Run Groups

[Phokaioglaukos]

From Wikipedia: Origin of the Phrase
The earliest citation comes from Sir William Hope’s The Compleat Fencing-Master, second edition, 1692, page 157: "What he doth, he doth by rule of thumb, and not by art"

The notion that the "rule of thumb" was a law that limited the width of a rod that a man may use to beat his wife has been partially discredited. Wife beating has been explicitly illegal in British law since the 1700s, and has never been legally sanctioned in America. However, at least four judges and other legal authorities from 1782 to 1897 have referred to the bogus law in spite of the fact that it never existed.The non-law gained popularity after feminist Del Martin wrote in 1976:

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Our law, based upon the old English common-law doctrines, explicitly permitted wife-beating for correctional purposes. However . . . 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.
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It is now firmly entrenched as an urban myth.