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Irregular Plurals in English

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In a previous lesson, you saw the regular plurals of nouns in English. You also saw words that change how you pronounce and spell the ending.

In this lesson, we will see irregular plural forms.

It is difficult to tell when a word has an irregular plural. The best way to learn them is to memorize the singular and plural forms together. Let’s look at the irregular plural of common words.

Review: Change in Pronunciation in Irregular Spelling

Sometimes there is a change in the pronunciation of the ending F or FE for some words, and you add -es to the end of those words. Other times, there is no change in pronunciation or spelling.

For nouns ending in F or FE, there are three ways to make the plural.

1. The F or FE changes to -ve before adding -s, so there is a change pronunciation of the ending.

knife - knives

life - lives

2. However, you just add -s to the end of some words, so the plural is completely regular.

chef - chefs

roof - roofs

3. Some nouns have both forms.

calf - calfs or calves

scarf - scarfs or scarves

For more examples of this type of plurals, see the lesson on regular plurals.

Irregular Plurals

Other irregular plurals have other changes in spelling, in pronunciation, or in both spelling and pronunciation.

No Change in the Plural

Words ending in -craft (meaning small boat or vessel)

one craft - many craft

one aircraft - many aircraft

one spacecraft - many spacecraft

Other words

one deer - many deer

one fish - many fish

one moose - many moose

one sheep - many sheep

one shrimp - many shrimp

one species - many species

one salmon - many salmon

one series - many series

Irregular Plurals with Word Change

Some words do not end in -s or -es in the plural form. The plural form

Irregular plurals

one child - many children

one foot - many feet

one goose - many geese

one man - many men

one ox - many oxen

one man - many men

one mouse - many mice

one tooth - many teeth

Note. Compound words ending in one of the above words keep the irregular plural.

one grandchild - many grandchildren

one schoolchild - many schoolchildren

one policeman - many policemen

one policewoman - many policewomen

Borrowed Words with Irregular Plurals

Many words in English come from other languages (e.g., Latin, Greek, French, Italian, Japanese). Many of these borrowed words kept the plural forms from the original language.

It does not matter what language an irregular plural came from. You just need to memorize it.

Singular -us  becomes -i  in the plural

The i is pronounced as the word “I.”

cactus - cacti

fungus - fungi

stimulus - stimuli

syllabus - syllabi

Note. Regular plurals for these words are also possible (“cactuses,” “funguses,” “syllabuses,” etc.), but the irregular plurals are much more common.

Singular -a becomes -ae

formula - formulae (pronounced as the “e” in “me”)

vertebra - vertebrae (pronounced as the “ey” in “hey”)

larva - larvae (pronounced as the “e” in “me”)

Note. Regular plurals are also possible for these words (formulas, vertebras, larvas), especially in spoken English.

Singular -ix or ex becomes -ices or -es

appendix - appendices

index - indices

vortex - vortices

Note. Regular plurals are also possible for these words (appendixes, indexes, vortexes), but the irregular plurals are more common in formal English.

Singular -on or -umbecomes a

bacterium - bacteria

criterion - criteria

medium - media

Singular -is becomes -es

The is and es are pronounced as “is" and “sees.”

analysis - analyses

basis - bases

crisis - crises

diagnosis - diagnoses

emphasis - emphases

parenthesis - parentheses


graffito - graffiti (Italian)

kimono - kimono (Japanese)

plateau - plateaux (French)

Note. Borrowed words such as the above may end up changing to the regular (for example, one kimono, two kimonos; one plateau, two plateaus). Although “graffiti” is a plural in Italian, it is generally used as a singular word in English (as are “spaghetti” and “ravioli").


Practice 1. Complete this short exercises to assess what you have learned.

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