There are a lot of stadia in this city, aren’t there? Do you think there are any octopi in the sea? I’m also curious about the cacti around here: in fact, I’m interested in all the flora and fauna!

You may not find much wrong with the above. Well, hopefully you’ll think “Who on Earth would actually say that!?” But in terms of grammar and vocabulary, it wouldn’t raise too many eyebrows.

What about this though:

There are lots of nice cafés here, but we eventually decided to go to a nice Mediterranean restaurant. We had two pizze for lunch, and two baklavá for dessert. Afterwards, we picked up our Rucksäcke and left.

You’re probably in agreement with my old friend Red Squiggly Line that some of those words are simply not English, only an animal would capitalise a non-proper noun in the middle of a sentence, and why yes of course the s in cafés is pronounced!

But if you look at things objectively in the cold light of general English practice, then the following words are all loanwords: stadium, octopus, cactus, flora, fauna, café, restaurant, pizza, baklava and rucksack. A loanword is a word that has entered the English language wholesale from another language.

What we usually do with loanwords is treat them exactly like other English words. In the case of making a loanword plural then, we usually just add an s. That’s why you order two pizzas, not two pizze (though you should really order only one. Come on).

But we don’t usually do that with the loanwords in the first piece. What sets them apart from the loanwords in the second piece is that they come from Latin, and we tend to treat Latin loanwords with a sort of reverence. We don’t vulgarly slap an s on their backsides and send them off onto the lonely streets of English pluralism, with nary a conjugation to their name. No, we keep their original plural forms, and some of us even take pride in ensuring we use the “correct” form.

But why?

Partly I think it’s because of the awe some people have for Latin, this perception of it as an Ur-language from which so many languages sprung.

There’s also the fact that during the Middle Ages, Latin was the language of Christianity and Learning, and therefore of power. While those days are obviously long gone, Latin seems to have retained some of its prestige, even if we don’t know why. We still use many Latin terms, especially legal terms. Traditionalist Catholics love their Latin Mass (and that was only done away with for regular Catholics in the 1960s). No self-respecting Premiership team of spoiled flouncing millionaires would go without a Latin motto. And who doesn’t get a little electric frisson of power when they know that a pair of those things with eight tentacles are called “octopi?” Probably not everyone, actually. Hopefully.

It’s an interesting case of the curious temporality of languages. Yes, they always evolve, much to the chagrin of purists, but equally some apparent anachronisms survive. I find it fascinating that some people will insist on using the ancient plural forms of certain words in complete disagreement with the normal conventions of their native tongue, all because of the social status that language enjoyed over 1,000 years ago that they’re probably not really aware of. Languages evolve slowly, but so does its relationship with society. Like a glacier, Latin receded slowly from relevance, but it dropped off little nuggets of language as it did so, an odd phrase here or there, or a vestigial convention that we still use today.

So finally, which is correct: octopuses or octopi?

The strict grammarian would say octopuses, because the word has entered the English language and must be treated like most other English nouns.

The realist would say octopi, because most people say that, and usage determines meaning.

I say, whichever one you use, most people will understand, so choose the one you prefer. But if you did go for octopi, take a moment to think of some Ancient Roman marine biologist using the same word. The classics never go out of fashion.