Irregular Plural Nouns in English

Most countable nouns in English form their plurals by adding -s or -es, such as book → books and box → boxes. However, some nouns form their plurals differently. These are called irregular plural nouns.

Irregular plurals may change their spelling or form completely, while some remain the same in both the singular and plural.

For example:

• man → men
• child → children
• mouse → mice
• person → people
• sheep → sheep

Because irregular plural nouns do not follow one single rule, their common forms and patterns need to be learned individually.

What Are Irregular Plural Nouns?

An irregular plural noun is a noun that does not form its plural by following the usual plural pattern of adding -s or -es.

Compare:

Examples:

• one man → two men
• one child → three children
• one mouse → several mice
• one sheep → five sheep

Do not add -s to a word that already has an irregular plural form:

• ✗ mans → ✓ men
• ✗ childs → ✓ children
• ✗ mouses → ✓ mice
• ✗ sheeps → ✓ sheep

Regular vs Irregular Plural Nouns

Regular and irregular nouns differ in how their plural forms are made.

Regular plurals follow normal plural-forming patterns:

• cat → cats
• bus → buses
• baby → babies
• wife → wives

Irregular plurals have forms that cannot be reliably produced by applying the usual plural rules:

• man → men
• child → children
• mouse → mice
• person → people
• sheep → sheep

Compare:

Not every plural involving a spelling change is an irregular plural in the same sense. Forms such as baby → babies, wife → wives, and hero → heroes follow recognizable plural spelling patterns and are usually taught as part of the general rules for forming plurals.

Why Are Some Plural Nouns Irregular?

English has developed over many centuries and has been influenced by different languages. As a result, some nouns preserve older English plural forms, while others retain plural forms from languages such as Latin and Greek.

For example:

• man → men
• foot → feet
• child → children
• ox → oxen
• analysis → analyses
• criterion → criteria

This is why there is no single rule that can form every irregular plural in English.

Types of Irregular Plural Nouns

Irregular plural nouns can be grouped according to how their plural forms change.

Internal Vowel Change

A vowel inside the word changes:

• man → men
• foot → feet
• mouse → mice

Special Ending

The noun takes an unusual plural ending:

• child → children
• ox → oxen

Substantial Change

The plural form changes considerably:

• person → people

No Change

The singular and plural forms are identical:

• sheep → sheep
• deer → deer
• species → species

Foreign or Classical Plural

Some borrowed nouns retain special plural forms:

• analysis → analyses
• criterion → criteria
• phenomenon → phenomena

Irregular Plurals with Internal Vowel Changes

Several common irregular nouns form their plurals by changing a vowel inside the word.

Examples:

• One man was waiting outside.
• Three men were waiting outside.
• My foot hurts.
• Both my feet hurt.
• The baby has one tooth.
• The child has several teeth.
• We saw a mouse in the kitchen.
• We saw two mice in the kitchen.

Do not use regular plural endings with these nouns:

• ✗ mans → ✓ men
• ✗ foots → ✓ feet
• ✗ tooths → ✓ teeth
• ✗ mouses → ✓ mice

These forms are best learned as singular–plural pairs.

Irregular Plurals with Special Endings

A small number of English nouns form their plurals with special endings.

Child → Children

The plural of child is children:

• one child
• two children
• many children

Examples:

• The child is playing.
• The children are playing.

Do not add another plural ending:

• ✗ childs
• ✗ childrens
• ✓ children

Ox → Oxen

The plural of ox is oxen:

• one ox
• two oxen

Example:

• Two oxen were pulling the cart.

The ending -en is not a general plural rule in modern English. It is better to learn ox → oxen as a singular–plural pair.

Irregular Plurals with Suppletive Forms

Some nouns have singular and plural forms that are considerably different.

The most important everyday example is:

person → people

Examples:

• One person is waiting.
• Five people are waiting.
• There were several people in the room.

In ordinary English, people is the normal plural of person.

Persons is also used, particularly in formal, legal, or official contexts:

• The lift has a maximum capacity of eight persons.

For everyday English, however, learners should normally use:

person → people

The word people can also refer to a nation or community. In this meaning, the plural peoples is possible:

• The region is home to several indigenous peoples.

Zero Plurals (Unchanged Plural Forms)

Some nouns have the same form in the singular and plural.

