What are Irregular Plurals?
In English, the vast majority of nouns form their plural routinely by adding -s or -es (e.g., cat → cats, box → boxes). However, a significant and highly common group of nouns follow no predictable rule when changing from singular to plural — these plurals must simply be memorized. These are called Irregular Plurals. Because many of these words operate as core vocabulary (e.g., men, women, children), knowing them is critical for grammatical accuracy and proper verb agreement.
Irregular Plurals Structure and Formula
While their spelling alters unpredictably, irregular plurals function grammatically exactly like regular plurals. They must be paired with plural verbs.
Structure:
- Irregular Plural Noun + V (plural) + O
Example: The children are playing outside. (S + V-plural + Adv)
How to Form Internal Vowel Changes (Umlaut Plurals)
Some of the oldest words in English indicate plurality changing one or two vowels in the middle of the word, rather than adding a suffix to the end.
| Singular | Plural Form | Phonetic/Spelling Note |
|---|---|---|
| man | men | a → e |
| woman | women | o → e (pronunciation drastically changes to /ˈwɪmɪn/) |
| foot | feet | oo → ee |
| tooth | teeth | oo → ee |
| goose | geese | oo → ee |
| mouse | mice | ou → i |
| louse | lice | ou → i |
💡 Tip: "Women" is one of the most mispronounced words. Even though the spelling changes from an O to an E, the first syllable is pronounced like "wim."
How to Identify Completely Different Forms
A small group of words changes structure radically or uses archaic endings (like -en).
| Singular | Plural Form | Note |
|---|---|---|
| child | children | Completely different |
| person | people | The word "persons" exists but is restricted strictly to legal/formal texts |
| ox | oxen | Archaic -en plural suffix |
How to Identify Zero Plurals (Same Form)
"Zero plurals" are nouns that remain identical in both their singular and plural forms. Context and verb agreement define their number.
| Noun | Singular Example | Plural Example |
|---|---|---|
| sheep | one sheep | fifty sheep |
| fish | one fish | many fish |
| deer | one deer | three deer |
| species | one species | many species |
| aircraft | one aircraft | ten aircraft |
| series | one series | two series |
- There is one sheep in the field. (V-singular)
- There are twenty sheep in the field. (V-plural)
When to Use Latin and Greek Borrowings
Many academic, scientific, and technical words keep their original Latin or Greek plural transformations.
| Singular | Plural Form | Origin / Rule |
|---|---|---|
| criterion | criteria | Greek (-on → -a) |
| phenomenon | phenomena | Greek (-on → -a) |
| curriculum | curricula | Latin (-um → -a) |
| datum | data | Latin (-um → -a) |
| formula | formulae / formulas | Latin (-a → -ae) |
| analysis | analyses | Greek (-is → -es) |
| basis | bases | Greek (-is → -es) |
| thesis | theses | Greek (-is → -es) |
| index | indices / indexes | Latin (-ex → -ices) |
| appendix | appendices / appendixes | Latin (-ix → -ices) |
How to Tell the Difference Between -f and -fe Endings
Many words ending in an 'f' or 'fe' sound drop the 'f' and replace it with -ves.
| Singular Form | Irregular Plural Form |
|---|---|
| leaf | leaves |
| loaf | loaves |
| half | halves |
| wolf | wolves |
| knife | knives |
| wife | wives |
| life | lives |
| self | selves |
Crucial Exceptions: Some words resist this and follow regular rules: roof → roofs (never rooves), chief → chiefs, cliff → cliffs.
Compound Nouns Pluralization
For compound nouns (words fused together with hyphens), the main head noun takes the plural "s", not the last word in the chain.
| Singular Compound | Plural Compound |
|---|---|
| passer-by | passers-by |
| mother-in-law | mothers-in-law |
| commander-in-chief | commanders-in-chief |
| grown-up | grown-ups (If there is no clear main noun, the 's' goes at the end) |
Real-life Examples of Irregular Plurals
- The children played with the mice in the science lab. (S + V + Prep Phrase)
- Two women and three men were elected to the committee.
- The research data were collected from five species of fish.
- The criteria for selection are strict — all theses must be original.
Summary & Cheatsheet for Irregular Plurals
| Rule Category | Transformation Pattern | Example |
|---|---|---|
| Vowel change | Internal vowel shifts | man → men, tooth → teeth |
| Total shift | Word changes heavily | child → children |
| Zero plural | No spelling change | sheep, fish, deer |
| Latin -um | -um → -a | datum → data |
| Greek -on | -on → -a | criterion → criteria |
| Greek -is | -is → -es | analysis → analyses |
| -f / -fe | -f / -fe → -ves | leaf → leaves |
| Compound | Main noun takes the plural | mother-in-law → mothers-in-law |
Frequently Asked Questions
Can I ever say "fishes"?
Generally, the plural of fish is "fish" (e.g., I caught ten fish). However, biologists use "fishes" when specifically talking about multiple different species of fish (e.g., The freshwater fishes of North America). In everyday English, stick to "fish."
Is "data" singular or plural?
Technically and academically, "data" is the plural form of "datum", so it requires a plural verb (e.g., The data show that...). However, in modern everyday English, "data" is increasingly treated as an uncountable mass noun with a singular verb (e.g., The data is clear). Both are accepted, but formal writing prefers the plural verb.
Why is it "roofs" but "wolves"?
This is an anomaly resulting from the historical evolution of English dialects. There is no strict logical rule; exceptions like "roofs," "chiefs," and "beliefs" must simply be memorized alongside the "-ves" changes.
Are words like "mathematics" and "news" irregular plurals?
No. Words like "mathematics," "physics," and "news" end in an "s", but they are actually singular, uncountable nouns. They take singular verbs (e.g., The news is good. S + V-singular). They are not plurals.