“This is mines!”
Mines? Can you really dig that?
It’s not standard English, that’s obvious: we’ve all learned that the predicate form of my is mine. Who hasn’t, in younger years, gotten something such as a Valentine card showing insects digging for gold with the text “Bee mine!” It wouldn’t ever be “Bee mines!” – would it? Even the monolexemic seagulls in Finding Nemo say “Mine! Mine!” not “Mines! Mines!”
And yet some people still use mines. And, as we sense instantly, it has an air of… immaturity? Youthful innocence? Something like that? It’s not exactly like the double-plural as seen in, for example, “Nasty hobbitses” – it doesn’t have that creepy tone. But it’s also not flavourless like the double plural in children. (What, didn’t you know that children is a double plural? The singular is child, and one old plural suffix – still seen in German – was –er, and another – also still seen in German, and evident in some old English words – was –en, and they got stacked together on child, with the first e dropped out. I’m tempted to say it’s because whenever there are several kids it always seems like there are twice as many as there actually are.)
Where does that extra –s come from? The Oxford English Dictionary explanation is straightforward and inarguable: it’s added by analogy with ours and yours. But somehow, because we have mine already, that –s can carry a flavour of some other –s suffixes.
Other? Sure. There’s the plural, of course, but if you can hear or see not just “These are mines” but also “That’s mines,” it’s clearly not a simple matching plural form. No, there are a couple more. One comes from the genitive used adverbially, which means the –(e)s that became –’s and –s’ but originally was much more widely used. We see it, among other places, in nights as in “She works nights” (contrast that with “She works hours,” which means not ‘she works hourly’ but ‘she works for a time period of multiple hours’), in besides to mean ‘in a by-the-side manner’, in anyways to mean ‘by any way’ (no, that’s not a plural foolishly added to an obviously singular word), and in amidst with an accidental extra t to give a sense that is very similar to amid but may signify something more distributive.
The other –s is what lexicographers call “hypocoristic,” which means it’s a diminutive form for nicknames, pet names, et cetera. You may know that Prince William’s nickname is Wills. There’s also Babs for Barbara, the friendly British term of address ducks (“I’ll ’ave it up right away, ducks”), din-dins for dinner, and so on. It’s related to the –sy suffix as seen in teensy, artsy-fartsy, Banksy, Betsy, and Nancy.
Neither the adverbial nor the hypocoristic is thought to have had a role in the addition of the s to mine. But they may influence its reception and use now. After all, few people look words up in etymological dictionaries before using them, but everyone makes conjectures based on other things that sound and feel similar. Saying “That’s mines” may make it feel more ongoing or widespread than “That’s mine,” or may make it feel cuter. Or may just make it feel like it matches “That’s yours” better.
Mainly, though, when you read it, it will make you think of who uses it – who you have heard or seen using it, or who you imagine would. If you’re in Scotland or the north of England, you may hear it from various people, as it is said to have a certain regional currency; it’s attested since the 1600s and isn’t out of use yet. But if you’re in the US or Canada, you’re more likely to associate it with youth who haven’t had it badgered out of them yet.
As I said, mines (in this sense, as opposed to the plural noun) isn’t standard English. You wouldn’t use it in most documents. But precisely because it has a particular tone and association, you can call it up when you need to set the tone or establish something about a character who’s speaking – or be cute or ironic. Even “wrong” words have their uses. Our lexicon is a great, vast mine full of varied gems; indeed, it’s several mines. Not every word is a diamond, but they’re nearly all valuable for one purpose or another. And if you don’t want this word, well, then, it’s mines. I’ll keep it to toss it in at just the right moment.