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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 the 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.

No Change in the Plural

Some words do not change in the singular and 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.

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

Words formed using 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

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

Singular -us becomes -i in the plural (pronounced as the word “I”)

  • cactus - cacti
  • fungus - fungi
  • syllabus - syllabi

Singular -a becomes -ae

  • formula - formulae (pronounced as the “e” in “me”) (formulas is also correct)
  • vertebra - vertebrae (pronounced as the “ey” in “hey”) (vertebras is also correct)
  • larva - larvae (pronounced as the “e” in “me”)

Singular -ix becomes -ices or -es

  • appendix - appendices (appendixes is also correct)
  • index - indices
  • vortex - vortices

Singular -on or -umbecomes a

  • bacterium - bacteria
  • criterion - criteria
  • medium - media

Singular -is becomes -es (pronounced as the “ees” in “fees”)

  • analysis - analyses
  • basis - bases
  • crisis - crises
  • diagnosis - diagnoses
  • emphasis - emphases


Complete a short exercise to assess what you have learned.

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