Forming Irregular Plural Nouns

Importance ★★


By far, the most common type of plural formation in English involves simply adding an -s to a singular noun:

  • book, books
  • house, houses

If the singular noun already ends in -s, you add -es (or -ses) to form the plural:

  • boss, bosses
  • bus, buses
  • gas, gases (or sometimes ‘gasses’)

Sometimes, but rarely, plural formation with an -s changes the spelling of the noun slightly:

  • potato, potatoes
  • hobby, hobbies
  • soliloquy, soliloquies

In some cases, plural formation affects how a word is pronounced.

Voicing audible but not reflected in writing:

mouth (voiceless), mouths (voiced)

Voicing audible and reflected in writing:

  • knife (voiceless), knives (voiced)
    • BUT: belief (voiceless), beliefs (voiceless)
  • life (voiceless), lives (voiced)
    • BUT: still life (voiceless), still lifes (voiceless)

There are, however, some nouns that do not conform to the -s model at all. Below are various types of irregular plural formation and some examples:

Vowel change, e.g.:

  • foot, feet
  • mouse, mice
  • woman, women

Zero plural, e.g.:

  • fish, fish
  • series, series
  • sheep, sheep

It should also be noted that some words are always plural, even though they have no visible plural form:

  • people (we talk about one person but in the plural, people is more common than persons)
  • police (if we are talking about the police, we always do so in the plural; otherwise we say policeman or police officer)

The plural form of some words is a clue to the their etymological roots, such as the Germanic -en:

  • child, children
  • ox, oxen

Many English words come from Greek or Latin, which is reflected in their plural forms:

  • addendum, addenda
  • alumna (feminine), alumnae
  • alumnus (masculine), alumni
  • analysis, analyses
  • antenna, antennae
  • appendix, appendices
  • corpus, corpora
  • criterion, criteria
  • curriculum, curricula
  • formula, formulae (formulas)
  • medium, media
  • phenomenon, phenomena
  • stimulus, stimuli


Although there are relatively few irregular nouns in English, there are many different categories to be aware of.

Further Discussion

In English, the morpheme -s serves a number of functions. When attached to a noun, it indicates plural. However, when attached to a verb, it indicates agreement with a third-person singular subject:

  • he/she/it talks

Together with an apostrophe, -s is also used to indicate the genitive case—that is, a possessive:

  • Harry’s Bar

Confusingly, the plural of letters (such as A, B, and C) is usually formed with ‘s:

  • Dot the I’s and cross the T’s.

Similarly, the plural of acronyms and decades is formed either with or without an apostrophe:

  • DVDs (or DVD’s), CEOs (or CEO’s), PCs (or PC’s)
  • the 1930s (or the 1930’s), the 2000s (or the 2000’s)

Note, however, that English never forms plurals or genitives using a colon (as happens in Swedish):

  • DVDs (not DVD:s)

Another source of confusion is the fact that sometimes, -s can be both plural and genitive at the same time. The genitive of a plural noun is indicated by an apostrophe following the plural -s:

  • He tried to sell his parents’ car.

Avoid unnecessary confusion by placing the apostrophe in the accurate position. Compare the following sentences:

  • He did not consider his girlfriend’s feelings.
  • He did not consider his girlfriends’ feelings.

In any situation in which the latter sentence is accurate grammatically, it is likely also to be accurate factually.