thumb is the standard of size for the instrument which he may use, as some of the old authorities have said.

And in another North Carolina case, North Carolina v. Richard Oliver (1873), the judge writes:

We may assume that the old doctrine that a husband had a right to whip his wife, provided he used a switch no larger than his thumb, is not law in North Carolina.

The closest anyone has come to identifying such a rule in English law is a supposed opinion of Francis Buller, a judge on the English bench from 1778 to 1800. In 1782, Buller held the opinion (it’s not clear whether his was a legal ruling or just a publicly stated personal opinion) that a man had the right to beat his wife. He was widely castigated in public and called such epithets as “Judge Thumb.” The reaction to Buller’s opinion makes it clear that this was not a widely held right.

So, what we have is a single English judge who in 1782 (probably) held that a man could beat his wife with a stick narrower than his thumb. But, despite belief to the contrary, this was never an established legal principle and is certainly not the origin of the phrase.

(Sources: Oxford English Dictionary, 2nd Edition; Pleck’s “Wife Beating in Nineteenth-Century America,” Victimology, Vol. 4, 1979)

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