Examples:

• one sheep → ten sheep
• one deer → four deer
• one species → several species
• one aircraft → three aircraft

Do not add an unnecessary -s:

• ✗ sheeps → ✓ sheep
• ✗ deers → ✓ deer
• ✗ aircrafts → ✓ aircraft

Several animal nouns also commonly have unchanged plurals:

• fish → fish
• bison → bison
• elk → elk
• moose → moose

Examples:

• We saw three deer.
• Several bison were grazing.
• Two moose crossed the road.

Distinguishing Singular and Plural Forms

When the singular and plural forms are identical, the surrounding words usually show whether the noun is singular or plural.

Compare:

• This sheep is young.
• These sheep are young.
• One species is endangered.
• Several species are endangered.

Numbers, determiners, quantifiers, and verbs can help show whether the noun is singular or plural.

Fish vs Fishes

Fish is the usual plural when referring to individual fish:

• one fish
• two fish
• many fish

Fishes is used especially when referring to different species or kinds of fish, particularly in scientific contexts.

• We caught five fish.
• The reef contains many different fishes.

For ordinary English, fish is normally the plural learners need.

Irregular Plurals with Variant Plural Forms

Some nouns have more than one accepted plural form.

The alternatives are not always used in exactly the same way. One form may be more common in everyday English, while another may be preferred in academic or technical contexts.

When you are unsure about a particular noun, check its plural in a current dictionary.

Foreign and Classical Irregular Plurals

English contains nouns borrowed from Latin and Greek that retain special plural forms. These are especially common in academic, scientific, medical, and formal English.

Common patterns include:

Be careful with singular and plural forms:

• one criterion → several criteria
• one phenomenon → several phenomena
• one analysis → several analyses

Common mistakes:

• ✗ a criteria → ✓ a criterion
• ✗ one phenomena → ✓ one phenomenon

These endings are patterns, not universal rules. Not every word with the same ending follows the classical pattern, and some nouns also have regular English plurals:

• cactus → cacti / cactuses
• formula → formulae / formulas
• index → indices / indexes

Therefore, classical plural endings should not be applied automatically to every similar-looking word.

Irregular Plurals in Compound Nouns

Some compound nouns contain irregular nouns and retain the irregular change when they become plural.

Compounds Ending in an Irregular Noun

Examples:

• The company hired two businessmen.
• Several schoolchildren visited the museum.
• Two policemen were standing outside.

Some compounds form their plurals by changing the main noun even when it does not appear at the end:

Examples:

• Both of her sisters-in-law attended the wedding.
• Several passers-by stopped to help.

Do not assume that every word ending in -man contains the noun man. For example:

• human → humans
• German → Germans

The structure of the word determines how its plural is formed.

Common Irregular Plural Nouns

Here is a quick reference to some of the most useful irregular plurals:

How to Identify an Irregular Plural Noun

To identify an irregular plural noun, compare its plural form with its singular form.

For example:

The children are playing outside.

• noun: children
• singular: child
• plural: children

Because child → children does not follow the usual plural-forming pattern, children is an irregular plural noun.

Another example:

Three sheep are standing near the gate.

• singular: sheep
• plural: sheep

The form does not change, but the number three and the plural verb are show that sheep is plural.

There is no single ending that identifies every irregular plural, so knowing the singular form and looking at the context are important.

Common Mistakes with Irregular Plural Nouns

Adding -s to an irregular plural

• ✗ childrens → ✓ children
• ✗ mens → ✓ men
• ✗ mices → ✓ mice

Using a regular plural instead of the irregular form

• ✗ mans → ✓ men
• ✗ tooths → ✓ teeth
• ✗ mouses → ✓ mice

Adding -s to an unchanged plural

• ✗ sheeps → ✓ sheep
• ✗ deers → ✓ deer

Using a plural form as singular

• ✗ a criteria → ✓ a criterion
• ✗ one phenomena → ✓ one phenomenon

Using singular agreement with a plural noun

• ✗ The children is playing.
• ✓ The children are playing.
• ✗ Three sheep is outside.
• ✓ Three sheep are outside.

