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Getting Smarter through Language

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 -s or -ae

  • antenna - antennas (common sense) or antennae (referring to insects’ sensory organs)
  • formula - formulas or formulae (pronunced as the “e” in “me”)
  • larva - larvae (pronounced as the “e” in “me”)
  • nebula - nebulas or nebulae (in astronomy)
  • vertebra - vertebras or vertebrae (pronunced as the “ey” in “hey”) (vertebras is also correct)
  • Note. As you can see above, it is pretty safe to use the regular plural for these words; however, sometimes many people mistakenly use the irregular plural for the singular (e.g., saying “vertebrae” instead of one vertebra).

Singular -ix becomes -ices or -es

  • apex - apices or apexes
  • appendix - appendices or appendixes
  • index - indices or indexes
  • vortex - vortices or vortexes

Singular -on or -umbecomes a

  • bacterium - bacteria
  • criterion - criteria
  • datum - data
  • erratum - errata
  • medium - media
  • stratum - strata

Singular -on or -umbecomes a or -ums

Note. On the list below, the more commonly used plural form is given first.

  • addendum - addenda or addendums
  • aquarium - aquariums or aquaria
  • atrium - atria or atriums
  • candelabrum - candelabra or candelabrums
  • curriculum - curricula or curriculums
  • memorandum - memorandums or memoranda
  • millennium - millennia or millenniums
  • moratorium - moratoriums or moratoria
  • podium - podiums or podia
  • referendum - referenda or referendums
  • spectrum - spectra or spectrums
  • symposium - symposiums or symposia

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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