Lesbian rule

A flexible curve: the modern counterpart of a lesbian rule

A lesbian rule was historically a flexible mason's rule made of lead that could be bent to the curves of a molding, and used to measure or reproduce irregular curves. Lesbian rules were originally constructed of a pliable kind of lead found on the island of Lesbos.

The rule is alluded to by Aristotle in his Nicomachean Ethics (bk V, ch. 10) as a metaphor for the importance of flexibility in equitable justice: "For what is itself indefinite can only be measured by an indefinite standard, like the leaden rule used by Lesbian builders; just as that rule is not rigid but can be bent to the shape of the stone, so a special ordinance is made to fit the circumstances of the case."

In the early modern period the term was often used figuratively (as Aristotle had used it) to mean a pliant, flexible and accommodating principle of judgement. In his famous letter to the Louvain theologian Martin Dorp, Thomas More referenced it when reproving Dorp for his attack on Erasmus' In Praise of Folly: "You praise Adriaan for being unbiased, yet you seem to suggest he is no more unbiased than a Lesbian rule, a rule made out of lead which, as Aristotle reminds us, is not always unbiased, since it bends to fit uneven shapes." Samuel Daniel in 1603 described equity as "that Lesbian square, that building fit, Plies to the worke, not forc'th the worke to it". In the later 17th century, the antiquary John Aubrey used the metaphor in a more pejorative sense, implying the distortion of evidence to fit a preconceived theory. He accused Inigo Jones, who had interpreted Stonehenge as a Roman monument, of having "made a Lesbians rule, which is conformed to the stone: that is, he framed the Monument to his own Hypothesis, which is much differing from the Thing it self".

See also

• Flat spline
• French curve