Pluralizing the wrong part of a compound

• ✗ mother-in-laws → ✓ mothers-in-law
• ✗ passer-bys → ✓ passers-by

How to Learn Irregular Plural Nouns

The most reliable way to learn irregular plurals is to learn the singular and plural forms together:

• man → men
• child → children
• mouse → mice
• sheep → sheep

Grouping similar forms can also help.

Vowel change:

• man → men
• foot → feet
• tooth → teeth
• mouse → mice

Special ending:

• child → children
• ox → oxen

No change:

• sheep → sheep
• deer → deer
• species → species

Classical forms:

• analysis → analyses
• criterion → criteria
• phenomenon → phenomena

It is also useful to practise the forms in sentences:

• One child is outside.
• Three children are outside.
• One sheep is missing.
• Five sheep are missing.

For uncommon nouns, borrowed words, and nouns with more than one accepted plural, check a reliable current dictionary.

Irregular Plural Nouns Practice

Write the Correct Plural

1. man → ______
2. woman → ______
3. child → ______
4. foot → ______
5. tooth → ______
6. mouse → ______
7. goose → ______
8. person → ______
9. sheep → ______
10. deer → ______
11. analysis → ______
12. criterion → ______
13. phenomenon → ______
14. ox → ______
15. mother-in-law → ______

Choose the Correct Form

1. Three man / men were waiting outside.
2. The childs / children are playing.
3. We saw six sheep / sheeps in the field.
4. These woman / women work together.
5. Several mouse / mice were hiding behind the cupboard.
6. We considered several criterion / criteria.
7. Scientists observed several phenomenon / phenomena.
8. Two mother-in-laws / mothers-in-law attended the meeting.
9. The people is / people are waiting.
10. Three deer was / deer were standing near the road.

Correct the Mistakes

1. The childrens are playing outside.
2. I saw three deers in the forest.
3. That people are waiting for us.
4. One criteria is especially important.
5. The womans are working upstairs.
6. My two sister-in-laws live nearby.
7. These sheeps are very young.
8. The mouses were under the table.
9. Three person were waiting outside.

Answers

Write the Correct Plural

1. men
2. women
3. children
4. feet
5. teeth
6. mice
7. geese
8. people
9. sheep
10. deer
11. analyses
12. criteria
13. phenomena
14. oxen
15. mothers-in-law

Choose the Correct Form

1. men
2. children
3. sheep
4. women
5. mice
6. criteria
7. phenomena
8. mothers-in-law
9. people are
10. deer were

Correct the Mistakes

1. The children are playing outside.
2. I saw three deer in the forest.
3. Those people are waiting for us.
4. One criterion is especially important.
5. The women are working upstairs.
6. My two sisters-in-law live nearby.
7. These sheep are very young.
8. The mice were under the table.
9. Three people were waiting outside.

FAQs

What is an irregular plural noun?

An irregular plural noun is a noun that does not form its plural by simply adding -s or -es. Examples include man → men, child → children, mouse → mice, and sheep → sheep.

What are some common irregular plural nouns?

Common examples include man → men, woman → women, child → children, person → people, foot → feet, tooth → teeth, mouse → mice, goose → geese, sheep → sheep, and deer → deer.

What are the main types of irregular plural nouns?

The main types include internal vowel changes such as foot → feet, special endings such as child → children, substantial changes such as person → people, unchanged plurals such as sheep → sheep, and foreign or classical plurals such as criterion → criteria.

Is children already plural?

Yes. Children is already the plural of child, so another -s should not be added.

• ✓ one child → two children
• ✗ two childrens

Is people the plural of person?

Yes. In everyday English, people is the normal plural of person:

• one person
• two people
• many people

Persons is also used in some formal, legal, and official contexts.

Is fish or fishes the correct plural of fish?

Both forms are correct, but they are used differently. Fish is the usual plural when referring to individual fish. Fishes is mainly used for different species or kinds of fish, especially in scientific contexts.

• We caught five fish.
• The reef is home to many different fishes.

Final Takeaway

Irregular plural nouns do not follow one single plural-forming rule. Their plural forms may involve:

• an internal vowel change: man → men
• a special ending: child → children
• a substantial change: person → people
• no change: sheep → sheep
• a foreign or classical form: criterion → criteria

The best way to learn irregular plurals is to learn common singular–plural pairs, recognize the main patterns, and practise the forms in context.

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