Declensions in English are less common than some other languages, but they are still used. One such use is for plurals, usually achieved by adding an s to the end of a word, e.g. cow vs. cows. However, this is not the only way we indicate plurality in English. Other forms exist, such as bus vs. buses. And sometimes we don’t even decline at all (sheep).
So, how do we pluralise virus?
Latin Origins
Many people argue that virus has Latin roots and should follow Latin rules, becoming “viri” in the plural form. However, this poses a few issues.
Firstly, “viri” is the genitive form of “vir,” which means “man” in Latin. Essentially, it indicates possession, as in “a man’s spear.”
Secondly, “vira” was the old Latin plural for “virus.” While New Latin does use “viri,” it shows that even in Latin, the rule isn’t as simple as changing “-us” to “-i.”
Lastly, and this one is more subjective, it simply doesn’t sound right. “Viri” is an odd word to say and doesn’t sound English at all.
The correct form, in fact, follows the same pattern as words ending in “-us”: add an “-es” to the end. Therefore, like “buses,” “virus” becomes “viruses.”
So, now we have resolved it. We can apply the same logic to other words where people try to make similar arguments. If you look up “virus” in the dictionary, it will confirm that the English declension is the correct one to use, not the Latin.
Therefore, it’s “walruses,” not “walri.” It’s “cactuses,” not “cacti.” It’s “funguses,” not “fungi.”
Wait, hold on. That last one doesn’t seem right. “Funguses”?
Why, Fungi, Why?
For some reason, as a native speaker, “funguses” sounds wrong. I have always heard and said “fungi.” “Funguses” just doesn’t sit right. If you look up the word, most sources will state that “fungi” is the plural. Why? Because it’s of Latin origin, of course!
It appears that English has adopted Latin declensions for certain words. Technically, “funguses” is also acceptable, but it is less common in modern English.
I also lied in the previous section. “Cacti” is actually a perfectly acceptable plural form of “cactus” as well. Personally, I prefer “cactuses,” but a quick Google search indicates that I’m in the minority on that one.
So, the real rule is that for words of Latin origin ending in “-us,” you should sometimes use the Latin declension, and sometimes use the English declension, depending on some arbitrary rule that isn’t explicitly defined.
Therefore, we can have “platypuses,” but not “platypi”; “walruses,” but not “walri”; “viruses,” but not “viri”. We can use both “funguses” or “fungi”, “cactuses” or “cacti.” We can also use either “octopuses” or “octopi.”
Wait, what?
Ode to the Kraken
Why is “octopi” an acceptable plural form for “octopus”? “Octopus” isn’t Latin, it’s Greek! If anything, it should follow the Greek declension and become “octopodes.”
It turns out that English doesn’t just borrow words from other languages; it also assimilates grammatical rules and applies them to words that never originally had them. Consequently, both “octopi” and “octopuses” are acceptable ways to pluralize “octopus.” Some people argue that we should say “octopodes,” but it doesn’t appear to be widely used.
So, the real real rule is that for words ending in “-us,” regardless of their origin, you should sometimes use the Latin declension and sometimes use the English declension, depending on some arbitrary rule that isn’t explicitly defined.
Actually, There Is No Rule
The actual rule is that there are no definitive rules. English, though of Germanic origin, has assimilated words and grammatical rules from Celtic, Latin, Greek, Chinese, and many other languages. We even have multiple ways of saying the same word sometimes. English is a descriptive language, meaning that the people dictate how it should be spoken, rather than a central authority telling us what is correct. The way we speak and the words we choose to use ultimately become the ones that sound right to us, the ones that we enjoy saying.
Sometimes there is no right or wrong answer. Should I say “cactuses” or “cacti”? Say whatever you prefer! As long as you enjoy saying it and people understand you, you’re saying it right.
Right?
