The monetary unit of Swaziland is the lilangeni. English speakers are helpfully reminded that the plural is emalangeni: one lilangeni, two emalangeni.
I don’t mean “Why does SiSwati, the language of the Swaziland, pluralize that way?” That’s easy: as with other Bantu languages, its nouns are in different classes, identified by prefixes, and plurals are a different class from singulars. No, I mean “Why do we feel obliged to use the SiSwati plural when we’re speaking English?”
It’s not normal, you know. It’s not normal for languages, when they borrow words from other languages, to borrow the morphology: the different forms for plurals, possessives, etc., and the different conjugations for verbs.
It’s not even normal for English to do that. We don’t borrow conjugations when we borrow verbs: we don’t say “They massacreront them!” instead of “They will massacre them!” We don’t borrow possessives when we borrow nouns: we don’t say “The radiorum length” instead of “The radiuses’ length” – oh, sorry, that should be “The radii’s length.” Right?
Because sometimes – just sometimes – when we borrow a noun we also borrow the plural form. This is especially true with newer borrowings and with borrowings in specialized areas (science, food, the arts). We’re not very consistent about it, so it can sneak up on you, like so many other ambush rules we have in English.
And there are so many borrowed plural forms – because there are so many plural forms to borrow. Read 9 confusing ways to pluralize words (by me) on TheWeek.com for details on ways and reasons.
But if we’re going to talk about pluralizing things the way we always have in English, there’s one other issue: we haven’t always pluralized using –s in English
Nope. In fact, a thousand years ago, when English nouns had three genders, only the masculine ones got –s (actually –as), and not all of those did either. Other ways of showing the plural were to add –u, –a, –e, or –n, or change the vowel, or do nothing. English has changed a whole lot since then. Noun and verb forms have gotten much, much simpler – thanks to interaction with speakers of other languages, especially Norse and French. You can really thank the French for the fact that we use –s/–es on most words now for the plural.
But since that’s what we do now, should we do it with all new words we steal, I mean borrow? Well, it’ll sure make life easier if we can settle on octopuses. But it might just sound kind of wrong and blah if we order paninos and look at graffitos on the wall. And it would be less fun if we couldn’t jokingly say to a bartender, “I’ll have a martinus. No, not martini – I only want one.” It’s the eternal struggle of English: do you want it easy, or do you want it fun?