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Explore some of the irregular plurals in English, including bacterium.

Irregular plurals in English

Bacteriasbacteriaebacterium: which of the three plurals of bacterium is the correct one? Read on, I’ll enlighten you soon as to the correct irregular plural.

Are you already awarding yourself a pat on the back for knowing the right answer? With English spelling and grammar setting a fair few traps for the unwary, it’s a reason for a heartfelt ‘phew’ of relief that many plurals of nouns are straightforward to form. In most cases, all you need to do is to tack an ‘s’ on to the end of the singular:

Singular Plural
shop shops
donkey donkeys
roof roofs
patio patios
epoch epochs
pizza pizzas

Although some other English plurals can be slightly more tricky, there are a few basic rules which are easy to follow: if you’d like a quick refresher course, why not visit our online guide?

Women, geese, teeth, and children: the Old English survivors

There are a handful of exceptions to these rules, mainly plurals of words that come from Old English. So instead of ‘a flock of gooses’ we say ‘a flock of geese’, we brush our teeth (not ‘our tooths’), my sister has three children, not ‘three childs’, and police arrested four men rather than ‘four mans’. The proportion of such plurals compared with the more usual formations is very small, so it’s easy to learn them. If you’re not sure, all good dictionaries will give the standard plural forms.

Unfortunately, the singular forms of some of these common English words now seem to be causing difficulty. There’s a recent trend to use the plural spelling ‘women’ as a singular noun. This mistake crops up in all types of writing, from news articles and academic journals to blogs:

Eileen was a lovely women, who went about her daily duties in a very refined way.

X  A single women can have a child now, but not without facing some human complications.

Although ‘men’, the plural of ‘man’, works in just the same way as the plural of ‘woman’, with the change of ‘a’ to ‘e’, for some reason the erroneous use of the plural spelling ‘men’ to refer to a man is much more rare… for now.

Old Norse eggs and Italian pianos

But I digress: one of the main causes of plural puzzlement lies in the fact that English is full of words that have been borrowed from other languages. These loanwords are believed to make up half of all English words, and have been enriching our language for over a thousand years. Many are so well established that we don’t realise they’re borrowings at all: Old Norse gave us freckle and egg; splinter and gherkin are Dutch; hazard and alcohol are Arabic.

Once they’ve been absorbed into English, most noun loanwords behave in the same way as other English words when it comes to forming their plurals: hazards, freckles, splinters, etc. The main categories of borrowed words that can cause problems for English speakers and writers are those which are sourced chiefly from Latin, ancient Greek, French, and Italian.

You can’t blame anyone for being confused: in effect, there are no hard and fast rules as to whether the plurals of such words are:

  • formed according to English rules: piano -> pianos (Italian); virus -> viruses (Latin)
  • formed according to the rules of the parent language: criterion -> criteria (ancient Greek); bacterium -> bacteria (Latin);  paparazzo -> paparazzi (Italian)
  • formed according to either English rules or those of the original language: cactus -> cacti/cactuses (Latin); virtuoso -> virtuosos/virtuosi (Italian); chateau -> chateaux/chateaus (French)

As before, the best way to ensure you’re correct is to check a good dictionary – it will always give the accepted plural forms of nouns.

Tangled up in the coils of the language octopus

X Sea lions are carnivores and eat fish, squid, octopi, crabs, clams, and lobsters.

As the above example (taken from a US scientific publication) shows, a little knowledge of Latin and Greek can be a dangerous thing and sometimes leads people into error. The writer clearly knows that some Latin plurals are formed by changing the ‘–us’ ending of a singular noun into ‘-i’ for the plural, as in alumnus -> alumni. However, octopus is ultimately borrowed from a Greek word and not a Latin one, so it’s incorrect to form the plural according to the Latin rules. If you wanted to be ultra-correct and conform to ancient Greek, you’d talk about octopodes, but this is very rare: the Anglicized plural, octopuses, is absolutely fine.

Given that people are unsure about the origins of English words and the correct formation of their plurals, it’s hardly surprising that a raft of mistakes have arisen. Take criterion, for example. It’s borrowed from ancient Greek, and the plural is formed according to Greek grammar: criteria. However, many people use criteria as if it were a singular noun (that is, they use it with a singular verb):

We thought that criteria was satisfied.

It gets worse: once people start thinking that words like criteria and phenomena are singular rather than plural, there’s a tendency for them to want to add an ‘s’ to form the ‘plural’, as these erroneous examples show:

First there were three criterias that were considered.

Some pilots fly to specific regions to witness natural phenomenas like hurricanes.

Compounding the errors yet further…

This brings us back to the question I posed at the outset, regarding the plural of bacterium. It’s time to come clean and admit that it was a trick question: all the ‘plurals’ given are wrong. The correct way of referring to more than one bacterium is bacteria:

√ Some bacteria are becoming increasingly resistant to antibiotics.

Her “wildest” theory is that a $30 device could zap disease-causing viruses, bacterias, and parasites.

Two bacteriums yielded enzymes capable of removing both A and B antigens from red blood cells.

How long does the bacteriae live on furniture, wooden products, etc ?

The last example indicates that some people believe bacteria to be a Latin singular and so the plural is formed according to the Latin rules for words such as alga -> algae. A commendably logical approach, and showing a partial understanding of Latin, but totally wrong because it’s based on the misconception that bacteria is singular. The bacteriae plural form appears to be pretty common, however, and appears in many online scientific papers, where the writers really should know better.

A similar thing happens with the Greek loanword, phenomenon. Because people think that phenomena is the singular and that it’s a Latin word, they commit a double faux pas and form the ‘plural’ by adding ‘e’ to phenomena:

Did records of events like the comet in the Bayeaux tapestry help early astronomers understand astronomical phenomenae?

Why do you feel compelled to quote ignorami [sic] and idiots?

So what about ignoramus? Should we emulate the above writer (it’s a real example, taken from the Oxford English Corpus) and refer to several ignorami? Nope! Ignoramus is something of an anomaly – true, it’s a Latin loanword, but it was never actually a noun. Those of you who chanted Latin verbs at school (who could forget amo, amas, amat, amamus, amatis, amant?) may dimly recall that the ‘–us’ ending is used for the first person plural form: ignoramus actually means ‘we do not know’. Being a verbal form rather than a noun means that it doesn’t follow that the plural is ignorami. To form the plural in English, you add ‘-es’ to the end (ignoramuses), just as you would with virus -> viruses. Ironically, the person who wrote the question above is revealing their own ignorance.

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