A few days ago, I mentioned that hadn’t seen the bathroom scales since before we moved house in early October. My wife replied that “it is in the kitchen cupboard”.
For me, scales are ‘uncountable plural’; that is, they always take are, were, these, those etc. Google Ngrams shows that the scale is/was is more common than the scales are/were. But this is complicated by the fact that there are three kinds of scales: snake/fish, weighing and music/map. Snake/fish and music/map scales are countable and therefore can be singular or plural, and Dictionary.com’s entry for weighing scales is “scale2 noun 1. Often scales”.
Weighing scales are “often” uncountable plural because they used to look like this:
where there is sense of “two” like glasses and trousers (and see also “a pair of compasses”).
But most modern scales look something like this:
where the idea of “two” has been lost. A shop owner might tell an assistant “Put it on the scale”. Indeed, soon after I found the scales, our niece asked “Where did you put that scale?”. I replied “I put them in our bathroom” (that is, my wife’s and my en suite). I have since put them in the main bathroom, which our niece uses, but we can go into as well (if she’s not in it). So maybe the “countability” of weighing scales is changing.
This raises an interesting point of second language acquisition. It is very unlikely that ESL lessons include anything about scales (in more than 10 years of ESL teaching, I’ve never encountered them, even in lessons about uncountable nouns). So second language learners/speakers first encounter a word “in real life” and have to figure out how it fits in to what they already know.
So are these three scales related?
Dictionary.com gives the origin of snake/fish scales (scale1) as “Middle English < Middle French escale < West Germanic *skāla; akin to scale2”, and of weighing scales (scale2) as “Middle English < Old Norse skālar (plural), cognate with Old English scealu scale (of a balance)”, so those two are both Germanic, though I’m not sure how they are “akin”. Music/map scales (scale3) is “Middle English < Latin scālae ladder, stairs”, which is in turn complicated by fact that ladders are countable and stairs are usually uncountable plural (though I am reminded of the verse which starts “As I was going up the stair* / I met a man who wasn’t there”). From what I understand from Wiktionary, a ladder was/is a scala and stairs were/are scalae. (*I remembered it as “The other day upon the stair”, but research.)
Never Pure and Rarely Simple 