Date: Tue, 11 Nov 1997 23:19:57 -0600
From: "Donald M. Lance" engdl[AT SYMBOL GOES HERE]SHOWME.MISSOURI.EDU
Subject: Re: Rima's rule of thumb
This is dueling folk-etymologies.
Yep. OK, I'll put in my two cents.
But without being an expert on this bit of lore, all I can add is that if
you read the OED2 cites of "rule of thumb" (back to 1692) there's no mention
of or hints at beating anywhere. There is however almost always a sense that
"rule of thumb" means something inexact -- hardly the sense of the word in
the "beating" account, where the "rule of thumb" refers to the exact size
something can legally be. I have heard accounts that tie "rule of thumb" to
sailing (measuring the needed thickness of a rope for a given task when as a
sailor you have no ruler) and tailoring (using the width of the thumb to
measure without a ruler or the like -- get it? *rule* of thumb.... Cf. OED2
rock n.3, meaning 1b, where "rock/rack of eye and rule of thumb" is a
tailors' phrase for inexact measurement).
If anyone has the *real* story and the evidence, maybe s/he'd cough it up.
I've always assumed, and have heard so from others, that the rule of thumb
refers to the use of the last joint of the thumb to be an approximation of
an inch. It's not too mucn of a stretch to imagine a taylor or seamstress
measuring the distance from the tip of the thumb or index finger to a spot
that would be an inch from the tip and then using that spot in making "rule
of thumb" measurements. My mother used a spot about so far past the first
crease in the index finger on her left hand. And it's not too much of a
stretch to see sailors (or pirates) using the thickness of the thumb or the
length of the first joint to determine whether a rope would be strong
enough for certain tasks.
To me, assuming that the origin of the thumb-term has something to do with
beating one's wife is like assuming that "Have a nice travel" is the origin
of "have a nice trip." As for the latter, I can imagine someone hearing
another say 'I'm going to travel next week" and responding with "Have a
nice travel," even though it isn't the usual idiomatic expression.