Saturday, 4 August 2012

origin of the phrase 'rule of thumb'

At a workshop today about edible weeds, we discussed the danger of tasting unknown plants, and the group agreed that it would be generally safe to try a tiny piece of foliage from a plant. (But I guess it would be most unfortunate if anyone tried that on a poisonous toadstool.)

One participant said he'd heard the phrase 'rule of thumb' originates from the idea that it's fairly safe to try a piece of leaf that's smaller than a man's thumb.

I can't see any references to this origin on the Internet. In fact, it seems more likely that the phrase comes from the use of the thumb as a rough measure of length. Wikipedia points out:
 The use of a single word or cognate for "inch" and "thumb" is common in many other Indo-European languages, for example, Frenchpouce inch/thumb; Italianpollice inch/thumb; Spanishpulgada inch, pulgar thumb;Portuguesepolegada inch, polegar thumb; Swedishtum inch, tumme thumb; Sanskritangulam inch, anguli finger; SlovakpalecSlovenepalec inch/thumb, Czechpalec inch/thumb.
By the way, it was a great workshop. I as I've said before and before and before, our thinking often depends on the words we use. If I call this lovely little plant a weed, it might irritate me to see it growing in my garden.

But if I call it a herb, or even a potherb, or just plain old 'food', then it's a different story. I think it's chickweed, but I'm not sure enough to say so straight out. I'd better sign up for another weed workshop, or perhaps I should consult Doris Pozzi's handbook of edible weeds. (She presented the workshop.) 


proud womon said...

rule of thumb was a big saying 'in my day' - that would be when we were growing up parlance - we do seem to be 'of an age'... and 1 inch was always associated with the end of thumb to first joint (although the average that figure is based on is dubious - womyn wouldn't have figured into the way they measured - nor small men!!)

i love the idea of an edible weeds workshop - but i too would be hesitant to try something i didn't know well - perhaps a green leafy plant i would take a bite - but a mushie, no (i'd wait until someone else tried it first - if they were okay then....)

parlance said...

proud womon, from things I've read on your blog, I'd say we're about the same vintage. Like fine wine, we're aging well.

One of the good things about the workshop was that we all reached down, pulled a leaf or two, and ate it. I felt quite brave. I still feel okay, lol.

parlance said...

proud womon, I forgot to say, I wouldn't even eat a mushie if the person was okay afterwards, because there's a danger the poisonous ones can kill you months later. They damage certain internal organs, forget which.