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What are irregular plurals in English

Last Updated

October 3, 2025

Table of Content

Tips for Natural Usage

Plurals That Break the Rules

We all have learned that to make something plural, just add “-s”. Like one book, two books. Easy, right?

But then…
You see words like child → children, man → men, or mouse → mice, and suddenly the rule doesn’t work.

These words are called irregular plurals- and yes, they break the usual rules. But don’t worry, once you understand the pattern (or sometimes lack of it!), you’ll get used to them.

Here, we’ll explore what irregular plurals are, why they’re different, and how you can remember them easily.

What Are Irregular Plurals?

Usually in English, to show that there is more than one of something, we simply add -s or -es.
Examples:

Book → Books
Apple → Apples
Box → Boxes

These are called regular plurals because they follow the basic rule.
But irregular plurals are different.
They don’t follow the normal pattern. Instead of adding -s, the word changes form completely—or in some cases, it doesn’t change at all.
Here’s what makes them unique:

Some words change inside the word
Tooth → Teeth
Some words change completely
Person → People
Some words stay the same in singular and plural
Sheep → Sheep

You can’t “guess” these. You just need to learn them over time.

Common Types of Irregular Plurals

To make things super easy, let’s look at the different types of irregular plurals in small groups. Each group shows how the word changes when it becomes plural.

1. Nouns Ending in -f or -fe Changing to -ves

Many nouns ending in -f or -fe form their plural by changing the f to v and adding -es.

Singular	Plural
leaf	leaves
wife	wives
knife	knives
wolf	wolves
life	lives
shelf	shelves
thief	thieves

Exceptions (Add -s instead of -ves):

Some nouns ending in -f don’t follow this pattern and take a regular -s in plural.

Singular	Plural
chief	chiefs
roof	roofs
cliff	cliffs
proof	proofs
safe	safes
belief	beliefs

Optional Forms:

Some nouns accept both forms, though one may be more common.

scarf → scarves / scarfs
hoof → hooves / hoofs
wharf → wharves / wharfs

2. Nouns with Internal Vowel Changes

These nouns change a vowel inside the word to form the plural. No -s or -es is added.

Singular	Plural
man	men
woman	women
foot	feet
tooth	teeth
goose	geese
louse	lice
mouse	mice

This type of change is one of the most noticeable in English and is important to memorize.

3. Nouns Ending in -on / -um → Change to -a

Many words of Latin or Greek origin that end in -on or -um change to -a in plural.

Singular	Plural
criterion	criteria
phenomenon	phenomena
datum	data
curriculum	curricula
medium	media
memorandum	memoranda

In informal usage, regular -s endings are becoming accepted (e.g., “stadiums”), but the original forms are still preferred in formal writing.

4. Nouns Ending in -is → Change to -es

Words of Greek origin ending in -is will form plurals by changing -is to -es.

Singular	Plural
analysis	analyses
basis	bases
crisis	crises
hypothesis	hypotheses
thesis	theses
axis	axes

5. Nouns with No Change (Zero Plural)

These nouns keep the same form in both singular and plural.

Singular	Plural
sheep	sheep
deer	deer
fish	fish
species	species
aircraft	aircraft
series	series
corps	corps

“Fishes” is also correct when referring to different species of fish.

6. Nouns That Use -en Plurals

Words borrowed from other languages often keep their original plural forms.

Singular	Plural
child	children
ox	oxen
brother	brethren (used in religious/formal context)

“Brothers” is now more commonly used in daily language.

7. Foreign-Origin Plurals

Words borrowed from other languages often keep their original plural forms.

Singular	Plural	Origin
appendix	appendices	Latin
bureau	bureaux	French
madam	mesdames	French
monsieur	messieurs	French
formula	formulae	Latin
vertebra	vertebrae	Latin

Both versions (e.g., formulas / formulae) are used depending on the context.

8. Compound Nouns

When a noun is made of multiple words (compound nouns), the main noun is pluralized.

Singular	Plural
mother-in-law	mothers-in-law
passer-by	passers-by
court-martial	courts-martial

f the compound is written as one word, add -s to the end:

cupful → cupfuls
handful → handfuls
spoonful → spoonfuls

9. Letters, Numbers & Symbols

To make letters, numbers, and symbols plural, add apostrophe + s (‘s) to avoid confusion.

A → A’s
7 → 7’s
& → &’s

This rule helps readers distinguish the plural form clearly in writing.

Tips to Remember Irregular Plurals

1. Group Similar Words Together
Instead of learning one by one, group similar types of changes.

Vowel change: woman → women, tooth → teeth
Complete change: child → children, person → people
No change: fish → fish, moose → moose

This way, your brain remembers them like a family.

2. Say Them Out Loud

Speak them like a game- “One goose, two geese!”
Saying them helps you hear the difference and remember faster.

3. Use Flashcards or Drawings

Write or draw one sheep and two sheep- you’ll never forget it again!
This works well if you’re a visual learner.

4. Don’t Stress About Mistakes

It’s okay if you say “childs” by accident. With practice, you’ll start saying “children” naturally.

5. Practice with Real Sentences

Use these words in simple sentences:

“The teeth are clean.”
“I saw many fish at the market.”
“Those children are playing.”

This makes learning practical, not just theory.

Want Help with Difficult Words Like These?

Irregular plurals are just one small part of English and yes, they can be confusing. But you don’t have to learn it all alone.

That’s where English Partner can help.

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Vishaleni

Vishaleni is a results-driven content creator and copywriter who turns ideas into powerful words. With a knack for engaging storytelling and SEO-savvy writing, she helps brands connect, convert, and grow.