Irregular Plural Nouns in English Grammar – List, Rules, and Examples

When learning English, one of the first grammar lessons we encounter is how to make plural nouns. Normally, we just add “-s” or “-es” to the end of a word (like book → books or box → boxes).

However, not all words follow this simple rule. Some words change completely, while others stay exactly the same. These are called irregular plural nouns.

This article explains what irregular plurals are, the rules behind them, and provides a complete list of examples for easy learning.

What Are Irregular Plural Nouns?

An irregular plural noun is a noun that does not follow the regular rule of adding -s or -es to form the plural.

For example:

• Man → Men (not mans)
• Child → Children (not childs)
• Foot → Feet (not foots)

These changes come from Old English, Latin, and Greek word origins, which explains why they look different.

Why Learn Irregular Plurals?

Learning irregular plurals is important because they are commonly used in everyday English — in writing, speaking, and exams. Using them correctly shows grammatical accuracy and fluency.

Reason	Why It Matters
Grammar accuracy	Helps you write and speak correctly.
Exam preparation	Appears in grammar tests and essays.
Daily usage	Many irregular nouns are common in conversations.
Better writing	Makes your writing natural and fluent.

Common Irregular Plural Noun Patterns

While irregular nouns don’t follow one fixed rule, there are a few common patterns that can help you remember them easily.

A. Vowel Change in the Middle of the Word

Some singular nouns form their plural by changing the vowel sound in the middle.

Singular	Plural	Example Sentence
Man	Men	There are three men in the room.
Woman	Women	Many women joined the event.
Tooth	Teeth	My teeth are clean.
Foot	Feet	His feet are cold.
Goose	Geese	The geese are flying south.

Tip:
Try to remember these as complete pairs rather than trying to apply a rule.

B. Completely Different Word

Some words change entirely when pluralized.

Singular	Plural	Example Sentence
Person	People	People love music.
Child	Children	The children are playing outside.
Ox	Oxen	The oxen are working in the field.

Tip:
These are rare but very important because they’re used frequently in daily life.

C. Words Ending in “-f” or “-fe” → Change to “-ves”

Certain nouns ending in -f or -fe change the ending to -ves when forming plurals.

Singular	Plural	Example Sentence
Leaf	Leaves	The leaves are green.
Knife	Knives	Be careful with sharp knives.
Life	Lives	Many lives were saved.
Wolf	Wolves	Wolves live in packs.

Exceptions:
Some “-f” nouns don’t change (like roof → roofs, chief → chiefs).

D. Words That Stay the Same (No Change in Plural)

Some nouns do not change at all in their plural form.

Singular	Plural	Example Sentence
Fish	Fish	I caught three fish.
Sheep	Sheep	The sheep are grazing.
Deer	Deer	We saw five deer in the park.
Aircraft	Aircraft	The aircraft are ready for takeoff.
Bison	Bison	Bison roam freely in the wild.

Tip:
The plural form looks exactly like the singular form — you understand the number by the context.

E. Words Ending in “-us,” “-is,” “-um,” or “-on” (From Latin/Greek)

These words come from Latin or Greek roots and have special plural endings used in academic or scientific contexts.

Ending Type	Singular	Plural	Example Sentence
-us → -i	Focus	Foci	The scientist adjusted the foci of the lenses.
	Nucleus	Nuclei	Atoms have nuclei.
-is → -es	Analysis	Analyses	The analyses were detailed.
	Diagnosis	Diagnoses	Doctors confirmed two diagnoses.
-um → -a	Curriculum	Curricula	The new curricula were approved.
	Datum	Data	The data show clear results.
-on → -a	Criterion	Criteria	You met all the criteria.
-ex/-ix → -ices	Index	Indices	The stock market indices are rising.
	Apex	Apices	The apices of the triangles are marked.

Tip:
These are common in academic, scientific, or formal English.

F. Words That Add “-es” or “-s” But Change Spelling

A few irregular plurals follow regular patterns but also change the spelling slightly.

Singular	Plural	Example Sentence
Quiz	Quizzes	The teacher gave two quizzes.
Crisis	Crises	The country faced several crises.
Oasis	Oases	The travelers rested at the oases.
Ellipsis	Ellipses	The writer used ellipses for suspense.

Full List of Irregular Plural Nouns (from the Image)

Singular	Plural
Person	People
Foot	Feet
Tooth	Teeth
Child	Children
Mouse	Mice
Sheep	Sheep
Fish	Fish
Leaf	Leaves
Goose	Geese
Woman	Women
Aircraft	Aircraft
Diagnosis	Diagnoses
Bison	Bison
Crisis	Crises
Curriculum	Curricula
Datum	Data
Focus	Foci
Series	Series
Vita	Vitae
Tuna	Tuna
Quiz	Quizzes
Index	Indices
Ellipsis	Ellipses
Codex	Codices
Alumna	Alumnae
Erratum	Errata
Ox	Oxen
Oasis	Oases
Swine	Swine
Trout	Trout
Genus	Genera
Apex	Apices
Analysis	Analyses
Man	Men

Practice Sentences with Irregular Plurals

1. My tooth hurts, but my other teeth are fine.
2. The child is playing with other children.
3. One fish is red, but the other fish are blue.
4. The woman helped several men with their bags.
5. Each analysis produced different analyses.
6. The datum is inaccurate; check the rest of the data.
7. The goose flew south with the other geese.

Quick Comparison: Regular vs Irregular Plurals

Type	Rule	Example (Singular → Plural)
Regular	Add -s	book → books
Regular	Add -es	box → boxes
Regular	Change -y to -ies	baby → babies
Irregular (Vowel Change)	Change middle sound	foot → feet
Irregular (Word Change)	Different word	person → people
Irregular (No Change)	Same word	sheep → sheep
Irregular (Foreign Ending)	Latin/Greek rule	datum → data

Common Mistakes to Avoid

Wrong	Correct
Tooths	Teeth
Childs	Children
Mouses	Mice
Womans	Women
Datas	Data
Criterias	Criteria
Gooses	Geese
Mens	Men

Tip:
If a word doesn’t sound right when you add “s” or “es,” check if it’s an irregular noun!

Fun Memory Tips

• 🦶 Foot → Feet: You have two e’s in feet → two feet!
• 🧒 Child → Children: Think “more than one child means more fun — children!”
• 🐭 Mouse → Mice: “Mice” rhyme with “ice,” both come in groups.
• 🦆 Goose → Geese: Both words have “oo,” but “ee” means more!

FAQ

Q1. What is an irregular plural noun?

It’s a plural noun that doesn’t follow the normal rule of adding “-s” or “-es.” Example: man → men.

Q2. Do all nouns ending in “f” change to “ves”?

No. Some do (leaf → leaves), but others don’t (roof → roofs).

Q3. Is “data” singular or plural?

Technically, data is plural (of datum), but in modern English, it’s often treated as singular:

The data is accurate. (Common usage)

Q4. What are zero plural nouns?

Nouns that don’t change in plural form, like sheep, fish, deer, and aircraft.

Q5. How can I remember irregular plurals easily?

Practice with flashcards, group them by pattern, and use them in short sentences daily.

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