Irregular Plural Nouns

English has a relatively simple set of rules for creating plural nouns out of singular nouns. Unfortunately, these rules are of only limited help to English language learners. This is because many commonly-used English nouns possess irregular plural forms. Today we’re going to look at the rules for regular plural nouns and how irregular plural nouns can deviate from those rules.


Note: The examples in this lesson are not exhaustive. Always consult a dictionary if you’re unsure whether a plural noun takes a regular or irregular form.


Regular Plural Nouns


The plural of most nouns is formed by simply adding a final –s:


Singular                      Plural

book                            books

cat                               cats

shirt                             shirts


Add a final –es to nouns ending in, –sh, -ch, -s, -z, and –x:


Singular                      Plural

box                              boxes

church                         churches

wish                            wishes


When a noun ends in a consonant + -y, replace the –y with –ies:


Singular                      Plural

agency                         agencies

baby                            babies

country                       countries


Irregular Plural Nouns


Several nouns have irregular plural forms that do not end in –s or have completely different spellings from their singular forms:


Singular                      Plural

man                             men

woman                        women

child                            children

ox                                oxen

foot                             feet

tooth                           teeth


Sometimes nouns that end in –o add –es to create their plural forms:


Singular                      Plural

echo                             echoes

hero                             heroes

potato                         potatoes

tomato                         tomatoes


However, other nouns ending in –o add only ­–s in their plural forms:


Singular                      Plural

auto                             autos

memo                          memos

photo                          photos

video                           videos


Some nouns ending in –o can take either an –s or an –­­­­es in their plural forms. The –es versions are more commonly used, but both spellings are equally correct:


Singular                      Plural

memento                     mementos/mementoes

mosquito                     mosquitos/mosquitoes

tornado                        tornados/tornadoes

zero                             zeros/zeroes


Sometimes a noun ending in –f or –fe uses a –ves ending in its plural form:


Singular                      Plural

calf                              calves

knife                            knives

life                               lives

wolf                             wolves


On the other hand, some nouns ending in ­–f/–fe simply take a final ­–s in plural forms:


Singular                      Plural

belief                           beliefs

chief                            chiefs

cliff                              cliffs

root                             roots


Confusingly, English contains some nouns with identical singular and plural forms. Whether the noun is considered singular or plural depends on the quantity being expressed:


Singular                      Plural

a deer/one deer            two deer/three deer

a fish/one fish              two fish/three fish

a species/one species  two species/three species


Finally, modern English contains numerous nouns borrowed from other languages. Some (but not all) of these nouns have plural forms consistent with their donor languages. Here is just a small sample of such borrowed nouns. It’s worth noting that even some native English speakers are not familiar with both the singular and plural forms of these nouns:


Singular                      Plural

criterion                       criteria

phenomenon               phenomena

bacterium                    bacteria

curriculum                   curricula

datum                          data

medium                       media

memorandum              memoranda

analysis                       analyses

basis                            bases

crisis                            crises

hypothesis                  hypotheses

parenthesis                  parentheses

thesis                           theses