Nissan Leafs or Nissan Leaves? Plurals of Proper Names
One Ford Mustang. Two Ford Mustangs. One Toyota Prius. Two Toyota Priuses. One Nissan Leaf. Two … what? Leaves? Leafs? And how about: One Toyota Camry. Two … what? Camrys. Camries?
We seldom stop to think about plurals of irregular words because they seldom pose a problem. We already know the rules and most of the exceptions. When you’re making a plural of most words, you just add an S. One pen, Two pens. Words that end in S, CH, SH or X, you just add ES. One boss. Two bosses. One match. Two matches.
The rest are all oddballs and irregulars: child/children, city/cities, knife/knives, man/men. And the nice thing about the irregulars is that, unlike the plurals that follow a formula, irregular plurals are listed right in the dictionary next to the singular form. Look up “goose” and right there you’ll see the plural is “geese.” Look up datum and you’ll see immediately that its plural is data.
So we can divide all common nouns into one of two categories: ones that form their plurals with the simple “add S or add ES” formula, and weird ones. But proper nouns are a different matter. Obviously, there’s no dictionary that contains every proper name that ever existed or could exist. That’s why the publishing industry has a standard guideline: when making plurals of proper names, just apply the basic formula to ALL of them -- regardless of whether they have a generic equivalent with an irregular plural.
“The plural of proper names is formed regularly, by adding S or ES to the singular,” writes “Words Into Type,” an influential guide in the publishing word. The authors add: “Proper names ending in Y form their plurals regularly, and do not change the Y to I as common nouns do.”
So one Camry plus another Camry is two Camrys.
Also one Nissan Leaf plus another is two Leafs.
And Prius, ending in S, if you're following professional publishing standards, takes an ES ending: One Prius, two Priuses. (Regardless of what a recent campaign by that company would have you say.)
It’s a good system because it allows for the rapidly changing and quirky nature of product naming. Sure, if proper nouns followed the formula for common nouns, we could follow the dictionary’s guide for “leaf” and get “Nissan Leaves.” But what if, the very next year, the company rolled out its brand-new Pleaf? No dictionary would help us there. So we’d end up with Nissan Leaves and Pleafs. And that would be just silly.
And by the way, publishers don't let companies tell them how to form capitals. So it doesn't matter that Nissan would have everyone write LEAF. Most publishers will follow their own styles, many of which call for Leaf.