English is a pretty weird language. (Link to article on English being weird). It’s a thrown together mishmash of words from Germanic, Old French, Latin, Greek, and even more out-there roots. Few other languages allow you to combine words from so many different sources into grammatically correct sentences.
Unfortunately, this also makes English a bit…irregular at times. And one of its most irregular aspects is its plural system. And I’m using the word “system” there, very very lightly.
The Simple Rules
Plurals in English start simply—but then get rapidly more complex. Let’s refresh the basic rules. For most words, you just add an “-s” onto the end. Cat becomes cats. Computer becomes computers. Okay, that’s simple enough, but what about all those words that don’t just take an “-s.” “Most” leaves the door open to a lot of other options.
Well, if the word ends with a vowel and then a “-y,” you just add an “-s” as normal. Boy becomes boys. Toy becomes toys. Pretty easy. On the other hand, if a word ends in a consonant then a “-y,” you strip the “-y” and replace it with “-ies.” Body becomes bodies. Memory becomes memories. That’s a little more complicated, but still kind of okay.
Now, if the word ends in “-ch,” “-s,” “-sh,” “-x,” or “-z,” add an “-es”. Bus becomes buses. Witch becomes witches. Dish becomes dishes.
And if the word ends in an “-o” you tack on an “-es” too. Hero becomes heroes. Potato becomes potatoes.
And, eh, yeah we’ve already hit some big problems. What about stomach? Its plural is stomachs, not stomaches. And piano? Its plural is pianos.
And thus we enter the wonderful world of exceptions—of which there are many. Stomachs is okay because there’s another, addendum rule that can be applied. If a word ends in a “-ch” that’s pronounced as a hard k like in the word eunuch, it just gets an “-s.” Eunuch becomes eunuchs, not eunuches.
But piano is a little trickier. Most words ending in “-o” really do take an “-es”—except all those that don’t. And most Italian loan-words ending in ”-o” (which piano is, it means soft) are in the group—except those that aren’t.
And really, this is where things fall off the wagon. Any and all attempts to add easy to learn plural rules are undercut by exceptions, edge-cases, and just plain weirdness. The plural of goose is geese so, of course, the plural of moose is meese. Or is it gooses and mooses?
Welcome to English, isn’t it fun?
Why Things Are This Way
As I mentioned at the start, English is a hodgepodge of different languages. And all these languages have their own, different plural systems. The weird plural rules and exceptions often occur when some words use the original plural (or some variation on it) and others use an anglicized version.
Take the word “appendix,” which comes from the Latin word, appendere meaning “to hang upon.” It has two acceptable plurals: appendices and appendixes. Appendices is the English interpretation of the appropriate Latin plural form, while appendixes is the Anglicised plural of the word—there’s just an “-es” on the end.
But some words with a Latin etymology only have one generally accepted plural form. For example:
- Matrix, matrices.
- Fungus, fungi.
- Cactus, cacti.
- Axis, axes.
- Parenthesis, parentheses.
Really, other than through just reading, listening to, and speaking English, there’s no way to know how to pluralize one of the many (many, many) irregular exceptions to any rule you could care to mention.
And overthinking things can lead you far astray. There’s a myth that the plural of octopus is octopi. It’s not: octopus is of Greek origin, so really, the plural form would be octopodes—but octopuses is totally acceptable. The plural of hippopotamus, on the other hand, is hippopotami—though, again, hippopotamuses is fine. Just don’t get caught out by rhinocerotes.