Irregular Plurals
Why Irregular?
Most English nouns add -s or -es:
- cat → cats
- box → boxes
But some nouns have irregular plurals from Old English, Latin, Greek, or other origins.
Old English Plurals
Vowel Changes
| Singular | Plural |
|---|---|
| man | men |
| woman | women |
| foot | feet |
| tooth | teeth |
| goose | geese |
| mouse | mice |
| louse | lice |
-en Endings
| Singular | Plural |
|---|---|
| child | children |
| ox | oxen |
Unchanged Plurals
Some nouns don’t change:
| Singular | Plural |
|---|---|
| sheep | sheep |
| deer | deer |
| fish | fish (or fishes) |
| species | species |
| series | series |
| aircraft | aircraft |
| moose | moose |
Latin Plurals
-us → -i
| Singular | Plural |
|---|---|
| cactus | cacti (or cactuses) |
| focus | foci (or focuses) |
| fungus | fungi |
| nucleus | nuclei |
| radius | radii |
| stimulus | stimuli |
| syllabus | syllabi (or syllabuses) |
-a → -ae
| Singular | Plural |
|---|---|
| alumna | alumnae |
| antenna | antennae (or antennas) |
| formula | formulae (or formulas) |
| larva | larvae |
-um → -a
| Singular | Plural |
|---|---|
| bacterium | bacteria |
| curriculum | curricula |
| datum | data |
| medium | media |
| memorandum | memoranda |
| millennium | millennia |
| stadium | stadia (or stadiums) |
| symposium | symposia |
-is → -es
| Singular | Plural |
|---|---|
| analysis | analyses |
| axis | axes |
| basis | bases |
| crisis | crises |
| diagnosis | diagnoses |
| hypothesis | hypotheses |
| oasis | oases |
| parenthesis | parentheses |
| thesis | theses |
Greek Plurals
-on → -a
| Singular | Plural |
|---|---|
| criterion | criteria |
| phenomenon | phenomena |
Common Mistakes
| Wrong | Right |
|---|---|
| childs | children |
| mouses (animals) | mice |
| phenomenons | phenomena |
| criterias | criteria |
| feets | feet |
| tooths | teeth |
| datas | data |
| medias | media |
Note on Usage
Many Latin/Greek plurals now have regular alternatives:
- formulas/formulae
- cactuses/cacti
- stadiums/stadia
The regular form is often more common in everyday use.
Many irregular plurals in English come from Old English (child → children, ox → oxen) or Latin/Greek (criterion → criteria, datum → data). Some words have the same singular and plural form: sheep, deer, fish.